Head and Neck Anatomy for Dental Medicine - Thieme; (January 26, 2010)

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Head and Neck Anatomy for Dental Medicine

Head and Neck Anatomy for Dental Medicine Edited by

Based on the work of

Eric W. Baker

Michael Schuenke Erik Schulte Udo Schumacher Illustrations by

Markus Voll Karl Wesker

Thieme New York · Stuttgart

Thieme Medical Publishers, Inc. 333 Seventh Avenue New York, New York 10001 Based on the work of Michael Schuenke, MD, PhD, Erik Schulte, MD, and Udo Schumacher, MD Eric W. Baker, MA, MPhil Educational Coordinator and Director of Human Gross Anatomy Department of Basic Science and Craniofacial Biology New York University College of Dentistry New York, New York 10010 Michael Schuenke, MD, PhD Institute of Anatomy Christian Albrecht University Kiel Olshausenstrasse 40 D-24098 Kiel Erik Schulte, MD Department of Anatomy and Cell Biology Johannes Gutenberg University Saarstrasse 19-21 D-55099 Mainz Udo Schumacher, MD, FRCPath, CBiol, FIBiol, DSc Institute of Anatomy II: Experimental Morphology Center for Experimental Medicine University Medical Center Hamburg-Eppendorf Martinistrasse 52 D-20246 Hamburg Library of Congress Cataloging-in-Publication Data Head and neck anatomy for dental medicine / edited by Eric W. Baker ; based on the work of Michael Schuenke, Erik Schulte, Udo Schumacher ; illustrations by Markus Voll, Karl Wesker. p. ; cm. Includes bibliographical references and index. ISBN 978-1-60406-209-0 (softcover : alk. paper) 1. Head—Anatomy— Atlases. 2. Neck—Anatomy—Atlases. I. Baker, Eric W. (Eric William), 1961– II. Schünke, Michael. III. Schulte, Erik. IV. Schumacher, Udo. [DNLM: 1. Head—anatomy & histology—Atlases. 2. Dentistry— Atlases. 3. Neck—anatomy & histology—Atlases. WE 17 H432 2010] QM535.H43 2010 611’.910223--dc22 2009041592

Developmental Editor: Bridget N. Queenan and Julie O’Meara Editorial Director, Educational Products: Cathrin Weinstein, MD, and Anne T. Vinnicombe Associate Manager, Book Production: Adelaide Elsie Starbecker International Production Director: Andreas Schabert Director of Sales: Ross Lumpkin Vice President, International Marketing and Sales: Cornelia Schulze Chief Financial Officer: James W. Mitos President: Brian D. Scanlan Illustrators: Markus Voll and Karl Wesker Compositor: MPS Content Services, A Macmillan Company Printer: Leo Paper Products Ltd. Copyright © 2010 by Thieme Medical Publishers, Inc. This book, including all parts thereof, is legally protected by copyright. Any use, exploitation, or commercialization outside the narrow limits set by copyright legislation without the publisher’s consent is illegal and liable to prosecution. This applies in particular to photostat reproduction, copying, mimeographing or duplication of any kind, translating, preparation of microfilms, and electronic data processing and storage. Important note: Medical knowledge is ever-changing. As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy may be required. The authors and editors of the material herein have consulted sources believed to be reliable in their efforts to provide information that is complete and in accord with the standards accepted at the time of publication. However, in view of the possibility of human error by the authors, editors, or publisher of the work herein or changes in medical knowledge, neither the authors, editors, nor publisher, nor any other party who has been involved in the preparation of this work, warrants that the information contained herein is in every respect accurate or complete, and they are not responsible for any errors or omissions or for the results obtained from use of such information. Readers are encouraged to confirm the information contained herein with other sources. For example, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this publication is accurate and that changes have not been made in the recommended dose or in the contraindications for administration. This recommendation is of particular importance in connection with new or infrequently used drugs.

ISBN 978-1-60406-209-0

Dedication

To my wonderful wife, Amy Curran Baker, and my awe-inspiring daughters, Phoebe and Claire.

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Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . XI

Head 1

Cranial Bones

4

Development of the Cranial Bones . . . . . . . . . . . . . . . . . . . . . . . 2 Skull: Lateral View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Skull: Anterior View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Skull: Posterior View & Cranial Sutures . . . . . . . . . . . . . . . . . . . 8 Calvaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Skull Base: External View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Skull Base: Internal View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Sphenoid Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Temporal Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Occipital Bone & Ethmoid Bones . . . . . . . . . . . . . . . . . . . . . . . 20 Mandible & Hyoid Bone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2

Organization of the Nervous System . . . . . . . . . . . . . . . . . . . . 54 Sensory Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Motor Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Skeletal Muscle: Innervation & Embryonic Development . . . . 60 Autonomic Motor Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Peripheral Nerves & Nerve Lesions . . . . . . . . . . . . . . . . . . . . . . 64 Cranial Nerves: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Cranial Nerve Nuclei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 CN I & II: Olfactory & Optic Nerves . . . . . . . . . . . . . . . . . . . . . . 70 CN III, IV & VI: Oculomotor, Trochlear & Abducent Nerves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 CN V: Trigeminal Nerve, Nuclei & Divisions . . . . . . . . . . . . . . . 74 CN V1: Trigeminal Nerve, Ophthalmic Division . . . . . . . . . . . . 76 CN V2: Trigeminal Nerve, Maxillary Division . . . . . . . . . . . . . . 78 CN V3: Trigeminal Nerve, Mandibular Division . . . . . . . . . . . . 80 CN VII: Facial Nerve, Nuclei & Internal Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 CN VII: Facial Nerve, External Branches & Ganglia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 CN VIII: Vestibulocochlear Nerve . . . . . . . . . . . . . . . . . . . . . . . 86 CN IX: Glossopharyngeal Nerve . . . . . . . . . . . . . . . . . . . . . . . . 88 CN X: Vagus Nerve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 CN XI & XII: Accessory Spinal & Hypoglossal Nerves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Neurovascular Pathways through the Skull Base . . . . . . . . . . . 94

Muscles of the Skull & Face Muscles of Facial Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Muscles of Facial Expression: Calvaria, Ear & Eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Muscles of Facial Expression: Mouth . . . . . . . . . . . . . . . . . . . . 28 Muscles of Mastication: Overview . . . . . . . . . . . . . . . . . . . . . . 30 Muscles of Mastication: Deep Muscles. . . . . . . . . . . . . . . . . . . 32 Temporomandibular Joint (TMJ): Biomechanics . . . . . . . . . . . 34 Temporomandibular Joint (TMJ) . . . . . . . . . . . . . . . . . . . . . . . . 36 Muscles of the Head: Origins & Insertions . . . . . . . . . . . . . . . . 38

3

Arteries & Veins of the Head & Neck Arteries of the Head: Overview . . . . . . . . . . . . . . . . . . . . . . . . 40 External Carotid Artery: Anterior, Medial & Posterior Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 External Carotid Artery: Maxillary Artery . . . . . . . . . . . . . . . . . 44 External Carotid Artery: Terminal Branches . . . . . . . . . . . . . . . 46 Internal Carotid Artery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Veins of the Head: Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Veins of the Head: Deep Veins . . . . . . . . . . . . . . . . . . . . . . . . . 52

Innervation of the Head & Neck

5

Neurovascular Topography of the Head Anterior Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Lateral Head: Superficial Layer . . . . . . . . . . . . . . . . . . . . . . . . . 98 Lateral Head: Intermediate Layer . . . . . . . . . . . . . . . . . . . . . . 100 Infratemporal Fossa: Contents . . . . . . . . . . . . . . . . . . . . . . . . 102 Pterygopalatine Fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

VII

Contents

Regions of the Head

6

Orbit & Eye Bones of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Communications of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . . 110 Extraocular Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Cranial Nerves of the Extraocular Muscles: Oculomotor (CN III), Trochlear (CN IV) & Abducent (CN VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Neurovasculature of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . 116 Topography of the Orbit (I) . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Topography of the Orbit (II) . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Lacrimal Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Eyeball . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Eye: Blood Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Eye: Lens & Cornea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Eye: Iris & Ocular Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Eye: Retina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Visual System (I): Overview & Geniculate Part. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 Visual System (II): Lesions & Nongeniculate Part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 Visual System (III): Reflexes . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Visual System (IV): Coordination of Eye Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

7

Nose & Nasal Cavity Nose: Nasal Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Nose: Paranasal Sinuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Nasal Cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Nasal Cavity: Neurovascular Supply . . . . . . . . . . . . . . . . . . . . 148 Nose & Paranasal Sinuses: Histology & Clinical Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Olfactory System (Smell) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

8

Temporal Bone & Ear Temporal Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Ear: Overview & External Ear . . . . . . . . . . . . . . . . . . . . . . . . . . 156 External Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158

VIII

Middle Ear (I): Tympanic Cavity & Pharyngotympanic Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Middle Ear (II): Auditory Ossicles & Tympanic Cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Inner Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Arteries & Veins of the Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Vestibulocochlear Nerve (CN VIII) . . . . . . . . . . . . . . . . . . . . . 168 Auditory Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Auditory Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Vestibular Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Vestibular System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

9

Oral Cavity & Perioral Regions Oral Cavity: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Permanent Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Structure of the Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Incisors, Canines & Premolars . . . . . . . . . . . . . . . . . . . . . . . . . 184 Molars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Deciduous Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Hard Palate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Mandible & Hyoid Bone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Temporomandibular Joint (TMJ) . . . . . . . . . . . . . . . . . . . . . . . 194 Temporomandibular Joint (TMJ): Biomechanics . . . . . . . . . . 196 Muscles of Mastication: Overview . . . . . . . . . . . . . . . . . . . . . 198 Muscles of Mastication: Deep Muscles. . . . . . . . . . . . . . . . . . 200 Suprahyoid Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Lingual Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 Lingual Mucosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 Pharynx & Tonsils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Pharynx: Divisions & Contents . . . . . . . . . . . . . . . . . . . . . . . . 210 Muscles of the Soft Palate & Pharynx . . . . . . . . . . . . . . . . . . . 212 Muscles of the Pharynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 Pharynx: Topography & Innervation. . . . . . . . . . . . . . . . . . . . 216 Salivary Glands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Neurovasculature of the Tongue . . . . . . . . . . . . . . . . . . . . . . 220 Gustatory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

Contents

Neck

Neuroanatomy

10

13

Bones, Ligaments & Muscles of the Neck Vertebral Column & Vertebrae . . . . . . . . . . . . . . . . . . . . . . . . 226 Ligaments of the Vertebral Column . . . . . . . . . . . . . . . . . . . . 228 Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Joints of the Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Ligaments of the Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . 234 Ligaments of the Craniovertebral Joints . . . . . . . . . . . . . . . . 236 Muscles of the Neck: Overview. . . . . . . . . . . . . . . . . . . . . . . . 238 Muscles of the Neck & Back (I) . . . . . . . . . . . . . . . . . . . . . . . . 240 Muscles of the Neck & Back (II). . . . . . . . . . . . . . . . . . . . . . . . 242 Muscles of the Posterior Neck . . . . . . . . . . . . . . . . . . . . . . . . 244 Intrinsic Back Muscles (I): Erector Spinae & Interspinales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Intrinsic Back Muscles (II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Intrinsic Back Muscles (III): Short Nuchal Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Prevertebral & Scalene Muscles . . . . . . . . . . . . . . . . . . . . . . . 252 Suprahyoid & Infrahyoid Muscles . . . . . . . . . . . . . . . . . . . . . . 254

11

Neuroanatomy Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Spinal Cord: Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Brain: Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Brain & Meninges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 Spinal Cord & Meninges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 Cerebrospinal Fluid (CSF) Spaces . . . . . . . . . . . . . . . . . . . . . . 300 Dural Sinuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 Arteries of the Brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 Neurons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Larynx Larynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Laryngeal Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Larynx: Neurovasculature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Larynx: Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Thyroid & Parathyroid Glands . . . . . . . . . . . . . . . . . . . . . . . . . 264

12

Neurovascular Topography of the Neck Arteries & Veins of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Lymphatics of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Cervical Plexus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Cervical Regions (Triangles) . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Cervical Fasciae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 Posterior Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Lateral Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Anterior Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Deep Anterolateral Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Parapharyngeal Space (I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Parapharyngeal Space (II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286

IX

Contents

Sectional Anatomy

Appendix

14

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348

Sectional Anatomy of the Head & Neck Coronal Sections of the Head (I): Anterior . . . . . . . . . . . . . . . 310 Coronal Sections of the Head (II): Posterior . . . . . . . . . . . . . 312 Coronal MRIs of the Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Coronal MRIs of the Neck (I): Anterior . . . . . . . . . . . . . . . . . . 316 Coronal MRIs of the Neck (II) . . . . . . . . . . . . . . . . . . . . . . . . . 318 Coronal MRIs of the Neck (III): Posterior . . . . . . . . . . . . . . . . 320 Transverse Sections of the Head (I): Cranial . . . . . . . . . . . . . 322 Transverse Sections of the Head (II) . . . . . . . . . . . . . . . . . . . . 324 Transverse Sections of the Head (III): Caudal . . . . . . . . . . . . 326 Transverse Sections of the Neck (I): Cranial. . . . . . . . . . . . . . 328 Transverse Sections of the Neck (II): Caudal . . . . . . . . . . . . . 330 Transverse MRIs of the Head. . . . . . . . . . . . . . . . . . . . . . . . . . 332 Transverse MRIs of the Oral Cavity . . . . . . . . . . . . . . . . . . . . . 334 Transverse MRIs of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Sagittal Sections of the Head (I): Medial . . . . . . . . . . . . . . . . 338 Sagittal Sections of the Head (II): Lateral. . . . . . . . . . . . . . . . 340 Sagittal MRIs of the Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 Sagittal MRIs of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

X

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

Preface

I was amazed and impressed with the extraordinary detail, accuracy, and beauty of the material that was created for the three-volume THIEME Atlas of Anatomy by authors Michael Schuenke, Erik Schulte, and Udo Schumacher and artists Markus Voll and Karl Wesker. I felt that these atlases and their pedagogical concepts were a significant addition to anatomical education. I was delighted to be invited to use this exceptional material as the cornerstone of an effort to create an atlas that specifically focuses on the structures of the head and neck as they are taught to students of dental medicine. Starting from the extensive coverage of these structures distributed across the three volumes of THIEME Atlas of Anatomy, I have organized, revised, and added new material to create Head and Neck Anatomy for Dental Medicine, a learning atlas for the first-year students of dental medicine taking a gross anatomy course. Because of the exceptional quality artwork and explanatory information concerning the structures of the head and the neck, it can also serve as a reference for practitioners of dental medicine and for students and practitioners in the more general field of dentistry (dental hygiene, dental assistants, etc.) and/or any field dealing primarily with the head and neck (ENT, speech pathology, ophthalmology, etc.). Some key features of this atlas are as follows: Organized in a user-friendly format in which each two-page spread is a self-contained guide to a specific topic. Intuitively arranged to facilitate learning. Coverage of each region begins by discussing the bones and joints and then adds the muscles, the vasculature, and the nerves. This information is then integrated in the topographic neurovascular anatomy coverage that follows. Features large, full-color, highly detailed artwork with clear and thorough labeling and descriptive captions, plus numerous schematics to elucidate concepts and tables to summarize key information for review and reference. Includes a full chapter devoted to sectional anatomy with radiographic images to demonstrate anatomy as seen in the clinical setting. The study of head and neck anatomy is challenging due to the intricacies of the structures involved, but this atlas manages to convey detailed anatomical information in a way that is both thorough and efficient, making for a very effective study tool.

I would like to thank Susana Tejada, class of 2010, Boston University School of Dental Medicine, and the group of dedicated anatomy instructors who provided feedback to Thieme as they were developing the concept for this atlas: Dr. Norman F. Capra, Department of Neural and Pain Sciences, University of Maryland Dental School, Baltimore, Maryland; Dr. Bob Hutchins, Associate Professor, Department of Biomedical Sciences, Baylor College of Dentistry, Dallas, Texas; Dr. Brian R. MacPherson, Professor and Vice-Chair, Department of Anatomy and Neurobiology, University of Kentucky, Lexington, Kentucky; and Dr. Nicholas Peter Piesco, Associate Professor, Department of Oral Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania. I would like to thank my colleagues at New York University who assisted me in this endeavor: Professor Terry Harrison, Department of Anthropology, for fostering my interests in comparative anatomy and instilling an appreciation for detail and accuracy in anatomical description; Dr. Richard Cotty for his keen eye in looking over the sectional anatomy in this atlas; Dr. Phyllis Slott, Dr. Elena Cunningham, Dr. Avelin Malyango, and Dr. Johanna Warshaw for assistance in all things anatomy related, including countless discussions on all aspects of current anatomical education and the need for a detailed head and neck anatomy atlas. Finally, I would like to thank Dr. Inder Singh for mentoring me as an anatomist and serving as an inspirational anatomy professor. I would like to thank my colleagues at Thieme Publishers who so professionally facilitated this effort. I wish to thank Cathrin Weinstein, MD, Editorial Director, Educational Products, for inviting me to create this atlas. I extend very special thanks and appreciation to Bridget Queenan, Developmental Editor, who edited and developed the manuscript with an outstanding talent for visualization and intuitive flow of information. I am also very grateful to her for catching many details along the way while always patiently responding to requests for artwork and labeling changes. Thanks to Julie O’Meara, Developmental Editor, for joining the team in the correction phase. She graciously reminded me of deadlines, while always being available to work with me on proofs and to troubleshoot problems. Finally, thanks to Elsie Starbecker, Associate Manager, Book Production, who with great care and speed produced this atlas with its over 900 illustrations. Their hard work has made Head and Neck Anatomy for Dental Medicine a reality. Eric W. Baker New York, New York

XI

Head 1

Cranial Bones

4

Development of the Cranial Bones . . . . . . . . . . . . . . . . . . . . . . . 2 Skull: Lateral View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Skull: Anterior View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Skull: Posterior View & Cranial Sutures . . . . . . . . . . . . . . . . . . . 8 Calvaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Skull Base: External View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Skull Base: Internal View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Sphenoid Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Temporal Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Occipital Bone & Ethmoid Bones . . . . . . . . . . . . . . . . . . . . . . . 20 Mandible & Hyoid Bone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2

Organization of the Nervous System . . . . . . . . . . . . . . . . . . . . 54 Sensory Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Motor Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Skeletal Muscle: Innervation & Embryonic Development . . . . 60 Autonomic Motor Pathways . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Peripheral Nerves & Nerve Lesions . . . . . . . . . . . . . . . . . . . . . . 64 Cranial Nerves: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 Cranial Nerve Nuclei . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 CN I & II: Olfactory & Optic Nerves . . . . . . . . . . . . . . . . . . . . . . 70 CN III, IV & VI: Oculomotor, Trochlear & Abducent Nerves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72 CN V: Trigeminal Nerve, Nuclei & Divisions . . . . . . . . . . . . . . . 74 CN V1: Trigeminal Nerve, Ophthalmic Division . . . . . . . . . . . . 76 CN V2: Trigeminal Nerve, Maxillary Division . . . . . . . . . . . . . . 78 CN V3: Trigeminal Nerve, Mandibular Division . . . . . . . . . . . . 80 CN VII: Facial Nerve, Nuclei & Internal Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 CN VII: Facial Nerve, External Branches & Ganglia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 CN VIII: Vestibulocochlear Nerve . . . . . . . . . . . . . . . . . . . . . . . 86 CN IX: Glossopharyngeal Nerve . . . . . . . . . . . . . . . . . . . . . . . . 88 CN X: Vagus Nerve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 CN XI & XII: Accessory Spinal & Hypoglossal Nerves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Neurovascular Pathways through the Skull Base . . . . . . . . . . . 94

Muscles of the Skull & Face Muscles of Facial Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Muscles of Facial Expression: Calvaria, Ear & Eye . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 Muscles of Facial Expression: Mouth . . . . . . . . . . . . . . . . . . . . 28 Muscles of Mastication: Overview . . . . . . . . . . . . . . . . . . . . . . 30 Muscles of Mastication: Deep Muscles. . . . . . . . . . . . . . . . . . . 32 Temporomandibular Joint (TMJ): Biomechanics . . . . . . . . . . . 34 Temporomandibular Joint (TMJ) . . . . . . . . . . . . . . . . . . . . . . . . 36 Muscles of the Head: Origins & Insertions . . . . . . . . . . . . . . . . 38

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Arteries & Veins of the Head & Neck Arteries of the Head: Overview . . . . . . . . . . . . . . . . . . . . . . . . 40 External Carotid Artery: Anterior, Medial & Posterior Branches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 External Carotid Artery: Maxillary Artery . . . . . . . . . . . . . . . . . 44 External Carotid Artery: Terminal Branches . . . . . . . . . . . . . . . 46 Internal Carotid Artery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Veins of the Head: Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 50 Veins of the Head: Deep Veins . . . . . . . . . . . . . . . . . . . . . . . . . 52

Innervation of the Head & Neck

5

Neurovascular Topography of the Head Anterior Face . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Lateral Head: Superficial Layer . . . . . . . . . . . . . . . . . . . . . . . . . 98 Lateral Head: Intermediate Layer . . . . . . . . . . . . . . . . . . . . . . 100 Infratemporal Fossa: Contents . . . . . . . . . . . . . . . . . . . . . . . . 102 Pterygopalatine Fossa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Head

1. Cranial Bones

Development of the Cranial Bones

Fig. 1.1 Bones of the skull Left lateral view. The skull forms a bony capsule that encloses the brain and viscera of the head. The bones of the skull are divided into two parts. The viscerocranium (orange), the facial skeleton, is formed primarily from the pharyngeal (branchial) arches (see p. 61). The neurocranium (gray), the cranial vault, is the bony capsule enclosing the brain. It is divided into two parts based on ossification (see Fig. 1.2). The cartilaginous neurocranium undergoes endochondral ossification to form the base of the skull. The membranous neurocranium undergoes intramembranous ossification.

Fig. 1.2 Ossification of the cranial bones Left lateral view. The bones of the skull develop either directly or indirectly from mesenchymal connective tissue. The bones of the desmocranium (gray) develop directly via intramembranous ossification of mesenchymal connective tissue. The bones of the chondrocranium (blue) develop indirectly via endochondral ossification of hyaline cartilage. Note: The skull base is formed exclusively by the chondrocranium. Elements formed via intramembranous and endochondral ossification may fuse to form a single bone (e.g., the elements of the occipital, temporal, and sphenoid bones contributing to the skull base are cartilaginous, while the rest of the bone is membranous).

Table 1.1 Development of the skull The bones of the skull can be understood using three major criteria: embryonic origins, location in the skull, and type of ossification. The majority of the viscerocranium (facial skeleton) is derived from the pharyngeal (brachial) arches (see p. 61). The neurocranium (cranial vault) is divided into membranous and cartilaginous parts based on ossification. The cartilaginous neurocranium (endochondral ossification) forms the skull base. Embryonic origins Cranium Ossification Adult bone V N I E Paraxial mesoderm Nm I Occipital bone (upper portion) Nc E Occipital bone (lower portion) Nm I Parietal bone Nm E Temporal bone (petrous part) Nm E Temporal bone (mastoid process) Neural crest Nm I Temporal bone (squamous part) Nm I Frontal bone Nc E Sphenoid bone V I Sphenoid bone (pterygoid process) V E Ethmoid bone Nc E Ethmoid bone (cribriform plate) 1st branchial arch, V I Maxilla Neural crest, maxillary process pharyngeal V I Nasal bone (branchial) arches V I Lacrimal bone V I Vomer V I Palatine bone V I Zygomatic bone V I Temporal bone (tympanic part) V E Inferior nasal turbinate V I Mandible 1st branchial arch, mandibular V E Malleus process V E Incus 2nd branchial arch V E Stapes V E Temporal bone (styloid process) V E Hyoid bone (superior part, lesser cornu) 3rd branchial arch V E Hyoid bone (inferior part, greater cornu) V = viscerocranium; N = neurocranium; Nm = neurocranium (membranous); Nc = neurocranium (cartilaginous); I = intramembranous; E = endochondral. Note: Tubular (long) bones undergo endochondral ossification. The clavicle is the only exception. Congenital defects of intramembranous ossification therefore affect both the skull and clavicle (cleidocranial dysostosis).

2

Head

1. Cranial Bones

Anterior fontanelle Anterior fontanelle

Coronal suture Sphenoid (anterolateral) fontanelle

Posterior fontanelle

Frontal suture

Lambdoid suture

Coronal suture

Mastoid (posterolateral) fontanelle

A

Fig. 1.3 Cranial sutures (craniosynostoses) and fontanelles A Left lateral view of neonatal skull. B Superior view of neonatal skull. The flat cranial bones grow as the brain expands; thus the sutures between them remain open after birth. In the neonate, there are six areas

Pterion

Sagittal suture Posterior fontanelle

B

(fontanelles) between the still-growing cranial bones that are occupied by unossified fibrous membrane. The posterior fontanelle provides a reference point for describing the position of the fetal head during childbirth. The anterior fontanelle provides access for drawing cerebrospinal fluid (CSF) samples in infants (e.g., in suspected meningitis).

Coronal suture

Coronal suture Sagittal suture

Sphenofrontal suture

Squamous suture Lambdoid suture Lambdoid suture

Lambda

Asterion

B

Bregma

Sphenosquamous suture

A

Fig. 1.4 Sutures in the adult skull A Left lateral view. B Superior view. Synostosis (the fusion of the cranial bones along the sutures) occurs during adulthood. Although the exact times of closure vary,

the order (sagittal, coronal, lambdoid) does not. Closure of each fontanelle yields a particular junction (see Table 1.2). Premature closure of the cranial sutures produces characteristic deformities (see Fig. 1.14, p. 9).

Table 1.2 Closure of sutures and fontanelles Fontanelle

Age at closure

Suture

Age at ossification

1 Posterior fontanelle

2–3 months (lambda)

Frontal suture

Childhood

2 Sphenoid (anterolateral) fontanelles

6 months (pterion)

Sagittal suture

20–30 years old

2 Mastoid fontanelles

18 months (asterion)

Coronal suture

30–40 years old

1 Anterior fontanelle

36 months (bregma)

Lambdoid suture

40–50 years old

3

1. Cranial Bones

Head

Skull: Lateral View Coronal suture

Pterion Frontal bone

Squamous suture Parietal bone

Sphenoparietal suture

Sphenofrontal suture

Sphenosquamous suture Supraorbital foramen Sphenoid bone, greater wing Ethmoid bone Lacrimal bone Nasal bone

Infraorbital foramen Anterior nasal spine Maxilla Lambdoid suture

Styloid process Articular tubercle Postglenoid tubercle

Mandible Zygomatic arch

Mental protuberance

Zygomatic bone Mental foramen

Fig. 1.5 Lateral view of the skull (cranium) Left lateral view. This view displays the greatest number of cranial bones (indicated by different colors in Fig. 1.6). The individual bones and their salient features are described in the pages that follow. The teeth are described on pp. 180–189.

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Mastoid process External acoustic meatus

Mastoid foramen Tympanomastoid fissure

Asterion

Head

1. Cranial Bones

Temporal bone, squamous part Frontal bone

Parietal bone

Sphenoid bone, greater wing

Ethmoid bone Lacrimal bone Nasal bone

Zygomatic bone

Maxilla Occipital bone Temporal bone, petromastoid part Mandible

Temporal bone, styloid process

Temporal bone, tympanic part

Fig. 1.6 Cranial bones: overview Left lateral view. Table 1.3 Bones of the skull The cranial bones are shown within the skull and some are also shown individually (see referenced pages; boldface page numbers are for bones shown individually). Bone

Page

Bone

Page

Frontal bone

5, 7, 9, 11, 14, 108, 142

Temporal bone: • Squamous part • Petrous part • Tympanic part • Styloid part

5, 7, 9, 12, 14, 18, 19

Nasal bone

5, 7, 11, 108, 142

Occipital bone

5, 9, 11, 12, 14, 20

Lacrimal bone

5, 108, 142

Parietal bone

5, 7, 9, 11, 12, 14

Ethmoid bone

5, 7, 14, 21, 108, 142, 190

Sphenoid bone: • Greater wing • Lesser wing • Pterygoid process

5, 7, 9, 14, 16, 17, 108, 142, 190

Maxilla

5, 7, 9, 12, 108, 142, 190

Vomer

9, 12, 142, 190

Palatine bone

9, 12, 108, 142, 190

Inferior nasal concha

7, 12, 142, 190

Zygomatic bone

5, 7, 12, 108

Hyoid bone

23

Mandible

5, 7, 9, 22

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Head

1. Cranial Bones

Skull: Anterior View

Nasion

Frontal bone

Parietal bone

Frontal incisure

Supraorbital foramen

Supraorbital margin Nasal bone

Sphenoid bone, greater wing

Sphenoid bone, lesser wing

Temporal bone Orbit

Ethmoid bone, perpendicular plate

Sphenoid bone, greater wing Zygomatic (malar) bone

Infraorbital margin Ethmoid bone, middle nasal concha

Piriform (anterior nasal) aperture Maxilla

Vomer Inferior nasal concha

Infraorbital foramen

Anterior nasal spine Intermaxillary suture

Mandible

Fig. 1.7 Anterior view of the skull The boundaries of the facial skeleton (viscerocranium) can be clearly appreciated in this view (the individual bones are shown in Fig. 1.8). The bony margins of the anterior nasal aperture mark the start of the respiratory tract in the skull. The nasal cavity, like the orbits, contains a

Teeth

Mental foramen

sensory organ (the olfactory mucosa). The paranasal sinuses are shown schematically in Fig. 1.9. The anterior view of the skull also displays the three clinically important openings through which sensory nerves pass to supply the face: the supraorbital foramen, infraorbital foramen, and mental foramen.

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Head

1. Cranial Bones

Frontal sinus

Frontal bone Parietal bone

Nasal bone Ethmoid bone, middle nasal concha

Sphenoid bone, greater wing

Ethmoid cells

Temporal bone

Sphenoid sinus

Sphenoid bone, greater wing

Maxillary sinus

Zygomatic bone

Inferior nasal concha

Nasal cavity

Maxilla

Mandible

Fig. 1.8 Cranial bones, anterior view

Frontonasal pillar

Vertical zygomatic pillar

Fig. 1.9 Paranasal sinuses Anterior view. Some of the bones of the facial skeleton are pneumatized; that is, they contain air-filled cavities that reduce the total weight of the bone. These cavities, called the paranasal sinuses, communicate with the nasal cavity and, like it, are lined by ciliated respiratory epithelium. Inflammations of the paranasal sinuses (sinusitis) and associated complaints are very common. Because some of the pain of sinusitis is projected to the skin overlying the sinuses, it is helpful to know the projections of the sinuses onto the surface of the skull.

Horizontal zygomatic pillar

A

Frontonasal pillar Vertical zygomatic pillar

B

I Horizontal zygomatic pillar

Fig. 1.10 Principal lines of force (blue) in the facial skeleton A Anterior view. B Lateral view. The pneumatized paranasal sinuses (Fig. 1.9) have a mechanical counterpart in the thickened bony “pillars” of the facial skeleton, which partially bound the sinuses. These pillars develop along the principal lines of force in response to local mechanical stresses (e.g., masticatory pressures). In visual terms, the framelike construction of the facial skeleton may be likened to that of a frame house: the paranasal sinuses represent the rooms, and the pillars (placed along major lines of force) represent the supporting columns.

II

III

Fig. 1.11 Le Fort classification of midfacial fractures The framelike construction of the facial skeleton leads to characteristic patterns of fracture lines in the midfacial region (Le Fort I, II, and III). Le Fort I: This fracture line runs across the maxilla and above the hard palate. The maxilla is separated from the upper facial skeleton, disrupting the integrity of the maxillary sinus (low transverse fracture). Le Fort II: The fracture line passes across the nasal root, ethmoid bone, maxilla, and zygomatic bone, creating a pyramid fracture that disrupts the integrity of the orbit. Le Fort III: The facial skeleton is separated from the base of the skull. The main fracture line passes through the orbits, and the fracture may additionally involve the ethmoid bones, frontal sinuses, sphenoid sinuses, and zygomatic bones.

7

1. Cranial Bones

Head

Skull: Posterior View & Cranial Sutures

Parietal foramina

Lambda Sagittal suture

Parietal bone

Lambdoid suture Occipital plane Temporal bone, squamous part

Supreme nuchal line

Temporal bone, petrous part

Asterion Superior nuchal line

External occipital protuberance

Median nuchal line (external occipital crest)

Mastoid foramina Mastoid notch

Inferior nuchal line

Temporal bone, mastoid process

Vomer Occipital condyle

Temporal bone, styloid process

Palatine bone

Sphenoid bone, pterygoid process

Mandibular foramen

Mylohyoid groove Maxilla, palatine process

Incisive foramen

Mandible

Teeth Mylohyoid line

Digastric fossa

Fig. 1.12 Posterior view of the skull The occipital bone, which is dominant in this view, articulates with the parietal bones, to which it is connected by the lambdoid suture. Wormian (sutural) bones are isolated bone plates often found in the lambdoid suture. The cranial sutures are a special type of syndesmosis

8

Genial (mental) spines

(i.e., ligamentous attachments that ossify with age). The outer surface of the occipital bone is contoured by muscular origins and insertions: the inferior, superior, median, and supreme nuchal lines.

Head

1. Cranial Bones

Parietal bone

Occipital bone

Temporal bone, squamous part

Temporal bone, petromastoid part

Vomer

Sphenoid bone

Palatine bone

Maxilla Mandible

Fig. 1.13 Posterior view of the cranial bones

A

B

C

D

Fig. 1.14 Premature closure of cranial sutures The premature closure of a cranial suture (craniosynostosis) may lead to characteristic cranial deformities: A B C D

Sagittal suture: scaphocephaly (long, narrow skull). Coronal suture: oxycephaly (pointed skull). Frontal suture: trigonocephaly (triangular skull). Asymmetrical suture closure, usually involving the coronal suture: plagiocephaly (asymmetric skull).

A

B

Fig. 1.15 Hydrocephalus and microcephaly A Hydrocephalus: When the brain becomes dilated due to CSF accumulation before the cranial sutures ossify, the neurocranium will expand, whereas the facial skeleton remains unchanged. B Microcephaly: Premature closure of the cranial sutures results in a small neurocranium with relatively large orbits.

9

1. Cranial Bones

Head

Calvaria Nasal bone Bregma

Frontal bone

Coronal suture

Parietal bone

Frontal bone

Frontal crest

Frontal sinus Groove for superior sagittal sinus

Sagittal suture

Superior and inferior temporal lines A

Parietal foramen

Occipital bone

Lambdoid suture Meningeal grooves Parietal bone

Granular foveolae

Fig. 1.16 Exterior (A) and interior (B) of the calvaria The external surface of the calvaria (A) is relatively smooth, unlike its internal surface (B). It is defined by the frontal, parietal, and occipital bones, which are interconnected by the coronal, sagittal, and lambdoid sutures. The smooth external surface is interrupted by the parietal foramina, which gives passage to the parietal emissary veins (see Fig. 1.21). The internal surface of the calvaria bears a number of pits and grooves: • Granular foveolae (small pits in the inner surface of the skull caused by saccular protrusions of the arachnoid membrane [arachnoid granulations] covering the brain) • Groove for the superior sagittal sinus (a dural venous sinus of the brain, see Fig. 1.21 and Fig. 3.21, p. 53)

10

B Groove for superior sagittal sinus

Parietal foramen

• Arterial grooves (which mark the positions of the arterial vessels of the dura mater, such as the middle meningeal artery, which supplies most of the dura mater and overlying bone) • Frontal crest (which gives attachment to the falx cerebri, a sickleshaped fold of dura mater between the cerebral hemispheres).

Head

1. Cranial Bones

Nasal bone Diploic veins

Emissary vein Endosteal layer of dura mater

Frontal bone

Scalp Outer table Diploë Dural sinus

Inner table Dura mater

Parietal bone

Meningeal layer of dura mater Falx cerebri

Occipital bone

Fig. 1.17 Exterior of the calvaria viewed from above

Fig. 1.18 The scalp and calvaria The three-layered calvaria consists of the outer table, the diploë, and the inner table. The diploë has a spongy structure and contains red (blood-forming) bone marrow. With a plasmacytoma (malignant transformation of certain white blood cells), many small nests of tumor cells may destroy the surrounding bony trabeculae, and radiographs will demonstrate multiple lucent areas (“punched-out lesions”) in the skull.

Fig. 1.19 Sensitivity of the inner table to trauma The inner table of the calvaria is very sensitive to external trauma and may fracture even when the outer table remains intact (look for corresponding evidence on CT images).

Superior sagittal sinus Parietal emissary vein and foramen

Anterior temporal diploic vein Frontal diploic vein

Posterior temporal diploic vein

Confluence of the sinuses Transverse sinus

Occipital emissary vein and foramen

Sigmoid sinus

Mastoid emissary vein and foramen

Occipital diploic vein

Condylar emissary vein External vertebral venous plexus

Fig. 1.20 Diploic veins in the calvaria The diploic veins are located in the cancellous or spongy tissue of the cranial bones (the diploë) and are visible when the outer table is removed. The diploic veins communicate with the dural venous sinuses and scalp veins by way of the emissary veins, which create a potential route for the spread of infection.

Fig. 1.21 Emissary veins of the occiput Emissary veins establish a direct connection between the dural venous sinuses and the extracranial veins. They pass through cranial openings such as the parietal foramen and mastoid foramen. The emissary veins are of clinical interest because they may allow bacteria from the scalp to enter the skull along these veins and infect the dura mater, causing meningitis.

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Head

1. Cranial Bones

Skull Base: External View Median palatine suture

Teeth

Transverse palatine suture

Palatine process Maxilla Zygomatic process Zygomatic bone

Palatine bone

Frontal bone

Inferior nasal concha

Sphenoid bone

Vomer

Temporal bone, zygomatic process

Lateral and medial plates, pterygoid process

Temporal bone, squamous part

Spheno-occipital synchrondrosis

Temporal bone, tympanic part Temporal bone, petrous part, mastoid part

Foramen magnum

Occipital bone Parietal bone

Fig. 1.22 Bones of the base of the skull Inferior view. The base of the skull is composed of a mosaic-like assembly of various bones. Cavernous sinus

Fig. 1.23 Relationship of the foramen lacerum to the carotid canal and internal carotid artery Left lateral view. The foramen lacerum is not a true aperture, being mostly occluded in life by a layer of fibrocartilage; it appears as an opening only in the dried skull. The foramen lacerum is closely related to the carotid canal and to the internal carotid artery that traverses the canal. The greater petrosal nerve and deep petrosal nerve pass across the superior surface of the foramen lacerum (see pp. 85, 94).

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Middle cranial fossa

Carotid canal Temporal bone, petrous part

Fibrocartilage Sphenoid sinus Foramen lacerum

Internal carotid artery

Head

1. Cranial Bones

Incisive foramen (canal) Posterior nasal spine

Palatine bone

Choana

Greater palatine foramen

Zygomatic bone, temporal surface

Lesser palatine foramen

Inferior orbital fissure

Infratemporal crest Zygomatic arch

Scaphoid fossa Sphenoidal foramen

Hamulus Pharyngeal canal

Foramen ovale

Vomerovaginal canal

Foramen spinosum

Pharyngeal tubercle

Foramen lacerum Petrotympanic fissure

Mandibular fossa

Carotid canal

Occipital condyle

Jugular foramen

Mastoid process

Stylomastoid foramen

Mastoid incisure (Posterior) condylar canal

Hypoglossal (anterior condylar) canal

Mastoid foramen

Foramen magnum Inferior nuchal line

Median nuchal line

Superior nuchal line

Supreme nuchal line

Fig. 1.24 The basal aspect of the skull Inferior view. Note the openings that transmit nerves and vessels. With abnormalities of bone growth, these openings may remain too small or may become narrowed, compressing the neurovascular structures that

External occipital protuberance

pass through them. The symptoms associated with these lesions depend on the affected opening. All of the structures depicted here will be considered in more detail in subsequent pages.

13

1. Cranial Bones

Head

Skull Base: Internal View

Frontal bone

Anterior cranial fossa

Ethmoid bone Jugum sphenoidale

Sphenoid bone Temporal bone, squamous part Temporal bone, petromastoid part

Parietal bone

Sphenoid bone, lesser wing

Dorsum sellae

Middle cranial fossa

Foramen magnum

Petrous ridge (crest)

Posterior cranial fossa

Occipital bone A

Anterior cranial fossa

Fig. 1.25 Bones of the base of the skull, internal view

Frontonasal pillar Anterior transverse pillar Pterygoid pillar Midlongitudinal pillar

A

B

14

Vertical zygomatic pillar Horizontal zygomatic pillar

Posterior transverse pillar

B

Middle cranial fossa

Posterior cranial fossa

Foramen magnum

Fig. 1.26 The cranial fossae A Interior view. B Midsagittal section. The interior of the skull base is deepened to form three successive fossae: the anterior, middle, and posterior cranial fossae. These depressions become progressively deeper in the frontal-to-occipital direction, forming a terraced arrangement that is displayed most clearly in B. The cranial fossae are bounded by the following structures: • Anterior to middle: lesser wings of the sphenoid bone and the jugum sphenoidale • Middle to posterior: superior border (ridge) of the petrous part of the temporal bone and the dorsum sellae

Fig. 1.27 Base of the skull: principal lines of force and common fracture lines A Principal lines of force. B Common fracture lines (interior views). In response to masticatory pressures and other mechanical stresses, the bones of the skull base are thickened to form “pillars” along the principal lines of force (compare with the force distribution in the anterior view on p. 7). The intervening areas that are not thickened are sites of predilection for bone fractures, resulting in the typical patterns of basal skull fracture lines shown here. An analogous phenomenon of typical fracture lines is found in the midfacial region (see the anterior views of Le Fort fractures on p. 7).

Head

Ethmoid bone, cribriform plate

Frontal crest

1. Cranial Bones

Frontal sinus

Chiasmatic groove

Optic canal Anterior clinoid process Foramen ovale Foramen spinosum Arterial groove Foramen lacerum Clivus Petro-occipital fissure Hypoglossal canal

Ethmoid bone, crista galli Frontal bone

Sphenoid bone, lesser wing Sphenoid bone, greater wing Sphenoid bone, hypophyseal fossa Posterior clinoid process Temporal bone, petrous part Internal acoustic meatus Jugular foramen

Groove for sigmoid sinus

Foramen magnum Cerebellar fossa Internal occipital crest

Groove for transverse sinus

Internal occipital protuberance Cerebral fossa

Fig. 1.28 Interior of the base of the skull The openings in the interior of the base of the skull do not always coincide with the openings visible in the external view because some neurovascular structures change direction when passing through the bone or pursue a relatively long intraosseous course. An example of this is the internal acoustic meatus, through which the facial nerve, among other structures, passes from the interior of the skull into the petrous part of the temporal bone. Most of its fibers then leave the petrous bone through the stylomastoid foramen, which is visible from the external aspect (see Fig. 4.35, p. 83, and Fig. 4.53, p. 94 for further details).

located in the anterior, middle, or posterior cranial fossa. The arrangement of the cranial fossae is shown in Fig. 1.26. The cribriform plate of the ethmoid bone connects the nasal cavity with the anterior cranial fossa and is perforated by numerous foramina for the passage of the olfactory fibers (see Fig. 7.15, p. 148). Note: Because the bone is so thin in this area, a frontal head injury may easily fracture the cribriform plate and lacerate the dura mater, allowing CSF to enter the nose. This poses a risk of meningitis, as bacteria from the nonsterile nasal cavity may enter the sterile CSF.

In learning the sites where neurovascular structures pass through the base of the skull, it is helpful initially to note whether these sites are

15

Head

1. Cranial Bones

Sphenoid Bone

Palatine bone Sphenoid bone

Vomer

Occipital bone

Temporal bone

A

Frontal bone

Sphenoid bone

Parietal bone

Occipital bone

Temporal bone

B Parietal bone

Fig. 1.29 Position of the sphenoid bone in the skull The sphenoid bone is the most structurally complex bone in the human body. It must be viewed from various aspects in order to appreciate all its features (see also Fig. 1.30): A Base of the skull, external aspect. The sphenoid bone combines with the occipital bone to form the load-bearing midline structure of the skull base. B Base of the skull, internal aspect. The lesser wing of the sphenoid bone forms the boundary between the anterior and middle cranial fossae. The openings for the passage of nerves and vessels are clearly displayed (see details in Fig. 1.30). C Lateral view. Portions of the greater wing of the sphenoid bone can be seen above the zygomatic arch, and portions of the pterygoid process can be seen below the zygomatic arch.

Frontal bone

Sphenoid bone, greater wing

C

Fig. 1.30 Isolated sphenoid bone A Inferior view (its position in situ is shown in Fig. 1.29). This view demonstrates the medial and lateral plates of the pterygoid process. Between them is the pterygoid fossa, which is occupied by the medial pterygoid muscle. The foramen spinosum and foramen ovale provide pathways through the base of the skull (see also in C). B Anterior view. This view illustrates why the sphenoid bone was originally called the sphecoid bone (“wasp bone”) before a transcription error turned it into the sphenoid (“wedge-shaped”) bone. The apertures of the sphenoid sinus on each side resemble the eyes of the wasp, and the pterygoid processes of the sphenoid bone form its dangling legs, between which are the pterygoid fossae. This view also displays the superior orbital fissure, which connects the middle cranial fossa with the orbit on each side. The two sphenoid sinuses are separated by an internal septum (see Fig. 7.11, p. 145).

16

Pterygoid process

Temporal bone

C Superior view. The superior view displays the sella turcica, whose central depression, the hypophyseal fossa, contains the pituitary gland. The foramen spinosum, foramen ovale, and foramen rotundum can be identified. D Posterior view. The superior orbital fissure is seen particularly clearly in this view, whereas the optic canal is almost completely obscured by the anterior clinoid process. The foramen rotundum is open from the middle cranial fossa to the pterygopalatine fossa of the skull (the foramen spinosum is not visible in this view; compare with A). Because the sphenoid and occipital bones fuse together during puberty (“tribasilar bone”), a suture is no longer present between the two bones. The cancellous trabeculae are exposed and have a porous appearance.

Head

Superior orbital fissure

Lesser wing

Sphenoid crest

1. Cranial Bones

Aperture of sphenoid sinus Greater wing Foramen rotundum

Greater wing

Medial plate Lateral plate Temporal surface

Pterygoid process

Foramen ovale Foramen spinosum

A

Pterygoid hamulus

Body

Pterygoid fossa Lesser wing

Sphenoid crest

Aperture of sphenoid sinus

Orbital surface

Greater wing

Temporal surface

Superior orbital fissure

Foramen rotundum

Pterygoid canal

B

Lesser wing

Medial plate

Pterygoid fossa

Optic canal

Lateral plate

Pterygoid hamulus

Jugum sphenoidale

Pterygoid process

Superior orbital fissure

Greater wing Chiasmic groove Foramen rotundum Foramen ovale

Anterior clinoid process

Foramen spinosum C

Sella turcica

Hypophyseal fossa

Posterior clinoid process Lesser wing

Optic canal

Posterior clinoid process Superior orbital fissure

Anterior clinoid process

Greater wing, cerebral surface Foramen rotundum

Pterygoid canal

Cancellous trabeculae

Foramen ovale D

Pterygoid fossa

Dorsum sellae

Medial plate Lateral plate

Pterygoid process

17

1. Cranial Bones

Head

Temporal Bone

Parietal bone

Fig. 1.31 Position of the temporal bone in the skull Left lateral view. The temporal bone is a major component of the base of the skull. It forms the capsule for the auditory and vestibular apparatus and bears the articular fossa of the temporomandibular joint (TMJ).

Temporal bone Occipital bone

Zygomatic bone

Sphenoid bone, greater wing Petrous pyramid

Mandibular fossa Squamous part

Styloid process

Squamous part

Tympanic part Tympanic part

Petromastoid part

Petromastoid part

Styloid process B

A

Fig. 1.32 Ossification centers of the left temporal bone A Left lateral view. B Inferior view. The temporal bone develops from four centers that fuse to form a single bone: • The squamous part, or temporal squama (light green), bears the articular fossa of the TMJ (mandibular fossa).

Chorda tympani

Facial nerve

Tympanic membrane Pharyngotympanic (auditory) tube Internal carotid artery Internal jugular vein

18

Mastoid process

Mastoid air cells

• The petromastoid part (pale green) contains the auditory and vestibular apparatus. • The tympanic part (darker green) forms large portions of the external auditory canal. • The styloid part (styloid process) develops from cartilage derived from the second branchial arch. It is a site of muscle attachment.

Fig. 1.33 Projection of clinically important structures onto the left temporal bone The tympanic membrane is shown translucent in this lateral view. Because the petrous bone contains the middle and inner ear and the tympanic membrane, a knowledge of its anatomy is of key importance in otological surgery. The internal surface of the petrous bone has openings (see Fig. 1.34) for the passage of the facial nerve, internal carotid artery, and internal jugular vein. A fine nerve, the chorda tympani, passes through the tympanic cavity and lies medial to the tympanic membrane. The chorda tympani arises from the facial nerve, which is susceptible to injury during surgical procedures (see Table 4.22, p. 82, and Fig. 4.34, p. 83). The mastoid process of the petrous bone forms air-filled chambers, the mastoid cells, that vary greatly in size. Because these chambers communicate with the middle ear, which in turn communicates with the nasopharynx via the pharyngotympanic (auditory) tube (also called eustachian tube), bacteria in the nasopharynx may pass up the pharyngotympanic tube and gain access to the middle ear. From there they may pass to the mastoid air cells and finally enter the cranial cavity, causing meningitis.

Head

1. Cranial Bones

Postglenoid tubercle

Zygomatic process

Temporal surface

External acoustic opening Articular tubercle

Mastoid foramen

Mandibular fossa

External acoustic meatus

Petrotympanic fissure

Tympanomastoid fissure Styloid process

A

Zygomatic process

Tympanic canaliculus

Mastoid process

Articular tubercle Mandibular fossa

Arcuate eminence

Groove for middle meningeal arteries

Carotid canal

External acoustic opening

Styloid process

Petrous ridge (groove for superior petrosal sinus)

Mastoid process

Jugular fossa Mastoid canaliculus

Mastoid notch

Stylomastoid foramen Occipital groove

Mastoid foramen

Aqueduct of the vestibule B Zygomatic process Internal acoustic meatus Mastoid foramen

C

Petrous apex Groove for sigmoid sinus

Styloid process

Fig. 1.34 Left temporal bone A Lateral view. An emissary vein passes through the mastoid foramen H[WHUQDO RULÀFH VKRZQ LQ A LQWHUQDO RULÀFH LQ C  DQG WKH FKRUGD W\PSDQL SDVVHV WKURXJK WKH PHGLDO SDUW RI WKH SHWURW\PSDQLF ÀVsure (see Fig. 4.35S 7KHPDVWRLGSURFHVVGHYHORSVJUDGXDOO\ LQ OLIH GXH WR WUDFWLRQ IURP WKH VWHUQRFOHLGRPDVWRLG PXVFOH DQG LV pneumatized from the inside (see Fig. 1.33). B Inferior view.7KHVKDOORZDUWLFXODUIRVVDRIWKHWHPSRURPDQGLEXODU MRLQWWKHPDQGLEXODUIRVVD LVFOHDUO\VHHQIURPWKHLQIHULRUYLHZ7KH IDFLDO QHUYH HPHUJHV IURP WKH EDVH RI WKH VNXOO WKURXJK WKH VW\OR

PDVWRLGIRUDPHQ7KHLQLWLDOSDUWRIWKHVXSHULRUMXJXODUEXOELVDGKHUHQW WR WKH MXJXODU IRVVD DQG WKH LQWHUQDO FDURWLG DUWHU\ SDVVHV WKURXJKWKHFDURWLGFDQDOWRHQWHUWKHVNXOO C Medial view. 7KLV YLHZ GLVSOD\V WKH LQWHUQDO RULÀFH RI WKH PDVWRLG I RUDPHQDQGWKHLQWHUQDODFRXVWLFPHDWXV7KHIDFLDOQHUYHDQGYHVWLEXORFRFKOHDU QHUYH DUH DPRQJ WKH VWUXFWXUHV WKDW SDVV WKURXJK WKHLQWHUQDOPHDWXVWRHQWHUWKHSHWURXVERQH7KHSDUWRIWKHSHWURXV ERQH VKRZQ KHUH LV DOVR FDOOHG WKH petrous pyramid ZKRVH DSH[RIWHQFDOOHGWKH´SHWURXVDSH[µ OLHVRQWKHLQWHULRURIWKHEDVH RIWKHVNXOO

19

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Head

1. Cranial Bones

Occipital Bone & Ethmoid Bones

Occipital squama

Hypoglossal canal (anterior condylar) Foramen magnum

Fig. 1.35 Integration of the occipital bone into the external base of the skull Inferior view. B

Jugular notch

Posterior condylar canal Jugular process

Basilar part

Hypoglossal (anterior condylar) canal

Groove for superior sagittal sinus

Pharyngeal tubercle

(Posterior) condylar canal

Internal occipital crest

Inferior nuchal line

Posterior condylar canal

Foramen magnum

Superior nuchal line

External occipital protuberance

Supreme nuchal line

Fig. 1.36 Isolated occipital bone A Inferior view. This view shows the basilar part of the occipital bone, whose anterior portion is fused to the sphenoid bone. The condylar canal terminates posterior to the occipital condyles, and the hypoglossal canal passes superior and opens anterior to the occipital condyles. The condylar canal is a venous channel that begins in the sigmoid sinus and ends in the occipital vein. The hypoglossal canal contains a venous plexus in addition to the hypoglossal nerve (CN XII). The pharyngeal tubercle gives attachment to the pharyngeal raphe, and the external occipital protuberance provides a palpable bony landmark on the occiput.

20

Groove for transverse sinus

Cruciform eminence

External occipital crest (median nuchal line)

A

Internal occipital protuberance

Occipital condyle

Foramen magnum

Jugular process C

Basilar part

B Left lateral view. The extent of the occipital squama, which lies above the foramen magnum, is clearly appreciated in this view. The internal openings of the condylar canal and hypoglossal canal are visible along with the jugular process, which forms part of the wall of the jugular foramen (see p. 13). C Internal surface. The grooves for the dural venous sinuses of the brain can be identified in this view. The cruciform eminence overlies the confluence of the superior sagittal sinus and transverse sinuses. The configuration of the eminence shows that in some cases the sagittal sinus drains predominantly into the left transverse sinus.

Head

Fig. 1.37 Integration of the ethmoid bone into the internal base of the skull Superior view. The superior part of the ethmoid bone forms part of the anterior cranial fossa, and its inferior portions contribute structurally to the nasal cavities and orbit. The ethmoid bone is bordered by the frontal and sphenoid bones.

1. Cranial Bones

Fig. 1.38 Integration of the ethmoid bone into the facial skeleton Anterior view. The ethmoid bone is the central bone of the nose and paranasal sinuses. It also forms the medial wall of each orbit.

Perpendicular plate

Crista galli

Crista galli Cribriform plate

Ethmoid air cells

Orbital plate

A

Crista galli

B Anterior ethmoid foramen

Ethmoid air cells

Orbital plate

Superior meatus

Middle concha

Crista galli

Posterior ethmoid foramen

Ethmoid air cells

Perpendicular plate

Orbital plate Superior concha

Ethmoid bulla Perpendicular plate

Middle concha C

Fig. 1.39 Isolated ethmoid bone A Superior view. This view demonstrates the crista galli, which gives attachment to the falx cerebri and the horizontally directed cribriform plate. The cribriform plate is perforated by foramina through which the olfactory fibers pass from the nasal cavity into the anterior cranial fossa (see Fig. 7.15, p. 148). With its numerous foramina, the cribriform plate is a mechanically weak structure that fractures easily in response to trauma. This type of fracture is manifested clinically by CSF leakage from the nose (“runny nose” in a patient with head injury). B Anterior view. The anterior view displays the midline structure that separates the two nasal cavities: the perpendicular plate. Note also the middle concha, which is part of the ethmoid bone (of the conchae, only the inferior concha is a separate bone), and the ethmoid cells, which are clustered on both sides of the middle conchae.

Ethmoid infundibulum

Uncinate process

D

Middle concha

Perpendicular plate

C Left lateral view. Viewing the bone from the left side, we observe the perpendicular plate and the opened anterior ethmoid cells. The orbit is separated from the ethmoid cells by a thin sheet of bone called the orbital plate. D Posterior view. This is the only view that displays the uncinate process, which is almost completely covered by the middle concha when in situ. It partially occludes the entrance to the maxillary sinus, the semilunar hiatus, and it is an important landmark during endoscopic surgery of the maxillary sinus. The narrow depression between the middle concha and uncinate process is called the ethmoid infundibulum. The frontal sinus, maxillary sinus, and anterior ethmoid air cells open into this “funnel.” The superior concha is located at the posterior end of the ethmoid bone.

21

1. Cranial Bones

Head

Mandible & Hyoid Bone

Head of mandible

Pterygoid fovea

Neck of mandible

Coronoid process Oblique line Ramus of mandible

Head of mandible

Alveolar part of mandible Mental foramen

Alveoli (tooth sockets)

Coronoid process Lingula

A

Mental protuberance

Body of mandible

Mandibular notch Coronoid process

Mandibular foramen Mylohyoid groove Head of condyle Pterygoid fovea Condylar process

Sublingual fossa

Submandibular fossa

Mandibular foramen

B

Lingula

Superior and inferior genial spines

Digastric fossa

Mylohyoid line

Ramus of mandible Alveolar part Mental tubercle

C

Angle

Mental foramen

Body of mandible

Oblique line

Fig. 1.40 Mandible A Anterior view. The mandible is connected to the viscerocranium at the temporomandibular joint, whose convex surface is the head of the mandibular condyle. This “head of the mandible” is situated atop the vertical (ascending) ramus of the mandible, which joins with the body of the mandible at the mandibular angle. The teeth are set in the alveolar processes (alveolar part) along the upper border of the mandibular body. This part of the mandible is subject to typical agerelated changes as a result of dental development (see Fig. 1.41). The mental branch of the trigeminal nerve exits through the mental foramen. The location of this foramen is important in clinical examinations, as the tenderness of the nerve to pressure can be tested at that location.

22

B Posterior view. The mandibular foramen is particularly well displayed in this view. It transmits the inferior alveolar nerve, which supplies sensory innervation to the mandibular teeth. Its terminal branch emerges from the mental foramen. The mandibular foramen and the mental foramen are interconnected by the mandibular canal. C Oblique left lateral view. This view displays the coronoid process, the condylar process, and the mandibular notch between them. The coronoid process is a site for muscular attachments, and the condylar process bears the head of the mandible, which articulates with the articular disk in the mandibular fossa of the temporal bone. A depression on the medial side of the condylar process, the pterygoid fovea, gives attachment to portions of the lateral pterygoid muscle.

Head

1. Cranial Bones

A

B

C

Fig. 1.41 Age-related changes in the mandible The structure of the mandible is greatly influenced by the alveolar processes of the teeth. Because the angle of the mandible adapts to changes in the alveolar process, the angle between the body and ramus also varies with age-related changes in the dentition. The angle measures approximately 150 degrees at birth and approximately 120 to 130 degrees in adults, decreasing to 140 degrees in the edentulous mandible of old age. A At birth the mandible is without teeth, and the alveolar part has not yet formed. B In children the mandible bears the deciduous teeth. The alveolar part is still relatively poorly developed because the deciduous teeth are considerably smaller than the permanent teeth.

Lesser horn

A

D

C In adults the mandible bears the permanent teeth, and the alveolar part of the bone is fully developed. D Old age is characterized by an edentulous mandible with resorption of the alveolar process. Note: The resorption of the alveolar process with advanced age leads to a change in the position of the mental foramen (which is normally located below the second premolar tooth, as in C). This change must be taken into account in surgery or dissections involving the mental nerve.

Greater horn

Lesser horn

B

Body

Greater horn

Body

Lesser horn

Greater horn

C

Fig. 1.42 Hyoid bone A Anterior view. B Posterior view. C Oblique left lateral view. The hyoid bone is suspended by muscles between the oral floor and larynx in the

neck. The greater horn and body of the hyoid bone are palpable in the neck. The physiological movement of the hyoid bone during swallowing is also palpable.

23

Head

2. Muscles of the Skull & Face

Muscles of Facial Expression

Galea aponeurotica (epicranial aponeurosis)

Occipitofrontalis, frontal belly

Corrugator supercilii

Procerus Levator labii superioris alaeque nasi

Orbicularis oculi

Levator labii superioris alaeque nasi Levator labii superioris

Nasalis

Zygomaticus minor

Levator labii superioris

Zygomaticus major

Zygomaticus minor

Levator anguli oris

Zygomaticus major

Parotid duct and gland Buccinator Buccal fat pad

Levator anguli oris Risorius

Depressor anguli oris Platysma Depressor labii inferioris

Fig. 2.1 Superficial facial muscles: anterior view Anterior view. The superficial layer of muscles is shown on the right side of the face. Certain muscles have been cut on the left to expose deeper muscles. The muscles of facial expression are the superficial layer of muscles that arise either directly from the periosteum or from adjacent muscles and insert onto other facial muscles or directly into the connective tissue of the skin. Because of their cutaneous attachments, the muscles of facial expression are able to move the facial skin (an action that may be temporarily abolished by botulinum toxin in-

24

Masseter (muscle of mastication) Orbicularis oris Depressor anguli oris Depressor labii inferioris Mentalis

jection). They also serve a protective function (especially for the eyes) and are active during food ingestion (closing the mouth). The muscles of facial expression are innervated by branches of the facial nerve (CN VII). As these muscles terminate directly in the subcutaneous fat, and because the superficial body fascia is absent in the face, surgeons must be particularly careful when dissecting this region. The muscles of mastication lie deep to the muscles of facial expression. They control the movement of the mandible and are innervated by branches of the trigeminal nerve (CN V).

Head

2. Muscles of the Skull & Face

Galea aponeurotica Superior auricular muscle Occipitofrontalis, frontal belly

Temporoparietalis (variable) Orbicularis oculi Anterior auricular muscle Nasalis Levator labii superioris alaeque nasi

Levator labii superioris Occipitofrontalis, occipital belly

Zygomaticus minor

Posterior auricular muscle

Orbicularis oris Zygomaticus major

Trapezius

Risorius

Sternocleidomastoid

Depressor labii inferioris Mentalis

Depressor anguli oris Platysma

Fig. 2.2 6XSHUÀFLDOIDFLDOPXVFOHVODWHUDOYLHZ Left lateral view. The galea aponeurotica is a tough tendinous sheet stretching over the calvaria; it is loosely attached to the periosteum. The muscles of the calvaria that arise from the galea aponeurotica (temporoparietalis and occipitofrontalis) are collectively known as the “epicranial muscles.” The occipitofrontalis has two bellies: frontal and RFFLSLWDO 7KH WUDSH]LXV DQG VWHUQRFOHLGRPDVWRLG PXVFOHV DUH VXSHUÀcial neck muscles.

25

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Head

2. Muscles of the Skull & Face

Muscles of Facial Expression: Calvaria, Ear & Eye

Galea aponeurotica

Epicranial aponeurosis

④ ②

① Orbicularis oculi

③

Procerus

Corrugator supercilii

A

B

Parotid gland

Fig. 2.3 Muscles of facial expression: calvaria and ear A Anterior view of calvaria. B Left lateral view of auricular muscles.

⑤

⑥

Orbicularis oculi, orbital part

⑦

Orbicularis oculi, orbital parts

Orbicularis oculi, palpebral parts

Orbicularis oculi, lacrimal part Posterior lacrimal crest

Zygomaticus major and minor

⑨

Alar cartilage

⑧

Levator labii superioris

A

Fig. 2.4 Muscles of facial expression: palpebral fissure and nose A Anterior view. The most functionally important muscle of this region is the orbicularis oculi, which closes the palpebral fissure (a protective reflex against foreign matter). As the orbicularis oculi closes the palpebral fissure, it does so by closing from lateral to medial, thus spreading lacrimal secretions across the cornea. If the action of the orbicularis oculi is lost because of facial nerve paralysis, the loss of this protective reflex will be accompanied by drying of the eye from prolonged exposure to the air. The function of the orbic-

26

Anterior lacrimal crest B

ularis oculi is tested by asking the patient to squeeze the eyelids tightly shut. B The orbicularis oculi has been dissected from the left orbit to the medial canthus of the eye and reflected anteriorly to demonstrate its lacrimal part (called the Horner muscle). This part of the orbicularis oculi arises mainly from the posterior lacrimal crest, and its action is a subject of debate (it may have a functional role in drainage of the lacrimal sac).

2. Muscles of the Skull & Face

Head

B

A

D

C

Fig. 2.5 Changes of facial expression: palpebral fissure and nose Anterior view. A Corrugator supercilii. B Orbicularis oculi. C Nasalis. D Levator labii superioris alaeque nasi.

Table 2.1 Muscles of facial expression: calvaria & ear, palbebral fissure & nose Muscle and parts

Origin

Insertion

I*

Main action(s)

Epicranial aponeurosis near coronal suture

Skin and subcutaneous tissue of eyebrows and forehead

T

Elevates eyebrows; wrinkles skin of forehead

T

Elevate ear

Calvaria and ear ① Occipitofrontalis, frontal belly

Auricularis muscles ②

Anterior

Temporal fascia (anterior portion)

Helix of the ear

• Pull ear superiorly and anteriorly

③

Posterior

Epicranial aponeurosis on side of head

Upper portion of auricle

• Elevate ear

④

Superior

Temporal fascia

Helix of the ear

Occipital bone (highest nuchal line) and temporal bone (mastoid part)

Epicranial aponeurosis near coronal suture

Occipitofrontalis, occipital belly

PA

• Pull ear superiorly and posteriorly Pulls scalp backwards

Palpebral fissure and nose ⑤

Orbicularis oculi

Whole muscle acts as orbital sphincter (closes eyelids) T/Z

• Voluntary closure of eyelids, furrowing of nose and eyebrows during squinting

• Orbital part

Medial orbital margin (frontal bone and maxilla) and medial palpebral ligament

Adjacent muscles (occipitofrontalis, corrugator supercilii, levator labii, etc.)

• Palpebral part

Medial palpebral ligament

Eyelids (as lateral palpebral raphe)

• Voluntary (sleeping) and involuntary closure (blinking) of eyelids

• Lacrimal part

Lacrimal crest

Tarsi of eyelids, lateral palpebral raphe

• Pulls eyelids medially

⑥

Procerus

Fascial aponeurosis of lower nasal bone

Skin between eyebrows

T/Z

Pulls eyebrows medially and inferiorly (frowning)

⑦

Corrugator supercilii

Bone of superciliary arch (medial end)

Skin above supraorbital margin

T

Acts with orbicularis oculi to pull eyebrows medially and inferiorly (during squinting)

⑧

Nasalis Maxilla

Aponeurosis at bridge of nose

B/Z

• Compresses nasal aperture (compressor naris)

• Transverse part • Alar part ⑨ Levator labii superioris alaeque nasi

Ala nasi Frontal process of maxilla

Greater alar cartilage and orbital muscles (levator labii superioris and orbicularis oris)

• Widens nasal aperture (flares nostril) by drawing ala toward nasal septum B/Z

Elevates upper lip, increases the curvature of the nasolabial furrow, dilates nostril

* Innervation: The muscles of facial expression are innervated by six branches of the facial nerve (CN VII). The posterior muscles are innervated by the posterior auricular (PA) nerve, which arises before the facial nerve enters the parotid gland (see p. 84). The anterior muscles are innervated by five branches off the parotid plexus of the facial nerve: temporal (T), zygomatic (Z), buccal (B), mandibular (M), and cervical (C).

27

Head

2. Muscles of the Skull & Face

Muscles of Facial Expression: Mouth ④

Orbicularis oculi

③ Levator anguli oris

Lateral pterygoid Temporomandibular joint

①

② Orbicularis oris Risorius

Masseter (muscle of mastication)

Masseter (cut)

⑤ B

A

Mentalis

Temporalis (cut) (muscle of mastication)

⑥

Levator labii superioris

Lateral pterygoid (muscle of mastication) Orbicularis oris

Medial pterygoid (muscle of mastication) Mandibular ramus (cut)

Depressor labii inferioris Mentalis

C

Depressor anguli oris

⑧

Masseter (cut) D

Depressor labii inferioris

⑦

Zygomaticus minor Zygomaticus major

Buccinator

Zygomaticus minor (cut) Levator labii superioris

Zygomaticus major (cut)

Parotid duct Levator anguli oris

Fig. 2.6 Muscles of facial expression: mouth Left lateral view. A Zygomaticus major and minor. B Levator labii superioris and depressor labii inferioris (exposed by removal of the depressor anguli oris). C Buccinator. D Levator anguli oris and depressor anguli oris. E Anterior view.

28

Levator anguli oris (cut) Buccinator

⑩

Masseter

Platysma

⑨

Depressor anguli oris E

Depressor anguli oris (cut) Depressor labii inferioris

⑪

Depressor labii inferioris (cut)

Head

A

B

C

D

E

F

G

H

2. Muscles of the Skull & Face

Fig. 2.7 Changes of facial expression: mouth Anterior view. A Orbicularis oris. B Buccinator. C Zygomaticus major. D Risorius. E Levator anguli oris. F Depressor anguli oris. G Depressor labii inferioris. H Mentalis.

Table 2.2 Muscles of facial expression: mouth Muscle ①

Zygomaticus major

②

Zygomaticus minor

Origin

Insertion

I*

Main action(s)

Zygomatic bone (lateral surface, posterior part)

Muscles at the angle of the mouth

Z

Pulls corner of mouth superiorly and laterally

Upper lip just medial to corner of the mouth

Pulls upper lip superiorly

③ Levator labii superioris alaeque nasi (see Fig. 2.1)

Maxilla (frontal process)

Upper lip and alar cartilage of nose

Levator labii superioris

Maxilla (frontal process) and infraorbital margin

Skin of upper lip

Mandible (anterior portion of oblique line)

Lower lip at midline; blends with muscle from opposite side

M

Pulls lower lip inferiorly and laterally, also contributes to eversion (pouting)

④

⑤ Depressor labii inferioris

B/Z

Elevates upper lip; flares nostril Elevates upper lip

⑥

Levator anguli oris

Maxilla (canine fossa, below infraorbital foramen)

Muscles at the angle of mouth

B/Z

Raises angle of mouth; helps form nasolabial furrow

⑦

Depressor anguli oris

Mandible (oblique line below canine, premolar, and 1st molar teeth)

Skin at corner of mouth; blends with orbicularis oris

B/M

Pulls angle of mouth inferiorly and laterally

⑧

Buccinator

Alveolar processes of maxilla and mandible (by molars); pterygomandibular raphe

Lips, orbicularis oris, submucosa of lips and cheek

B

• Suckling in nursing infant • Presses cheek against molar teeth, working with tongue to keep food between occlusal surfaces and out of oral vestibule; expels air from oral cavity/resists distention when blowing Unilateral: draws mouth to one side

⑨

Orbicularis oris

Deep surface of skin Superiorly: Maxilla (median plane) Inferiorly: Mandible

Mucous membrane of lips

B/M

Acts as oral sphincter • Compresses and protrudes lip (e.g., whistling, sucking, kissing) • Resists distention (when blowing)

⑩

Risorius

Fascia and superficial muscles over masseter

Skin of corner of mouth

B

Retracts corner of mouth as in smiling, laughing, grimacing

⑪

Mentalis

Frenulum of lower lip

Skin of chin

M

Elevates and protrudes lower lip (drinking)

Skin over lower neck and upper lateral thorax

Mandible (inferior border); skin over lower face; angle of mouth

C

Depresses and wrinkles skin of lower face and mouth; tenses skin of neck; aids in forced depression of the mandible

Platysma

* Innervation: The muscles of facial expression are innervated by six branches of the facial nerve (CN VII). The posterior muscles are innervated by the posterior auricular (PA) nerve, which arises before the facial nerve enters the parotid gland (see p. 84). The anterior muscles are innervated by five branches off the parotid plexus of the facial nerve: temporal (T), zygomatic (Z), buccal (B), mandibular (M), and cervical (C).

29

Head

2. Muscles of the Skull & Face

Muscles of Mastication: Overview The muscles of mastication are located at various depths in the parotid and infratemporal regions of the face. They attach to the mandible and

receive their motor innervation from the mandibular division of the trigeminal nerve (CN V3).

Table 2.3 Masseter and temporalis muscles Muscle

Masseter

Origin

Insertion

Innervation*

Action

①

Superficial head

Zygomatic bone (maxillary process) and zygomatic arch (lateral aspect of anterior ⅔)

Mandibular angle and ramus (inferior lateral surface)

Masseteric n. (anterior division of CN V3)

Elevates mandible; also assists in protraction, retraction, and side-to-side motion

Middle head

Zygomatic arch (medial aspect of anterior ⅔)

Mandibular ramus (central part of occlusal surface)

Zygomatic arch (deep surface of posterior ⅓)

Mandibular ramus (superior lateral surface) and inferior coronoid process

Temporal fascia

Coronoid process of mandible (apex, medial surface, and anterior surface of mandibular ramus)

Deep temporal nn. (anterior division of CN V3)

Vertical (anterior) fibers: Elevate mandible Horizontal (posterior) fibers: Retract (retrude) mandible Unilateral: Lateral movement of mandible (chewing)

②

Temporalis

Deep head

Superficial head ③

④

Deep head

Temporal fossa (inferior temporal line)

* The muscles of mastication are innervated by motor branches of the mandibular nerve (CN V3), the 3rd division of the trigeminal nerve (CN V).

⑤

④ ③

⑥ ⑦

① ② ⑧

Fig. 2.8 Masseter

Fig. 2.9 Temporalis

Fig. 2.10 Pterygoids

Table 2.4 Lateral and medial pterygoid muscles Muscle

Lateral pterygoid

Medial pterygoid

Origin

Insertion

Innervation

Action

⑤

Superior (upper) head

Greater wing of sphenoid bone (infratemporal crest)

Mandible (pterygoid fovea) and temporomandibular joint (articular disk)

⑥

Inferior (lower) head

Lateral pterygoid plate (lateral surface)

Mandible (pterygoid fovea and condylar process)

Mandibular n. (anterior division of CN V3) via lateral pterygoid n.

Bilateral: Protrudes mandible (pulls articular disk forward) Unilateral: Lateral movements of mandible (chewing)

⑦

Superficial (external) head

Maxilla (maxillary tuberosity) and palatine bone (pyramidal process)

Pterygoid rugosity on medial surface of the mandibular angle

Elevates (adducts) mandible

Deep (internal) head

Medial surface of lateral pterygoid plate and pterygoid fossa

Mandibular n. (anterior division of CN V3) via medial pterygoid n.

⑧

30

2. Muscles of the Skull & Face

Head

Zygomatic arch

Frontal bone

Parietal bone Inferior temporal line Superior temporal line

Masseter, deep part

Temporalis

Temporal bone External acoustic meatus Mastoid process Zygomatic arch (cut)

Joint capsule of temporomandibular joint

Temporalis

Styloid process A

Masseter, superficial part

Lateral ligament

Fig. 2.11 Temporalis and masseter Left lateral view. A Superficial dissection. B Deep dissection. The masseter and zygomatic arch have been partially removed to show the full extent of the temporalis. The temporalis is the most powerful muscle of mastication, doing approximately half the work. It works with the masseter (consisting of a superficial, an intermediate, and a deep part) to elevate the mandible and close the mouth. Note: A small portion of the lateral pterygoid is visible in B.

Joint capsule Lateral ligament Lateral pterygoid B

Coronoid process

Masseter (cut)

31

Head

2. Muscles of the Skull & Face

Muscles of Mastication: Deep Muscles

Temporalis (cut)

Lateral pterygoid, superior head (cut)

Lateral pterygoid, superior head

Articular disk

Temporomandibular joint capsule

Lateral pterygoid, inferior head (cut)

Lateral pterygoid, inferior head

Medial pterygoid, deep (internal) head

Medial pterygoid (superficial and deep heads)

Pterygoid process, lateral plate

Masseter (cut) A

Fig. 2.12 Lateral and medial pterygoid muscles Left lateral views. A The coronoid process of the mandible has been removed here along with the lower part of the temporalis so that both pterygoid muscles are observed (see Fig. 2.11B). B Here the temporalis has been completely removed, and the inferior head of the lateral pterygoid has been windowed. The lateral pterygoid initiates depression of the mandible, which is then continued by the suprahyoid and infrahyoid muscles and gravity. With

B

Medial pterygoid, superficial (external) head

the temporomandibular joint opened, we can see that fibers from the superior head of the lateral pterygoid blend with the articular disk. The lateral pterygoid functions as the guide muscle of the temporomandibular joint. The medial pterygoid runs almost perpendicular to the lateral pterygoid and contributes to the formation of a muscular sling that partially encompasses the mandible (see Fig. 2.13). Note how the inferior head of the lateral pterygoid originates between the two heads of the medial pterygoid.

Pterygoid process, lateral plate Temporalis

Temporalis Upper and lower compartments Lateral pterygoid, superior head

Articular disk Head (condyle) of mandible, articular surface

Lateral pterygoid, inferior head

Coronoid process (with temporalis)

Fig. 2.13 Masticatory muscular sling Oblique posterior view. The masseter and medial pterygoid form a muscular sling in which the mandible is suspended. By combining the actions of both muscles into a functional unit, this sling enables powerful closure of the jaws and side-to-side movements when acting unilaterally. Note: The space between the medial border of the mandible and the medial pterygoid is referred to as the pterygomandibular space. It is important as it is the target area for administering local anesthesia to the inferior alveolar nerve.

32

Masseter, deep head Medial pterygoid, deep (internal) head Masseter, superficial head Mandibular angle

Pterygoid process, medial plate

Head

2. Muscles of the Skull & Face

Superior sagittal sinus

Falx cerebri

Frontal lobe

Inferior sagittal sinus

Superficial and deep temporal fascia

Dura mater

Temporal lobe Optic nerve (CN II)

Ethmoid air cells

Temporalis (deep and superfical heads)

Sphenoid sinus

Lateral pterygoid, superior head

Zygomatic arch

Masseter, deep head

Coronoid process Nasopharynx

Lateral pterygoid, inferior head Lateral pterygoid plate Medial pterygoid

Parotid gland Oropharynx

Masseter, superficial head

Tongue

Inferior alveolar nerve (from posterior division of CN V3) in mandibular canal

Mandible

Lingual septum

Submandibular gland (extraoral lobe)

Platysma

Geniohyoid

Hyoglossus

Digastric, anterior belly

Mylohyoid

Fig. 2.14 Muscles of mastication, coronal section at the level of the sphenoid sinus Posterior view. The topography of the muscles of mastication and neighboring structures is particularly well displayed in this section.

33

Head

2. Muscles of the Skull & Face

Temporomandibular Joint (TMJ): Biomechanics

Retrusion

Transverse axis through head of mandible (axis of rotation)

150°

A

Head (condyle) of mandible

B

Median plane

Protrusion

Axis of rotation

Axis of rotation

Resting condyle Swinging condyle

Balance side (mediotrusion)

Working side (laterotrusion) Working side

C

Bennett angle

Fig. 2.15 Movements of the mandible in the TMJ Superior view. Most of the movements in the TMJ are complex motions that have three main components: • Rotation (opening and closing the mouth) • Translation (protrusion and retrusion of the mandible) • Grinding movements during mastication A Rotation. The axis for joint rotation runs transversely through both heads of the mandible. The two axes intersect at an angle of approximately 150 degrees (range of 110–180 degrees between individuals). During this movement the TMJ acts as a hinge joint (abduction/depression and adduction/elevation of the mandible). In humans, pure rotation in the TMJ usually occurs only during sleep with the mouth slightly open (aperture angle up to approximately 15 degrees, see Fig. 2.16B). When the mouth is opened past 15 degrees, rotation is combined with translation (gliding) of the mandibular head.

34

Balance side

D

B Translation. In this movement the mandible is advanced (protruded) and retracted (retruded). The axes for this movement are parallel to the median axes through the center of the mandibular heads. C Grinding movements in the left TMJ. In describing these lateral movements, a distinction is made between the “resting condyle” and the “swinging condyle.” The resting condyle on the left working side rotates about an almost vertical axis through the head of the mandible (also a rotational axis), whereas the swinging condyle on the right balance side swings forward and inward in a translational movement. The lateral excursion of the mandible is measured in degrees and is called the Bennett angle. During this movement the mandible moves in laterotrusion on the working side and in mediotrusion on the balance side. D Grinding movements in the right TMJ. Here, the right TMJ is the working side. The right resting condyle rotates about an almost vertical axis, and the left condyle on the balance side swings forward and inward.

Head

Lateral pterygoid muscle, superior head

2. Muscles of the Skull & Face

Articular tubercle Mandibular fossa Articular disk Head of mandible Joint capsule Lateral pterygoid muscle, inferior head

A

Lateral pterygoid muscle, superior head Articular disk Head of mandible Joint capsule Lateral pterygoid muscle, inferior head

15°

Axis of rotation

B Lateral pterygoid muscle, superior head Mandibular fossa Upper compartment Articular disk Joint capsule Lateral pterygoid muscle, inferior head

>15°

C

Fig. 2.16 Movements of the TMJ Left lateral view. Each drawing shows the left TMJ (including the articular disk and capsule) and the lateral pterygoid muscle. Note: The gap between the heads of the lateral pterygoid is exaggerated. Each schematic diagram at right shows the corresponding axis of joint movement. The muscle, capsule, and disk form a functionally coordinated musculo-disco-capsular system and work closely together when the mouth is opened and closed.

A Mouth closed. When the mouth is in a closed position, the head of the mandible rests against the mandibular (glenoid) fossa of the temporal bone. B Mouth opened to 15 degrees. Up to 15 degrees of abduction, the head of the mandible remains in the mandibular fossa. C Mouth opened past 15 degrees. At this point the head of the mandible glides forward onto the articular tubercle. The joint axis that runs transversely through the mandibular head is shifted forward. The articular disk is pulled forward by the superior part of the lateral pterygoid muscle, and the head (condyle) of the mandible is drawn forward by the inferior part of that muscle.

35

Head

2. Muscles of the Skull & Face

Temporomandibular Joint (TMJ)

Foramen spinosum

Zygomatic bone Pterygoid process, medial and lateral plates Foramen ovale (conducts CN V3)

Zygomatic process of temporal bone

Articular tubercle

Spine of sphenoid bone Petrotympanic fissure Tympanosquamosal suture Styloid process

Mandibular (glenoid) fossa External acoustic meatus (auditory canal)

Mastoid process

Stylomastoid foramen Jugular foramen

Fig. 2.17 Mandibular (glenoid) fossa of the TMJ Inferior view. The head of the mandible articulates with the articular disk in the mandibular (glenoid) fossa of the temporal bone. The mandibular fossa is a depression in the squamous part of the temporal bone. The articular tubercle is located on the anterior side of the mandibular fossa. The head of the mandible is markedly smaller than the mandibular fossa, allowing it to have an adequate range of movement (see p. 35). Unlike other articular surfaces, the mandibular fossa is covered by fibrocartilage rather than hyaline cartilage. As a result, it is not

Carotid canal

as clearly delineated on the skull as other articular surfaces. The external auditory canal lies just posterior to the mandibular fossa. Trauma to the mandible may damage the auditory canal. Note: The mandibular fossa is divided into two compartments (anterior and posterior), separated by the tympanosquamosal and petrotympanic fissures. The posterior compartment is nonarticulatory, and the chorda tympani nerve and inferior tympanic artery are able to pass through this space without being compressed. The glenoid lobe of the parotid gland may also project into the posterior compartment.

Head of mandible

Joint capsule

Pterygoid fovea

Neck of mandible

Coronoid process Neck of mandible

Lingula Mandibular foramen

A

B

Stylomandibular ligament

Mylohyoid groove

Fig. 2.18 Processes of the mandible A Anterior view. B Posterior view. The head of the mandible not only is markedly smaller than the articular fossa but also has a cylindrical shape. This shape increases the mobility of the mandibular head, as it allows rotational movements about a vertical axis.

36

Lateral ligament

Fig. 2.19 Ligaments of the left TMJ Lateral view. The TMJ is surrounded by a relatively lax capsule, which permits physiological dislocation during jaw opening. The joint is stabilized by three ligaments: lateral (temporomandibular), stylomandibular, and sphenomandibular. This lateral view demonstrates the strongest of these ligaments, the lateral ligament, which stretches over the capsule and is blended with it.

Head

Pterygoid process, lateral plate

2. Muscles of the Skull & Face

Articular tubercle

Pterygospinous ligament (variable)

Articular disk

Mandibular notch

Joint capsule

Sphenomandibular ligament

Head of mandible

Stylomandibular ligament

Stylomandibular ligament

Pterygoid process, medial plate Mandibular foramen

Fig. 2.20 Ligaments of the right TMJ Medial view. The sphenomandibular ligament can be identified in this view.

Articular tubercle

Fig. 2.21 Opened left TMJ Lateral view. The capsule extends posteriorly to the petrotympanic fissure (not shown here). Interposed between the mandibular head and fossa is the articular disk, which is attached to the joint capsule on all sides. Note: The articular disk (meniscus) divides the TMJ into upper and lower compartments. Gliding (translational) movement occcurs in the upper compartment, hinge (rotational) movement in the lower compartment. Auriculotemporal nerve

Mandibular fossa

Posterior division

Mandibular nerve (CN V3) Anterior division Posterior temporal nerve (from deep temporal nerve)

Masseteric nerve

Fig. 2.22 Dislocation of the TMJ The head of the mandible may slide past the articular tubercle when the mouth is opened, dislocating the TMJ. This may result from heavy yawning or a blow to the opened mandible. When the joint dislocates, the mandible becomes locked in a protruded position and can no longer be closed. This condition is easily diagnosed clinically and is reduced by pressing on the mandibular row of teeth.

Fig. 2.23 Sensory innervation of the TMJ capsule (after Schmidt) Superior view. The TMJ capsule is supplied by articular branches arising from three branches of the mandibular division of the trigeminal nerve (CN V3): • Auriculotemporal nerve (posterior division of CN V3) • Posterior deep temporal nerve (anterior division of CN V3) • Masseteric nerve (anterior division of CN V3) Note: While the masseteric and posterior deep temporal nerves are generally considered to be motor nerves, they also innervate the TMJ.

37

Head

2. Muscles of the Skull & Face

Muscles of the Head: Origins & Insertions The bony origins and insertions of the muscles are indicated by color shading: origins (red) and insertions (blue).

Muscles of facial expression (CN VII)

Sternocleidomastoid and trapezius (CN XI)

Occipitofrontalis, occipital belly

Sternocleidomastoid

Corrugator supercilii Orbicularis oculi

Trapezius

Orbital part Lacrimal part

Levator labii superioris alaeque nasi Nuchal muscles, intrinsic back muscles (dorsal rami of cervical nerve)

Zygomaticus major Zygomaticus minor Levator anguli oris

Semispinalis capitis Nasalis

Transverse part Alar part

Obliquus capitis superior

Depressor septi nasi

Rectus capitis posterior major

Orbicularis oris

Rectus capitis posterior minor

Buccinator Mentalis

Muscles of mastication (CN V3)

Orbicularis oris

Splenius capitis Longissimus capitis

Masseter Depressor labii inferioris

Lateral pterygoid (see B and C)

Depressor anguli oris

Temporalis

Platysma

Medial pterygoid (see B and C)

A

Lateral pterygoid, superior head* Temporalis

Fig. 2.24 Origins and insertions on the skull A Left lateral view. B Inner surface of right hemimandible. C Inferior view of skull base.

Lateral pterygoid, inferior head

Buccinator

Medial pterygoid

Genioglossus Mylohyoid Geniohyoid B

38

Digastric, anterior belly *Primarily innervates articular disk.

Head

2. Muscles of the Skull & Face

Muscles of mastication (CN V3)

Masseter Medial pterygoid Lateral pterygoid Temporalis Pharyngeal muscles

Tensor veli palatini (CN V) Levator veli palatini (pharyngeal plexus) Stylopharyngeus (CN IX)

Styloglossus (CN XII) Stylohyoid Prevertebral muscles (ventral cervical nerve rami and cervical plexus)

Digastric, posterior belly (CN VII) Nuchal muscles, intrinsic back muscles (dorsal rami of cervical nerves)

Rectus capitis lateralis Longus capitis

Splenius capitis

Rectus capitis anterior

Longissimus capitis Obliquus capitis superior Rectus capitis posterior major

Sternocleidomastoid and trapezius (CN XI)

Rectus capitis posterior minor

Sternocleidomastoid

Semispinalis capitis

Trapezius C

39

Head

3. Arteries & Veins of the Head & Neck

Arteries of the Head: Overview

Superficial temporal artery

Ophthalmic artery

Posterior auricular artery

Angular artery

Ascending pharyngeal artery

Maxillary artery

Occipital artery

Internal carotid artery

Facial artery

Lingual artery

External carotid artery Superior thyroid artery Vertebral artery

Common carotid artery

Fig. 3.1 Arteries of the head Left lateral view. The common carotid artery divides into the internal carotid artery (purple) and the external carotid artery (gray) at the carotid bifurcation (at the level of the C4 vertebra, between the thyroid cartilage and hyoid bone). The external carotid artery divides into eight major branches that supply the scalp, face, and structures of the head

40

Subclavian artery

and neck. These eight branches can be arranged into four groups: anterior (red), medial (blue), posterior (green), and terminal (yellow). The internal carotid artery does not branch before entering the skull. It gives off branches within the cranial cavity. The ophthalmic branch of the internal carotid artery provides branches that will anastomose with branches of the facial artery on the face (see Fig. 3.2).

Head

3. Arteries & Veins of the Head & Neck

Superficial temporal artery, frontal branch Supratrochlear artery Supraorbital artery Lateral palpebral arteries Medial palpebral arteries Superficial temporal artery

Dorsal nasal artery

Infraorbital artery

Angular artery

Superior and inferior labial arteries

Facial artery

Mental artery External carotid artery

Fig. 3.2 Branches of the carotid arteries The external carotid artery may be arranged into four groups of branches. The facial artery (red) communicates with certain branches of the ophthalmic artery, which arises from the internal carotid artery (purple).

External carotid artery

Internal carotid artery

Table 3.1 Branches of the external carotid artery

Facial artery Lingual artery Superior thyroid artery A

D

B

E

C

F

Fig. 3.3 Variants in external carotid artery branching A Typically (50%), the anterior branches (facial, lingual, and superior thyroid arteries) arise from the external carotid artery above the carotid bifurcation. B, C D–F

Variants: The superior thyroid artery arises at the level of the carotid bifurcation (20%) or from the common carotid artery (10%). Two or three branches combine to form a common trunk: linguofacial (18%), thyrolingual (2%), or thyrolinguofacial (1%).

Anterior branches (red)

Region supplied

Superior thyroid a.

Larynx, thyroid gland, pharynx

Lingual a.

Oral cavity, tongue

Facial a.

Superficial facial region, submandibular gland, neck

Medial branch (blue)

Region supplied

Ascending pharyngeal a.

Pharynx

Posterior branches (green)

Region supplied

Occipital a.

Occipital region

Posterior auricular a.

Ear, posterior scalp

Terminal branches (yellow)

Region supplied

Maxillary a.

Mandibular (via inferior alveolar branch) and maxillary dentition, masticatory muscles, posteromedial facial skeleton, meninges, nasal cavity and face (via infraorbital and mental arteries)

Superficial temporal a.

Temporal region, ear, parotid gland

41

Head

3. Arteries & Veins of the Head & Neck

External Carotid Artery: Anterior, Medial & Posterior Branches

Supratrochlear artery* Dorsal nasal artery*

Transverse facial artery

Angular artery

Occipital branches Superficial temporal artery

Superior labial artery

Descending branch Posterior auricular artery Maxillary artery

Inferior labial artery

Occipital artery

Ascending palatine artery

Tonsillar branch Facial artery

Ascending pharyngeal artery Facial artery Lingual artery

Submental artery A

Glandular branches

Superior thyroid artery

External carotid artery Common carotid artery

* Branches of the ophthalmic artery

Auricular branch

Fig. 3.4 Anterior and posterior branches Left lateral view. Anterior branches (A): The facial artery has four cervical and four facial branches. The four cervical branches (ascending palatine, tonsillar, glandular, and submental arteries) arise in the neck before the facial artery crosses the mandible to reach the face. The four facial branches (inferior and superior labial, lateral nasal, and angular arteries) supply the superficial face. The facial branches anastomose with branches of the internal carotid artery. Due to the extensive arterial anastomoses, facial injuries tend to bleed profusely but also heal quickly. Posterior branches (B): The two posterior branches of the external carotid artery are the occipital artery and the posterior auricular artery.

42

Posterior auricular artery Posterior tympanic artery Parotid branch

External carotid artery B

Occipital artery

Head

Inferior tympanic artery

Posterior meningeal artery

3. Arteries & Veins of the Head & Neck

Deep lingual artery

Sublingual artery

Dorsal lingual branches Lingual artery Suprahyoid branch Ascending pharyngeal artery

Superior laryngeal artery

Pharyngeal branches

External carotid artery Superior thyroid artery

Lingual artery External carotid artery Internal carotid artery

Infrahyoid branch

Sternocleidomastoid branch

Superior thyroid artery

Lateral glandular branch

Superior laryngeal artery

Fig. 3.7 Lingual artery and its branches Left lateral view. The lingual artery is the second anterior branch of the external carotid artery. It has a relatively large caliber, providing the tongue and oral cavity with its rich blood supply. It also gives off branches to the tonsils. Table 3.2 Anterior, medial, and posterior branches Branch

Cricothyroid branch Anterior glandular branch

Common carotid artery

Branches and distribution

Anterior

Superior thyroid a.

Glandular branches: thyroid gland Superior laryngeal a.: larynx Sternocleidomastoid branch: sternocleidomastoid m.

Thyroid ima artery

Pharyngeal branches: pharynx Lingual a.

Dorsal lingual branches: base of tongue, epiglottis Suprahyoid branch: suprahyoid mm. Sublingual a.: sublingual gland, tongue, floor of oral cavity

Fig. 3.5 Anterior and medial branches Left lateral view. The superior thyroid artery is typically the first branch to arise from the external carotid artery. One of the anterior branches, it supplies the larynx (via the superior laryngeal branch) and thyroid gland. The ascending pharyngeal artery springs from the medial side of the external carotid artery, usually arising above the level of the superior thyroid artery.

Deep lingual a.: tongue Facial a.

Ascending palatine a.: pharyngeal wall, soft palate, pharyngotympanic tube, palatine tonsil Tonsillar a.: tonsils Glandular branch: submandibular gland Submental a.: anterior digastric and mylohyoid, submandibular gland Superior and inferior labial aa.: lips Lateral nasal branch: dorsum of nose

Internal carotid artery

Occipital artery

Facial artery

Ascending pharyngeal artery

Angular a.: nasal root Medial

Ascending pharyngeal a.

External carotid artery

Pharyngeal branches: pharyngeal wall Inferior tympanic a.: mucosa of middle ear Posterior meningeal a.: dura, posterior cranial fossa

A

B

C

D

Fig. 3.6 Origin of the ascending pharyngeal artery: typical case and variants (after Lippert and Pabst) A In typical cases (70 %) the ascending pharyngeal artery arises from the external carotid artery. B–D Variants: The ascending pharyngeal artery arises from B the occipital artery (20 %), C the internal carotid artery (8 %), or D the facial artery (2 %).

Posterior

Occipital a.

Occipital branches: scalp of occipital region Descending branch: posterior neck muscles

Posterior auricular branch

Stylomastoid a.: facial n. in facial canal, tympanic cavity Posterior tympanic a.: tympanic cavity Auricular branch: posterior side of auricle Occipital branch: occiput Parotid branch: parotid gland

Note: The two terminal branches are covered in Table 3.4.

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3. Arteries & Veins of the Head & Neck

External Carotid Artery: Maxillary Artery The maxillary artery is the largest of the two terminal branches of the external carotid artery (see p. 42). It supplies the maxilla and mandible

(including the teeth), the muscles of mastication, the palate, the nose, and the dural covering of the brain.

Infraorbital artery Sphenopalatine artery Deep temporal arteries Posterior superior alveolar artery Anterior and middle superior alveolar arteries

Pterygoid branch Middle meningeal artery Deep auricular artery Anterior tympanic artery Superficial temporal artery Maxillary artery

A

Posterior auricular artery Masseteric artery Buccal artery

Fig. 3.8 Maxillary artery Left lateral view. A Schematic. B Course of the maxillary artery. The maxillary artery can be divided into three parts: mandibular (blue), pterygoid (green), and pterygopalatine (yellow). See Table 3.3.

Facial artery Occipital artery Lingual artery

Mylohyoid branch

Mental branch

B

Maxillary artery

Temporomandibular joint capsule

Zygomatic process

Buccal nerve

Lateral pterygoid muscle A

Superior thyroid artery

Inferior alveolar artery

B Ramus of mandible

External carotid artery

C

Inferior alveolar nerve

Lingual nerve

Inferior alveolar nerve

Lingual nerve

Maxillary artery

Buccal nerve

Buccal nerve

Fig. 3.9 Variants of the maxillary artery Left lateral view.

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D

Inferior alveolar nerve

Lingual nerve

E

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3. Arteries & Veins of the Head & Neck

Table 3.3 Branches of the maxillary artery Branch

Course

Distribution

Mandibular part (blue): Also known as the bony part or 1st part, this portion runs medial to the neck of the mandible and gives off 5 major branches, all of which enter bone. Inferior alveolar a.

Gives off a lingual and a mylohyoid branch before entering the mandibular foramen to travel along the mandibular canal; it splits into 2 terminal branches (incisive and mental)

Mandibular molars and premolars with associated gingiva, mandible

• Lingual branch

Lingual mucous membrane

• Mylohyoid branch

Mylohyoid

• Incisive branch

Mandibular incisors

• Mental branch

Chin

Anterior tympanic a.

Runs through the petrotympanic fissure along with the chorda tympani

Middle ear

Deep auricular a.

Travels through the wall of the external acoustic meatus

Lateral tympanic membrane, skin of external acoustic meatus

• Branch to temporomandibular joint

Temporomandibular joint

Middle meningeal a.

Runs through the foramen spinosum to the middle cranial cavity

Bones of the cranial vault, dura of anterior and middle cranial fossae

Accessory meningeal a.

Runs through the foramen ovale to the middle cranial fossa

Medial and lateral pterygoid, tensor veli palatini, sphenoid bone, dura, trigeminal ganglion

Pterygoid part (green): Also known as the muscular part or 2nd part, this portion runs between the temporalis and lateral pterygoid. It gives off 5 major branches, all of which supply muscle. Masseteric a.

Runs through the mandibular incisure (notch)

Masseter, temporomandibular joint

Deep temporal aa.

Consist of anterior, middle, and posterior branches, which course deep to the temporalis

Temporalis

Lateral pterygoid a.

Runs directly to the lateral pterygoid muscle

Lateral pterygoid

Medial pterygoid a.

Runs directly to the medial pterygoid muscle

Medial pterygoid

Buccal a.

Accompanies the buccal n.

Buccal mucosa and skin, buccinator

Pterygopalatine part or 3rd part (yellow): This portion runs through the pterygomaxillary fissure to enter the pterygopalatine fossa. It gives off 6 major branches, which accompany the branches of the maxillary nerve (CN V2).* Posterior superior alveolar a.

Runs through the pterygomaxillary fissure; may arise from the infraorbital a.

Maxillary molars and premolars, with associated gingiva; maxillary sinus

Infraorbital a.

Runs through the inferior orbital fissure into the orbit, where it runs along the infraorbital groove and canal, exiting onto the face via the infraorbital foramen

Cheek, upper lip, nose, lower eyelid

• Anterior and middle superior alveolar aa.

Maxillary teeth and maxillary sinus

Greater palatine a.: runs via the greater (anterior) palatine canal; in the canal it gives off several lesser palatine aa.; continues through greater palatine foramen onto hard palate

Roof of hard palate, nasal cavity (inferior meatus), maxillary gingiva

• Lesser palatine aa.: run via the lesser palatine foramen

Soft palate

• Anastomosing branch: runs via the incisive canal; joins with the sphenopalatine a.

Nasal septum

Descending palatine a.

Sphenopalatine a.

Runs via the sphenopalatine foramen to the nasal cavity; gives off posterior lateral nasal branches, then travels to the nasal septum, where it terminates as posterior septal branches • Posterior lateral nasal aa.: anastomose with the ethmoidal aa. and nasal branches of the greater palatine a.

Nasal air sinuses (frontal, maxillary, ethmoidal, and sphenoidal)

• Posterior septal branches: anastomose with the ethmoidal arteries on the nasal septum

Nasal conchae and nasal septum

A. of the pterygoid canal

Runs through the pterygoid canal

Pharyngotympanic tube, tympanic cavity, upper pharynx

Pharyngeal a.

Runs through the palatovaginal canal

Nasopharynx, sphenoidal sinus, and pharyngotympanic tube; mucosa of nasal cavity

*All branches are named for the nerve they travel with except for the sphenopalatine artery, which travels with the nasopalatine nerve.

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3. Arteries & Veins of the Head & Neck

External Carotid Artery: Terminal Branches There are two terminal branches of the external carotid artery: the maxillary artery and the superficial temporal artery. The external carotid artery divides into the maxillary and superficial temporal arteries

within the substance of the parotid gland. The extent of the maxillary artery makes it difficult to visualize. Three clinically relevant branches have been included here in greater detail.

Infraorbital artery

Sphenopalatine artery Artery of pterygoid canal Descending palatine artery

Dental branches

Anterior superior alveolar artery

Lateral posterior nasal arteries

Posterior septal branches

Fig. 3.10 Infraorbital artery Left lateral view. The infraorbital artery arises from the pterygopalatine part of the maxillary artery (a terminal branch of the external carotid artery), and the supraorbital artery (not shown) arises from the internal carotid artery (via the ophthalmic branch). These vessels therefore provide a path for potential anastomosis between the internal and external carotid arteries on the face. Anastomotic branch with lacrimal artery

Frontal branch

Sphenopalatine artery Artery of pterygoid canal Descending palatine artery

Parietal branch

Lesser palatine artery Greater palatine artery

Fig. 3.11 Sphenopalatine artery Medial view of right nasal wall and right sphenopalatine artery. The sphenopalatine artery enters the nasal cavity through the sphenopalatine foramen. The anterior portion of the nasal septum contains a highly vascularized region (Kiesselbach’s area), which is supplied by both the posterior septal branches of the sphenopalatine artery (external carotid artery) and the anterior septal branches of the anterior ethmoidal artery (internal carotid artery via ophthalmic artery). When severe nasopharyngeal bleeding occurs, it may be necessary to ligate the maxillary artery in the pterygopalatine fossa.

Middle meningeal artery

Petrous branch

Fig. 3.12 Middle meningeal artery Medial view of right middle meningeal artery. The middle meningeal artery arises from the mandibular portion of the maxillary artery. It passes through the foramen spinosum into the middle cranial fossa. Despite its name, it supplies blood not just to the meninges, but also to the overlying calvaria. Rupture of the middle meningeal artery by head trauma results in an epidural hematoma.

46

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Fig. 3.13 Superficial temporal artery Left lateral view. The superficial temporal artery is the second of the two terminal branches of the external carotid artery. Particularly in elderly or cachectic patients, the often tortuous course of the frontal branch of this vessel can be easily traced across the temple. The superficial temporal artery may be involved in an inflammatory immune disease (temporal arteritis), which can be confirmed by biopsy of this vessel. The patients, usually elderly men, complain of severe headaches.

3. Arteries & Veins of the Head & Neck

Parietal bone branch

Frontal branch

Middle temporal artery

Zygomaticoorbital artery Transverse facial artery

Superficial temporal artery Maxillary artery External carotid artery

Table 3.4 Terminal branches of the external carotid artery Branch

Parts/Branches

Maxillary a. (see p. 45)

Mandibular (1st; bony) part

Pterygoid (2nd; muscular) part

Pterygopalatine (3rd) part

Superficial temporal a.

Distribution

Inferior alveolar a.

Mandibular teeth and gingiva, mandible

Anterior tympanic a.

Middle ear

Deep auricular a.

Temporomandibular joint and external auditory canal

Middle meningeal a.

Cranial vault, dura, anterior and middle cranial fossae

Accessory meningeal a.

Dura, trigeminal ganglion

Masseteric a.

Masseter, temporomandibular joint

Deep temporal branches

Temporalis

Medial pterygoid branches

Medial pterygoid

Lateral pterygoid branches

Lateral pterygoid

Buccal a.

Buccal mucosa and skin, buccinator

Posterior superior alveolar a.

Maxillary molars and gingiva, maxillary sinus

Infraorbital a.

Maxillary alveoli, maxillary dentition (via anterior and middle superior alveolar arteries)

Descending palatine a.

Nasal cavity (inferior meatus), roof of hard palate, maxillary gingiva, soft palate, nasal septum

Sphenopalatine a.

Lateral wall of nasal cavity, conchae, nasal septum

A. of the pterygoid canal

Pharyngotympanic tube, tympanic cavity, upper pharynx

Pharyngeal a.

Nasopharynx, sphenoidal sinus, and pharyngotympanic tube; mucosa of nasal cavity

Transverse facial a.

Soft tissues below zygomatic arch

Frontal branches

Scalp of forehead

Parietal branches

Scalp of vertex

Zygomatico-orbital a.

Lateral external orbital wall

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3. Arteries & Veins of the Head & Neck

Internal Carotid Artery

Cerebral part

Cavernous part

Petrous part

Cervical part

A

Fig. 3.14 Subdivisions of the internal carotid artery A Medial view of the right internal carotid artery in its passage through the bones of the skull. B Anatomical segments of the internal carotid artery and their branches. The internal carotid artery is distributed chiefly to the brain but also supplies extracerebral regions of the head. It consists of four parts (listed from bottom to top): • • • •

Cervical part Petrous part Cavernous part Cerebral part

The petrous part of the internal carotid artery (traversing the carotid canal) and the cavernous part (traversing the cavernous sinus) have a role in supplying extracerebral structures of the head. They give off additional small branches that supply local structures and are usually named for the areas they supply. Of the branches not supplying the brain, of special importance is the ophthalmic artery, which arises from the cerebral part of the internal carotid artery. Note: The ophthalmic artery forms an anastomosis with the artery of the pterygoid canal derived from the maxillary artery.

48

Ophthalmic artery

Anterior choroidal artery Posterior communicating artery Superior hypophyseal artery

Cerebral part

Basal tentorial branch Marginal tentorial branch Inferior hypophyseal artery

>SBOKLRP M>OQ

Trigeminal ganglion branch

Neural branch

Meningeal branch

Petrous part Caroticotympanic arteries

Cavernous sinus branch Artery of pterygoid canal B

Cervical part

Head

Supratrochlear artery

3. Arteries & Veins of the Head & Neck

Supraorbital artery Lacrimal artery

Middle palpebral artery

Short posterior ciliary artery

Anterior ethmoidal artery

Long posterior ciliary artery

Posterior ethmoidal artery Anastomotic branch,* through lacrimal foramen in greater wing of sphenoid

Ophthalmic artery Optic canal (opened)

* See Fig. 3.12

Internal carotid artery Middle meningeal artery

A

Supraorbital artery Supratrochlear artery Superior palpebral arch

Middle palpebral artery

Lateral palpebral artery Inferior palpebral arch

Dorsal nasal artery

B

Posterior ethmoidal artery

Ophthalmic artery

Anterior ethmoidal artery

Sphenopalatine artery Kiesselbach’s area

Maxillary artery Internal carotid artery

Fig. 3.15 Ophthalmic artery A Superior view of the right orbit. B Anterior view of the facial branches of the right ophthalmic artery. The ophthalmic artery supplies blood to the eyeball itself and to the orbital structures. Some of its terminal branches are distributed to portions of the face (e.g., forehead, eyelids, and nose). Other terminal branches (anterior and posterior ethmoidal arteries) contribute to the supply of the nasal septum (see Fig. 3.16). Note: Branches of the lateral palpebral artery and supraorbital artery may form an anastomosis with the frontal branch of the superficial temporal artery (territory of the external carotid artery). With atherosclerosis of the internal carotid artery, this anastomosis may become an important alternative route for blood to the brain. In addition, there are anastomoses between the dorsal nasal artery and the angular artery.

Fig. 3.16 Vascular supply of the nasal septum Left lateral view. The nasal septum is another region in which the internal carotid artery (anterior and posterior ethmoidal arteries, green) meets the external carotid artery (sphenopalatine artery, yellow). A richly vascularized area on the anterior part of the nasal septum, called Kiesselbach’s area (blue), is the most common site of nosebleed. Because Kiesselbach’s area is an area of anastomosis, it may be necessary to ligate the sphenopalatine/maxillary artery and/or the ethmoidal arteries through an orbital approach, depending on the source of the bleeding. (See also Fig. 7.17.)

External carotid artery

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3. Arteries & Veins of the Head & Neck

Veins of the Head: Overview

Supraorbital vein

Superior ophthalmic vein

Inferior ophthalmic vein

Superficial temporal vein

Maxillary vein

Angular vein Pterygoid plexus Posterior auricular vein

Deep facial vein

Occipital vein

Retromandibular vein

Posterior division of retromandibular vein Facial vein

Anterior division of retromandibular vein

Common facial vein

Deep cervical vein

Lingual vein

Internal jugular vein

Superior and middle thyroid veins Anterior jugular vein

Left brachiocephalic vein

Fig. 3.17 Veins of the head and neck Left lateral view. The principal vein of the head and neck is the internal jugular vein. This drains blood from both the exterior and the interior of the skull (including the brain) in addition to receiving venous blood from the neck. It receives blood from the common facial vein (formed by the union of the facial vein and the anterior division of the retromandibular vein), the lingual, superior thyroid, and middle thyroid veins,

50

External jugular vein

Suprascapular vein

Subclavian vein

and the inferior petrosal sinus. Enclosed in the carotid sheath, the internal jugular vein descends from the jugular foramen to its union with the subclavian vein to form the brachiocephalic vein. The external jugular vein receives blood from the posterior division of the retromandibular vein and the posterior auricular vein. The occipital vein normally drains to the deep cervical veins.

Head

Superior trochlear vein Supraorbital vein

Superior ophthalmic vein

Cavernous sinus

Maxillary vein Infraorbital vein

3. Arteries & Veins of the Head & Neck

Superficial temporal vein

Dural sinuses

Sigmoid sinus Deep facial vein

Retromandibular vein

Pterygoid plexus

Posterior auricular vein

Facial vein

Posterior division of retromandibular vein

Anterior division of retromandibular vein

Occipital vein Lingual vein Anterior jugular vein

Internal jugular vein

Common facial vein

Fig. 3.18 Veins of the head: overview The superficial veins of the head communicate with each other and with the dural sinuses via the deep veins of the head (pterygoid plexus and cavernous sinus). The pterygoid plexus connects the facial vein and the

Extermal jugular vein

retromandibular vein (via the deep facial vein and maxillary vein, respectively). The cavernous sinus connects the facial vein to the sigmoid sinus (via the ophthalmic veins and the petrosal sinuses, respectively).

Table 3.5 Venous drainage of the head and neck Vein

Location

Tributaries

Region drained

Internal jugular v.

Within carotid sheath

Common facial v. — Facial v. — Retromandibular v., anterior division — Lingual v. — Superior and middle thyroid vv.

Skull, anterior and lateral face, oral cavity, neck

Sigmoid sinus and inferior petrosal sinuses

Interior of skull (including brain)

Retromandibular v., posterior division

Lateral skull

Posterior auricular v.

Occiput

External jugular v.

Anterior jugular v.

Within superficial cervical fascia

Anterior neck

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3. Arteries & Veins of the Head & Neck

Veins of the Head: Deep Veins Parietal emissary vein

Inferior sagittal sinus

Superior sagittal sinus

Basilar vein

Straight sinus

Frontal vein

Superior petrosal sinus

Superior ophthalmic vein Angular vein

Occipital emissary vein

Inferior ophthalmic vein

Occipital vein Confluence of the sinuses

Cavernous sinus

Posterior auricular vein

Venous plexus of foramen ovale

Sigmoid sinus

Pterygoid plexus

Mastoid emissary vein

Inferior petrosal sinus

Condylar emissary vein

Maxillary vein

Deep cervical vein

Common facial vein Vertebral vein

External jugular vein

Fig. 3.19 Venous drainage of the head The superficial veins of the head have extensive connections with the deep veins of the head and the dural sinuses. The meninges and brain are drained by the dural sinuses, which lie within the skull. Emissary

Retromandibular vein Facial vein

Internal jugular vein

veins connect the superficial veins of the skull directly to the dural sinuses. In addition, the deep veins of the head (e.g., pterygoid plexus) are intermediaries between the superficial veins of the face and the dural venous sinuses.

Table 3.6 Venous anastomoses as portals of infection The extracranial veins of the head are connected to the deep veins and dural sinuses. Patients who sustain midfacial fractures may bleed profusely due to the extensive venous anastomoses. Because the veins are generally valveless, extracranial bacteria may migrate to the deep veins, causing infections (e.g., bacteria from boils on the upper lip or nose may enter the angular vein and travel to the cavernous sinus). Bacteria in the cavernous sinus may cause thrombosis. Extracranial vein

Connecting vein

Venous sinus

Angular v.

Superior ophthalmic v.

Cavernous sinus

Vv. of palatine tonsil

Pterygoid plexus, inferior ophthalmic v.

Superficial temporal v.

Parietal emissary v.

Superior sagittal sinus

Occipital v.

Occipital emissary v.

Transverse sinus, confluence of the sinuses

Mastoid emissary v.

Sigmoid sinus

Posterior auricular v. External vertebral venous plexus

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Condylar emissary v.

Head

Supratrochlear vein

Supraorbital vein

Deep Cavernous temporal veins sinus

3. Arteries & Veins of the Head & Neck

Superficial temporal vein Sphenoidal emissary veins

Superior ophthalmic vein

Superior and inferior petrosal sinuses

Angular vein

Sigmoid sinus

Facial vein Deep facial vein Pterygoid plexus Maxillary vein Retromandibular vein

Posterior division of retromandibular vein Internal jugular vein Anterior division of retromandibular vein Common facial vein Facial vein

Lingual vein

External palatine vein

Fig. 3.20 Deep veins of the head Left lateral view. The pterygoid plexus is a venous network situated behind the mandibular ramus and embedded in the pterygoid muscles. Because the veins of the face have no valves (small valves may be present but are generally nonfunctional), the movement of the pterygoid muscles forces blood from the pterygoid plexus into the jugular veins.

The pterygoid plexus is linked to the facial vein via the deep facial vein and to the retromandibular vein via the maxillary vein. The plexus is also linked to the cavernous sinus via the sphenoidal emissary vein. The cavernous sinus receives blood from the superior and inferior ophthalmic veins. Parietal emissary vein

Superior sagittal sinus Confluence of the sinuses Occipital emissary vein

Fig. 3.21 Veins of the occiput Posterior view. The dural sinuses are the series of venous channels that drain the brain (see p. 302). The superficial veins of the occiput communicate with the dural sinuses by way of the emissary veins. The emissary veins enter a similarly named foramen to communicate with the dural sinuses.

Venous plexus around the foramen magnum Venous plexus of the hypoglossal nerve canal External vertebral venous plexus

Transverse sinus

Mastoid emissary vein Condylar emissary vein Internal jugular vein Occipital vein

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4. Innervation of the Head & Neck

Organization of the Nervous System Fig. 4.1 Nervous system A Anterior view. B Posterior view. The nervous system is a collection of neurons that can be divided anatomically into two groups:

Cerebrum

• Central nervous system (CNS, pink): Brain and spinal cord. • Peripheral nervous system (PNS, yellow): Nerves emerging from the CNS. These are divided into two types depending on their site of emergence: ◦ Cranial nerves: 12 pairs of nerves emerge from the brain (telencephalon, diencephalon, and brainstem only). These nerves may contain sensory and/or motor fibers. ◦ Spinal nerves: 31 pairs of nerves emerge from the spinal cord. Spinal nerves contain both sensory and motor fibers that emerge from the spinal cord as separate roots and unite to form the mixed nerve. In certain regions, the spinal nerves may combine to form plexuses (e.g., cervical, brachial, or lumbosacral). The cranial nerves are discussed in this chapter. The spinal nerves and CNS are discussed in Chapter 13: Neuroanatomy. The innervation of the neck is discussed in Chapter 12: Neurovascular Topography of the Neck.

Cranial nerves

Brain

Cerebellum

Brachial plexus Spinal nerves Spinal cord Spinal cord Spinal nerve

Lumbosacral plexus Cauda equina

A

B

Afferent (sensory)

Efferent (motor)

Joints, skin, skeletal muscle

Skeletal muscle

Somatosensory fibers

Somatic

Somatomotor fibers

CNS

Autonomic (visceral)

Viscerosensory fibers

Viscera, vessels

Fig. 4.2 Organization of the nervous system The nervous system is a vast network that can be divided according to two criteria: 1. Type of information: Afferent (sensory) cells and pathways receive information and transmit it to the CNS. Efferent (motor) cells and pathways convey information from the CNS.

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Visceromotor fibers

Glands, smooth muscle, cardiac muscle

2. Destination/origin: The somatic division of the nervous system primarily mediates interaction with the external environment. These processes are often voluntary. The autonomic (visceral) nervous system primarily mediates regulation of the internal environment. These processes are frequently involuntary. The two criteria yield four types of nerve fibers that connect the CNS to the PNS.

Head

Presynaptic terminal

Cell body (soma)

4. Innervation of the Head & Neck

Dendrites

Cell bodies

Axons

Axon A Peripheral process (dendrite)

A

B

C

D Cell body

B

Axon

Presynaptic terminal

Fig. 4.3 Neurons and nerves A Neuron structure. B Convention of drawing neurons. Neurons are the specialized cells of the nervous system that convey information in the CNS and PNS. Neurons consist of a cell body (soma) with two types of projections: • Dendrites: Receptor segments that receive impulses from other neurons or cells. • Axons: Projecting segments that transmit impulses to other neurons or cells. The number and organization of the projections reflect the function of the neuron (see Fig. 4.4). Neurons convey impulses to each other at synapses: neurotransmitters released from the presynaptic terminal (bouton) of the axon are bound by receptors on the postsynaptic membrane of the next neuron’s dendrite. The impulse can then be relayed along the axon.

Epineurium

Fibrofatty tissue

Nerve fiber (unmyelinated)

Fig. 4.4 Types of neurons Neurons are divided functionally into three main groups: sensory neurons, interneurons, and motor neurons. The structure of the neurons reflects their function. Sensory neurons: Collect sensory information and transport it to the CNS. These neurons tend to have long peripheral processes (dendrites) and long central processes (axons). • Bipolar neuron (A): Named for the two long processes (peripheral and central) on opposite sides of the cell body. (E.g., retinal cells.) • Pseudounipolar neuron (B): The dendrite and axon appear to arise from the same projection from the cell body. (E.g., primary afferent neurons.) Interneurons (C): Convey information between sensory and motor neurons within the CNS. This multipolar interneuron has numerous dendrites and a short axon. Motor neurons (D): Originate motor impulses and transmit them from the CNS. This multipolar motor neuron has numerous dendrites and a long axon. Nerve fiber (myelinated)

Blood vessels

Endoneurium Perineurium

A

Axon of second-order sensory neuron

Spinal ganglion (containing cell bodies of first-order sensory neuron)

Fig. 4.5 Neurons in the CNS and PNS A Nerve fibers. B Nerves/tracts and ganglia/nuclei. Bundles of axons travel together to synapse on the cell bodies of other neurons. In the PNS, these axon bundles are called nerves; in the CNS, they are called tracts. The axon bundles can be covered with myelin to increase the speed of impulse transmission. As myelin is composed primarily of fatty acids, myelinated areas appear white (white matter). The unmyelinated cell bodies of the neurons appear darker (gray matter). Cell bodies are considerably larger than cell processes. Clusters of cell bodies therefore produce characteristic bulges: in the PNS these are called ganglia; in the CNS they are called nuclei.

Dendrite (peripheral process)

Axon (central process)

Dorsal horn (containing cell bodies of second-order sensory neuron)

B

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4. Innervation of the Head & Neck

Sensory Pathways Interneuron

Table 4.1 Sensory (afferent) pathways Sensory information is traditionally relayed from sensory organs to the cortex by a three-neuron pathway:

Third-order (tertiary) sensory neuron

1st order

Primary (first-order) neurons: Collect sensory data from the sensory organ and convey it to the CNS. These neurons are often pseudounipolar (with cell bodies located in sensory ganglia). Note: Although most neurons are activated by the release of neurotransmitters, first-order neurons may be activated by other inputs (e.g., photons [sight], vibrations [sound], olfactory stimuli [smell]). The axons of first-order neurons enter the CNS to synapse on second-order neurons.

2nd order

Secondary (second-order) neurons: Located in the CNS, these neurons receive impulses from first-order neurons in the PNS. The axons of second-order neurons ascend as tracts to synapse on third-order neurons in the thalamus.

3rd order

Tertiary (third-order) neurons: Located in the thalamus, these neurons project to the appropriate area of the sensory cortex.

Upper motor neuron

Thalamus

Second-order (secondary) sensory neuron First-order (primary) sensory neuron

Lower motor neuron

A

Fig. 4.6 Sensory and motor pathways: overview A Sensory (afferent) pathways. B Motor (efferent) pathways. The sensory (afferent) pathways detect and relay information from sensory organs to the cerebral cortex, generally via a three-neuron

B

pathway (see Table 4.1). The motor (efferent) pathways produce and transmit impulses from the cortex via a two-neuron (motor) pathway or a three-neuron (autonomic) pathway (see Fig. 4.8). The sensory and motor pathways are connected by interneurons.

Table 4.2 Sensory pathways in the spinal and cranial nerves Both the spinal and cranial nerves use the three-neuron sensory pathway. Neuron

Location of cell body (soma) Spinal nerve

Cranial nerve

1st order

Spinal ganglia of dorsal root: All 31 spinal nerve pairs have a dorsal sensory root and a ventral motor root. Only the dorsal root has the characteristic bulge of a sensory ganglion (motor cells are not pseudounipolar).

Sensory ganglia near brainstem: Of the 12 cranial nerves, only 7 are sensory (CN I, II, V, VII, VIII, IX, and X). These seven nerves are associated with eight sensory ganglia; two cranial nerves (CN V and VII) have a single sensory ganglion, while three (CN VIII, IX, and X) have two sensory ganglia each.

2nd order

Sensory nuclei in dorsal horn of the spinal cord: The dorsal horn is the posterior portion of the gray matter of the spinal cord. It contains exclusively sensory neurons. Axons ascend via white matter tracts to the thalamus.

Sensory nuclei in dorsolateral brainstem: The sensory nuclei are arranged as a longitudinal nuclear column in the dorsolateral portion of the brainstem. Axons ascend via white matter tracts to the thalamus.

3rd order Cortical

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Thalamus Sensory cortex

Head

4. Innervation of the Head & Neck

Primary sensory cortex

Third-order sensory neurons

Second-order sensory neurons

Thalamus

Central processes of first-order sensory neuron

Dorsal horn

Peripheral processes Dorsal root ganglion

Dorsal ramus

Trigeminal ganglion Dorsal rootlets Trigeminal nucleus

Dorsal root

Ventral ramus Ventral rootlets

Fig. 4.7 Sensory pathways: cranial and spinal nerves Left: Cranial nerves. Right: Spinal nerves. Sensory information is relayed to the sensory cortex via a three-step pathway. 1. First-order pseudounipolar neurons receive impulses from the periphery. They convey these impulses along their peripheral processes to their central process (axons) that synapse in the CNS. The cell bodies of first-order neurons are located in sensory ganglia.

First-order sensory neuron

Ventral root

2. Second-order neurons with cell bodies in the gray matter of the CNS receive impulses from first-order neurons. The axons of second-order neurons ascend as white matter tracts to the thalamus. 3. Third-order neurons with cell bodies in the thalamus receive impulses from ascending tracts. The axons of third-order neurons ascend to the sensory cortex.

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Motor Pathways Table 4.3 Motor (efferent) pathways

Upper motor neurons

Lower motor neuron

Preganglionic neuron

Ganglion

A

Fig. 4.8 Motor pathways A Two-neuron motor pathway. B Three-neuron (autonomic) motor pathway. The two major types of skeletal muscle (somatic and branchial, see pp. 60–61) are innervated by the classic two-neuron motor pathway (somatomotor and branchiomotor, respectively), with impulses originating in the cortex. Smooth muscle, cardiac muscle, and

Skeletal muscle is innervated by a traditional two-neuron motor pathway. Upper motor neuron

Upper motor neurons are located in the motor cortex. Their axons descend via white matter tracts to lower motor neurons in the brainstem and spinal cord.

Lower motor neuron

Lower motor neurons are located in the brainstem (cranial nerves) and spinal cord (spinal nerves). Their axons leave the CNS to synapse on target cells. Autonomic lower motor neurons synapse before they reach their target cells (see p. 62).

Postganglionic neuron B

glands are innervated by autonomic motor pathways that involve a third neuron, with impulses originating in the hypothalamus (see p. 62). Note: Outside of the CNS (spinal cord and brain), the ANS involves two neurons (one preganglionic and one postganglionic), whereas the branchial and somatic motor pathways have a single neuron (the lower motor neuron).

Table 4.4 Motor (efferent) pathways Neuron

Location of cell body (soma) Spinal nerve

Upper motor neuron

Cranial nerve

Motor cortex: The cell bodies of skeletal muscle upper motor neurons are located in the gray matter of the cortex. Their axons descend via white matter tracts.

Hypothalamus: The cell bodies of autonomic upper motor neurons are located in the hypothalamus. Their axons descend via white matter tracts. Lower motor neuron

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Motor nuclei in ventral horn of spinal cord: The ventral horn is the anterior portion of the gray matter of the spinal cord. It contains exclusively motor neurons. The axons of these neurons leave the CNS as the motor root of the spinal nerves. The motor root combines with the dorsal root outside the spinal cord to form the mixed spinal nerve. Note: Unlike the dorsal root, the motor root has no ganglion.

Motor nuclei in dorsomedial margin of brainstem: Of the 12 cranial nerves, all but 3 have motor nuclei. The motor nuclei are arranged in longitudinal nuclear columns. The axons of these neurons leave the CNS as the motor roots of the cranial nerves. Unlike the spinal nerves, the motor and sensory roots of the cranial nerves combine before exiting the CNS. Note: CN V is the only exception to this: its motor root combines with the sensory root of CN V3 as it passes through the foramen ovale.

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4. Innervation of the Head & Neck

Primary motor cortex

Upper motor neuron

Corticospinal fibers

Upper motor neuron

Corticonuclear fibers

Dorsal rootlets

Dorsal root ganglion

Dorsal ramus

Lower motor neuron

Lower motor neuron Ventral horn

Pons VII

XII

Spinal nerve

Medulla oblongata Decussation of pyramids

Ventral rootlets

Ventral root Meningeal branch

Fig. 4.9 Motor pathways: cranial and spinal nerves Left: Cranial nerves. Right: Spinal nerves. Motor information is relayed from the motor cortex via a two-step pathway. 1. Upper motor neurons: Neurons in the gray matter of the motor cortex project axons that descend via white matter tracts to the brain and spinal cord.

Ventral ramus

2. Lower motor neurons: Neurons in the motor nuclei of the brainstem (cranial nerves) or ventral horn of the spinal cord (spinal nerves) project axons that emerge from the CNS as the motor roots of the nerves. These axons synapse on target skeletal muscle cells. Note: Lower motor neurons in the autonomic nervous system synapse before reaching their targets (smooth muscle, cardiac muscle, and glands).

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Skeletal Muscle: Innervation & Embryonic Development Pharyngeal (branchial) arches

Table 4.5 Skeletal muscle: development and innervation Skeletal muscle has one of two embryonic origins: somites or branchial (pharyngeal) arches. Nerves migrate with muscle cells during embryonic development, explaining the pattern of adult innervation. Neural tube

Upper limb bud

Connecting stalk (with umbilical vessels)

Lower limb bud

Muscle

Somatic muscle

Branchial muscle

Derivation

Somites

Branchial (pharyngeal) arches

Germ layer

Mesoderm (paraxial mesenchyme)

Location

Throughout body (including head and neck)

Head and neck

Nerve fibers

Somatomotor fibers

Branchiomotor fibers

Nerves

Spinal and cranial nerves

Cranial nerves

Fig. 4.10 Five-week-old embryo

Neural crest

Neural groove

Amnion A Amniotic cavity

Neural tube

Myotome Sclerotome

Notocord

Somite

Ectoderm

Dermatome

Paired aorta

Mesoderm Endoderm

Neural tube

Dorsal horns of spinal cord

Dermatome

E

Surface ectoderm

Dorsal root

F

D Vertebra (sclerotome derivative)

Dorsal root (with ganglion)

Epaxial muscles (intrinsic back muscles)

Dorsal ramus (to epaxial muscles)

Ventral ramus (to hypaxial muscles)

Ventral horns of spinal cord

Yolk sac

C

B

Myotome

Aorta

Body cavity

Yolk sac A

Migrating sclerotome cells

Gut tube

Gut tube

Epidermis and dermis (dermatome derivative) G

H Hypaxial muscles (trunk and limbs)

Fig. 4.11 Somatic muscle: embryonic development Gastrulation occurs in week 3 of human embryonic development. It produces three germ layers in the embryonic disk: ectoderm (light gray), mesoderm (red), and endoderm (dark gray). Somatic muscle develops from the mesoderm. A Day 19: The three layers are visible in the embryonic disk. The amnion forms the amniotic cavity dorsally, and the endoderm encloses the yolk sac. B Day 20: Somites form, and the neural groove begins to close. C Day 22: Eight pairs of somites flank the closed neural tube (CNS precursor). The yolk sac elongates ventrally to form the gut tube and yolk sac. D Day 24: Each somite divides into a dermatome (cutaneous), myotome (muscular), and sclerotome (vertebral). This section does not cut the connecting stalk (derived from the yolk sac). E Day 28: Sclerotomes migrate to form the vertebral column

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around the notocord (primitive spinal cord). F Day 30: All 34 or 35 somite pairs have formed. The neural tube differentiates into a primitive spinal cord. Motor and sensory neurons differentiate in the ventral and dorsal horns of the spinal cord, respectively. G By day 40: The dorsal and ventral roots form the mixed spinal nerve. The dorsal branch supplies the epaxial muscles (future intrinsic back muscles); the ventral branch supplies the hypaxial muscles (ventral muscles, including all muscles except the intrinsic back musculature). H Week 8: The epaxial and hypaxial muscles have differentiated into the skeletal muscles of the trunk. Cells from the sclerotomes also migrate into the limbs. During this migration, the spinal nerves form plexuses (cervical, brachial, and lumbosacral), which innervate the muscles of the neck, upper limb, and lower limb, respectively.

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Cranial nerve

4. Innervation of the Head & Neck

CN V (1st arch)

Aortic arch

CN VII (2nd arch) CN IX (3rd arch)

Skeletal element

Mesenchyme (musculature)

CN X (4th and 6th arches)

Ectodermal cleft Endodermal pouch A Pharyngeal gut

A Neural tube

Pharyngeal (branchial) arches

B

Fig. 4.12 Branchial muscle: embryonic development Branchial muscles are derived from five pharyngeal arches contained within four pharyngeal pouches. (Note: The 5th pharyngeal arch is only rudimentary.) These pouches emerge in week 4 of embryonic development and give rise to structures of the head and face. A Each pharyngeal arch consists of mesodermal cells (future branchial muscles) with an embedded nerve, artery, and skeletal element. The mesodermal mesenchyme is surrounded by an outer ectodermal layer and an inner endodermal layer. B The paired pharyngeal pouches surround the pharyngeal gut.

B

C

Fig. 4.13 Branchial derivatives Each of the four pharyngeal pouches contains a cranial nerve (A), which, during the course of development, migrates to its final position (B) with the branchial muscles derived from that arch (C).

Table 4.6 Skeletal muscle of the head The vast majority of the muscles of the head are derived from the pharyngeal arches (the extraocular muscles and extrinsic and intrinsic lingual muscles are somite derivatives). However, of the eight cranial nerves that innervate the skeletal muscle of the head, four convey somatomotor fibers to these somatic derivatives, and four convey branchiomotor fibers to the branchial arch derivatives. Muscle origin

Muscles

Prochordal mesenchyme

Somatic

Branchial

• Levator palpebrae superioris • Inferior oblique*

Cranial nerve

• Superior rectus* • Medial rectus* • Inferior rectus*

Oculomotor n. (CN III)

• Superior oblique*

Trochlear n. (CN IV)

• Lateral rectus*

Abducent n. (CN VI)

Occipital somites

• Extrinsic muscles of the tongue (except palatoglossus) • Intrinsic muscles of the tongue

Hypoglossal n. (CN XII)

1st branchial arch

• • • •

Trigeminal n., mandibular division (CN V3)

2nd branchial arch

• Muscles of facial expression • Stylohyoid • Digastric (posterior belly) and stapedius

Facial n. (CN VII)

3rd branchial arch

• Stylopharyngeus

Glossopharyngeal n. (CN IX)

4th and 6th branchial arches

• Pharyngeal muscles • Levator veli palatini • Muscule uvulae

Maxillomandibular mesenchyme

Temporalis** Masseter** Lateral pterygoid** Medial pterygoid**

• • • •

Mylohyoid Digastric (anterior belly) Tensor tympani Tensor veli palatini

• Palatoglossus • Laryngeal muscles

Vagus n. (CN X)

*Extraocular muscle (six total). **Muscle of mastication (four total).

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Autonomic Motor Pathways Table 4.7 Autonomic (efferent) pathways Viscera (smooth muscle, cardiac muscle, and glands) are innervated by a threeneuron motor pathway. Upper motor neuron

In the two-neuron pathway, the axon of an upper motor neuron descends from the hypothalamus to synapse on a lower motor neuron located in the brainstem or spinal cord.

Preganglionic neuron

Lower motor neurons are located in the brainstem nuclei (cranial nerves) or lateral horn of the spinal cord (spinal nerves). The axons of these secondary neurons emerge from the CNS and synapse before reaching the target cells.

Postganglionic neuron

The cell bodies of the tertiary (postganglionic) neurons form the autonomic ganglia. In general, sympathetic ganglia are located close to the CNS, and parasympathetic ganglia are located close to their target organs.

Upper motor neuron

Upper motor neuron

Parasympathetic ganglion

Sympathetic ganglion

B

A

Fig. 4.14 Autonomic pathways Unlike skeletal muscle, which is innervated by a two-neuron motor pathway, viscera (smooth muscle, cardiac muscle, and glands) are innervated by the three-neuron motor pathways of the autonomic nervous system. The autonomic nervous system is divided into two

parts: parasympathetic (A) and sympathetic (B). The parasympathetic ganglia are usually located close to their target structures (longer preganglionic and shorter postganglionic axons); the sympathetic ganglia are usually located close to the CNS (shorter preganglionic and longer postganglionic axons).

Table 4.8 Sympathetic pathways Neuron

Location of cell body (soma)

Upper motor neuron

Hypothalamus: The cell bodies of autonomic upper motor neurons are located in the hypothalamus. Their axons descend via white matter tracts.

Preganglionic neuron

Lateral horn of spinal cord (T1–L2): The lateral horn is the middle portion of the gray matter of the spinal cord, situated between the ventral and dorsal horns. It contains exclusively autonomic (sympathetic) neurons. The axons of these neurons leave the CNS as the motor root of the spinal nerves and enter the paravertebral ganglia via the white rami communicantes (myelinated).

Preganglionic neurons in paravertebral ganglia

All preganglionic sympathetic neurons enter the sympathetic chain. There they may synapse in a chain ganglion or ascend or descend to synapse. Preganglionic sympathetic neurons synapse in one of two places, yielding two types of sympathetic ganglia. Synapse in the paravertebral ganglia

Pass without synapsing through the parasympathetic ganglia. These fibers travel in the thoracic, lumbar, and sacral splanchnic nerves to synapse in the prevertebral ganglia.

Postganglionic neuron

Paravertebral ganglia: These ganglia form the sympathetic nerve trunks that flank the spinal cord. Postganglionic axons leave the sympathetic trunk via the gray rami communicantes (unmyelinated).

Prevertebral ganglia: Associated with peripheral plexuses, which spread along the abdominal aorta. There are three primary prevertebral ganglia: • Celiac ganglion • Superior mesenteric ganglion • Inferior mesenteric ganglion

Distribution of postganglionic fibers

Postganglionic fibers are distributed in two ways: 1. Spinal nerves: Postganglionic neurons may re-enter the spinal nerves via the gray rami communicantes. These sympathetic neurons induce constriction of blood vessels, sweat glands, and arrector pili (muscle fibers attached to hair follicles, “goose bumps”). 2. Arteries and ducts: Nerve plexuses may form along existing structures. Postganglionic sympathetic fibers may travel with arteries to target structures. Viscera are innervated by this method (e.g., sympathetic innervation concerning vasoconstriction, bronchial dilatation, glandular secretions, pupillary dilatation, smooth muscle contraction).

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Parasympathetic ganglia (in the head)

Sympathetic nervous system

Eye

Superior cervical ganglion

Parasympathetic nervous system

CN VII

CN III

Lacrimal and salivary glands

Parasympathetic ganglia (close to organs)

Sympathetic trunk

Cranial part: brainstem with parasympathetic nuclei

CN IX

Cranial vessels

CN X

Stellate ganglion* Heart T1 T2 T3 T4 T5 T6

Lung

Greater splanchnic nerve

Stomach Celiac ganglion

Liver

T7 T8

Pancreas

T9

Kidney

T 10 T 11

Intestine

T 12 L1

Superior mesenteric ganglion

L2

Inferior mesenteric ganglion

L3

Parts of the colon, rectum

L4 L5

Bladder Genitalia

A

Inferior hypogastric plexus

* Stellate ganglion = inferior cervical ganglion and T1 sympathetic ganglion

Pelvic splanchnic nerves

S1 S2 S3 S4 S5

Sacral part: sacral cord with parasympathetic nuclei B

Fig. 4.15 Autonomic nervous system A Sympathetic nervous system. B Parasympathetic nervous system. Table 4.9 Parasympathetic pathways Neuron

Location of cell body (soma)

Upper motor neuron

Hypothalamus: The cell bodies of autonomic upper motor neurons are located in the hypothalamus. Their axons descend via white matter tracts.

Preganglionic neuron

The parasympathetic nervous system is divided into two parts (cranial and sacral), based on the location of the preganglionic parasympathetic neurons. Brainstem cranial nerve nuclei: The axons of these secondary neurons leave the CNS as the motor root of cranial nerves III, VII, IX, and X.

Spinal cord (S2–S4): The axons of these secondary neurons leave the CNS (S2–S4) as the pelvic splanchnic nerves. These nerves travel in the dorsal rami of the S2–S4 spinal nerves and are distributed via the sympathetic plexuses to the pelvic viscera.

Postganglionic neuron

Cranial nerve parasympathetic ganglia: The parasympathetic cranial nerves of the head each have at least one ganglion: • CN III: Ciliary ganglion • CN VII: Pterygopalatine ganglion and submandibular ganglion • CN IX: Otic ganglion • CN X: Small unnamed ganglia close to target structures

Distribution of postganglionic fibers

Parasympathetic fibers course with other fiber types to their targets. In the head, the postganglionic fibers from the pterygopalatine ganglion (CN VII) and otic ganglion (CN IX) are distributed via branches of the trigeminal nerve (CN V). Postganglionic fibers from the ciliary ganglion (CN III) course with sympathetic and sensory fibers in the short ciliary nerves (preganglionic fibers travel with the somatomotor fibers of CN III). In the thorax, abdomen, and pelvis, preganglionic parasympathetic fibers from CN X and the pelvic splanchnic nerves combine with postganglionic sympathetic fibers to form plexuses (e.g., cardiac, pulmonary, esophageal).

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Peripheral Nerves & Nerve Lesions

Brachial plexus (C5–T1)

Cervical spinal nerves (C1– C8)

Thoracic spinal nerves (T1–T12)

Lumbar spinal nerves (L1–L5)

Lumbosacral plexus (L1–S4) Sacral spinal nerves (S1–S5)

Fig. 4.16 Peripheral nerves Peripheral nerves emerge from the CNS (brain and spinal cord) at various levels. These nerves may convey afferent (sensory) and/or efferent (motor) neurons to regions of the body. The patterns of innervation can be understood through the embryonic migration of cell populations (see p. 60). The least invasive way of exploring nerve territories is by examining the sensory innervation of the skin. The patterns of cutaneous sensory innervation may be used to determine the level of nerve lesions (see Fig. 4.18). Cutaneous sensory innervation: With the exception of the face (see Fig. 4.17), the body receives cutaneous sensory innervation (touch, pain, and temperature) from branches of the spinal nerves. Sensory fibers emerge from the spinal cord as the dorsal root, which combines with the ventral (motor) root in the intervertebral foramen to form the mixed spinal nerve. Embryonic development (see p. 60): During development, each spinal nerve is associated with a somite pair on either side of the spinal cord. Each somite divides into a dermatome (cutaneous), myotome (muscular), and sclerotome (vertebral). As these cells migrate, the spinal nerves migrate with them. Due to migration patterns, the regions of the body can be divided into two groups: • Trunk: In the trunk, the spinal nerves course reasonably horizontally to innervate a narrow strip of bone, muscle, and skin corresponding to their spinal cord level (e.g., intercostal nerves). This is due to the segmental migration of the trunk muscles during development. In this region, the peripheral nerves are therefore the ventral and dorsal rami of the spinal nerves. They will give off direct cutaneous branches. • Limbs: In the limbs, the migration of the muscle cells causes the spinal nerves to form plexuses (cervical, brachial, and lumbosacral). These plexuses subsequently give off peripheral nerves, which innervate specific regions of the body (see Fig. 4.18). Peripheral nerves in the limbs may be derived from multiple spinal cord levels. Note: Motor lesions cause paralysis of the innervated muscle. Depending on the level of the lesion, this may or may not coincide with sensory loss.

Caudal Nuclear columns of CN V spinal nucleus

CN V1

Middle Cranial

CN V2 Dorsal rami of spinal nerves

CN V3

A

Fig. 4.17 Cutaneous sensory innervation of the face Unlike the rest of the skin, the face is derived from the pharyngeal arches. Like all structures derived from the pharyngeal arches, it receives innervation from cranial nerves. The trigeminal nerve (CN V) provides general sensory innervation (touch, pain, and temperature) to most of the face. If a nerve lesion occurs in the peripheral nerve (CN V1, CN V2, or CN V3), the pattern of general sensory loss will resemble

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Cervical plexus (ventral rami of spinal nerves)

B

B. If a nerve lesion occurs within the CNS (in the spinal nucleus of the trigeminal nerve), the pattern of sensory loss will resemble A. The concentric pattern corresponds to the organization of the spinal nucleus: the higher (more cranial) portion of the nucleus innervates the periphery, and the lower (more caudal) portion innervates the center of the face.

Head

Sensory dorsal root

Spinal nerve in the intervertebral foramen

Peripheral nerve

Cutaneous nerve

4. Innervation of the Head & Neck

Maximum area supplied by a cutaneous nerve

Autonomous area of a cutaneous nerve Overlapping territories of two cutaneous nerves

A

Plexus

Greater occipital nerve

C2

Lesser occipital nerve

C3 C4 T2

C5

Axillary nerve T1

T6

Dorsal rami of spinal nerves

Radial nerve

C6 L1

Ulnar nerve

S5 C7

C8

Femoral nerve

L3 S1

Saphenous nerve

Tibial nerve

L5

B

Fig. 4.18 Cutaneous innervation and nerve lesions Cutaneous sensory innervation occurs via cutaneous branches of peripheral nerves (A). In the trunk, the peripheral nerves are the rami of the spinal nerves. In the limbs (neck, upper limb, and lower limb), the peripheral nerves are formed by nerve plexuses, in which the ventral rami fibers from multiple spinal cord levels combine (e.g., the femoral nerve contains fibers from L2–L4). Lesions can occur at the segmental (dark gray), peripheral (light gray), or cutaneous (white) level. Segmental (radicular) sensory innervation (B): The superficial skin area corresponding to a specific spinal cord root is called a dermatome. Lesions of the dorsal root of a spinal nerve or of the corresponding sensory nuclei in the spinal cord (dark gray area in A) will cause this pattern of sensory loss. For example, a herniated disk between the C4 and

C

C5 vertebrae may press against the spinal cord at the C6 level. This will cause sensory loss in the C6 dermatome (lateral forearm and hand). Peripheral sensory innervation (C): Lesions of a peripheral nerve (light gray area in A) will produce sensory loss in its cutaneous territories. (Note: These are not necessarily contiguous.) For example, chronic use of crutches may compress the radial nerve (which contains fibers from C5–T1). This will result in sensory loss in the territory of the radial nerve (i.e., posterior arm and forearm [dark red]). Contrast this to sensory loss of the C5–T1 dermatomes (i.e., no cutaneous sensation in entire arm). Cutaneous sensory innervation: Lesions of a cutaneous nerve (white area in A) will affect only the territory of that branch (see individual lines in C).

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Cranial Nerves: Overview Table 4.10 Cranial nerves Cranial nerve

CN I

Attachment to brain

Fiber type (Table 4.11) Afferent

CN II

Efferent

CN I: Olfactory n.

Telencephalon

CN II: Optic n.

Diencephalon

CN IV

CN III: Oculomotor n.

Mesencephalon

CN VI

CN III

CN V

CN IV: Trochlear n.

CN VII

CN V: Trigeminal n.

Pons

CN VIII

CN VI: Abducent n.

Pontomedullary junction

CN IX CN X

CN VII: Facial n.

CN XI

CN VIII: Vestibulocochlear n. CN XII

CN IX: Glossopharyngeal n.

Medulla oblongata

Fig. 4.19 Cranial nerves Whereas the 31 spinal nerve pairs emerge from the spinal cord, the 12 pairs of cranial nerves emerge from the brain at various levels (Table 4.10). They are numbered according to the order of their emergence. (Note: Cranial nerves I and II are not true peripheral nerves but are instead extensions of the telencephalon [CN I] and diencephalon [CN II].) Unlike the spinal nerves, which each have a dorsal sensory and a ventral motor root, the cranial nerves may contain afferent (sensory) and/or efferent (motor) fibers. The types of fibers (Table 4.11) correspond to the function of the nerve (Table 4.12).

CN X: Vagus n. CN XI: Accessory n. CN XII: Hypoglossal n.

Table 4.11 Cranial nerve fiber types The seven types of cranial nerve fibers are classified according to three criteria (reflected in the three-letter codes): 1. General (G) vs. Special (S), 2. Somatic (S) vs. Visceral (V), 3. Afferent (A) vs. Efferent (E). Each fiber type has an associated color used throughout this chapter. Afferent (sensory) fibers

General fibers

Special fibers

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Efferent (motor) fibers

GSA

General somatosensory

General sensation (touch, pain, and temperature) from somite derivatives (skin, skeletal muscle, and mucosa)

GSE

Somatomotor

Motor innervation to striated (skeletal) muscle derived from somites

GVA

General viscerosensory

General sensation from viscera (smooth muscle, cardiac muscle, and glands)

GVE

Parasympathetic

Motor innervation to viscera (smooth muscle, cardiac muscle, glands, etc.)

SSA

Special somatosensory

Sight, hearing, and balance

SVA

Special viscerosensory

Taste and smell

SVE

Branchiomotor

Fibers to striated (skeletal) muscle derived from the branchial arches

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4. Innervation of the Head & Neck

Table 4.12 Cranial nerve function Cranial nerve

Passage through skull

Fiber A

Sensory territory (afferent) / Target organ (efferent)

E

CN I: Olfactory n. (p. 70)

Ethmoid bone (cribriform plate)

Smell: special viscerosensory fibers from olfactory mucosa of nasal cavity

CN II: Optic n. (p. 71)

Optic canal

Sight: special somatosensory fibers from retina

CN III: Oculomotor n. (pp. 72–73)

Superior orbital fissure

Somatomotor innervation: to levator palpebrae superioris and four extraocular mm. (superior, medial, and inferior rectus, and inferior oblique) Parasympathetic innervation: preganglionic fibers to ciliary ganglion; postganglionic fibers to intraocular mm. (ciliary mm. and pupillary sphincter)

CN IV: Trochlear n. (pp. 72–73)

Superior orbital fissure

Somatomotor innervation: to one extraocular m. (superior oblique)

CN V: Trigeminal n. (pp. 74–75)

CN V1 (pp. 76–77)

Superior orbital fissure

General somatic sensation: from orbit, nasal cavity, paranasal sinuses, and face

CN V2 (pp. 78–79)

Foramen rotundum

General somatic sensation: from nasal cavity, paranasal sinuses, superior nasopharynx, upper oral cavity, internal skull, and face

CN V3 (pp. 80–81)

Foramen ovale

General somatic sensation: from lower oral cavity, ear, internal skull, and face Branchiomotor innervation: to the eight mm. derived from the 1st branchial arch (including mm. of mastication)

CN VI: Abducent n. (pp. 72–73)

Superior orbital fissure

Somatomotor innervation: to one extraocular m. (lateral rectus)

CN VII: Facial n. (pp. 82–85)

Internal acoustic meatus

General somatic sensation: from external ear Taste: special viscerosensory fibers from tongue (anterior ⅔) and soft palate Parasympathetic innervation: preganglionic fibers to submandibular and pterygopalatine ganglia; postganglionic fibers to glands (e.g., lacrimal, submandibular, sublingual, palatine) and mucosa of nasal cavity, palate, and paranasal sinuses Branchiomotor innervation: to mm. derived from the 2nd branchial arch (including mm. of facial expression, stylohyoid, and stapedius)

CN VIII: Vestibulocochlear n. (pp. 86–87)

Internal acoustic meatus

Hearing and balance: special somatosensory fibers from cochlea (hearing) and vestibular apparatus (balance)

CN IX: Glossopharyngeal n. (pp. 88–89)

Jugular foramen

General somatic sensation: from oral cavity, pharynx, tongue (posterior ⅓), and middle ear Taste: special visceral sensation from tongue (posterior ⅓) General visceral sensation: from carotid body and sinus Parasympathetic innervation: preganglionic fibers to otic ganglion; postganglionic fibers to parotid gland and inferior labial glands Branchiomotor innervation: to the one m. derived from the 3rd branchial arch (stylopharyngeus)

CN X: Vagus n. (pp. 90–91)

Jugular foramen

General somatic sensation: from ear and internal skull Taste: special visceral sensation from epiglottis General visceral sensation: from aortic body, laryngopharynx and larynx, respiratory tract, and thoracoabdominal viscera Parasympathetic innervation: preganglionic fibers to small, unnamed ganglia near target organs or embedded in smooth muscle walls; postganglionic fibers to glands, mucosa, and smooth muscle of pharynx, larynx, and thoracic and abdominal viscera Branchiomotor innervation: to mm. derived from the 4th and 6th branchial arches; also distributes branchiomotor fibers from CN XI

CN XI: Accessory n. (p. 92)

Jugular foramen

CN XII: Hypoglossal n. (p. 93)

Hypoglossal canal

Somatomotor innervation: to trapezius and sternocleidomastoid Branchiomotor innervation: to laryngeal mm. (except cricothyroid) via pharyngeal plexus and CN X (Note: The branchiomotor fibers from the cranial root of CN XI are distributed by CN X [vagus n.].) Somatomotor innervation: to all intrinsic and extrinsic lingual mm. (except palatoglossus)

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Cranial Nerve Nuclei Fig. 4.20 Cranial nerve nuclei: topographic arrangement Cross sections through the spinal cord and brainstem, superior view. Yellow = Somatic sensation. Green = Visceral sensation. Blue = Visceromotor function. Red = Somatomotor function. The nuclei of the spinal and cranial nerves have a topographic arrangement based on embryonic migration of neuron populations. A Embryonic spinal cord: Initially, the developing spinal cord demonstrates a dorsoventral arrangement in which the sensory (afferent) neurons are dorsal and the motor (efferent) neurons are ventral. This pattern is continued into the adult spinal cord: the cell bodies of afferent neurons (generally secondary neurons) are located in the dorsal horn, and the cell bodies of efferent neurons (lower motor neurons and preganglionic autonomic neurons) are located in the ventral and lateral horns, respectively. B Early embryonic brainstem: Sensory neurons (in the alar plate) migrate laterally, whereas motor nuclei (in the basal plate) migrate medially. This produces a mediolateral arrangement of nuclear columns (functionally similar nuclei stacked longitudinally). C Adult brainstem: The four longitudinal nuclear columns have a mediolateral arrangement (from medial to lateral): somatic efferent, visceral efferent, visceral afferent, and somatic afferent.

Dorsal

Roof plate Alar plate

Basal plate Floor plate

Ventral

Nuclei

Cranial nerve

Somatic afferent nuclear column (yellow) General somatosensory: Three nuclei that are primarily associated with CN V but receive fibers from other nerves.

• Mesencephalic nucleus • Principal (pontine) sensory nucleus • Spinal nucleus

CN V (via trigeminal ganglion) CN IX (via superior ganglion) CN X (via superior ganglion) Possibly CN VII (via geniculate ganglion)

Special somatosensory: Six nuclei that are associated with CN VIII.* The nerve and nuclei are divided into a vestibular part (balance) and a cochlear part (hearing).

• Medial, lateral, superior, and inferior vestibular nuclei

CN VIII, vestibular root (via vestibular ganglion)

• Anterior and posterior cochlear nuclei

CN VIII, cochlear root (via spiral ganglia)

General and special viscerosensory: One nuclear complex in the brainstem that consists of a superior (taste) and inferior (general visceral sensation) part and is associated with three cranial nerves.**

• Nucleus of the solitary tract, inferior part

CN IX (via inferior ganglion)

• Nucleus of the solitary tract, superior part

CN VII (via geniculate ganglion)

CN X (via inferior ganglion) CN IX (via inferior ganglion) CN X (via inferior ganglion)

Floor of the fourth ventricle (rhomboid fossa)

Visceral motor nuclear column (blue) Parasympathetic (general visceromotor): Four nuclei that each have an associated cranial nerve and one or more ganglia.

B

Medial

Nucleus of solitary tract, upper part

Dorsal vagal nucleus

Lateral

Nucleus of solitary tract, lower part Nuclei of vestibulocochlear nerve

Nucleus of hypoglossal nerve

Spinal nucleus of trigeminal nerve

Nucleus ambiguus

Vagus nerve C

There is not a 1-to-1 relationship between cranial nerve fiber types and cranial nerve nuclei. Some nerves derive similar fibers from multiple nuclei (e.g., CN V and CN VIII). Other nuclei are associated with multiple nerves. Note: The five sensory cranial nerves have eight associated sensory ganglia (cell bodies of first-order sensory neurons). The three parasympathetic cranial nerves have four associated autonomic ganglia (cell bodies of postganglionic neurons).

Visceral afferent nuclear column (green) Central canal

A

Table 4.13 Cranial nerve nuclei

Olive

Hypoglossal nerve

• Edinger-Westphal nucleus

CN III (via ciliary ganglion)

• Superior salivatory nucleus

CN VII (via submandibular and pterygopalatine ganglia)

• Inferior salivatory nucleus

CN IX (via otic ganglion)

• Dorsal motor nucleus

CN X (via myriad unnamed ganglia near target organs)

Branchiomotor (special visceromotor): Three nuclei that innervate the muscles of the pharyngeal arches via four cranial nerves.

• Trigeminal motor nucleus

CN V

• Facial nucleus

CN VII

• Nucleus ambiguus

CN IX CN X (with fibers from CN XI)

Somatomotor nuclear column (red)

Five nuclei, each associated with a separate nerve. • Nucleus of the oculomotor n.

CN III

• Nucleus of the trochlear n.

CN IV

• Nucleus of the abducent n.

CN VI

• Nucleus of the accessory n.

CN XI

• Nucleus of the hypoglossal n.

CN XII

*There are no brainstem nuclei associated with CN II because it emerges from the diencephalon. **The special visceral afferent fibers in the olfactory nerve (CN I) project to the telencephalon.

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Edinger-Westphal nucleus (CN III) Nucleus of oculomotor nerve (CN III) Mesencephalic nucleus of trigeminal nerve (CN V)

Nucleus of trochlear nerve (CN IV) Trigeminal motor nucleus (CN V)

CN V

Principal (pontine) sensory nucleus of trigeminal nerve (CN V)

Nucleus of abducent nerve (CN VI)

Cochlear nucleus of vestibulocochlear nerve (CN VIII)

Facial motor nucleus (CN VII)

Vestibular nuclei of vestibulocochlear nerve (CN VIII) Nucleus of hypoglossal nerve (CN XII)

Superior salivatory nucleus (CN VII) Inferior salivatory nucleus (CN IX)

CN VII CN VIII

CN VI

CN IX CN X

CN XI

Nucleus ambiguus (CN IX, X, XI)

Nucleus of the solitary tract (CN VII, IX, X)

Dorsal motor nucleus (CN X)

Spinal nucleus of trigeminal nerve (CN V)

Nucleus of accessory nerve (CN XI)

A

CN IV

B

Nucleus of oculomotor nerve Visceral oculomotor nucleus

Olfactory tract

Nucleus of trochlear nerve Optic chiasm

Mesencephalic nucleus of trigeminal nerve

Principal (pontine) sensory nucleus of trigeminal nerve

Motor nucleus of trigeminal nerve Nucleus of abducent nerve

Superior salivatory nucleus

Dorsal vagal nucleus

Inferior salivatory nucleus Vestibulocochlear nerve

Nucleus of hypoglossal nerve

Nucleus ambiguus

Nucleus of solitary tract

Spinal nucleus of trigeminal nerve

General somatic efferent nuclei General visceral efferent nuclei Special visceral efferent nuclei General somatic afferent nuclei Special somatic afferent nuclei

Spinal nucleus of accessory nerve

General visceral afferent nuclei Special visceral afferent nuclei C

Fig. 4.21 Cranial nerve nuclei: location A,B Posterior view of brainstem (cerebellum removed). C Left lateral view of midsagittal section. Note: The cranial nerves are numbered and described according to the level of their emergence from the brainstem. This does not necessarily correspond to the level of the cranial nerve nuclei associated with the nerve.

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CN I & II: Olfactory & Optic Nerves Neither the olfactory nerve nor the optic nerve is a true peripheral nerve. They are extensions of the brain (telencephalon and diencephalon, respectively). They are therefore both sheathed in meninges (removed here) and contain CNS-specific cells (oligodendrocytes and microglia).

Fig. 4.22 Olfactory nerve (CN I) A Left lateral view of left nasal septum and right lateral nasal wall (the posterior part of the nasal septum is cut). B Inferior view of brain. (*Shaded structures are deep to the basal surface.) The olfactory nerve relays smell information (special visceral afferent) to the cortex via a classical three-neuron pathway. 1. First-order sensory neurons are located in the mucosa of the upper nasal septum and superior nasal concha (A). These bipolar neurons form 20 or so fiber bundles collectively called the olfactory nerves (CN I). As the “olfactory region” is limited by the extent of these fibers (2–4 cm2), the nasal conchae create turbulence, which ensures that air (and olfactory stimuli) passes over this area. The thin, unmyelinated olfactory fibers enter the anterior cranial fossa via the cribriform plate of the ethmoid bone. 2. Second-order sensory neurons are located in the olfactory bulb (B). Their axons course in the olfactory tract to the medial or lateral olfactory striae. These axons synapse in the amygdala, the prepiriform area, or neighboring areas (see p. 152). 3. Third-order neurons relay the information to the cerebral cortex.

Olfactory bulb (second-order sensory neurons)

Olfactory tract

Frontal sinus

Cribriform plate (ethmoid bone)

Olfactory fibers (CN I, first-order sensory neurons)

Superior concha Nasal septum (cut)

Nasal septum

Middle concha

A

The first-order neurons have a limited lifespan (several months) and are continuously replenished from a pool of precursor cells in the olfactory mucosa. The regenerative capacity of the olfactory mucosa diminishes with age. Injuries to the cribriform plate may damage the meningeal covering of the olfactory fibers, causing olfactory disturbances and cerebrospinal fluid leakage (“runny nose” after head trauma). See p. 153 for the mechanisms of smell.

Medial olfactory stria Lateral olfactory stria

Olfactory bulb (secondorder sensory neurons) Olfactory tract

Anterior perforated substance Semilunar gyrus Ambient gyrus

B

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Prepiriform area* Amygdala*

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Fig. 4.23 Optic nerve (CN II) A Inferior view of brain. B Left lateral view of opened orbit. C Left posterolateral view of brainstem. The optic nerve (special somatic afferent) relays sight information from the retina to the visual cortex (striate area) via a four-neuron pathway (see p. 134). First-order neurons (rods and cones) in the retina translate incoming photons into impulses, which are relayed to second-order bipolar neurons and third-order ganglion cells. These retinal ganglion cells combine to form the optic nerve (CN II). The optic nerve passes from the orbit into the middle cranial fossa via the optic canal (the optic canal is medial to the superior orbital fissure by which the other cranial nerves enter the orbit, B). Ninety percent of the third-order neurons in the optic nerve synapse in the lateral geniculate body (C), which then projects to the striate area. Ten percent of the third-order neurons synapse in the mesencephalon. This nongeniculate part of the visual pathway functions in unconscious and reflex action. See p. 133 for the mechanisms of sight.

4. Innervation of the Head & Neck

Optic nerve (CN II)

Optic chiasm Optic tract

Lateral geniculate body Medial geniculate body Optic radiation

Occipital pole

A

Optic nerve (CN II) passing through optic canal

Optic tract

Lateral geniculate body

Thalamus

Optic chiasm

Optic tract

B

Ophthalmic nerve (CN V1) passing through superior orbital fissure

Optic nerve (CN II)

Superior colliculus Optic chiasm

C

Mesencephalon

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CN III, IV & VI: Oculomotor, Trochlear & Abducent Nerves Cerebral peduncles of mesencephalon

Cerebral aqueduct

Oculomotor nerve (CN III)

Trochlear nerve (CN IV)

Edinger-Westphal nucleus

Nucleus of trochlear nerve

Nucleus of oculomotor nerve

Pons

Tectum Edinger-Westphal nucleus

Central gray substance

Nucleus of oculomotor nerve

Red nucleus Substantia nigra

Cerebral peduncle

B

Abducent nerve (CN VI) Nucleus of abducent nerve

Medulla oblongata

Table 4.15 Trochlear nerve (CN IV) Nucleus and fiber distribution Somatomotor (red)

A

Fig. 4.24 Cranial nerves of the extraocular muscles A Anterior view of brainstem. B Superior view of cross section through the mesencephalon. CN III, IV, and VI are the three cranial nerves that collectively innervate the six extraocular muscles. (Note: CN III is also involved with the parasympathetic supply to the intraocular muscles.) CN III and IV arise from nuclei in the mesencephalon (midbrain, the highest level of the brainstem) and emerge at roughly the same level. CN VI arises from nuclei in the pons and emerges from the brainstem at the pontomedullary junction. Table 4.14 Oculomotor nerve (CN III) Nuclei, ganglion, and fiber distribution Somatomotor (red)

Nucleus of the oculomotor nerve (mesencephalon)

Lower motor neurons innervate: • Levator palpebrae superioris • Superior, medial, and inferior rectus muscles • Inferior oblique

Parasympathetic (blue)

Edinger-Westphal nucleus (mesencephalon)

Preganglionic neurons travel in the inferior division of CN III Postganglionic neurons in the ciliary ganglion innervate: Intraocular muscles (pupillary sphincter and ciliary muscle)

Course

CN III emerges from the mesencephalon, the highest level of the brainstem. It runs anteriorly through the lateral wall of the cavernous sinus to enter the orbit through the superior orbital fissure. After passing through the common tendinous ring, CN III divides into a superior and an inferior division. Lesions

Lesions cause oculomotor palsy of various extents. Complete oculomotor palsy is marked by paralysis of all the innervated muscles, causing: • Ptosis (drooping of eyelid) = disabled levator palpebrae superioris • Inferolateral deviation of affected eye, causing diplopia (double vision) = disabled extraocular muscles • Mydriasis (pupil dilation) = disabled pupillary sphincter • Accommodation difficulties (difficulty focusing) = disabled ciliary muscle

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Nucleus of the trochlear nerve (mesencephalon)

Lower motor neurons innervate: • Superior oblique

Course

CN IV is the only cranial nerve to emerge from the dorsal side (posterior surface) of the brainstem. After emerging from the mesencephalon, it courses anteriorly around the cerebral peduncle. CN IV then enters the orbit through the superior orbital fissure, passing lateral to the common tendinous ring. It has the longest intradural course of the three extraocular motor nerves. Lesions

Lesions cause trochlear nerve palsy: • Superomedial deviation of the affected eye, causing diplopia = disabled superior oblique Note: Because CN IV crosses to the opposite side, lesions close to the nucleus result in trochlear nerve palsy on the opposite side (contralateral palsy). Lesions past the site where the nerve crosses the midline cause palsy on the same side (ipsilateral palsy).

Table 4.16 Abducent nerve (CN VI) Nucleus and fiber distribution Somatomotor (red)

Nucleus of the abducent nerve (pons)

Lower motor neurons innervate: • Lateral rectus

Course

CN VI follows a long extradural path. It emerges from the pontomedullary junction (inferior border of pons) and runs through the cavernous sinus in close proximity to the internal carotid artery. CN VI enters the orbit through the superior orbital fissure and courses through the common tendinous ring. Lesions

Lesions cause abducent nerve palsy: • Medial deviation of the affected eye, causing diplopia = disabled lateral rectus Note: The path of CN VI through the cavernous sinus exposes it to injury. Cavernous sinus thrombosis, aneurysms of the internal carotid artery, meningitis, and subdural hemorrhage may all compress the nerve, resulting in nerve palsy. Excessive fall in CSF pressure (e.g., due to lumbar puncture) may cause the brainstem to descend, exerting traction on the nerve.

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Short ciliary nerves

Levator palpebrae superioris

4. Innervation of the Head & Neck

Superior rectus

Trochlea

Ciliary ganglion

Superior oblique

Common tendinous ring

CN III Mesencephalon

Lateral rectus (cut) Pons

Pontomedullary junction CN VI

A

Inferior oblique

CN IV Internal carotid artery and plexus Lateral rectus (cut) Supraorbital nerve (cut)

CN III, inferior division

Sympathetic root (postganglionic fibers from superior cervical ganglion via internal carotid plexus)

Parasympathetic root (preganglionic fibers from CN III)

Trochlea

Levator palpebrae superioris

Superior oblique

Superior rectus

Medial rectus

Lacrimal gland

Inferior rectus

Lateral rectus

Frontal nerve (CN V1)

CN VI

CN IV

CN IV

Superior ophthalmic vein

Levator palpebrae superioris

Superior rectus Lacrimal nerve (CN V1)

Superior oblique

CN III

Optic nerve (CN II)

Optic nerve (CN II)

Medial rectus CN III Inferior rectus

B

Fig. 4.25 Nerves supplying the ocular muscles Right orbit. A Lateral view with temporal wall removed. B Superior view of opened orbit. C Anterior view. Cranial nerves III, IV, and VI enter the orbit through the superior orbital fissure, lateral to the optic canal (CN IV then passes lateral to the common tendinous ring, and CN III and VI pass through it). All three nerves supply somatomotor innervation to the extraocular muscles. The ciliary ganglion communicates three types of fibers (parasympathetic, sympathetic, and sensory) to and from the intraocular muscles via the short ciliary nerves. (Only parasympathetics synapse in the ciliary ganglion. All other fibers pass through without synapsing.) The ciliary ganglion therefore has three roots: • Parasympathetic (motor) root: Preganglionic parasympathetic fibers travel with the inferior division of CN III to the ciliary ganglion. Only the parasympathetic fibers synapse in the ciliary ganglion (the other

C

Lateral rectus

CN VI

Inferior oblique

two fiber types pass through the ganglion without synapsing). • Sympathetic root: Postganglionic sympathetic fibers from the superior cervical ganglion travel on the internal carotid artery to enter the superior orbital fissure, where they may course along the ophthalmic artery to enter the short ciliary nerves via the ciliary ganglion. • Sensory root: Sensory fibers (from the eyeball) travel to the nasociliary nerve (CN V1) via the ciliary ganglion. The short ciliary nerves therefore contain sensory fibers from the eyeball and postganglionic sympathetic and parasympathetic fibers from the superior cervical and ciliary ganglion, respectively. Note: Sympathetic fibers from the superior cervical ganglion may also travel with the nasociliary nerve (CN V1) and reach the intraocular muscles via the long ciliary nerves.

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CN V: Trigeminal Nerve, Nuclei & Divisions

Trigeminal ganglion (sensory)

CN V1 (ophthalmic division)

B

CN V2 (maxillary division)

D

C

CN V3 (mandibular division)

A

E

Fig. 4.26 Trigeminal nerve divisions and distribution A Left lateral view of trigeminal divisions. B–D Somatosensory nerve territories. E Branchiomotor nerve territories. The trigeminal nerve is the major sensory nerve of the face. It has three major divisions (A) that convey general somatic sensation (touch, pain,

and proprioception) from the face (B) and select mucosa (C and D). The trigeminal nerve also contains branchiomotor fibers that innervate the eight muscles derived from the first branchial arch (E).

Table 4.17 Trigeminal nerve (CN V) divisions and distribution CN V consists of a large sensory root and a small motor root, which emerge from the brainstem separately in the middle cranial fossa at the level of the pons. Sensory root Fibers

General somatosensory (yellow): Convey general sensation (touch, pain, and temperature) from the sensory territories of CN V (see Fig. 4.26). The cell bodies of these first-order pseudounipolar neurons are primarily located in the trigeminal ganglion.

Course

The sensory root is formed by three divisions that unite as the trigeminal ganglion in the middle cranial fossa.

Nuclei

Afferent axons from all three divisions synapse on three brainstem nuclei located in the mesencephalon, pons, and medulla oblongata of the spinal cord.

Division

Distribution

CN V1 (ophthalmic division)

From orbit via superior orbital fissure (see p. 76)

CN V2 (maxillary division)

From pterygopalatine fossa via foramen rotundum (see p. 94)

CN V3 (mandibular division)

From inferior skull base via foramen ovale (see pp. 80, 94)

Nuclei

Sensation

Mesencephalic nucleus

Proprioception (see Table 4.18)

Principal (pontine) sensory nucleus

Touch

Spinal nucleus

Pain and temperature

• • • •

• • • •

Motor root

Masseter Temporalis Lateral pterygoid Medial pterygoid

Fibers

Branchiomotor (purple): Conveys motor fibers to the eight muscles derived from the 1st branchial (pharyngeal) arch:

Course

The motor root emerges separately from the pons and unites with CN V3 in the foramen ovale.

Nucleus

Motor nucleus (located in pons)

Tensor veli palatini Tensor tympani Mylohyoid Digastric, anterior belly

“Scaffolding”: CN V is used as scaffolding for the distribution of autonomic (sympathetic and parasympathetic) and taste fibers from other cranial nerves. Parasympathetic

All three branches of CN V are used to convey postganglionic parasympathetic fibers from parasympathetic ganglia. • CN VII: Preganglionic fibers from CN VII synapse in the pterygopalatine or the submandibular ganglion, associated with CN V2 and CN V3, respectively. Postganglionic parasympathetic fibers then travel with the sensory branches of CN V to reach their targets. • CN IX: Preganglionic fibers synapse in the otic ganglion; postganglionic fibers are distributed along branches of CN V3.

Sympathetic

Postganglionic sympathetic fibers from the superior cervical ganglion may also be distributed by the sensory branches of CN V.

Taste

Taste fibers from the presulcal tongue travel via the lingual nerve (CN V3) to the chorda tympani (CN VII) and nuclei of CN VII.

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Ophthalmic division (CN V1)

Mesencephalic nucleus

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Table 4.18 Trigeminal nerve nuclei and lesions Nuclei

Trigeminal ganglion

Somatosensory (yellow)

Maxillary division (CN V2)

Afferent neurons from the sensory territories of all three trigeminal divisions synapse in three brainstem nuclei named for their location.

Mandibular division (CN V3)

Nucleus

Location

Sensation

Mesencephalic nucleus

Mesencephalon

Proprioception (Note: The first-order sensory cell bodies of proprioceptive fibers associated with CN V have their cell bodies located in the mesencephalic nucleus.)

Principal (pontine) sensory nucleus

Pons

Touch

Spinal nucleus

Medulla oblongata

Pain and temperature

Trigeminal nerve (CN V) Motor nucleus Principal (pontine) sensory nucleus

Spinal nucleus

Note: These sensory nuclei contain the cell bodies of second-order neurons. The mesencephalic nucleus is an exception — it contains the cell bodies of first-order pseudounipolar neurons, which have migrated into the brain.

A

Mesencephalic nucleus

Fourth ventricle

Pons

Principal nucleus

Branchiomotor (purple)

Lower motor neurons are located in the motor nucleus of the trigeminal nerve. They innervate the eight muscles derived from the 1st branchial arch: • • • •

Motor nucleus

• • • •

Masseter Temporalis Lateral pterygoid Medial pterygoid

Tensor veli palatini Tensor tympani Mylohyoid Digastric, anterior belly

Lesions

Trigeminal nerve (CN V) B

Fig. 4.27 Trigeminal nerve nuclei A Anterior view of brainstem. B Superior view of cross section through the pons. Afferent neurons in the trigeminal nerve divisions convey general somatic sensation (touch, pain, and temperature) to the CNS. The neurons from all three divisions synapse in three brainstem nuclei named for their locations (see Table 4.18): • Mesencephalic nucleus • Principal (pontine) sensory nucleus • Spinal nucleus Efferent fibers arise from lower motor neurons in the motor nucleus. These fibers exit at the motor root of the trigeminal nerve and unite with the mandibular division (CN V3) in the foramen ovale. The branchiomotor fibers innervate the muscles of the first branchial arch.

Fig. 4.28 Trigeminal nerve lesions Lesions of the trigeminal nerve divisions (peripheral nerves) will produce sensory loss following the pattern in Fig. 4.26B and potentially motor paralysis. Lesions of the spinal nucleus of the trigeminal cord will produce sensory loss (pain and temperature) in the pattern shown here (Sölder lines). These concentric circles correspond to the somatotopic organization of the spinal cord nucleus: more cranial portions receive axons from the center of the face, and more caudal portions receive axons from the periphery.

Traumatic lesions of the trigeminal nerve may cause sensory loss in corresponding territories or paralysis to the target muscles. Note: The afferent fibers of the trigeminal nerve compose the afferent limb of the corneal reflex (reflex eyelid closure). • Trigeminal neuralgia is a disorder of CN V causing intense, crippling pain in the sensory territories.

Mesencephalic nucleus

Principal (pontine) sensory nucleus

Spinal nucleus B

Sölder lines

A

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CN V1: Trigeminal Nerve, Ophthalmic Division Fig. 4.29 Ophthalmic division (CN V1) of the trigeminal nerve Lateral view of the partially opened right orbit. The ophthalmic nerve divides into three major branches before reaching the superior orbital fissure: the lacrimal (L), frontal (F), and nasociliary (N) nerves. These nerves run roughly in the lateral, middle, and medial portions of the upper orbit, respectively. The lacrimal and frontal nerves enter the orbit superior to the common tendinous ring, and the nasociliary nerve enters through it. See Table 4.19 for labels.

Superior orbital fissure (opened)

F

Supratrochlear artery Cribriform plate with anterior ethmoidal artery N4

with posterior ethmoidal artery N3

N

CN IV A

Superior ophthamic vein

F2

N5

CN V1

Trigeminal ganglion CN V3

N1

N

Ciliary ganglion

F1 ,

medial and lateral branches with supraorbital artery

N4 N3

Short ciliary nerves with short posterior ciliary arteries

L

N2

CN II

CN VI

F

F1

N5

Superior rectus

Ophthalmic vein

L with lacrimal gland

Levator palpebrae superioris and superior rectus (cut)

Levator palpebrae superioris

Lacrimal gland and artery

Communicating branch with CN V2

Short ciliary nerves

F2 F2

Fig. 4.30 Ophthalmic nerve divisions in the orbit Superior view of orbit. (Removed: Bony roof, periorbita, and periorbital fat.) See Table 4.19 for labels. A Lacrimal, frontal, and nasociliary divisions. B Nasociliary nerve and ciliary ganglion. (Removed: Superior rectus and levator palpebrae superioris.) The extraocular muscles receive somatomotor innervation from the oculomotor (CN III), trochlear (CN IV), and abducent (CN VI) nerves. The intraocular muscles receive autonomic (sympathetic and parasympathetic) innervation via the short and long ciliary nerves. Sympa-

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N2

M

CN V2

N5 with trochlea

N3

CN II in optic canal

F1

N4

N F

(cut)

Lacrimal gland and artery L

Inferior ophthalmic vein CN VI Ciliary ganglion N1

CN III

B

thetic fibers from the superior cervical ganglion ascend on the internal carotid artery and travel in two manners: they may join the nasociliary nerve (CN V1), which distributes them as the long ciliary nerves, or they may course along the ophthalmic artery to enter the ciliary ganglion as the sympathetic root. The ciliary ganglion also receives parasympathetic fibers from CN III (via the parasympathetic root). The ganglion distributes these sympathetic and parasympathetic fibers via the short ciliary nerves. The short ciliary nerves contain sensory fibers, which enter the nasociliary nerve via the sensory root of the ciliary ganglion.

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4. Innervation of the Head & Neck

Table 4.19 Ophthalmic nerve (CN V1) The ophthalmic nerve (CN V1) is a sensory nerve* that conveys fibers from structures of the superior facial skeleton to the trigeminal ganglion. CN V1 gives off one branch in the middle cranial fossa before dividing into three major branches, which pass through the superior orbital fissure into the orbit. The lacrimal, frontal, and nasociliary nerves travel in the lateral, middle, and medial portions of the upper orbit, respectively. M

Meningeal n.

Sensory: Dura mater of the middle cranial fossa.

L

Lacrimal n.

The smallest of the three major branches, the lacrimal nerve runs in the superolateral orbit.

Opening

Superior orbital fissure (above the common tendinous ring).

Course

Runs (with the lacrimal artery) along the superior surface of the lateral rectus, through the lacrimal gland and orbital septum to the skin of the upper eyelid.

Innervation

Sensory: Upper eyelid (skin and conjunctiva) and lacrimal gland. Sensory and parasympathetic: Lacrimal gland. Postganglionic parasympathetic secretomotor fibers from the pterygopalatine ganglion of the facial nerve (CN VII) travel with the zygomatic and zygomaticotemporal nerves (CN V2). They enter the sensory lacrimal nerve (CN V1) via a communicating branch and are distributed to the gland. Postganglionic sympathetic fibers follow a similar path.

F

Frontal n.

The largest of the three major branches, the lacrimal nerve runs in the middle of the upper orbit.

Opening

Superior orbital fissure (above the common tendinous ring).

Course and branches

Runs along the superior surface of the levator palpebrae superioris, below the periosteum. At roughly the level of the posterior eyeball, the frontal nerve divides into two terminal branches:

Innervation

N

Nasociliary n.

F1

Supraorbital n.

Continues on the superior surface of the levator palpebrae superioris and passes through the supraorbital foramen (notch).

F2

Supratrochlear n.

Courses anteromedially with the supratrochlear artery toward the trochlea (tendon of superior oblique) and passes through the frontal notch.

Sensory: Upper eyelid (skin and conjunctiva) and the skin of the forehead (both branches). The supraorbital n. also receives fibers from frontal sinus mucosa; the supratrochlear n. communicates with the infratrochlear nerve. The nasociliary nerve runs in the middle and medial parts of the upper orbit.

Opening

Superior orbital fissure (via the common tendinous ring).

Course and branches

Runs medially (across the optic nerve [CN II]) and then anteriorly between the superior oblique and medial rectus. Gives off three branches (two sensory and one sympathetic) before dividing into two terminal branches (anterior ethmoid and infratrochlear nerves). N1 Sensory root of the ciliary ganglion

Innervation

Sensory: Fibers from the short ciliary nerves pass without synapsing through the ciliary ganglion and enter the nasociliary nerve via the sensory root.

N2

Long ciliary nn.

Sensory: Eye (e.g., cornea and sclera).

N3

Posterior ethmoid n.

Sensory: Ethmoid air cells and sphenoid sinus. Fibers run in the ethmoid bone (posterior ethmoid canal) to the nasociliary nerve.

N4

Anterior ethmoid n.

Sensory: Superficial nose and anterior nasal cavity. • Internal nasal n.: Mucosa of the anterior portions of the nasal septum (medial internal nasal n.) and lateral nasal wall (lateral internal nasal n.). • External nasal n.: Skin of the nose (courses under the nasalis muscle). Fibers from these two terminal branches ascend via the nasal bone, course posteriorly in the cranial cavity over the cribriform plate, and enter the orbit via the anterior ethmoid canal.

N5

Infratrochlear n.

Sensory: Medial aspect of the upper eyelid (skin and conjunctiva) and the lacrimal sac. Fibers enter the orbit near the trochlea (tendon of superior oblique) and course posteriorly to the nasociliary nerve.

Sensory: Ethmoid air cells, sphenoid sinus, anterior nasal cavity, superficial nose, upper eyelid, lacrimal sac, and eye.

*Note: Nerve courses are traditionally described proximal to distal (CNS to periphery). However, for sensory nerves, the sensory relay is in the opposite direction. It is more appropriate to talk of sensory nerves collecting fibers than to talk of them branching to supply a region.

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CN V2: Trigeminal Nerve, Maxillary Division Trigeminal ganglion

I

Communicating branch with CN V1

Z

CN V2

CN V1

CN V3

I I , anterior superior alveolar nerve I , middle superior alveolar nerve

M

Superior alveolar plexus

G

Pterygopalatine ganglion P

A

Cribriform plate

Frontal sinus

Anterior ethmoidal nerve (CN V1)

G1 G

Olfactory fibers (CN I)

CN V2

Medial nasal branches Medial posterior superior nasal nerves M

G2 entering incisive canal

B

Sphenoid sinus

Olfactory bulb

Pterygopalatine ganglion

Sphenopalatine foramen (opened)

G3

G2

Cribriform plate

Olfactory fibers (CN I) G3 ,

lateral posterior superior nasal nerves

External nasal branch Internal nasal branch

Anterior ethmoidal nerve (CN V1)

Lateral nasal branches

Pterygopalatine ganglion G4

G4 , lesser palatine nerve

C

G4 , greater palatine nerve

G4 , greater palatine nerve, posterior inferior nasal branches

Fig. 4.31 Maxillary division (CN V2) of the trigeminal nerve Right lateral view. See Table 4.20 for labels. A Opened right maxillary sinus. B Nasal septum in right nasal cavity. C Left lateral nasal wall.

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4. Innervation of the Head & Neck

Table 4.20 Maxillary nerve (CN V2) Like the ophthalmic nerve (CN V1), the maxillary nerve (CN V2 LVDVHQVRU\QHUYH WKDWFRQYH\VÀEHUVIURPVWUXFWXUHVRIWKHIDFLDOVNHOHWRQWRWKH trigeminal ganglion. CN V2JLYHVR̥RQHEUDQFKLQWKHPLGGOHFUDQLDOIRVVDEHIRUHHQWHULQJWKHIRUDPHQURWXQGXPWRWKHSWHU\JRSDODWLQHIRVVD,QWKH SWHU\JRSDODWLQHIRVVDWKHPD[LOODU\QHUYHGLYLGHVLQWREUDQFKHVHJ]\JRPDWLFSRVWHULRUVXSHULRUDOYHRODUDQGLQIUDRUELWDOQHUYHV DQGUHFHLYHV JDQJOLRQLFEUDQFKHVIURPWKHSWHU\JRSDODWLQHJDQJOLRQ7KLVJDQJOLRQKDVÀYHPDMRUEUDQFKHVZKLFKGLVWULEXWH&192ÀEHUV7KHVHVHQVRU\&192 ÀEHUVFRQYH\DXWRQRPLFÀEHUVIURPWKHSWHU\JRSDODWLQHJDQJOLRQ Direct branches of the maxillary n. (CN V2) M

Middle meningeal n.

6HQVRU\0HQLQJHVRIWKHPLGGOHFUDQLDOIRVVD

G

Ganglionic branches

*HQHUDOO\WZRJDQJOLRQLFEUDQFKHVVXVSHQGSDVVWKURXJK WKHpterygopalatine ganglionIURP&192VHHEHORZ 

Z

Zygomatic n.

6HQVRU\6NLQRIWKHWHPSOHzygomaticotemporal nerve DQGFKHHNzygomaticofacial nerve )LEHUVHQWHUWKHRUELWYLD FDQDOVLQWKH]\JRPDWLFERQHDQGFRXUVHLQWKHODWHUDORUELWZDOOWR&192YLDWKHLQIHULRURUELWDOÀVVXUH

P Posterior superior alveolar n.

,

Infraorbital n.

6HQVRU\0D[LOODU\PRODUVZLWKDVVRFLDWHGJLQJLYDHDQGEXFFDOPXFRVD DQGPD[LOODU\VLQXV)LEHUVFRXUVHRQWKH LQIUDWHPSRUDOVXUIDFHRIWKHPD[LOOD7KHSRVWHULRUVXSHULRUDOYHRODUQHUYHFRQWULEXWHVWRWKHsuperior alveolar plexus DQWHULRUPLGGOHDQGVXSHULRUDOYHRODUQQ  6HQVRU\/RZHUH\HOLGVNLQDQGFRQMXQFWLYD PD[LOODU\VLQXVDQGPD[LOODU\WHHWKYLDDQWHULRUDQGPLGGOHVXSHULRU DOYHRODUEUDQFKHV  ‡ M  iddle superior alveolar nerve:6HQVRU\ÀEHUVIURPWKHPD[LOODU\SUHPRODUVZLWKDVVRFLDWHGJLQJLYDHEXFFDOPXFRVDDQG PD[LOODU\VLQXV  ‡ A  nterior superior alveolar nerve:6HQVRU\ÀEHUVIURPWKHPD[LOODU\LQFLVRUVDQGFDQLQHVZLWKDVVRFLDWHGJLQJLYDH OLQJXDOPXFRVDDQGPD[LOODU\VLQXV 1DVDOEUDQFK6HQVRU\ÀEHUVIURPDQWHULRUSRUWLRQVRIWKHQDVDOZDOOÁRRUDQG VHSWXP 7KHVHÀEHUVHQWHUWKHLQIUDRUELWDOFDQDODQGHPHUJHIURPWKHLQIUDRUELWDOJURRYH

Branches passing through the pterygopalatine ganglion:7KHSWHU\JRSDODWLQHJDQJOLRQLVDSDUDV\PSDWKHWLFJDQJOLRQRIWKHIDFLDOQHUYH&19,, ,W FRQYH\VÀUVWRUGHUVHQVRU\ÀEHUVWR&192IURPÀYHPDMRUEUDQFKHVVXSSO\LQJWKHRUELWQDVDOFDYLW\KDUGDQGVRIWSDODWHVDQGQDVRSKDU\Q[ G1

Orbital branches

6HQVRU\2UELWDOSHULRVWHXPYLDLQIHULRURUELWDOÀVVXUH DQGSDUDQDVDOVLQXVHVHWKPRLGDLUFHOOVDQGVSKHQRLGVLQXVYLD WKHSRVWHULRUHWKPRLGFDQDO 

G2

Nasopalatine n.

6HQVRU\$QWHULRUKDUGSDODWHDQGWKHLQIHULRUQDVDOVHSWXP7KHOHIWDQGULJKWQDVRSDODWLQHQHUYHVDVFHQGLQWKHDQWHULRU DQGSRVWHULRULQFLVLYHIRUDPLQDUHVSHFWLYHO\ DQGFRQYHUJHLQWKHLQFLVLYHIRVVD7KH\WUDYHOSRVWHURVXSHULRUO\RQWKHQDVDO VHSWXPYRPHU WKURXJKWKHVSKHQRSDODWLQHIRUDPHQ

G3 Posterior superior nasal nn.

6HQVRU\3RVWHURVXSHULRUQDVDOFDYLW\Note:7KHDQWHULRUHWKPRLGQHUYH>&191@FRQYH\VÀEHUVIURPWKHDQWHURVXSHULRUSRUWLRQ ‡ Lateral posterior superior nasal nn.:3RVWHULRUHWKPRLGDLUFHOOVDQGPXFRVDLQWKHSRVWHULRURIWKHVXSHULRUDQGPLGGOH nasal conchae. ‡ M  edial posterior superior nasal nn.:0XFRVDRIWKHSRVWHULRUQDVDOURRIDQGVHSWXP

G4

Palatine nn.

6HQVRU\+DUGDQGVRIWSDODWHV ‡ G  reater palatine n.:+DUGSDODWHJLQJLYDHPXFRVDDQGJODQGV DQGVRIWSDODWHYLDJUHDWHUSDODWLQHFDQDO5HFHLYHV ÀEHUVIURPWKHLQIHULRUQDVDOFRQFKDDQGZDOOVRIWKHPLGGOHDQGLQIHULRUQDVDOPHDWXVHVWKURXJKWKHSHUSHQGLFXODU SODWHRIWKHHWKPRLGERQHSRVWHULRULQIHULRUQDVDOEUDQFKHV  ‡ L esser palatine n.:6RIWSDODWHSDODWLQHWRQVLOVDQGXYXODYLDOHVVHUSDODWLQHFDQDO 7KHJUHDWHUDQGOHVVHUSDODWLQHQHUYHVFRQYHUJHLQWKHJUHDWHUSDODWLQHFDQDO

G5

Pharyngeal n.

6HQVRU\0XFRVDRIWKHVXSHULRUQDVRSKDU\Q[YLDSDODWRYDJLQDOSKDU\QJHDO FDQDO

$XWRQRPLFVFD̦ROGLQJ7KHSWHU\JRSDODWLQHJDQJOLRQLVD̦OLDWHGZLWKWKHVHQVRU\&1923RVWJDQJOLRQLFDXWRQRPLFÀEHUVDUHGLVWULEXWHGE\VHQVRU\ ÀEHUVRI&192. Pterygopalatine ganglion&19,,

Motor root:3UHJDQJOLRQLFSDUDV\PSDWKHWLFÀEHUVIURPWKHIDFLDOQHUYH&19,, WUDYHOLQWKHgreater petrosal nerve MRLQV ZLWKGHHSSHWURVDOQHUYHWRIRUPQHUYHRISWHU\JRLGFDQDO . Sympathetic root:3RVWJDQJOLRQLFV\PSDWKHWLFÀEHUVIURPWKHVXSHULRUFHUYLFDOJDQJOLRQDVFHQGYLDWKHLQWHUQDOFDURWLG SOH[XV DQGWUDYHOLQWKHdeep petrosal nerveMRLQVZLWKJUHDWHUSHWURVDOQHUYHWRIRUPQHUYHRISWHU\JRLGFDQDO . Sensory root:6HQVRU\ÀEHUVSDVVWKURXJKWKHJDQJOLRQIURPÀYHVHQVRU\EUDQFKHVVHHDERYH 

‡ L acrimal gland:3RVWJDQJOLRQLFSDUDV\PSDWKHWLFVHFUHWRPRWRUÀEHUVWRWKHODFULPDOJODQGOHDYHWKHSWHU\JRSDODWLQHJDQJOLRQRQWKH]\JRPDWLF nerve (CN V2 7KH\WUDYHOZLWKWKH]\JRPDWLFRWHPSRUDOQHUYHWRWKHODFULPDOQHUYH&191 YLDDFRPPXQLFDWLQJEUDQFK ‡ G  lands of the oral cavity:3RVWJDQJOLRQLFSDUDV\PSDWKHWLFÀEHUVWRWKHJODQGVRIWKHSDODWLQHSKDU\QJHDODQGQDVDOPXFRVDUHDFKWKHLUWDUJHWVYLD FRUUHVSRQGLQJVHQVRU\EUDQFKHVRI&192. ‡ Blood vessels:3RVWJDQJOLRQLFV\PSDWKHWLFÀEHUVDUHGLVWULEXWHGE\&192. ‡ T  aste &19,, :7DVWHÀEHUVVSHFLDOYLVFHUDOD̥HUHQW DVVRFLDWHGZLWK&19,,DVFHQGIURPWKHSDODWHWRWKHJUHDWHUSHWURVDOQHUYHDQGJHQLFXODWH JDQJOLRQRI&19,,YLDWKHSDODWLQHQHUYHV *Note:1HUYHFRXUVHVDUHWUDGLWLRQDOO\GHVFULEHGSUR[LPDOWRGLVWDO&16WRSHULSKHU\ +RZHYHUIRUVHQVRU\QHUYHVWKHVHQVRU\UHOD\LVLQWKHRSSRVLWH GLUHFWLRQ,WLVPRUHDSSURSULDWHWRWDONRIVHQVRU\QHUYHVFROOHFWLQJÀEHUVWKDQWRWDONRIWKHPEUDQFKLQJWRVXSSO\DUHJLRQ

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CN V3: Trigeminal Nerve, Mandibular Division Trigeminal ganglion

Mandibular division

Foramen ovale

Deep temporal nerves

Recurrent meningeal nerve (nervus spinosus)

Infraorbital foramen

Middle meningeal artery

Lateral pterygoid muscle Buccal nerve (long buccal nerve)

Auriculotemporal nerve

Nerve to medial pterygoid Masseteric nerve

Mandibular canal

Medial pterygoid muscle

Inferior dental branches

Lingual nerve

Mental nerve Mental foramen Masseter muscle

A

Inferior alveolar nerve

CN V1 (mandibular nerve) Nerve of tensor tympani Foramen ovale

Nerve of medial pterygoid

Facial nerve Lesser petrosal nerve

Nerve of tensor veli palatini

Stylomastoid foramen Auriculotemporal nerve

Chorda tympani

Communicating branch to auriculotemporal nerve

Otic ganglion

Medial pterygoid muscle Lingual nerve

Inferior alveolar nerve B

80

Submandibular ganglion Nerve to mylohyoid

Fig. 4.32 Mandibular division (CN V3) of the trigeminal nerve Right lateral view. A Partially opened mandible with middle cranial fossa windowed. B Opened oral cavity (right half of mandible removed). The trunk of CN V3 gives off two branches (recurrent meningeal and medial pterygoid nerves) before splitting into an anterior and a posterior division (see Table 4.21). The nerve to the medial pterygoid conveys branchiomotor fibers to the otic ganglion; these fibers pass without synapsing to innervate the tensors tympani and veli palatini. The otic ganglion is the parasympathetic ganglion of the glossopharyngeal nerve (CN IX). Preganglionic fibers enter via the lesser petrosal nerve (reconstituted from the tympanic plexus; see pp. 160–161). Postganglionic fibers leave with the auriculotemporal nerve (CN V3) to innervate the buccal gland. Taste fibers of CN VII travel in the lingual nerve (CN V3) to the chorda tympani (which they enter either directly or indirectly via the otic ganglion). These fibers ascend in the chorda tympani via the tympanic cavity to the facial nerve (CN VII; see p. 83).

Head

4. Innervation of the Head & Neck

Table 4.21 Mandibular nerve (CN V3) The mandibular nerve (CN V3) is the mixed afferent-efferent branch of CN V, containing general sensory fibers and branchiomotor fibers to the eight muscles derived from the 1st pharyngeal arch. The large sensory and small motor roots of CN V leave the middle cranial fossa via the foramen ovale. In the infratemporal fossa, they unite to form the CN V3 trunk. The trunk gives off two branches before splitting into an anterior and a posterior division. Of the eight branchial arch muscles, three are supplied by the trunk, three by the anterior division, and two by the posterior division. Trunk: The trunk of CN V3 gives off one sensory and one motor branch. The motor branch conveys branchiomotor fibers to three of the eight muscles of the 1st pharyngeal arch. R Recurrent meningeal branch (nervus spinosum) MP

Medial pterygoid n.

Sensory: Dura of the middle cranial fossa (also anterior cranial fossa and calvarium). The nervus spinosum arises in the infratemporal fossa and re-enters the middle cranial fossa via the foramen spinosum. Branchiomotor: Directly to the medial pterygoid. Certain fibers enter the otic ganglion via the motor root and pass without synapsing to: • N. to tensor veli palatini: Tensor veli palatini. • N. to tensor tympani: Tensor tympani.

Anterior division: The anterior division of CN V3 contains predominantly efferent fibers (with one sensory branch, the buccal nerve.) The branchiomotor fibers innervate three of the eight muscles of the 1st pharyngeal arch. M

Masseter n.

Branchiomotor: Masseter. Sensory: Temporomandibular joint (articular branches).

T

Deep temporal nn.

Branchiomotor: Temporalis via two branches: • Anterior deep temporal n. • Posterior deep temporal n.

LP

Lateral pterygoid n.

Branchiomotor: Lateral pterygoid.

B

Buccal (long buccal) n.

Sensory: Cheek (skin and mucosa) and buccal gingivae of the molars.

Posterior division: The larger posterior division of CN V3 contains predominantly afferent fibers (with one motor branch, the mylohyoid nerve). The mylohyoid nerve arises from the inferior alveolar nerve and supplies the remaining two muscles of the 1st pharyngeal arch. A

Auriculotemporal n.

Sensory: Skin of the ear and temple. Fibers pass through the parotid gland, behind the temporomandibular joint, and into the infratemporal fossa. The nerve typically splits around the middle meningeal artery (a branch of the maxillary artery) before joining the posterior division. Distributes postganglionic parasympathetic fibers from the otic ganglion.

L

Lingual n.

Sensory: Mucosa of the oral cavity (presulcal tongue, oral floor, and gingival covering of lingual surface of mandibular teeth). In the infratemporal fossa, the lingual nerve combines with the chorda tympani (CN VII).

I

Inferior alveolar n.

Sensory: Mandibular teeth and chin: • Incisive branch: Incisors, canines, and 1st premolars (with associated labial gingivae). • Mental n.: Labial gingivae of the incisors and the skin of the lower lip and chin. The mental nerve enters the mental foramen and combines with the incisive branch in the mandibular canal. The inferior alveolar nerve exits the mandible via the mandibular foramen and combines to form the posterior division of CN V3. Note: 2nd premolars and mandibular molars are supplied by the inferior alveolar nerve before it splits into its terminal branches. Branchiomotor: Fibers branch just proximal to the mandibular foramen: • Mylohyoid n.: Mylohyoid and anterior belly of the digastric.

Autonomic scaffolding: The parasympathetic ganglia of CN VII (submandibular ganglion) and CN IX (otic ganglion) are functionally associated with CN V3. Submandibular ganglion (CN VII)

Otic ganglion (CN IX)

Parasympathetic root

Preganglionic parasympathetic fibers from the facial nerve (CN VII) travel to the ganglion in the chorda tympani, facial nerve, and lingual nerve (CN V3).

Sympathetic root

Sympathetic fibers from the superior cervical ganglion ascend (via the internal carotid plexus) and travel in a plexus on the facial artery.

Parasympathetic root

Preganglionic parasympathetic fibers enter from CN IX via the lesser petrosal nerve.

Sympathetic root

Postganglionic sympathetic fibers from the superior cervical ganglion enter via a plexus on the middle meningeal artery.

• Parotid gland: Postganglionic parasympathetic fibers from the otic ganglion travel to the parotid gland via the auriculotemporal n. (CN V3). • Submandibular and sublingual glands: Postganglionic autonomic fibers to the submandibular and sublingual glands travel from the submandibular ganglion via glandular branches. • Taste (CN VII): Taste fibers (special viscerosensory fibers) to CN VII may travel via the lingual nerve (CN V3) to the chorda tympani (CN VII). Note: Nerve courses are traditionally described proximal to distal (CNS to periphery). However, for sensory nerves, the sensory relay is in the opposite direction. It is more appropriate to talk of sensory nerves collecting fibers than to talk of them branching to supply a region.

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CN VII: Facial Nerve, Nuclei & Internal Branches

Nucleus of the abducent nerve (CN VI)

Table 4.22 Facial nerve (CN VII)

Pons

Nuclei, ganglia, and fiber distribution Branchiomotor (purple)

Superior salivatory nucleus

Facial motor nucleus

Facial motor nucleus Nervus intermedius Geniculate ganglion Stylomastoid foramen Branches of the parotid plexus A

Lower motor neurons innervate all muscles of the 2nd branchial (pharyngeal) arch: • Muscles of facial expression • Stylohyoid • Digastric, posterior belly • Stapedius

Parasympathetic (blue)

Superior salivatory nucleus

Nucleus of solitary tract

Nucleus of the abducent nerve (CN VI)

Internal genu of facial nerve

Nucleus of solitary tract, superior part Superior salivatory nucleus Facial motor nucleus Facial nerve B

Fig. 4.33 Facial nerve (CN VII) A Anterior view of brainstem. B Superior view of cross section through pons. Fibers: The facial nerve provides branchiomotor innervation to the muscles of the second branchial arch and parasympathetic motor innervation to most salivary glands (via the pterygopalatine and submandibular ganglia). Taste fibers are conveyed via pseudounipolar sensory neurons with cell bodies in the geniculate ganglion. The facial nerve also receives general sensation from the external ear. Branches: The superficial branches of CN VII are primarily branchiomotor (only the posterior auricular nerve may contain sensory fibers as well as motor). Taste and preganglionic parasympathetic fibers travel in both the chorda tympani and greater petrosal nerves. These fibers converge in the external genu and enter the brainstem together as the nervus intermedius.

Preganglionic neurons synapse in the pterygopalatine or submandibular ganglion. Postganglionic neurons innervate: • Lacrimal gland • Submandibular and sublingual glands • Small glands of the oral and nasal cavities

Special visceral afferent (light green)

Nucleus of the solitary tract, superior part

First-order pseudounipolar cells in the geniculate ganglion relay taste sensation from the presulcal tongue and soft palate (via the chorda tympani and greater petrosal nerve).

General somatic afferent (not shown)

First-order pseudounipolar cells in the geniculate ganglion relay general sensation from the external ear (auricle and skin of the auditory canal) and lateral tympanic membrane. Course Emergence: Axons from the superior salivatory nucleus and the nucleus of the solitary tract form the nervus intermedius. These combine with the branchiomotor and somatosensory fibers to emerge from the brainstem as CN VII. Internal branches: CN VII enters the petrous bone via the internal acoustic meatus. Within the facial canal, it gives off one branchiomotor branch (nerve to the stapedius) and two nerves (greater petrosal nerve and chorda tympani) containing both parasympathetic and taste fibers. External branches: The remaining fibers emerge via the stylomastoid foramen. Three direct branches arise before the fibers enter the parotid gland (nerve to posterior digastric, nerve to stylohyoid, and posterior auricular nerve). In the gland, the branchiomotor fibers branch to form the parotid plexus, which innervates the muscles of the 2nd branchial arch. Lesions

CN VII is most easily injured in its distal portions (after emerging from the parotid gland). Nerve lesions of the parotid plexus cause muscle paralysis. Temporal bone fractures may injure the nerve within the facial canal, causing disturbances of taste, lacrimation, salivation, etc. (see Fig. 4.34).

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Fig. 4.34 Branches of the facial nerve The facial nerve enters the facial canal of the petrous bone via the internal acoustic meatus. Most branchiomotor fibers and all somatosensory fibers emerge via the stylomastoid foramen. Within the facial canal, CN VII gives off one branchiomotor branch and two nerves containing both parasympathetic and taste fibers (greater petrosal nerve and chorda tympani). Temporal bone fractures may injure the facial nerve at various levels:

1 Internal acoustic meatus CN VIII

2

Greater petrosal nerve 3 Nerve to the stapedius Chorda tympani

Stylomastoid foramen

4. Innervation of the Head & Neck

1 Internal acoustic meatus: Lesions affect CN VII and the vestibulocochlear nerve (CN VIII). Peripheral motor facial paralysis is accompanied by hearing loss and dizziness. 2 External genu of facial nerve: Peripheral motor facial paralysis is accompanied by disturbances of taste sensation, lacrimation, and salivation (greater petrosal nerve). 3 Motor paralysis is accompanied by disturbances of salivation and taste (chorda tympani). Paralysis of the stapedius causes hyperacusis (hypersensitivity to normal sounds). 4 Facial paralysis is accompanied by disturbances of taste and salivation (chorda tympani). 5 Facial paralysis is the only manifestation of a lesion at this level.

4

5

Posterior auricular nerve Nerves to the stylohyoid and posterior digastric

Parotid plexus

Fig. 4.35 Course of the facial nerve Right lateral view of right temporal bone (petrous part). Both the facial nerve and vestibulocochlear nerve (CN VIII, not shown) pass through the internal acoustic meatus on the posterior surface of the petrous bone. The facial nerve courses laterally in the bone to the external genu, which contains the geniculate ganglion (cell bodies of first-order pseudounipolar sensory neurons). At the genu (L. genu = knee), CN VII bends and descends in the facial canal. It gives off three branches between the geniculate ganglion and the stylomastoid foramen: • Greater petrosal nerve: Parasympathetic and taste (special visceral afferent) fibers branch from the geniculate ganglion in the greater petrosal canal. They emerge on the anterior surface of the petrous pyramid and continue across the surface of the foramen lacerum. The greater petrosal nerve combines with the deep petrosal nerve in the pterygoid canal (nerve of the pterygoid canal, vidian). The greater petrosal nerve contains the fibers that form the motor root of the pterygopalatine ganglion (the parasympathetic ganglion of CN VII). The pterygopalatine ganglion distributes autonomic fibers via the trigeminal nerve (primarily the maxillary division, CN V2). • Stapedial nerve: Branchiomotor fibers innervate the stapedius muscle. • Chorda tympani: The remaining parasympathetic and taste fibers leave the facial nerve as the chorda tympani. This nerve runs through the tympanic cavity and petrotympanic fissure to the infratemporal fossa, where it unites with the lingual nerve (CN V3).

Facial nerve (CN VII) in facial canal

Geniculate ganglion

Trigeminal nerve (CN V)

Hiatus of greater petrosal canal

Stapedial nerve and muscle

Trigeminal ganglion CN V1 CN V3

Greater petrosal nerve

CN V2

Tympanic cavity

Chorda tympani

Posterior auricular nerve

Stylomastoid foramen

Petrotympanic fissure

Pterygopalatine ganglion

Lingual nerve (CN V3)

Stylohyoid muscle with nerve Branchiomotor fibers to parotid plexus

Digastric muscle, posterior belly with nerve

The remaining fibers (branchiomotor with some general sensory) exit via the stylomastoid foramen.

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CN VII: Facial Nerve, External Branches & Ganglia Fig. 4.36 Innervation of the second branchial arch muscles Left lateral view. The branchiomotor fibers of CN VII innervate all the muscles derived from the second branchial arch. With the exception of the stapedial nerve (to the stapedius), all branchiomotor fibers in the facial nerve emerge from the facial canal via the stylomastoid foramen. Three branches arise before the parotid plexus: • Posterior auricular nerve (Note: This may also contain general somatosensory fibers.) • Nerve to the digastric (posterior belly) • Nerve to the stylohyoid The remaining branchiomotor fibers then enter the parotid gland where they divide into two trunks (temporofacial and cervicofacial) and five major branches, which innervate the muscles of facial expression: • • • • •

Temporal branches

Parotid plexus Zygomatic branches

Posterior auricular nerve

Buccal branches Marginal mandibular branch

Facial nerve Nerve to digastric (posterior belly) Cervical branch

Nerve to stylohyoid

Temporal Zygomatic Buccal Mandibular (marginal mandibular) Cervical

The branching of the plexus is variable.

Fig. 4.37 Facial paralysis A Upper motor neurons in the primary somatomotor cortex (precentral gyrus) descend to the cell bodies of lower motor neurons in the facial motor nucleus. The axons of these lower motor neurons innervate the muscles derived from the second branchial arch. The facial motor nucleus has a “bipartite” structure: its cranial (upper) part supplies the muscles of the calvaria and palpebral fissure, and its caudal (lower) part supplies the muscles of the lower face. The cranial part of the nucleus receives bilateral innervation (from upper motor neurons in both hemispheres). The caudal part receives contralateral innervation (from cortical neurons on the other side). B Central (supranuclear) paralysis: Loss of upper motor neurons (shown here for the left hemisphere) causes contralateral paralysis in the lower half of the face but no paralysis in the upper half. For example, the patient’s mouth will sag on the right (contralateral paralysis of lower muscles), but the ability to wrinkle the forehead and close the eyes is intact. C Peripheral (infranuclear) paralysis: Loss of lower motor neurons (shown here for right brainstem) causes complete ipsilateral paralysis. For example, the whole right side of the face is paralyzed. Depending on the site of the lesion, additional deficits may be present (decreased lacrimation or salivation, loss of taste sensation in the presulcal tongue).

84

Precentral gyrus

Corticonuclear fibers

B

A

Facial nerve (CN VII)

Facial motor nucleus

C

Head

Maxillary division

Internal carotid artery with internal carotid plexus

Trigeminal nerve

Trigeminal Deep ganglion petrosal nerve Geniculate ganglion

4. Innervation of the Head & Neck

Lacrimal gland Via communicating branch to lacrimal nerve Postganglionic sympathetic fibers Nasal glands

Superior salivatory nucleus Facial nerve Nucleus of the solitary tract Mandibular division Greater petrosal nerve

Pterygopalatine ganglion Taste buds of soft palate Submandibular ganglion

Stylomastoid foramen

Pterygoid canal with nerve of pterygoid canal

Glandular branches Sublingual gland

Lingual nerve Chorda tympani

Fig. 4.38 Facial nerve ganglia $XWRQRPLFDQGWDVWHÀEHUVRIWHQWUDYHOZLWKVHQVRU\ÀEHUVIURPRWKHU QHUYHV WR UHDFK WKHLU WDUJHWV 3DUDV\PSDWKHWLF DQG WDVWH ÀEHUV OHDYH WKHIDFLDOQHUYHYLDWZREUDQFKHVWKHJUHDWHUSHWURVDOQHUYHDQGWKH FKRUGDW\PSDQL ‡ Greater petrosal nerve: 3UHJDQJOLRQLF SDUDV\PSDWKHWLF DQG WDVWH ÀEHUV IURP WKH JHQLFXODWH JDQJOLRQ FRXUVH LQ WKH JUHDWHU SHWURVDO FDQDO 7KH\ DUH MRLQHG E\ WKH GHHS SHWURVDO QHUYH ZKLFK FRQYH\V SRVWJDQJOLRQLF V\PSDWKHWLF ÀEHUV IURP WKH VXSHULRU FHUYLFDO JDQJOLRQYLDWKHLQWHUQDOFDURWLGSOH[XV 7KHJUHDWHUDQGGHHSSHWURVDO QHUYHV FRPELQH WR IRUP WKH QHUYH RI WKH SWHU\JRLG FDQDO YLGLDQ  ZKLFK FRQYH\V V\PSDWKHWLF SDUDV\PSDWKHWLF DQG WDVWH ÀEHUV WR WKHSWHU\JRSDODWLQHJDQJOLRQRQO\SDUDV\PSDWKHWLFVZLOOV\QDSVHDW WKHJDQJOLRQDOORWKHUÀEHUW\SHVSDVVWKURXJKZLWKRXWV\QDSVLQJ  %UDQFKHVRI&192WKHQGLVWULEXWHWKHÀEHUVWRWKHLUWDUJHWV  ̑ L acrimal gland:$XWRQRPLFÀEHUVV\PSDWKHWLFDQGSDUDV\PSDWKHWLF  UXQ ZLWK EUDQFKHV RI &1 92 ]\JRPDWLF DQG ]\JRPDWLFR WHPSRUDOQHUYHV WRDFRPPXQLFDWLQJEUDQFKZKLFKFRQYH\VWKHP WRWKHODFULPDOQHUYH&191 DQGWKXVWRWKHODFULPDOJODQG  ̑ S  mall glands of the nasal and oral cavities: $XWRQRPLF ÀEHUV UXQZLWKEUDQFKHVRI&192WRWKHVPDOOJODQGVLQWKHPXFRVDRI WKHQDVDOFDYLW\PD[LOODU\VLQXVHVDQGSDODWLQHWRQVLOV  ̑ T  aste:7DVWHÀEHUVUXQZLWKEUDQFKHVRI&192WRWKHVRIWSDODWH

Submandibular gland

‡ Chorda tympani: 3UHJDQJOLRQLF SDUDV\PSDWKHWLF DQG WDVWH ÀEHUV FRXUVHWKURXJKWKHFKRUGDW\PSDQL7KH\HPHUJHIURPWKHSHWURW\PSDQLFÀVVXUHDQGFRPELQHZLWKWKHOLQJXDOQHUYH&193 LQWKH LQIUDWHPSRUDOIRVVD7KH\DUHFRQYH\HGWRWKHVXEPDQGLEXODUJDQJOLRQE\WKHOLQJXDOQHUYHDQGIURPWKHUHSRVWJDQJOLRQLFEUDQFKHV WUDYHOWRWKHLUWDUJHWVYLDEUDQFKHVRI&193  ̑ Submandibular and sublingual glands:3RVWJDQJOLRQLFSDUDV\PSDWKHWLFÀEHUVUXQZLWKEUDQFKHVRI&193WRWKHJODQGV  ̑ T  aste buds of tongue:7KHWDVWHEXGVRQWKHSUHVXOFDOSRUWLRQRI WKHWRQJXHUHFHLYHWDVWHÀEHUVIURPWKHFKRUGDW\PSDQLYLDWKH OLQJXDOQHUYH&193 Note:7KHSRVWVXOFDOSRUWLRQRIWKHWRQJXH DQG WKH RURSKDU\Q[ UHFHLYH WDVWH ÀEHUV IURP &1 ,; 7KH URRW RI WKHWRQJXHDQGHSLJORWWLVUHFHLYHWDVWHÀEHUVIURP&1; Note:7KHlesser petrosal nerveUXQVLQWKHOHVVHUSHWURVDOFDQDOURXJKO\ SDUDOOHOWRWKHJUHDWHUSHWURVDOQHUYH7KHOHVVHUSHWURVDOQHUYHFRQYH\V SUHJDQJOLRQLFSDUDV\PSDWKHWLFÀEHUVIURPWKHW\PSDQLFSOH[XV&1,;  WRWKHRWLFJDQJOLRQ7KHVHÀEHUVLQQHUYDWHWKHSDURWLGEXFFDODQGLQIHULRUODELDOJODQGVZLWKSRVWJDQJOLRQLFÀEHUVGLVWULEXWHGYLDEUDQFKHV RI&193

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4. Innervation of the Head & Neck

CN VIII: Vestibulocochlear Nerve

Vestibular ganglion, superior part

Vestibulocochlear nerve (CN VIII) Vestibular root

Anterior ampullary nerve

Utricular nerve

Cochlear root

Vestibular ganglion, inferior part

Lateral ampullary nerve

Spiral ganglia Posterior ampullary nerve Saccular nerve

Fig. 4.39 Vestibulocochlear nerve (CN VIII) The vestibulocochlear nerve consists of two parts. The vestibular root conveys afferent impulses from the vestibular apparatus (balance). The cochlear root conveys afferent impulses from the auditory apparatus (hearing).

Table 4.23 Vestibulocochlear nerve (CN VIII) Nuclei, ganglia, and fiber distribution Special somatic afferent (orange): Special somatic sensory neurons convey sensory fibers from the vestibular apparatus (balance) and auditory apparatus (hearing). Both parts of the nerve contain first-order bipolar sensory neurons. Neurons

Vestibular root

Cochlear root

Peripheral processes

In the sensory cells of the semicircular canals, the saccule, and the utricle.

In the hair cells of the organ of Corti.

Cell bodies

Vestibular ganglion • Inferior part: Peripheral processes from saccule and posterior semicircular canal. • Superior part: Peripheral processes from anterior and lateral semicircular canals and utricle.

Spiral ganglia. The peripheral processes from the neurons in these myriad ganglia radiate outward to receive sensory input from the spiral modiolus.

Central processes (axons)

To four vestibular nuclei in the medulla oblongata (floor of the rhomboid fossa). A few pass directly to the cerebellum via the inferior cerebellar peduncle.

To two cochlear nuclei lateral to the vestibular nuclei.

Nuclei

Superior, lateral, medial, and inferior vestibular nuclei.

Anterior and posterior cochlear nuclei.

Lesions

Dizziness.

Hearing loss (ranging to deafness).

Course

The vestibular and cochlear roots unite in the internal acoustic meatus to form the vestibulocochlear nerve, which is covered by a common connective tissue sheath. The nerve emerges from the internal acoustic meatus on the medial surface of the petrous bone and enters the brainstem at the level of the pontomedullary junction, in particular at the cerebellopontine angle.

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4. Innervation of the Head & Neck

Superior vestibular nucleus

Flocculus of cerebellum

Medial vestibular nucleus

Lateral vestibular nucleus

Direct fibers to cerebellum Superior vestibular nucleus

Vestibulocochlear nerve (CN VIII) Vestibular root

Medial vestibular nucleus

Vestibular ganglion, superior and inferior parts

B

Lateral vestibular nucleus

Semicircular canals

Fig. 4.40 Vestibular root and nuclei A Anterior view of the medulla oblongata and pons. B Cross section through the upper medulla oblongata.

Inferior vestibular nucleus A

Posterior cochlear nucleus Anterior cochlear nucleus

Anterior cochlear nucleus

Posterior cochlear nucleus

B

Cochlear root A

Cochlea with spiral ganglia

Vestibulocochlear nerve (CN VIII)

Fig. 4.42 Acoustic neuroma in the cerebellopontine angle Acoustic neuromas (more accurately, vestibular schwannomas) are benign tumors of the cerebellopontine angle arising from the Schwann cells of the vestibular root of CN VIII. As they grow, they compress and displace the adjacent structures and cause slowly progressive hearing loss and gait ataxia. Large tumors can impair the egress of CSF from the 4th ventricle, causing hydrocephalus and symptomatic intracranial hyper tension (vomiting, impairment of consciousness).

Fig. 4.41 Cochlear root and nuclei A Anterior view of the medulla oblongata and pons. B Cross section through the upper medulla oblongata.

Cerebellopontine angle Acoustic neuroma (vestibular schwannoma)

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4. Innervation of the Head & Neck

CN IX: Glossopharyngeal Nerve

Inferior salivatory nucleus

Nucleus of the solitary tract, superior part

Inferior salivatory nucleus

Nucleus of the solitary tract, inferior part

Nucleus ambiguus

Nucleus ambiguus

B

Nucleus of the solitary tract, superior part

Fig. 4.43 Glossopharyngeal nerve nuclei A Anterior view of brainstem. B Cross section through the medulla oblongata.

Nucleus of the solitary tract, inferior part

Table 4.24 Glossopharyngeal nerve (CN IX)

Jugular foramen Tympanic nerve Inferior ganglion

Muscular branch

A

Glossopharyngeal nerve

Nuclei, ganglia, and fiber distribution

Superior ganglion

Branchiomotor (purple)

Nucleus ambiguus

Carotid branch Pharyngeal branches

Spinal nucleus of trigeminal nerve

Lower motor neurons innervate the muscles derived from the 3rd, 4th, and 6th branchial arches via CN IX, X, and XI. • CN IX innervates the derivative of the 3rd branchial arch (stylopharyngeus)

Parasympathetic (blue)

Inferior salivatory nucleus

Preganglionic neurons synapse in the otic ganglion. Postganglionic neurons innervate: • Parotid gland (Fig. 4.44A) • Buccal glands • Inferior labial glands

General somatic afferent (yellow)

Spinal nucleus of CN V

A

B

First-order pseudounipolar cells in the superior ganglion of CN IX innervate: • Nasopharynx, oropharynx, postsulcal tongue, palatine tonsils, and uvula (Fig. 4.44B,C). These fibers include the afferent limb of the gag reflex. • Tympanic cavity and pharyngotympanic tube (Fig. 4.44D).

Viscerosensory (green)

First-order pseudounipolar cells in the inferior ganglion relay taste and visceral sensation to the nucleus of the solitary tract. This nuclear complex consists of a superior part (taste) and inferior part (general visceral sensation). Nucleus of the solitary tract

Visceral sensation (Fig. 4.44F): General viscerosensory fibers from the carotid body (chemoreceptors) and carotid sinus (pressure receptors) synapse in the inferior part.

D

C

Taste (Fig. 4.44E): Special viscerosensory fibers from the postsulcal tongue synapse in the superior part.

Course

The glossopharyngeal nerve arises from the medulla oblongata and exits the skull by passing through the jugular foramen. It has two sensory ganglia with first-order pseudounipolar sensory cells: the superior ganglion (somatosensory) is within the cranial cavity, and the inferior ganglion (viscerosensory) is distal to the jugular foramen. E

Fig. 4.44 Distribution of CN IX fibers

88

F

Lesions

Isolated CN IX lesions are rare. Lesions tend to occur during basal skull fractures, which disrupt the jugular foramen. Such injuries would affect CN IX, X, and XI.

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Greater petrosal nerve Tubarian branch

Table 4.25 Glossopharyngeal nerve branches

Caroticotympanic nerve

Lesser petrosal nerve

Ty

Lesser petrosal nerve

Tympanic canaliculus with tympanic nerve Ty Superior and inferior ganglia CN IX

Tympanic plexus

A

CN IX

Tympanic n.

Somatosensory and preganglionic parasympathetic fibers branch at the inferior ganglion and travel through the tympanic canaliculus as the tympanic nerve. • Tympanic plexus: The tympanic nerve combines with postganglionic sympathetic fibers from the superior cervical ganglion (via carotid plexus and caroticotympanic nerve) and branches to form the tympanic plexus. This plexus provides general somatosensory innervation to the tympanic cavity, pharyngotympanic tube, and mastoid air cells. • Lesser petrosal n.: The preganglionic parasympathetic fibers in the tympanic plexus are reconstituted as the lesser petrosal nerve, which runs in the lesser petrosal canal to synapse in the otic ganglion. • Otic ganglion: The postganglionic parasympathetic fibers innervate the parotid, buccal, and inferior labial glands by traveling with branches of CN V3.

Carotid plexus on internal carotid artery

CN X Superior ganglion

Ty

L

4. Innervation of the Head & Neck

Inferior ganglion

To

C

General viscerosensory fibers from the carotid sinus (pressure receptors) and carotid body (chemoreceptors) ascend on the internal carotid artery to join CN IX or X on their way to the inferior part of the nucleus of the solitary tract. P

C

P

CN X, branch to carotid sinus CN X, pharyngeal branches Carotid body Carotid sinus

B

Fig. 4.45 Glossopharyngeal nerve branches A Left anterolateral view of opened tympanic cavity. B Left lateral view.

Pharyngeal branches

The pharyngeal plexus consists of general somatosensory fibers (from CN IX), sympathetic fibers (from the sympathetic trunk), and motor fibers (from CN X). • CN IX receives sensory fibers from the mucosa of the naso- and oropharynx via the pharyngeal plexus.

M

Pharyngeal plexus

Carotid branch

M

Muscular branch

The branchiomotor fibers in CN IX innervate the derivative of the 3rd branchial arch, the stylopharyngeus. To

Tonsillar branches

General somatosensory fibers from the palatine tonsils and mucosa of the oropharynx. L

Lingual branches

General somatosensory and special viscerosensory (taste) fibers from the postsulcal tongue.

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4. Innervation of the Head & Neck

CN X: Vagus Nerve

Table 4.26 Vagus nerve (CN X) 1XFOHLJDQJOLDDQGÀEHUGLVWULEXWLRQ Dorsal motor nucleus

%UDQFKLRPRWRU (purple)

Nucleus ambiguus

Nucleus ambiguus

Nucleus of the solitary tract, superior part Nucleus of the solitary tract, inferior part Superior ganglion

3DUDV\PSDWKHWLF (blue)

Inferior ganglion Pharyngeal branch

Jugular foramen

Dorsal motor nucleus

Spinal nucleus of trigeminal nerve

A

Dorsal motor nucleus

Nucleus of the solitary tract, superior part Nucleus of the solitary tract, inferior part

3UHJDQJOLRQLFQHXURQVV\QDSVHLQVPDOOXQQDPHG ganglia close to target structures. 3RVWJDQJOLRQLFQHXURQVLQQHUYDWH ‡ 6  PRRWKPXVFOHVDQGJODQGVRIWKRUDFLFDQG abdominal viscera (Fig. 4.48G)

Superior laryngeal nerve

*HQHUDOVRPDWLFD̦HUHQW\HOORZ

6SLQDO nucleus of CN V

First-order pseudounipolar cells in the VXSHULRU MXJXODU JDQJOLRQ innervate: ‡ '  XUDRIWKHSRVWHULRUFUDQLDOIRVVDFig. 4.48F) ‡ ( [WHUQDODXGLWRU\FDQDODQGODWHUDOW\PSDQLF membrane (Fig. 4.48B,C) ‡ 0  XFRVDRIWKHRURSKDU\Q[DQGODU\QJRSKDU\Q[

9LVFHURVHQVRU\ (green)

Spinal nucleus of trigeminal nerve

First-order pseudounipolar cells in the LQIHULRUQRGRVH JDQJOLRQ UHOD\WDVWHDQGYLVFHUDOVHQVDWLRQWRWKHQXFOHXVRIWKHVROLWDU\WUDFW. 7KLVQXFOHDUFRPSOH[FRQVLVWVRIDVXSHULRUSDUWWDVWH DQGLQIHULRU part (general visceral sensation).

Nucleus ambiguus B

Lower motor neurons innervate the muscles derived from the 3rd, 4th, and 6th branchial arches via CN IX, X, and XI. CN X innervates the derivatives of the 4th and 6th branchial arches: ‡ 3  KDU\QJHDOPXVFOHVSKDU\QJHDOFRQVWULFWRUV ‡ 0  XVFOHVRIWKHVRIWSDODWHOHYDWRUYHOLSDODWLQL PXVFXOXVXYXODHSDODWRJORVVXVSDODWRSKDU\QJHXV ‡ ,QWULQVLFODU\QJHDOPXVFOHV

Olive

Fig. 4.46 Vagus nerve nuclei A $QWHULRU YLHZ RI PHGXOOD REORQJDWD B Cross section through the medulla oblongata. 7KHYDJXVQHUYHKDVWKHPRVWH[WHQVLYHGLVWULEXWLRQRIDOOWKHFUDQLDO nerves (L. vagus YDJDERQG 3DUDV\PSDWKHWLFÀEHUVGHVFHQGLQWRWKH WKRUD[DQGDEGRPHQ7KHVHÀEHUVIRUPDXWRQRPLFSOH[XVHVZLWKSRVWJDQJOLRQLFV\PSDWKHWLFÀEHUVIURPWKHV\PSDWKHWLFWUXQNDQGDEGRPLQDOJDQJOLD 7KHSOH[XVHVH[WHQGDORQJRUJDQVDQGEORRGYHVVHOVDQG provide motor innervation to the thoracic and abdominal viscera. GenHUDOYLVFHURVHQVRU\ÀEHUVDVFHQGYLD&1;WRWKHLQIHULRUSDUWRIWKHQXFOHXVRIWKHVROLWDU\WUDFW

Nucleus of the VROLWDU\ tract

Taste (Fig. 4.48D): Fibers from the epiglottis and the URRWRIWKHWRQJXHDUHFRQYH\HGWRWKHVXSHULRUSDUW of WKHQXFOHXVRIWKHVROLWDU\WUDFW Visceral sensation (Fig. 4.48G )LEHUVDUHUHOD\HGWRWKH LQIHULRUSDUWRIWKHQXFOHXVRIWKHVROLWDU\WUDFWIURP ‡ 0  XFRVDRIWKHODU\QJRSKDU\Q[DQGODU\Q[Fig. 4.48A) ‡ $  RUWLFDUFKSUHVVXUHUHFHSWRUV DQGSDUDDRUWLFERG\ (chemoreceptors) (Fig. 4.48E) ‡ 7  KRUDFLFDQGDEGRPLQDOYLVFHUDFig. 4.48G)

&RXUVH

The vagus nerve arises from the medulla oblongata and emerges IURPWKHVNXOOYLDWKHMXJXODUIRUDPHQ,WKDVWZRVHQVRU\JDQJOLDZLWK ÀUVWRUGHUSVHXGRXQLSRODUFHOOVWKHVXSHULRUMXJXODU JDQJOLRQVRPDWRVHQVRU\ LVZLWKLQWKHFUDQLDOFDYLW\DQGWKHLQIHULRUQRGRVH  JDQJOLRQYLVFHURVHQVRU\ LVGLVWDOWRWKHMXJXODUIRUDPHQ /HVLRQV

7KHUHFXUUHQWODU\QJHDOQHUYHVXSSOLHVSDUDV\PSDWKHWLFLQQHUYDWLRQ WRWKHLQWULQVLFODU\QJHDOPXVFOHVH[FHSWWKHFULFRWK\URLG 7KLV LQFOXGHVWKHSRVWHULRUFULFRDU\WHQRLGWKHRQO\PXVFOHWKDWDEGXFWV the vocal cords. Unilateral lesions of this nerve cause hoarseness; ELODWHUDOGHVWUXFWLRQOHDGVWRUHVSLUDWRU\GLVWUHVVG\VSQHD 

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4. Innervation of the Head & Neck

Table 4.27 Vagus nerve branches

CN X Thyrohyoid membrane

Meningeal branches Pharyngeal branches

Superior laryngeal nerve

General somatosensory fibers from the dura of the posterior cranial fossa. Auricular branch

Internal laryngeal nerve

External laryngeal nerve

General somatosensory fibers from external ear (auricle, external acoustic canal, and part of lateral side of tympanic membrane). Pharyngeal branches

Cricothyroid muscle Right recurrent laryngeal nerve

The pharyngeal plexus consists of general somatosensory fibers (from CN IX), sympathetic fibers (from the sympathetic trunk), and motor fibers (from CN X). • CN X conveys branchiomotor fibers to the pharyngeal muscles.

Left recurrent laryngeal nerve

Carotid branch

General viscerosensory fibers from the carotid body (chemoreceptors) ascend on the internal carotid artery to join CN IX or X on their way to the inferior part of the nucleus of the solitary tract.

Subclavian artery Brachiocephalic trunk

Superior laryngeal n. Aortic arch

Combines with a sympathetic branch from the superior cervical ganglion and divides into: • Internal laryngeal n.: Sensory fibers from the mucosa of the laryngopharynx and larynx. • External laryngeal n.: Parasympathetic motor innervation to the cricothyroid.

Left recurrent laryngeal nerve Cervical cardiac branches

Recurrent laryngeal n.

The recurrent laryngeal nerve is asymmetrical: • Right recurrent laryngeal n.: Recurs behind the right subclavian artery. • Left recurrent laryngeal n.: Recurs behind the aortic arch. Ascends between the trachea and esophagus. The recurrent laryngeal nerves supply: • Motor innervation to the laryngeal muscles (except the cricothyroid). • Viscerosensory innervation to the laryngeal mucosa.

Anterior esophageal plexus

Branches to the thorax and abdomen

The vagus nerve also conveys parasympathetic and general viscerosensory fibers from the cardiac, pulmonary, esophageal, celiac, renal, hepatic, and gastric plexuses (Fig. 4.48G)

Fig. 4.47 Vagus nerve branches in the neck Anterior view.

B

C

A

D

E

F

G

Fig. 4.48 Distribution of the vagus nerve (CN X)

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4. Innervation of the Head & Neck

CN XI & XII: Accessory Spinal & Hypoglossal Nerves Table 4.28 Accessory nerve (CN XI) Nuclei, ganglia, and fiber distribution Branchiomotor (purple) Jugular foramen

Nucleus ambiguus

Vagus nerve (CN X) Corticobulbar fibers

To laryngeal muscles via pharyngeal plexus and recurrent laryngeal nerve

Nucleus ambiguus Foramen magnum

Cranial root

Accessory nerve (CN XI), external branch

Spinal root

Trapezius

A

Fig. 4.49 Accessory nerve A Posterior view of brainstem. B Right lateral view of sternocleidomastoid and trapezius.

General somatomotor (red)

Spinal nucleus of CN XI

Sternocleidomastoid

Spinal nucleus of accessory nerve

Lower motor neurons innervate the muscles derived from the 3rd, 4th, and 6th branchial arches via CN IX, X, and XI. • CN XI innervates the laryngeal muscles (except cricoarytenoid).

Lower motor neurons in the lateral part of the ventral horn of C2–C6 spinal cord segments innervate: • Trapezius (upper part). • Sternocleidomastoid.

Course

CN XI arises and courses in two parts that unite briefly distal to the jugular foramen:

B

(Note: For didactic reasons, the right muscles are displayed though they are innervated by the right cranial nerve nuclei.)

Cranial root: Branchiomotor fibers emerge from the medulla oblongata and pass through the jugular foramen. They briefly unite with the spinal root before joining CN X at the inferior ganglion. CN X distributes the branchiomotor fibers via the pharyngeal plexus and the external and recurrent laryngeal nerves. Spinal root: General somatomotor fibers emerge as rootlets from the spinal medulla. They unite and ascend through the foramen magnum. The spinal root then passes through the jugular foramen, courses briefly with the cranial root, and then descends to innervate the sternocleidomastoid and trapezius. Lesions

B

Trapezius paralysis: Unilateral lesions may occur during operations in the neck (e.g., lymph node biopsies), causing: • Drooping of the shoulder on the affected side. • Difficulty raising the arm above the horizontal.

A

Fig. 4.50 Accessory nerve lesions Accessory nerve lesions cause partial paralysis of the trapezius and complete (flaccid) paralysis of the sternocleidomastoid (see Table 4.28). Both lesions shown here are unilateral

92

The sternocleidomastoid is exclusively innervated by CN XI, and the lower portions of the trapezius are innervated by C3–C5. Accessory nerve lesions therefore cause complete (flaccid) sternocleidomastoid paralysis but only partial trapezius paralysis.

(right side). A Posterior view. Partial paralysis of the trapezius causes drooping of the shoulder on the affected side. B Right anterolateral view. Flaccid paralysis of the sternocleidomastoid causes torticollis (wry neck).

Sternocleidomastoid paralysis: • Unilateral lesions: Flaccid paralysis causes torticollis (wry neck, i.e., difficulty turning the head to the opposite side). • Bilateral lesions: Difficulty holding the head upright.

Head

Hypoglossal trigone (in rhomboid fossa)

4. Innervation of the Head & Neck

Table 4.29 Hypoglossal nerve (CN XII) Nucleus of the hypoglossal nerve (CN XII)

Pyramid

Olive

Nuclei, ganglia, and fiber distribution General somatomotor (red)

Nucleus of the hypoglossal nerve

CN XII

Nucleus of CN XII

Foramen magnum

Lower motor neurons innervate: • Extrinsic lingual muscles (except palatoglossus). • Intrinsic lingual muscles.

Course Pyramid

Olive

Anterior condylar canal

A

Fig. 4.51 Hypoglossal nerve nuclei The nucleus of the hypoglossal nerve is located in the floor of the rhomboid fossa. Rootlets emerge between the pyramid and the olive.

B

C1 spinal nerve

A Cross section through the medulla oblongata. The proximity of the nuclei to the midline causes extensive lesions to involve both nuclei. B Anterior view of medulla oblongata.

The hypoglossal nerve emerges from the medulla oblongata as rootlets between the olive and pyramid. These rootlets combine into CN XII, which courses through the hypoglossal (anterior condylar) canal. CN XII enters the root of the tongue superior to the hyoid bone and lateral to the hyoglossus. • C1 motor fibers from the cervical plexus travel with the hypoglossal nerve: some branch to form the superior root of the ansa cervicalis (not shown), whereas others continue with CN XII to supply the geniohyoid and thyrohyoid muscles. Lesions

Precentral gyrus

Left and right genioglossus muscles

B Corticobulbar fibers

Paralyzed genioglossus

C Tongue Styloglossus muscle

CN X

C1

Nucleus of the hypoglossal nerve

Anterior condylar canal

CN XII

Upper motor neurons innervate the lower motor neurons in the contralateral nucleus of the hypoglossal nerve. Supranuclear lesions (central hypoglossal paralysis) will therefore cause the tongue to deviate away from the affected side. Nuclear or peripheral lesions will cause the tongue to deviate toward the affected side (Fig. 4.52C).

Genioglossus muscle

Fig. 4.52 Hypoglossal nerve A Course of the hypoglossal nerve. Upper motor neurons synapse on lower motor neurons on the contralateral nucleus of the hypoglossal nerve. Supranuclear lesions will therefore cause contralateral paralysis; peripheral lesions will cause ipsilateral paralysis (same side). B The functional genioglossus extends the tongue anteriorly. C Unilateral paralysis due to a peripheral lesion causes the tongue to deviate toward the affected side (dominance of the intact genioglossus).

Hyoglossus muscle

A

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4. Innervation of the Head & Neck

Neurovascular Pathways through the Skull Base

Cribriform plate

Incisive canal

CN I, ethmoidal aa. and vv.

Nasopalatine n. and a., greater palatine a. Greater palatine foramen

Optic canal

Greater palatine n. and a.

CN II, ophthalmic a.

Lesser palatine foramina

Superior orbital fissure Superior and inferior ophthalmic v. Lacrimal n. Frontal n.

Lesser palatine n. and a.

CN IV CN VI

Foramen lacerum

CN III

Deep and greater petrosal nn. (across superior surface)

Nasociliary n.

Foramen spinosum

Foramen rotundum CN V2 Foramen ovale

Carotid canal

CN V3, lesser petrosal n. (CN IX)

Internal carotid a., internal carotid plexus

Carotid canal Internal carotid a. with sympathetic plexus

Petrotympanic fissure

A

Anterior tympanic a., chorda tympani

B

Foramen spinosum

Stylomastoid foramen

Middle meningeal a., recurrent meningeal branch of CN V3

Facial n., stylomastoid a.

Hiatus of canal for lesser petrosal n.

Jugular foramen

Lesser petrosal n., superior tympanic a.

Internal jugular v. –

See opposite

Hiatus of canal for greater petrosal n. Greater petrosal n. Internal acoustic meatus Labyrinthine a. and v. A

CN VII

B

CN VIII

Mastoid foramen Emissary v. Hypoglossal canal

Jugular foramen Sigmoid sinus CN IX CN X

A

CN XI

Inferior petrosal sinus Posterior meningeal a.

Foramen magnum Emissary vv.

Vertebral a.

Anterior and posterior spinal aa.

Spinal cord

Fig. 4.53 Passage of neurovascular structures through the skull base A Superior view of cranial cavity. B Inferior view of base of skull. This image and the corresponding table only address structures entering

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CN XI, spinal root

CN XII, venous plexus of hypoglossal canal (Posterior) condylar canal Condylar emissary v.

B

and exiting the skull. Many neurovascular structures pass through bony canals within the skull (to pterygopalatine fossa, infratemporal fossa, etc.).

Head

4. Innervation of the Head & Neck

Table 4.30 Openings in the skull base Cranial cavity

Opening

Transmitted structures Nerves

Arteries and veins

Internal view, base of the skull

Anterior cranial fossa

Cribriform plate

• CN I (olfactory fibers collected to form olfactory n.)

• Anterior and posterior ethmoidal aa. (from ophthalmic a.) • Ethmoidal vv. (to superior ophthalmic v.)

Middle cranial fossa

Optic canal

• CN II (optic n.)

• Ophthalmic a. (from internal carotid a.)

Superior orbital fissure

• • • •

• Superior and inferior ophthalmic vv. (to cavernous sinus) (Note: The inferior ophthalmic v. also drains through the inferior orbital fissure to the pterygoid plexus.)

Foramen rotundum*

• CN V2 (maxillary n.)

Foramen ovale

• CN V3 (mandibular n.) • Lesser petrosal n. (CN IX)

• Accessory meningeal a. (from mandibular part of maxillary a.)

Foramen spinosum

• CN V3, recurrent meningeal branch

• Middle meningeal a. (from mandibular part of maxillary a.)

Carotid canal

• Carotid plexus (postganglionic sympathetics from superior cervical ganglion)

• Internal carotid a.

Hiatus of canal for greater petrosal n.

• Greater petrosal n. (CN VII)

Hiatus of canal for lesser petrosal n.

• Lesser petrosal n. (CN IX)

• Superior tympanic a. (from middle meningeal a.)

Internal acoustic meatus

• CN VII (facial n.) • CN VIII (vestibulocochlear n.)

• Labyrinthine a. (from vertebral a.) • Labyrinthine vv. (to superior petrosal or transverse sinus)

Jugular foramen

• CN IX (glossopharyngeal n.) • CN X (vagus n.) • CN XI (accessory n., cranial root)

• Internal jugular v. (bulb) • Sigmoid sinus (to bulb of internal jugular v.) • Posterior meningeal a. (from ascending pharyngeal a.)

Hypoglossal canal

• CN XII (hypoglossal n.)

• Venous plexus of hypoglossal canal

Foramen magnum

• Medulla oblongata with meningeal coverings • CN XI (accessory n.)

• Vertebral aa. • Anterior and posterior spinal aa. (from vertebral a.) • Emissary vv.

Posterior cranial fossa

CN III (oculomotor n.) CN IV (trochlear n.) CN IV (abducent n.) CN V1 (ophthalmic n.) divisions (lacrimal, frontal, and nasociliary nn.)

External aspect, base of the skull (where different from internal aspect)

Incisive canal

• Nasopalatine n. (from CN V2)

• Branch of greater palatine a.

Greater palatine foramen

• Greater palatine n. (from CN V2)

• Greater palatine a. (from pterygopalatine part of maxillary a.)

Lesser palatine foramen

• Lesser palatine n. (from CN V2)

• Lesser palatine aa. (from pterygopalatine part of maxillary a. or as branch of greater palatine a. or descending palatine a.)

Foramen lacerum**

• Deep petrosal n. (from superior cervical ganglion via carotid plexus) • Greater petrosal n. (from CN VII)

Petrotympanic fissure

• Chorda tympani (from CN VII)

• Anterior tympanic a. (from mandibular part of maxillary a.)

Stylomastoid foramen

• Facial n. (CN VII)

• Stylomastoid a. (from posterior auricular a.)

(Posterior) condylar canal

• Condylar emissary v. (to sigmoid sinus)

Mastoid foramen

• Mastoid emissary v. (to sigmoid sinus)

*The external opening of the foramen rotundum is located in the pterygopalatine fossa, which is located deep on the lateral surface of the base of the skull and is not visible here. **Structures travel over the superior surface of the foramen lacerum, not through it (with the possible exception of lymphatic vessels and emissary veins).

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5. Neurovascular Topography of the Head

Anterior Face The bones and muscles of the skull are shown in isolation in Chapter 1 and Chapter 2, respectively. The arteries and veins are discussed in Chapter 3; the nerves are found in Chapter 4.

Supratrochlear nerve Supraorbital nerve, lateral branch Lacrimal nerve

Supraorbital nerve, medial branch Dorsal nasal artery

Facial nerve, temporal branches

Lateral nasal artery Auriculotemporal nerve

Angular artery and vein

Superficial temporal artery and vein Infraorbital artery and nerve (via infraorbital foramen)

Facial nerve, zygomatic branches

Transverse facial artery Facial nerve, buccal branches Parotid gland

Facial nerve, marginal mandibular branch Facial artery and vein

Fig. 5.1 Superficial neurovasculature of the anterior face Removed: Skin and fatty tissue. The muscles of facial expression have been partially removed on the left side to display underlying musculature and neurovascular structures. The muscles of facial expression receive motor innervation from the facial nerve (CN VII), which emerges laterally from the parotid gland. The muscles of mastication receive motor innervation from the mandibular division of the trigemi-

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Parotid duct

Masseter

Mental artery and nerve (via mental foramen)

nal nerve (CN V3). The face receives sensory innervation primarily from the terminal branches of the three divisions of the trigeminal nerve (CN V), but also from the great auricular nerve, which arises from the cervical plexus (see Fig. 5.10). The face receives blood supply primarily from branches of the external carotid artery, though these do anastomose on the face with facial branches of the internal carotid artery (see Fig. 5.2).

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Supratrochlear artery Medial palpebral arteries, superior and inferior

5. Neurovascular Topography of the Head

Supraorbital artery

Lacrimal artery Dorsal nasal artery

Lateral palpebral arteries, superior and inferior

Angular artery

Infraorbital artery Maxillary artery (cut) Superior labial artery Mental artery

Superficial temporal artery Inferior labial artery Facial artery External carotid artery Submental artery

Fig. 5.2 Arterial anastomoses in the face Branches of the external carotid artery (e.g., facial, superficial temporal, and maxillary arteries) and the internal carotid artery (e.g., dorsal nasal, supraorbital, and lacrimal arteries) anastomose in certain facial regions to ensure blood flow to the face and head. Anastomoses occur between the angular artery and the dorsal nasal artery, as well as between the superficial temporal artery and the supraorbital artery.

This extensive vascular supply to the face causes head injuries to bleed profusely but also heal quickly. The anastomoses are also important in cases of reduced blood flow (e.g., atherosclerosis). Cerebral ischemia, which can result from atherosclerosis of the internal carotid artery, may be avoided if there is sufficient blood flow through the superficial temporal and facial arteries.

Supraorbital nerve (branch of CN V1)

Infraorbital nerve (branch of CN V2)

Mental nerve (branch of CN V3)

Fig. 5.3 Venous “danger zone” in the face The superficial veins of the face have extensive connections with the deep veins of the head (e.g., the pterygoid plexus) and dural sinuses (e.g., the cavernous sinus) (see p. 53). Veins in the triangular danger zone are, in general, valveless. There is therefore a particularly high risk of bacterial dissemination into the cranial cavity. For example, bacteria from a boil on the lip may enter the facial vein and cause meningitis by passing through venous communications with the cavernous sinus.

Fig. 5.4 Emergence of the trigeminal nerve The trigeminal nerve (CN V) is the major somatic sensory nerve of the head. Its three large sensory branches emerge from three foramina: • CN V1: Supraorbital nerve (through supraorbital foramen) • CN V2: Infraorbital nerve (through infraorbital foramen) • CN V3: Mental nerve (through mental foramen)

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5. Neurovascular Topography of the Head

Lateral Head: Superficial Layer

Superficial temporal artery, frontal branch

Superficial temporal artery and vein

Superficial temporal artery, parietal branch

Supraorbital nerve (branch of trigeminal nerve)

Supratrochlear nerve (branch of CN V1) Zygomaticoorbital artery Auriculotemporal nerve (branch of CN V3) Angular vein External nasal nerve (branch of CN V1) Transverse facial artery Infraorbital nerve (branch of CN V2)

Occipital artery

Parotid duct

Greater occipital nerve (C2)

Buccinator

Lesser occipital nerve (from cervical plexus [C2]) Sternocleidomastoid

Mental nerve (branch of CN V3)

Posterior auricular vein

Parotid gland Facial vein Masseter

Branches of parotid plexus of facial nerve

Fig. 5.5 Superficial neurovasculature of the lateral head Left lateral view. The arteries supplying the lateral head arise from branches of the external carotid artery (see Fig. 5.6). Blood drains primarily into the internal, external, and anterior jugular veins (see p. 52). The muscles of facial expression receive motor innervation from the

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External jugular vein

Great auricular nerve (from cervical plexus [C2–C3])

facial nerve (CN VII), which emerges laterally from the parotid gland (see p. 84). The muscles of mastication receive motor innervation from the mandibular division of the trigeminal nerve (CN V3, see p. 81). The sensory innervation of the face is shown in Fig. 5.7.

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5. Neurovascular Topography of the Head

Middle temporal artery

Zygomatico-orbital artery

Transverse facial artery Angular artery

Superficial temporal artery

Inferior alveolar artery

Maxillary artery

Superior labial artery

Occipital artery

Inferior labial artery

Facial artery External carotid artery

Mental artery Submental artery

Fig. 5.6 Superficial arteries of the head Left lateral view. The superficial face is supplied primarily by branches of the external carotid artery (e.g., facial, superficial temporal, and maxil-

Internal carotid artery

lary arteries). However, there is limited contribution from branches derived from the internal carotid artery in the region of the orbital rim.

Ophthalmic division (CN V1)

Trigeminal nerve (CN V)

Maxillary division (CN V2)

Mandibular division (CN V3) Transverse cervical nerve (cervical plexus [C2–C3]) Greater auricular nerve (cervical plexus [C2–C3])

Fig. 5.7 Sensory innervation of the lateral head and neck Left lateral view. The head receives sensory innervation primarily from the trigeminal nerve (orange), the cervical plexus (green and gray), and the dorsal rami of the spinal nerves (blue). Sensory supply to the face is primarily from the terminal branches of the three trigeminal nerve divisions. The occiput and nuchal region are supplied primarily

Greater occipital nerve (dorsal ramus of C2)

Spinal nerves (dorsal rami) Lesser occipital nerve (cervical plexus [C2]) Supraclavicular nerves (cervical plexus [C3–C4])

by dorsal rami of the spinal nerves. The ventral rami of the first four spinal nerves combine to form the cervical plexus. The cervical plexus gives off four cutaneous branches that supply the lateral head and neck (nerves listed with their associated spinal nerve fibers): lesser occipital (C2, occasionally C3), greater auricular (C2–C3), transverse cervical (C2–C3), and supraclavicular (C3–C4) nerves.

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5. Neurovascular Topography of the Head

Lateral Head: Intermediate Layer Accessory parotid gland

Superficial temporal artery and vein

Parotid gland

Parotid duct

Parotid gland, superficial part Parotid plexus Facial nerve (CN VII) Buccinator Masseter A

Facial artery and vein

Submandibular gland

Sternocleidomastoid

B

Fig. 5.8 Parotid bed Left lateral view. A Superficial dissection. B Deep dissection. The largest of the salivary glands, the parotid gland secretes saliva into the oral cavity via the parotid duct. The facial nerve divides into branches

Parotid gland, deep part

Sternocleidomastoid

within the parotid gland and is vulnerable during the surgical removal of parotid tumors. The best landmark for locating the nerve trunk is the tip of the cartilaginous auditory canal.

Temporal branches

Parotid plexus Zygomatic branches

Posterior auricular nerve

Buccal branches Marginal mandibular branch

Facial nerve Nerve to digastric (posterior belly) Cervical branch

Fig. 5.9 Branching of the facial nerve (CN VII) Left lateral view. The large branchiomotor branch of the facial nerve (CN VII) exits the skull through the stylomastoid foramen. It gives off three branches immediately: the posterior auricular nerve and the

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Nerve to stylohyoid

nerves to the digastric muscle (posterior belly) and stylohyoid. It then enters the parotid gland, where it divides into two trunks: temporofacial and cervicofacial. These trunks give off five major branches that course anteriorly: temporal, zygomatic, buccal, mandibular, and cervical.

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5. Neurovascular Topography of the Head

Superficial temporal artery, parietal and occipital branches

Temporofacial trunk Supraorbital nerve (branch of CN V1)

Supratrochlear nerve (branch of CN V1) Auriculotemporal nerve (branch of CN V3) Infratrochlear nerve (branch of CN V1) Temporal branches of parotid plexus (CN VII) External nasal nerve (branch of CN V1) Infraorbital nerve (branch of CN V2)

Occipital artery Greater occipital nerve (dorsal ramus of C2)

Zygomatic branches of parotid plexus (CN VII)

Posterior auricular nerve (CN VII)

Parotid duct Buccal branches of parotid plexus (CN VII)

Lesser occipital nerve (cervical plexus [C2]) Sternocleidomastoid

Mental nerve (branch of CN V3)

Nerve to the stylohyoid (CN VII) Nerve to the digastric, posterior belly (CN VII) Masseter Mandibular branch of parotid plexus (CN VII)

Cervicofacial Cervical trunk branch of parotid plexus (CN VII)

Fig. 5.10 Nerves of the intermediate layer Left lateral view. The parotid gland has been removed to demonstrate the structure of the parotid plexus of the facial nerve (see Fig. 5.9). The

Intraparotid plexus of the facial nerve (CN VII)

External jugular vein

Great auricular nerve (cervical plexus [C2–C3])

occiput receives sensory innervation from the greater occipital nerve, which arises from the dorsal primary ramus of C2, and the lesser occipital nerve, which arises from the cervical plexus (ventral rami of C2).

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5. Neurovascular Topography of the Head

Infratemporal Fossa: Contents The infratemporal fossa is located lateral to the lateral pterygoid plate of the sphenoid, medial to the ramus of the mandible, posterior to the maxilla, anterior to the styloid process (and the carotid sheath and its contents), and inferior to the greater wing of the sphenoid and a small part of the temporal bone. It is continuous with the pterygopalatine

fossa (through the pterygomaxillary fissure). The maxillary artery gives rise to its mandibular (bony, first part) and pterygoid (muscular, second part) branches in the infratemporal fossa. The mandibular division of the trigeminal nerve (CN V3) divides into its terminal branches in the infratemporal fossa.

Temporalis muscle (cut)

Superficial temporal artery and vein

Deep temporal nerves (CN V3) Deep temporal arteries

Superior alveolar nerves, posterior superior alveolar branches (CN V2)

Auriculotemporal nerve (CN V3)

Maxillary artery

Lateral pterygoid muscle, superior and inferior heads

Buccal artery and nerve (CN V3) Medial pterygoid muscle, superficial and deep heads

Facial nerve (CN VII)

Lingual nerve (CN V3)

Ramus of mandible (cut)

Facial artery and vein

Inferior alveolar artery and nerve (CN V3)

Masseter (cut)

Sternocleidomastoid

Fig. 5.11 Infratemporal fossa, superficial dissection Left lateral view. Removed: Masseter, anterior portion of the mandibular ramus, and zygomatic arch. The pterygoid plexus normally is embedded between the medial and lateral pterygoids. It drains to the

maxillary vein, a tributary of the retromandibular vein. The inferior alveolar artery and nerve can be seen entering the mandibular canal (the accompanying vein has been removed).

Table 5.1 Muscles and vessels of the infratemporal fossa Muscle

Artery

Vein

Lateral and medial pterygoids

Maxillary artery • Mandibular branches • Pterygoid branches

Pterygoid plexus

Temporalis tendon

Maxillary vein Deep facial vein (deep portion) Emissary veins

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5. Neurovascular Topography of the Head

Superficial temporal artery and vein

Temporalis muscle (cut) Deep temporal nerves (CN V3)

Lateral pterygoid muscle (cut)

Infraorbital artery

Auriculotemporal nerve

Sphenopalatine artery

Trigeminal nerve, mandibular division (CN V3)

Posterior superior alveolar artery Buccal artery and nerve (CN V3)

Middle meningeal artery

Buccinator Medial pterygoid muscle, superficial head

Maxillary artery

Lingual nerve (CN V3)

Medial pterygoid muscle, deep head

Facial artery and vein

Facial nerve (CN VII) Inferior alveolar artery and nerve (CN V3)

Masseter (cut)

Fig. 5.12 Infratemporal fossa, deep dissection Left lateral view. Removed: Both heads of the lateral pterygoid muscle. The branches of the maxillary artery and mandibular division of the trigeminal nerve (CN V3) can be identified. Note: By careful dissection, it is possible to define the site where the auriculotemporal nerve

(branch of the mandibular division) splits around the middle meningeal artery before the artery enters the middle cranial fossa through the foramen spinosum (see p. 46). Branches of the third part of the maxillary artery can be observed in the pterygopalatine fossa, which is medial to the infratemporal fossa.

Table 5.2 Nerves in the infratemporal fossa CN V3

Trunk of CN V3 and direct branches: • Recurrent meningeal branch • Medial pterygoid n.

CN V2

Posterior superior alveolar n.

Other

Otic ganglion

Anterior division: • Masseteric n. • Deep temporal nn. • Buccal n. • Lateral pterygoid n.

Posterior division: • Auriculotemporal n. • Lingual n. • Inferior alveolar n. • Mylohyoid n.

Lesser petrosal n.

Chorda tympani (CN VII)

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5. Neurovascular Topography of the Head

Pterygopalatine Fossa

Frontal bone, zygomatic process

Greater wing of sphenoid bone, temporal surface

Temporal bone, squamous part

Ethmoid bone Sphenosquamous suture

Sphenopalatine foramen

Pterygopalatine fossa

Zygomatic bone

See detail in Fig. 5.14

Maxillary tuberosity

A

Pterygoid hamulus of medial pterygoid plate

Pterygoid process of lateral pterygoid plate

Fig. 5.13 Pterygopalatine fossa A Left lateral view of left infratemporal fossa and pterygopalatine fossa. B Inferior view of right infratemporal fossa and lateral approach to pterygopalatine fossa. The pterygopalatine fossa is a crossroads between the orbit, nasal cavity, oral cavity, nasopharynx, and middle cranial fossa. It is traversed by many nerves and vessels supplying these structures. The pterygopalatine fossa is continuous laterally with the infratemporal fossa through the pterygopalatine fissure. The lateral approach through the infratemporal fossa is used in surgical operations on tumors of the pterygopalatine fossa (e.g., nasopharyngeal fibroma).

Inferior orbital fissure

Lateral approach to pterygopalatine fossa

Greater wing of sphenoid bone, infratemporal surface

Choana Palatine bone, pyramidal process

Infratemporal crest

Pterygoid process, medial plate

Pterygoid process, lateral plate

B

Foramen spinosum

Foramen ovale

Table 5.3 Borders of the pterygopalatine fossa Border

Structure

Border

Structure

Superior

Sphenoid bone (greater wing) and junction with the inferior orbital fissure

Inferior

Greater palatine canal

Anterior

Maxilla

Posterior

Sphenoid, root of pterygoid process

Medial

Palatine bone (perpendicular plate)

Lateral

Pterygomaxillary fissure

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Fig. 5.14 Communications of the pterygopalatine fossa Left lateral view of left fossa (detail from Fig. 5.13A). The pterygopalatine fossa contains the pterygopalatine ganglion, the parasympathetic ganglion of CN VII that is affiliated with the maxillary nerve (CN V2, sensory). Sensory fibers from the face, maxillary dentition, nasal cavity, oral cavity, nasopharynx, and paranasal sinuses pass through the ganglion without synapsing and enter the middle cranial fossa as the maxillary nerve (CN V2). These sensory fibers also serve as “scaffolding” for the peripheral distribution of postganglionic autonomic parasympathetic fibers from the pterygopalatine ganglion and postganglionic sympathetic fibers derived from the internal carotid plexus. See Table 4.20 for a complete treatment of the maxillary nerve and pterygopalatine ganglion.

5. Neurovascular Topography of the Head

Inferior orbital fissure (to orbit) Sphenopalatine foramen (to nasal cavity) Greater palatine canal (to oral cavity)

Foramen rotundum (from middle cranial fossa) Pterygoid canal (from middle cranial fossa) Pterygopalatine fossa

Table 5.4 Communications of the pterygopalatine fossa Communication

Direction

Via

Transmitted structures

Middle cranial fossa

Posterosuperiorly

Foramen rotundum

• Maxillary n. (CN V2)

Middle cranial fossa

Posteriorly in anterior wall of foramen lacerum

Pterygoid canal

• N. of pterygoid canal, formed from: ◦ Greater petrosal n. (preganglionic parasympathetic fibers from CN VII) ◦ Deep petrosal n. (postganglionic sympathetic fibers from internal carotid plexus) • A. of pterygoid canal • Vv. of pterygoid canal

Orbit

Anterosuperiorly

Inferior orbital fissure

• Branches of maxillary n. (CN V2): ◦ Infraorbital n. ◦ Zygomatic n. • Infraorbital a. and vv. • Communicating vv. between inferior ophthalmic v. and pterygoid plexus of vv.

Nasal cavity

Medially

Sphenopalatine foramen

• Nasopalatine n. (CN V2), lateral and medial superior posterior nasal branches • Sphenopalatine a. and vv.

Oral cavity

Inferiorly

Greater palatine canal (foramen)

• Greater (descending) palatine n. (CN V2) and a. • Branches that emerge through lesser palatine canals: ◦ Lesser palatine nn. (CN V2) and aa.

Nasopharynx

Inferoposteriorly

Palatovaginal (pharyngeal) canal

• CN V2, pharyngeal branches, and pharyngeal a.

Infratemporal fossa

Laterally

Pterygomaxillary fissure

• Maxillary a., pterygoid (third) part • Posterior superior alveolar n., a., and v.

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Regions of the Head 6

Orbit & Eye Bones of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 Communications of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . . 110 Extraocular Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Cranial Nerves of the Extraocular Muscles: Oculomotor (CN III), Trochlear (CN IV) & Abducent (CN VI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Neurovasculature of the Orbit . . . . . . . . . . . . . . . . . . . . . . . . 116 Topography of the Orbit (I) . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 Topography of the Orbit (II) . . . . . . . . . . . . . . . . . . . . . . . . . . 120 Lacrimal Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 Eyeball . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 Eye: Blood Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 Eye: Lens & Cornea. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Eye: Iris & Ocular Chambers . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Eye: Retina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 Visual System (I): Overview & Geniculate Part . . . . . . . . . . . 134 Visual System (II): Lesions & Nongeniculate Part . . . . . . . . . 136 Visual System (III): Reflexes . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Visual System (IV): Coordination of Eye Movement . . . . . . . 140

7

Nose & Nasal Cavity Nose: Nasal Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142 Nose: Paranasal Sinuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 Nasal Cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 Nasal Cavity: Neurovascular Supply . . . . . . . . . . . . . . . . . . . . 148 Nose & Paranasal Sinuses: Histology & Clinical Anatomy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Olfactory System (Smell) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152

8

Temporal Bone & Ear Temporal Bone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 Ear: Overview & External Ear . . . . . . . . . . . . . . . . . . . . . . . . . . 156 External Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 Middle Ear (I): Tympanic Cavity & Pharyngotympanic Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 Middle Ear (II): Auditory Ossicles & Tympanic Cavity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 Inner Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164 Arteries & Veins of the Ear . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Vestibulocochlear Nerve (CN VIII) . . . . . . . . . . . . . . . . . . . . . 168 Auditory Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 Auditory Pathway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172 Vestibular Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Vestibular System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

9

Oral Cavity & Perioral Regions Oral Cavity: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 Permanent Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 Structure of the Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Incisors, Canines & Premolars . . . . . . . . . . . . . . . . . . . . . . . . . 184 Molars . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Deciduous Teeth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 Hard Palate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190 Mandible & Hyoid Bone. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192 Temporomandibular Joint (TMJ) . . . . . . . . . . . . . . . . . . . . . . . 194 Temporomandibular Joint (TMJ): Biomechanics . . . . . . . . . . 196 Muscles of Mastication: Overview . . . . . . . . . . . . . . . . . . . . . 198 Muscles of Mastication: Deep Muscles. . . . . . . . . . . . . . . . . . 200 Suprahyoid Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 Lingual Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 Lingual Mucosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 Pharynx & Tonsils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Pharynx: Divisions & Contents . . . . . . . . . . . . . . . . . . . . . . . . 210 Muscles of the Soft Palate & Pharynx . . . . . . . . . . . . . . . . . . . 212 Muscles of the Pharynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214 Pharynx: Topography & Innervation. . . . . . . . . . . . . . . . . . . . 216 Salivary Glands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 Neurovasculature of the Tongue . . . . . . . . . . . . . . . . . . . . . . 220 Gustatory System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222

Regions of the Head

6. Orbit & Eye

Bones of the Orbit

Frontal bone, supraorbital margin

Frontal bone, orbital surface Sphenoid bone, orbital surface of lesser wing Ethmoid bone, orbital plate (lamina papyracea)

Sphenoid bone, orbital surface of greater wing

Maxilla, frontal process Zygomatic bone, frontal process

Nasal bone

Zygomatic bone, orbital surface

Anterior cranial fossa

Lacrimal bone, orbital surface

Frontal bone, orbital surface

Palatine bone A

Maxilla, zygomatic process

Frontal bone, supraorbital margin

Maxilla, orbital surface

Nasion Nasal bone Sphenoid bone, lesser wing Ethmoid bone, orbital plate (lamina papyracea) B Frontal bone, orbital surface Zygomatic bone, orbital surface Maxilla, orbital surface (floor) Infraorbital canal Maxillary sinus

Maxilla, frontal process Palatine bone

Maxilla, orbital surface (floor)

Lacrimal bone, orbital surface

Sphenoid bone, lesser wing Sphenoid bone, greater wing Inferior orbital fissure

Pterygomaxillary fissure Palatine bone, pyramidal process

C

Fig. 6.1 Bones of the orbit Right orbit. A,D Anterior view. B,E Lateral view with lateral orbital wall removed. C,F Medial view with medial orbit wall removed. The orbit is formed by seven bones: the frontal, zygomatic, ethmoid, sphenoid, lacrimal, and palatine bones, and the maxilla. The neurovascular structures of the orbit communicate with the surrounding spaces via several major passages (see Table 6.1): the superior and inferior orbital

108

fissures, the optic canal, the anterior and posterior ethmoidal foramina, the infraorbital canal, and the nasolacrimal duct. The neurovascular structures of the orbit also communicate with the superficial face by passing through the orbital rim. Note: The exposed maxillary sinus can be seen in E. The maxillary hiatus contains the ostium by which the maxillary sinus opens into the nasal cavity superior to the inferior nasal concha.

Regions of the Head

6. Orbit & Eye

Frontal incisure Supraorbital foramen

Posterior ethmoidal foramen Anterior ethmoidal foramen

Zygomaticoorbital foramen

Optic canal Nasal bone

Superior orbital fissure

Lacrimal bone Inferior orbital fissure Infraorbital groove

D

Infraorbital foramen

Lacrimal bone

Frontal sinus

Glabella Anterior ethmoidal foramen

Nasion Posterior lacrimal crest (lacrimal bone)

Posterior ethmoidal foramen

Anterior lacrimal crest (maxilla)

Optic canal

Fossa of lacrimal sac (with opening for nasolacrimal duct)

Superior orbital fissure (opened) Foramen rotundum Inferior orbital fissure Pterygomaxillary fissure E

Frontal sinus

Infraorbital canal Pterygopalatine fossa

Maxillary ostium

Maxillary sinus

Infraorbital foramen

Superior orbital fissure

Lacrimal fossa Zygomaticoorbital foramen

Sphenoid bone, lesser wing Sphenoid bone, greater wing

Maxilla, orbital surface Infraorbital canal Inferior orbital fissure

Pterygomaxillary fissure

Maxillary sinus

F

109

Regions of the Head

6. Orbit & Eye

Communications of the Orbit

Fig. 6.2 Bones of the orbits and adjacent cavities The bones of the orbit also form portions of the walls of neighboring cavities. The following adjacent structures are visible in the diagram: • • • • •

Anterior cranial fossa Frontal sinus Middle cranial fossa Ethmoid air cells Maxillary sinus

Disease processes may originate in the orbit and spread to these cavities, or originate in these cavities and spread to the orbit.

Frontal sinus

Ethmoid bone

Anterior cranial fossa

Optic canal (leads to middle cranial fossa) Frontal bone, orbital surface

Parietal bone

Sphenoid bone, orbital surface of lesser wing

Temporal bone Ethmoid air cells

Sphenoid bone, orbital surface of greater wing

Superior orbital fissure (leads to middle cranial fossa)

Zygomatic bone, orbital surface

Maxilla, orbital surface

Maxillary sinus

Inferior nasal concha

Frontal sinus

Vomer

Crista galli

Ethmoid air cells

Ethmoid bone, perpendicular plate

Optic canal Ethmoid bone, orbital plate (lamina papyracea)

Superior orbital fissure Superior nasal concha (ethmoid bone)

Middle nasal meatus

Inferior orbital fissure Infraorbital canal

Orbital floor (maxilla) Middle nasal concha (ethmoid bone) Inferior nasal concha and meatus

Maxillary sinus Palatine process of the maxilla

Fig. 6.3 Orbits and neighboring structures Coronal section through both orbits, viewed from the front. The walls separating the orbit from the ethmoid air cells (0.3 mm, lamina papyracea) and from the maxillary sinus (0.5 mm, orbital floor) are very thin. Thus, both of these walls are susceptible to fractures and provide

110

Vomer Alveolar process of maxilla

routes for the spread of tumors and inflammatory processes into or out of the orbit. The superior orbital fissure communicates with the middle cranial fossa, and so several structures that are not pictured here—the sphenoid sinus, pituitary gland, and optic chiasm—are also closely related to the orbit.

Regions of the Head

6. Orbit & Eye

Table 6.1 Communications of the orbit Structure

Communicates

Via

Neurovascular structures in canal/fissure

Frontal sinus and anterior ethmoid air cells

Superiorly

Unnamed canaliculi

• Sensory filaments

Medially

Anterior ethmoidal canal

• Anterior ethmoidal a. (from ophthalmic a.) • Anterior ethmoidal v. (to superior ophthalmic v.) • Anterior ethmoidal n. (CN V1)

Sphenoid sinus and posterior ethmoid air cells

Medially

Posterior ethmoidal canal

• Posterior ethmoidal a. (from ophthalmic a.) • Posterior ethmoidal v. (to superior ophthalmic v.) • Posterior ethmoidal n. (CN V1)

Middle cranial fossa

Posteriorly

Superior orbital fissure

• Cranial nerves to the extraocular muscles (oculomotor n. [CN III], trochlear n. [CN IV], and abducent n. [CN VI]) • Ophthalmic n. (CN V1) and branches: ◦ Lacrimal n. ◦ Frontal n. (branches into supraorbital and supratrochlear nn.) ◦ Nasociliary n. • Superior (and occasionally inferior) ophthalmic v. (to cavernous sinus) • Recurrent meningeal branch of lacrimal a. (anastomoses with middle meningeal a.)

Posteriorly

Optic canal

• Optic n. (CN II) • Ophthalmic a. (from internal carotid a.)

Pterygopalatine fossa

Posteroinferiorly (medially)

Inferior orbital fissure*

Infratemporal fossa

Posteroinferiorly (laterally)

• • • • •

Nasal cavity

Inferomedially

Nasolacrimal canal

• Nasolacrimal duct

Maxillary sinus

Inferiorly

Unnamed canaliculi

• Sensory filaments

Face and temporal fossa

Anteriorly

Zygomaticofacial canal

• Zygomaticofacial n. (CN V2) • Anastomotic branch of lacrimal a. (to transverse facial and zygomaticoorbital aa.)

Zygomaticotemporal canal

• Zygomaticotemporal n. (CN V2) • Anastomotic branch of lacrimal a. (to deep temporal aa.)

Supraorbital foramen (notch)

• Supraorbital n., lateral branch (CN V1) • Supraorbital a. (from ophthalmic a.) • Supraorbital v. (to angular v.)

Frontal incisure

• Supratrochlear a. (from ophthalmic a.) • Supratrochlear n. (CN V1) • Supraorbital n., medial branch (CN V1)

Orbital rim, medial aspect

• Infratrochlear n. (CN V1) • Dorsal nasal a. (from ophthalmic a.) • Dorsal nasal v. (to angular v.)

Orbital rim, lateral aspect

• Lacrimal n. (CN V1) • Lacrimal a. (from ophthalmic a.) • Lacrimal v. (to superior ophthalmic v.)

Face

Anteriorly

Infraorbital a. (from maxillary a.) Infraorbital v. (to pterygoid plexus)* Infraorbital n. (CN V2) Zygomatic n. (CN V2) Inferior ophthalmic v. (variable, to cavernous sinus)

* The infraorbital a., v., and n. travel in the infraorbital canal on the lateral floor of the orbit and emerge at the inferior orbital fissure. The inferior orbital fissure is continuous inferiorly with the pterygomaxillary fissure, which is the boundary between the infratemporal and the pterygopalatine fossa. The infratemporal fossa lies on the lateral side of the pterygomaxillary fissure; the pterygopalatine fossa lies on the medial side.

111

Regions of the Head

6. Orbit & Eye

Extraocular Muscles

Inferior oblique

Tendon of superior oblique

Trochlea

Superior rectus

Superior oblique

Superior rectus

Superior oblique Inferior rectus Medial rectus Common tendinous ring

Lateral rectus

Lateral rectus

Inferior rectus

Optic canal (opened)

Fig. 6.4 Extraocular (extrinsic eye) muscles Right eye. A Superior view. B Anterior view. The eyeball is moved in the orbit by four rectus muscles (superior, medial, inferior, lateral) and two oblique muscles (superior and inferior). The four rectus muscles arise from a tendinous ring around the optic canal (common tendinous ring, common annular tendon) and insert on the sclera of the eyeball. The superior and inferior obliques arise from the body of the sphenoid and the medial orbital margin of the maxilla, respectively. The superior oblique passes through a tendinous loop (trochlea) attached to the

Superior orbital fissure (opened) Optic nerve (CN II)

Common tendinous ring

Internal carotid artery

Medial rectus

Superior oblique Superior rectus

Inferior oblique

Abducent nerve (CN VI)

Inferior rectus

Foramen rotundum

Inferior orbital fissure

Clivus Foramen spinosum

Sphenoid bone

Sphenopalatine foramen

Fig. 6.5 Innervation of the extraocular muscles Right eye, lateral view with the lateral wall of the orbit removed. The extraocular muscles are supplied by cranial nerves III, IV, and VI (see Table 6.2). Note: Levator palpebrae superioris is also supplied by CN III. After emerging from the brainstem, these cranial nerves first

112

superomedial orbital margin (frontal bone); this redirects it at an acute angle to its insertion on the superior surface of the eyeball. The coordinated interaction of all six functionally competent extraocular muscles is necessary for directing both eyes toward the visual target. The brain then processes the two perceived retinal images in a way that provides binocular vision perception. Impaired function of one or more extraocular muscles causes deviation of the eye from its normal position, resulting in diplopia (double vision).

Lateral rectus

Trochlear nerve (CN IV)

Foramen ovale

B

Levator palpebrae superioris

Oculomotor nerve (CN III)

Medial rectus

Inferior oblique

Levator palpebrae superioris (cut)

Optic nerve (CN II) A

Maxillary sinus

traverse the cavernous sinus, where they are in close proximity to the internal carotid artery. From there they pass through the superior orbital fissure to enter the orbit and supply their respective muscles. The optic nerve (CN II) enters the orbit via the more medially located optic canal (see Fig. 6.1E).

Regions of the Head

6. Orbit & Eye

Fig. 6.6 Actions of the extraocular muscles Right eye, superior view with orbital roof removed. Primary actions (red), secondary actions (blue).

A

B

D

C

F

E

Table 6.2 Actions and innervation of the extraocular muscles Muscle

Primary action

Secondary action

Innervation

A Lateral rectus

Abduction

—

Abducent n. (CN VI)

B Medial rectus

Adduction

—

C Inferior rectus

Depression

Adduction and lateral rotation

D Inferior oblique

Elevation and abduction

Lateral rotation

E Superior rectus

Elevation

Adduction and medial rotation

Oculomotor n. (CN III), superior branch

F Superior oblique

Depression and abduction

Medial rotation

Trochlear n. (CN IV)

Inferior oblique

Oculomotor n. (CN III), inferior branch

B

Superior rectus

Lateral rectus

Inferior oblique

Medial rectus

Superior oblique

Inferior oblique

Lateral rectus

Inferior rectus

Up and to the right

Superior rectus

Superior oblique Up and to the left

Superior rectus

To the right

Lateral rectus

Down and to the right

Superior oblique

Inferior oblique To the left

Medial rectus

Inferior rectus

Fig. 6.7 The six cardinal directions of gaze In the clinical evaluation of ocular motility to diagnose oculomotor palsies, six cardinal directions of gaze are tested (see arrows). Note that different muscles may be activated in each eye for any particular direction of gaze. For example, gaze to the right is effected by the com-

A

Medial rectus

Lateral rectus

Down and to the left

Inferior rectus

Superior oblique

bined actions of the lateral rectus of the right eye and the medial rectus of the left eye. These two muscles, moreover, are supplied by different cranial nerves (VI and III, respectively). If one muscle is weak or paralyzed, deviation of the eye will be noted during certain ocular movements (see Fig. 6.8).

C

Fig. 6.8 Oculomotor palsies Palsy of the right side shown during attempted straight-ahead gaze. A Complete oculomotor palsy. B Trochlear palsy. C Abducent palsy. Oculomotor palsies may result from lesions involving the cranial nerve nucleus, the course of the nerve, or the eye muscle itself. Depending on the involved muscle, symptoms may include deviated position of the affected eye and diplopia. The patient attempts to compensate for this by adjusting the position of the head. A Complete oculomotor (CN III) palsy: Affects four extraocular muscles, two intraocular muscles (see p. 114), and the levator palpebrae superioris. Symptoms and affected muscle(s): Eyeball deviates toward lower outer quadrant = disabled superior, inferior, and medial recti and inferior oblique. Mydriasis (pupil dilation) = disabled pupillary sphincter. Loss of near accommodation = disabled ciliary muscle. Ptosis (drooping of eyelid) = disabled levator palpebrae superioris. The palpebral fissure cannot be opened during complete ptosis in which both the levator palpebrae superioris (CN III) and superior tarsus (sympathetic) muscles are paralyzed. Diplopia will therefore not be observed. B Trochlear nerve (CN IV) palsy: Eye deviates slightly superomedially, causing diplopia = disabled superior oblique. C Abducent nerve (CN VI) palsy: Eye deviates medially, causing diplopia = disabled lateral rectus.

113

Regions of the Head

6. Orbit & Eye

Cranial Nerves of the Extraocular Muscles: Oculomotor (CN III), Trochlear (CN IV) & Abducent (CN VI) Cerebral peduncles of mesencephalon Trochlear nerve Nucleus of trochlear nerve Pons

Oculomotor nerve Visceral oculomotor nucleus Nucleus of oculomotor nerve

Cerebral aqueduct

Tectum

Central gray substance Red nucleus Substantia nigra

Edinger-Westphal (visceral oculomotor) nucleus Nucleus of oculomotor nerve Cerebral peduncle

Abducent nerve Nucleus of abducent nerve

Medulla oblongata

Fig. 6.10 Topography of the oculomotor nucleus Cross section through the brainstem at the level of the oculomotor nucleus, superior view. Note: The visceral efferent, parasympathetic nuclear complex (Edinger-Westphal [visceral oculomotor] nucleus) can be distinguished from the somatic efferent nuclear complex (nucleus of the oculomotor nerve). Table 6.4 Trochlear nerve (CN IV): overview

Fig. 6.9 Emergence of the nerves from the brainstem Anterior view. All three nerves that supply the extraocular muscles emerge from the brainstem. The nuclei of the oculomotor nerve and trochlear nerve are located in the midbrain (mesencephalon), and the nucleus of the abducent nerve is located in the pons. Note: The oculomotor (CN III) is the only one of the three that contains somatic efferent and visceral efferent fibers and supplies multiple extraocular muscles.

Fibers: Somatic efferent fibers (red) Course: CN IV is the only cranial nerve to emerge from the dorsal side (posterior surface) of the brainstem. It is also the only cranial nerve in which all fibers cross to the opposite side. It enters the orbit through the superior orbital fissure, passing lateral to the common tendinous ring. It has the longest intradural course of the three extraocular motor nerves. Nuclei and distribution: • Somatic efferent fibers from the nucleus of the trochlear nerve emerge from the midbrain and supply motor innervation to the superior oblique.

Table 6.3 Oculomotor nerve (CN III): overview

Lesions: Trochlear nerve palsy: • Superomedial deviation of the affected eye, causing diplopia = disabled superior oblique Note: Because CN IV crosses to the opposite side, lesions close to the nucleus result in trochlear nerve palsy on the opposite side (contralateral palsy). Lesions past the site where the nerve crosses the midline cause palsy on the same side (ipsilateral palsy).

Fibers: Somatic efferent (red) and visceral efferent (blue) fibers Course: CN III runs anteriorly from the mesencephalon (midbrain, highest level of the brainstem) and travels through the lateral wall of the cavernous sinus to enter the orbit through the superior orbital fissure. After passing through the common tendinous ring, CN III divides into a superior and an inferior division. Nuclei and distribution: • Somatic efferents (red): Efferents from the nucleus of the oculomotor nerve in the midbrain supply the levator palepebrae superioris and four extraocular muscles (the superior, medial, and inferior rectus muscles, and the inferior oblique). • Visceral efferents (blue): Parasympathetic preganglionic efferents from the Edinger-Westphal (visceral oculomotor) nucleus travel with the inferior division of CN III to synapse with neurons in the ciliary ganglion. The postganglionic neurons innervate the intraocular muscles (pupillary sphincter and ciliary muscle). Lesions: Oculomotor palsy of various extents. Complete oculomotor palsy is marked by paralysis of all the innervated muscles, causing: • Ptosis (drooping of eyelid) = disabled levator palpebrae superioris • Inferolateral deviation of affected eye causing diplopia (double vision) = disabled extraocular muscles • Mydriasis (pupil dilation) = disabled pupillary sphincter • Accommodation difficulties = disabled ciliary muscle

114

Table 6.5 Abducent nerve (CN VI): overview Fibers: Somatic efferent fibers (red) Course: CN VI follows a long extradural path. It emerges from the pons (midlevel brainstem) and runs through the cavernous sinus in close proximity to the internal carotid artery and enters the orbit through the superior orbital fissure. Nuclei and distribution: • Somatic efferent fibers from the nucleus of the abducent nerve emerge from the inferior border of the pons (midlevel brainstem) and supply motor innervation to the lateral rectus. Lesions: Abducent nerve palsy: • Medial deviation of the affected eye, causing diplopia = disabled lateral rectus Note: The long extradural path of the CN VI exposes it to injury. Cavernous sinus thrombosis, aneurysms of the internal carotid artery, meningitis, or subdural hemorrhage may all compress the nerve, resulting in nerve palsy. Excessive fall in cerebrospinal fluid (CSF) pressure (e.g., due to lumbar puncture) may cause the brainstem to descend, exerting traction on the nerve.

Regions of the Head

Sympathetic fibers from cervical plexus (sympathetic root of ciliary ganglion)

Oculomotor nerve (CN III)

CN III, superior division

Levator palpebrae superioris

Superior rectus

6. Orbit & Eye

Superior oblique

Trochlea

Ciliary ganglion

Common tendinous ring

Mesencephalon

Lateral rectus (cut)

Pons

Trochlear nerve (CN IV)

Medulla oblongata

Abducent nerve (CN VI)

A

Internal carotid plexus

Lateral rectus (cut)

Short ciliary nerves CN III, inferior division

Medial rectus

Inferior rectus

Parasympathetic preganglionic fibers from CN III (motor root of ciliary ganglion)

Inferior oblique

Supraorbital nerve (CN V1)

Levator palpebrae superioris Superior oblique

Superior rectus

Medial rectus

Lacrimal gland

Lacrimal nerve (CN V1)

Inferior rectus

Lateral rectus

Frontal nerve (CN V1)

Trochlear nerve (CN IV) Oculomotor nerve (CN III)

Superior ophthalmic vein

Levator palpebrae superioris

Superior rectus

Trochlear nerve (CN IV)

Abducent nerve (CN VI)

Superior oblique Optic nerve (CN II) Medial rectus

Optic nerve (CN II)

Oculomotor nerve (CN III)

Internal carotid artery

B

Fig. 6.11 Nerves supplying the ocular muscles Right orbit. A Lateral view with lateral wall removed. B Superior view of opened orbit. C Anterior view. Cranial nerves III, IV, and VI enter the orbit through the superior orbital fissure, lateral to the optic canal (CN IV then passes lateral to the common tendinous ring, and CN III and VI pass through it). All three nerves supply somatic efferent fibers (somatomotor innervation) to the extraocular muscles. In addition, CN III carries parasympathetic motor innervation for the intraocular muscles. Parasympathetic preganglionic fibers travel with the inferior division of CN III, forming the parasympathetic (motor) root of the ciliary gan-

Inferior rectus

C

Lateral rectus

Abducent nerve (CN VI)

Inferior oblique

glion. Two other fiber types pass through the ciliary ganglion without synapsing: sympathetic and sensory. Sympathetic (postganglionic) fibers from the superior cervical ganglion travel on the internal carotid artery to enter the superior orbital fissure, where they run with the nasociliary nerve (CN V1) or enter the ciliary ganglion by coursing along the ophthalmic artery. Sensory fibers from the eyeball travel to the nasociliary nerve (CN V1) via the sensory root of the ciliary ganglion. The sensory, sympathetic, and parasympathetic fibers in the ciliary ganglion are relayed in the short ciliary nerves. Note: Sympathetic fibers also reach the intraocular muscles via the long ciliary nerves.

115

Regions of the Head

6. Orbit & Eye

Neurovasculature of the Orbit Episcleral space

Orbital roof

Bulbar fascia (Tenon’s capsule)

Periorbita

Levator palpebrae superioris

Periorbital fat

Ophthalmic artery Superior orbital septum

Superior rectus

Eyeball

Optic nerve (CN II) with dural sheath Inferior rectus

Inferior orbital septum

Central retinal artery

Inferior oblique Sclera Infraorbital nerve (CN V2)

Orbital floor

Fig. 6.12 Upper, middle, and lower levels of the orbit Right orbit. Sagittal section viewed from the medial side. The orbit is lined with periosteum (periorbita) and filled with periorbital fat, which is bounded anteriorly by the orbital septa and toward the eyeball by a mobile sheath of connective tissue (bulbar fascia, Tenon’s capsule). The narrow space between the bulbar fascia and sclera is called the episcleral space. Embedded in the periorbital fat are the eyeball, optic

Table 6.6

Maxillary sinus

nerve, lacrimal gland, extraocular muscles, and associated neurovascular structures. Topographically, the orbit is divided into three levels: • Upper level: orbital roof to levator palpebrae superioris • Middle level: superior rectus to optic nerve • Lower level: optic nerve to orbital floor

Neurovascular contents of the orbit

Orbital level

Arteries and veins

Nerves

Upper level

• • • •

• Lacrimal n. (CN V1) • Frontal n. (CN V1) and terminal branches: ◦ Supraorbital n. ◦ Supratrochlear n. • Trochlear n. (CN IV)

Middle level

• Ophthalmic a. (from internal carotid a.) and branches: ◦ Central retinal a. ◦ Posterior ciliary aa. • Superior ophthalmic v. (to cavernous sinus)

• Nasociliary n. (CN V1) • Abducent n. (CN VI) • Oculomotor n. (CN III), superior branch and fibers from inferior branch (to ciliary ganglion) • Optic n. (CN II) • Ciliary ganglion and roots: ◦ Parasympathetic root (presynaptic autonomic fibers from CN III) ◦ Sympathetic root (postsynaptic fibers from superior cervical ganglion) ◦ Sensory root (sensory fibers from eyeball to nasociliary n.) • Short ciliary nn. (fibers from/to ciliary ganglion)

Lower level

• Infraorbital a. (terminal branch of maxillary a.) • Inferior ophthalmic v. (to cavernous sinus)

• Infraorbital n. (CN V2) • Oculomotor n. (CN III), inferior branch

116

Lacrimal a. (from ophthalmic a.) Lacrimal v. (to superior ophthalmic v.) Supraorbital a. (terminal branch of ophthalmic a.) Supraorbital v. (forms angular v. with supratrochlear vv.)

Regions of the Head

Supratrochlear artery

Dorsal nasal vein

Dorsal nasal artery Supraorbital artery

Medial palpebral artery

Lacrimal vein Cavernous sinus

Lacrimal artery

Anterior ethmoidal artery

Supraorbital vein Supratrochlear vein Angular vein

Superior ophthalmic vein

Long posterior ciliary arteries

Short posterior ciliary arteries

6. Orbit & Eye

Ophthalmic artery

Posterior ethmoidal artery Optic nerve (CN II) Optic canal (opened) Internal carotid artery

Ophthalmic vein

Inferior ophthalmic vein

Infraorbital vein

Facial vein

Fig. 6.14 Veins of the orbit Superior orbital fissure

Middle meningeal artery

Right orbit, lateral view with the lateral orbital wall removed and the Anastomotic branch through lacrimal foramen maxillary sinus opened. The veins of the orbit communicate with the (sphenoid bone) veins of the superficial and deep facial region and with the cavernous sinus (potential spread of infectious pathogens, see Fig. 3.20).

Fig. 6.13 Branches of the ophthalmic artery Superior view of opened right orbit. While running below CN II in the optic canal, the ophthalmic artery gives off the central retinal artery, which pierces and travels with CN II. The ophthalmic artery then exits the canal and branches to supply the intraorbital structures (including the eyeball).

Internal carotid artery with internal carotid plexus

CN III

Communicating branch between lacrimal (CN V1) and zygomatic (CN V2) nerves Frontal CN III, nerve superior (CN V1) branch

Lacrimal nerve (CN V1) Supraorbital nerve (CN V1) Lacrimal gland Infratrochlear nerve (CN V1) Long ciliary nerves

CN IV

Nasociliary nerve (CN V1)

CN V1

Short ciliary nerves (from ciliary ganglion)

CN V

Ciliary ganglion

Trigeminal ganglion

CN V3

CN VI

Parasympathetic (motor) root of ciliary ganglion (from CN III)

CN V2 CN II CN III, inferior branch

Zygomatic nerve (CN V2) conveying parasympathetic fibers from pterygopalatine ganglion

Fig. 6.15 Innervation of the orbit Lateral view of opened right orbit. The extraocular muscles receive motor innervation from three cranial nerves: oculomotor (CN III), trochlear (CN IV), and abducent (CN VI). The ciliary ganglion distributes parasympathetic fibers to the intraocular muscles via the short ciliary nerves. Parasympathetic fibers reach the ganglion via the inferior branch of CN III. Sympathetic fibers from the superior cervical ganglion travel along the internal carotid artery to the superior orbital fissure. In the orbit, sympathetic fibers run with the nasociliary nerve (CN V1) and/or ophthal-

Sympathetic root of ciliary ganglion (from superior cervical ganglion)

Sensory root of ciliary ganglion (to nasociliary nerve)

mic artery and pass through the ciliary ganglion (the nasociliary nerve also gives off direct sensory branches, the long ciliary nerves, which may carry postganglionic sympathetic fibers). Sensory fibers from the eyeball pass through the ciliary ganglion to the nasociliary nerve (CN V1). Note: Parasympathetic fibers to the lacrimal gland are distributed by the lacrimal nerve (CN V1), which communicates with the zygomatic nerve (CN V2) via a communicating branch from the zygomaticotemporal nerve. The zygomatic nerve conveys the postganglionic fibers from the pterygopalatine ganglion (the preganglionic fibers arise from CN VII).

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Regions of the Head

6. Orbit & Eye

Topography of the Orbit (I)

Fig. 6.16 Intracavernous course of the cranial nerves that enter to the orbit Anterior and middle cranial fossae on the right side, superior view. The lateral and superior walls of the cavernous sinus have been opened. The trigeminal ganglion has been retracted slightly laterally, the orbital roof has been removed, and the periorbita has been fenestrated. All three of the cranial nerves that supply the ocular muscles (oculomotor nerve, trochlear nerve, and abducent nerve) enter the cavernous sinus, where they come into close relationship with the first and second divisions of the trigeminal nerve and with the internal carotid artery. While the third and fourth cranial nerves course in the lateral wall of the cavernous sinus with the ophthalmic and maxillary divisions of the trigeminal nerve, the abducent nerve runs directly through the cavernous sinus in close proximity to the internal carotid artery. Because of this relationship, the abducent nerve may be damaged as a result of sinus thrombosis or an intracavernous aneurysm of the internal carotid artery.

Periorbita (periosteum of the orbit) Medial branch Lateral branch

Supraorbital nerve

Supratrochlear nerve Periorbital fat

Frontal nerve (CN V1)

Anterior cranial fossa

Ophthalmic artery Internal carotid artery Optic chiasm (CN II) Trochlear nerve (CN IV) Oculomotor nerve (CN III) Cavernous sinus

Abducent nerve (CN VI)

Trigeminal ganglion

Superior orbital fissure

Fig. 6.17 Neurovasculature in the optic canal and superior orbital fissure Right orbit, anterior view with most of the orbital contents removed. Optic canal: optic nerve (CN II) and ophthalmic artery. Superior orbital fissure (inside common tendinous ring): abducent (CN VI), nasociliary (CN V1), and oculomotor (CN III) nerves. Superior orbital fissure (outside common tendinous ring): superior and inferior ophthalmic veins, frontal (CN V1), lacrimal (CN V1), and trochlear (CN IV) nerves. Inferior orbital fissure (contents not shown): zygomatic (CN V2) nerve and branches of CN V2, infraorbital artery, vein, and nerve in infraorbital canal.

Frontal nerve (CN V1)

Trigeminal nerve (CN V), sensory root

Levator palpebrae superioris

Middle cranial fossa

Superior rectus Superior oblique

Lacrimal nerve (CN V1) Superior ophthalmic vein

Optic nerve (CN II) Common tendinous ring

Trochlear nerve (CN IV)

Ophthalmic artery

Oculomotor nerve (CN III), superior branch

Superior orbital fissure

Nasociliary nerve (CN V1)

Medial rectus

Lateral rectus Inferior orbital fissure

Oculomotor nerve (CN III), inferior branch Abducent nerve (CN VI)

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Trigeminal nerve (CN V), motor root

Infraorbital groove and canal

Inferior ophthalmic vein

Inferior rectus

Regions of the Head

6. Orbit & Eye

Trochlea Infratrochlear nerve Cribriform plate Anterior ethmoidal artery and nerve Supratrochlear artery Posterior ethmoidal artery and nerve

Medial branch Lateral branch

Supraorbital nerve

Supratrochlear nerve Levator palpebrae superioris Lacrimal gland Lacrimal artery and nerve (CN V1)

Supraorbital nerve

Superior rectus

Supraorbital artery

Abducent nerve (CN VI)

Nasociliary nerve (CN V1) Trochlear nerve (CN IV)

Superior ophthalmic vein Frontal nerve (CN V1)

Ophthalmic artery Optic nerve (CN II) Internal carotid artery Optic chiasm

Fig. 6.18 Topography of the right orbit: contents of the upper level Superior view. The bony roof of the orbit, the periorbita, and the retro-orbital fat have been removed.

Infundibulum Oculomotor nerve (CN III) Trochlear nerve (CN IV)

Medial rectus Superior oblique Superior ophthalmic vein Anterior ethmoidal artery and nerve

Levator palpebrae superioris Superior rectus

Posterior ethmoidal artery and nerve

Lacrimal gland

Nasociliary nerve

Lacrimal artery and nerve

Short ciliary nerves Long ciliary nerves

Eyeball

Lateral rectus

CN IV Ophthalmic artery Short posterior ciliary arteries CN II CN III

Inferior ophthalmic vein CN VI Ciliary ganglion

Fig. 6.19 Topography of the right orbit: contents of the middle level Superior view. The levator palpebrae superioris and the superior rectus have been divided and reflected backward, and all fatty tissue has been removed to better expose the optic nerve. Note: The ciliary ganglion is approximately 2 mm in diameter and lies lateral to the optic nerve approximately 2 cm behind the eyeball. The ciliary ganglion relays parasympathetic fibers to the eye and intraocular muscles via the short ciliary nerves. The short ciliary nerves also contain sensory and sympathetic fibers (see Fig. 6.15).

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Regions of the Head

6. Orbit & Eye

Topography of the Orbit (II)

Site of emergence of lacrimal artery and nerve

Dorsal nasal artery and vein, with infratrochlear nerve

Supraorbital artery and nerve

Supratrochlear artery, vein, and nerve

Depressor supercilii

Procerus

Orbicularis oculi, palpebral part

Superior palpebral branches of supraorbital nerve

Orbicularis oculi, orbital part

Orbital septum

A

Infraorbital nerve and artery

Levator palpebrae superioris

Facial artery and vein

Supraorbital artery and nerve

Medial palpebral ligament

Angular artery and vein

Supratrochlear nerve

Superior oblique

Trochlea

Superior tarsal muscle

Infratrochlear nerve

Orbital septum

Dorsal nasal artery and vein

Lacrimal gland, orbital part

Lacrimal sac

Lacrimal gland, palpebral part

Angular artery and vein

Lateral palpebral ligament Superior tarsus

B

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Nasalis

Inferior tarsus

Infraorbital nerve and artery

Facial artery

Lateral nasal artery

Levator labii superioris alaeque nasi

Inferior palpebral branches of infraorbital nerve

Fig. 6.20 Superficial and deep neurovascular structures of the orbital region Right eye, anterior view. A Superficial layer. The orbital septum on the right side has been exposed by removal of the orbicularis oculi. B Deep layer. Anterior orbital structures have been exposed by partial removal of the orbital septum. The regions supplied by the internal carotid artery (supraorbital artery) and external carotid artery (infraorbital artery, facial artery) meet in this region. The extensive anastomosis between the angular vein (extracranial) and superior ophthalmic veins (intracranial) creates a portal of entry by which microorganisms may reach the cavernous sinus (risk of sinus thrombosis, meningitis, see p. 53). It is sometimes necessary to ligate this anastomosis in the orbital region, as in patients with extensive infections of the external facial region. Note the passage of the supra- and infraorbital nerves (branches of CN V1 and CN V2) through the accordingly named foramina. The sensory function of these two trigeminal nerve divisions can be tested at these nerve exit points.

Regions of the Head

Lateral canthus of eyelids

Fig. 6.21 Surface anatomy of the eye Right eye, anterior view. The measurements indicate the width of the normal palpebral fissure. It is important to know these measurements because there are a number of diseases in which they are altered. For example, the palpebral fissure may be widened in peripheral facial paralysis or narrowed in ptosis (= drooping of the eyelid) due to oculomotor palsy.

Eyebrow

Upper eyelid 3 mm

2 mm 9 mm (6–10)

Palpebral fissure Orbital roof

6. Orbit & Eye

Medial canthus of eyelids

28–30 mm

Lower eyelid

Periorbita

Levator palpebrae superioris

Superior orbital septum

Superior rectus Superior conjunctival fornix

Orbicularis oculi, orbital part

Superior tarsal muscle Superior tarsus with tarsal glands Lens

Upper eyelid

Superior fornix

Cornea Iris Ciliary body

Ocular conjunctiva

Inferior tarsus Ciliary and sebaceous glands Palpebral fissure

Retina

Palpebral (tarsal) conjunctiva

Sclera Inferior tarsal muscle Lower eyelid

Inferior orbital septum

Fornical conjunctiva

Orbicularis oculi, palpebral part

Inferior fornix

Infraorbital nerve A

B

Fig. 6.22 Structure of the eyelids and conjunctiva A Sagittal section through the anterior orbital cavity. B Anatomy of the conjunctiva. The eyelid consists clinically of an outer and an inner layer with the following components:

tiva (tunica conjunctiva) is a vascularized, thin, glistening mucous membrane that is subdivided into the palpebral conjunctiva (green), fornical conjunctiva (red), and ocular conjunctiva (yellow). The ocular conjunctiva borders directly on the corneal surface and combines with it to form the conjunctival sac, whose functions include:

• Outer layer: palpebral skin, sweat glands, ciliary glands (= modified sweat glands, Moll glands), sebaceous glands (Zeis glands), and two striated muscles, the orbicularis oculi and levator palpebrae (upper eyelid only), innervated by the facial nerve and the oculomotor nerve, respectively. • Inner layer: the tarsus (fibrous tissue plate), the superior and inferior tarsal muscles (of Müller; smooth muscle innervated by sympathetic fibers), the tarsal or palpebral conjunctiva, and the tarsal glands (meibomian glands).

• facilitating ocular movements, • enabling painless motion of the palpebral conjunctiva and ocular conjunctiva relative to each other (lubricated by lacrimal fluid), and • protecting against infectious pathogens (collections of lymphocytes along the fornices).

Regular blinking (20 to 30 times per minute) keeps the eyes from drying out by evenly distributing the lacrimal fluid and glandular secretions. Mechanical irritants (e.g., grains of sand) evoke the blink reflex, which also serves to protect the cornea and conjunctiva. The conjunc-

The superior and inferior fornices are the sites where the conjunctiva is reflected from the upper and lower eyelid, respectively, onto the eyeball. They are convenient sites for the instillation of ophthalmic medications. Inflammation of the conjunctiva is common and causes a dilation of the conjunctival vessels resulting in “pink eye.” Conversely, a deficiency of red blood cells (anemia) may lessen the prominence of vascular markings in the conjunctiva. This is why the conjunctiva should be routinely inspected in every clinical examination.

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Regions of the Head

6. Orbit & Eye

Lacrimal Apparatus Supraorbital foramen

Frontal incisure (notch)

Levator palpebrae superioris

Orbital septum

Periorbital fat Lacrimal caruncle

Lacrimal gland, orbital part

Superior and inferior lacrimal canaliculi

Lacrimal gland, palpebral part

Medial palpebral ligament

Upper eyelid Lacrimal sac Superior and inferior puncta

Lower eyelid

Nasolacrimal duct Nasolacrimal canal

Infraorbital foramen

Fig. 6.23 Lacrimal apparatus Right eye, anterior view. The orbital septum has been partially removed, and the tendon of insertion of the levator palpebrae superioris has been divided. The hazelnut-sized lacrimal gland is located in the lacrimal fossa of the frontal bone and produces most of the lacrimal fluid. Smaller accessory lacrimal glands (Krause or Wolfring glands) are also present. The tendon of levator palpebrae subdivides the lacrimal gland, which normally is not visible or palpable, into an orbital lobe (two thirds of gland) and a palpebral lobe (one third). The sympathetic fibers innervating the lacrimal gland originate from the superior cervical ganglion and travel along arteries to reach the lacrimal gland. Parasympathetic fibers reach the lacrimal gland via the lacrimal nerve (CN V1). The lacrimal nerve communicates with the zygomatic nerve (CN V2), which re-

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Inferior nasal concha

lays postganglionic parasympathetic fibers from the pterygopalatine ganglion. The preganglionic parasympathetic fibers that synapse in the pterygopalatine ganglion travel as the greater petrosal nerve, which arises from the genu of the facial nerve (CN VII) (see Fig. 4.38). The lacrimal apparatus can be understood by tracing the flow of lacrimal fluid obliquely downward from the superolateral margin of the orbit (by the lacrimal gland) to the inferomedial margin (see Fig. 6.25). From the superior and inferior puncta, the lacrimal fluid enters the superior and inferior lacrimal canaliculi, which direct the fluid into the lacrimal sac. Finally, it drains through the nasolacrimal duct to an outlet below the inferior concha of the nose. “Watery eyes” are a typical cold symptom caused by obstruction of the inferior opening of the nasolacrimal duct.

Regions of the Head

6. Orbit & Eye

Temporal

Nasal

Goblet cells

Superior and inferior puncta Superior and inferior lacrimal canaliculi

Lacrimal sac

Orbicularis oculi

Fig. 6.24 Distribution of goblet cells in the conjunctiva Goblet cells are mucus-secreting cells with an epithelial covering. Their secretions (mucins) are an important constituent of the lacrimal fluid. Mucins are also secreted by the main lacrimal gland.

Fig. 6.25 Mechanical propulsion of the lacrimal fluid During closure of the eyelids, contraction of the orbicularis oculi proceeds in a temporal-to-nasal direction. The successive contraction of these muscle fibers propels the lacrimal fluid toward the lacrimal passages. Note: Facial paralysis prevents closure of the eyelids, causing the eye to dry out.

Superior lacrimal canaliculi

Lipid layer, approx. 0.1 μm

Meibomian glands

Prevents rapid evaporation Irrigation tube Aqueous layer, approx. 8 μm

Lacrimal gland

A

B

Inferior lacrimal canaliculus

Irrigating fluid, smoothes surface irregularities Mucin layer, approx. 0.8 μm

Conjunctival goblet cells

Gel-like consistency stabilizes the tear film

Fig. 6.26 Structure of the tear film The tear film is a complex fluid with several morphologically distinct layers, whose components are produced by individual glands. The outer lipid layer, produced by the meibomian glands, protects the aqueous middle layer of the tear film from evaporating.

C

Common lacrimal canaliculus

D

Lacrimal sac

Fig. 6.27 Obstructions to lacrimal drainage Sites of obstruction in the lacrimal drainage system can be located by irrigating the system with a special fluid. A No obstruction to lacrimal drainage. B,C Stenosis in the inferior or common lacrimal canaliculus. The stenosis causes a damming back of lacrimal fluid behind the obstructed site. In B the fluid refluxes through the inferior lacrimal canaliculus, and in C it flows through the superior lacrimal canaliculus. D Stenosis below the level of the lacrimal sac (postlacrimal sac stenosis). When the entire lacrimal sac has filled with fluid, the fluid begins to reflux into the superior lacrimal canaliculus. In such cases, the lacrimal fluid often has a purulent, gelatinous appearance.

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6. Orbit & Eye

Eyeball

Iris

Lens

Cornea Anterior chamber

Posterior chamber

Chamber angle

Canal of Schlemm

Corneoscleral limbus

Pigment epithelium of the ciliary body

Ciliary body, ciliary muscle

Ocular conjunctiva

Zonular fibers

Hyaloid fossa

Ora serrata

Vitreous body

Lateral rectus

Medial rectus

Retina Choroid

Layers of the eyeball

Optic disk Sclera Lamina cribrosa Central retinal artery (from ophthalmic artery)

Fovea centralis Optic nerve (CN II)

Fig. 6.28 Eyeball Right eye, superior view of transverse section. Most of the eyeball is composed of three concentric layers surrounding vitreous humor: the sclera, the choroid, and the retina. Posterior portion of the eyeball: The sclera is the posterior portion of the outer coat of the eyeball. It is a firm layer of connective tissue that gives attachment to the tendons of all the extraocular muscles. The middle layer of the eye, the choroid, is the most highly vascularized region in the body and serves to regulate the temperature of the eye and to supply blood to the outer layers of the retina. The inner layer of the eye, the retina, includes an inner layer of photosensitive cells (sensory retina) and an outer layer of retinal pigment epithelium. The axons of the optic nerve (CN II) pierce the lamina cribrosa of the sclera at the optic disk. The fovea centralis is a depressed area in the central retina approximately 4 mm temporal to the optic disk. Incident light is normally focused on the fovea centralis, the site of greatest visual acuity.

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Anterior portion: The anterior portion of the eyeball has a different structure that is continuous with the posterior portion. The outer fibrous coat is the cornea, the “window of the eye,” which bulges forward. At the corneoscleral limbus, the cornea is continuous with the less convex sclera. In the angle of the anterior chamber, the sclera forms the trabecular meshwork, which is connected to the canal of Schlemm. Beneath the sclera is the vascular coat of the eye, also called the uveal tract. It consists of three parts: the iris, ciliary body, and choroid. The iris shields the eye from excessive light and covers the lens. Its root is continuous with the ciliary body, which contains the ciliary muscle for visual accommodation (alters the refractive power of the lens). The epithelium of the ciliary body produces the aqueous humor. The ciliary body is continuous at the ora serrata with the choroid. The outer layer of the retina (pigment epithelium) is continued forward as the pigment epithelium of the ciliary body and the epithelium of the iris.

Regions of the Head

Attachment to ora serrata (vitreous base of Salzmann)

Cornea

6. Orbit & Eye

Attachment to posterior lens capsule (Wieger ligament) Hannover space Garnier space

Meridian

Petit space Berger space

Equator

Hyaloid canal Attachment to optic disk (Martegiani ring)

Vitreous body

Optic nerve (CN II)

Fovea centralis Optic nerve (CN II)

Fig. 6.29 Reference lines and points on the eye The line marking the greatest circumference of the eyeball is the equator. Lines perpendicular to the equator are called meridians.

Myopia (nearsightedness) Incident light rays

Normal (emmetropic) eye

Fig. 6.30 Vitreous body (vitreous humor) Right eye, transverse section viewed from above. Sites where the vitreous body is attached to other ocular structures are shown in red, and adjacent spaces are shown in green. The vitreous body stabilizes the eyeball and protects against retinal detachment. Devoid of nerves and vessels, it consists of 98% water and 2% hyaluronic acid and collagen. The “hyaloid canal” is an embryological remnant of the hyaloid artery. For the treatment of some diseases, the vitreous body may be surgically removed (vitrectomy) and the resulting cavity filled with physiological saline solution.

Hyperopia (farsightedness)

Eyeball

Cornea

Retina

Superior rectus

Lens

Medial rectus

Fig. 6.31 Light refraction In a normal (emmetropic) eye, parallel rays from a distant light source are refracted by the cornea and lens to a focal point on the retinal surface. • In myopia (nearsightedness), the rays are focused to a point in front of the retina. • In hyperopia (farsightedness), the rays are focused behind the retina.

Superior oblique

Lateral rectus

23°

Optical axis

Orbital axes

Fig. 6.32 Optical axis and orbital axis Superior view of both eyes showing the medial, lateral, and superior recti and the superior oblique. The optical axis deviates from the orbital axis by 23 degrees. Because of this disparity, the point of maximum visual acuity, the fovea centralis, is lateral to the “blind spot” of the optic disk.

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Regions of the Head

6. Orbit & Eye

Eye: Blood Supply

Lesser arterial circle of iris

Cornea

Scleral venous sinus

Iris

Anterior conjunctival artery

Greater arterial circle of iris

Lens

Anterior ciliary arteries

Retina Sclera

Arterial circle of Zinn (and von Haller)

Choroid (choroidocapillary layer)

Short posterior ciliary arteries Pial vascular plexus

Vorticose vein

Long posterior ciliary arteries

Central retinal artery and vein Optic nerve

Fig. 6.33 Blood supply of the eye Horizontal section through the right eye at the level of the optic nerve, viewed from above. All of the arteries that supply the eye arise from the ophthalmic artery, a branch of the internal carotid artery. Its ocular branches are: • Central retinal artery to the retina • Short posterior ciliary arteries to the choroid

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• Long posterior ciliary arteries to the ciliary body and iris, where they supply the greater and lesser arterial circles of the iris (see Fig. 6.43) • Anterior ciliary arteries, which arise from the vessels of the rectus muscles of the eye and anastomose with the posterior ciliary vessels Blood is drained from the eyeball by four to eight vorticose veins, which pierce the sclera behind the equator and open into the superior or inferior ophthalmic vein.

Regions of the Head

6. Orbit & Eye

Vessels to optic nerve

Fig. 6.34 Arteries of the optic nerve (CN II) Lateral view. The central retinal artery, the first branch of the ophthalmic artery, enters the optic nerve from below approximately 1 cm behind the eyeball and courses with it to the retina while giving off multiple small branches. The posterior ciliary artery also gives off several small branches that supply the optic nerve. The distal part of the optic nerve receives its arterial blood supply from an arterial ring (circle of Zinn and von Haller) formed by anastomoses among the side branches of the short posterior ciliary arteries and central retinal artery.

Long posterior ciliary arteries Short posterior ciliary arteries Circle of Zinn (and von Haller)

Ophthalmic artery

Posterior ciliary artery

Nasal

Central retinal artery

Temporal

Fovea centralis

Physiological cup Optic disk (blind spot) Sites of entry and emergence of central retinal artery and vein Branch of central retinal vein Branch of central retinal artery A

Fig. 6.35 Ophthalmoscopic examination of the optic fundus A Examination technique (direct ophthalmoscopy). B Normal appearance of the optic fundus. In direct ophthalmoscopy, the following structures of the optic fundus can be directly evaluated at approximately 16 x magnification: • • • •

The condition of the retina The blood vessels (particularly the central retinal artery) The optic disk (where the optic nerve emerges from the eyeball) The macula lutea and fovea centralis

Because the retina is transparent, the color of the optic fundus is determined chiefly by the pigment epithelium and the blood vessels of the choroid. It is uniformly pale red in light-skinned persons and is considerably browner in dark-skinned persons. Abnormal detachment of the retina is usually associated with a loss of retinal transparency, and the

Macula lutea (yellow spot) B

retina assumes a yellowish white color. The central retinal artery and vein can be distinguished from each other by their color and caliber: arteries have a brighter red color and a smaller caliber than the veins. This provides a means for the early detection of vascular changes (e.g., stenosis, wall thickening, microaneurysms), such as those occurring in diabetes mellitus (diabetic retinopathy) or hypertension. The optic disk normally has sharp margins, a yellow-orange color, and a central depression, the physiological cup. The disk is subject to changes in pathological conditions such as elevated intracranial pressure (papilledema with ill-defined disk margins). On examination of the macula lutea, which is 3 to 4 mm temporal to the optic disk, it can be seen that numerous branches of the central retinal artery radiate toward the macula but do not reach its center, the fovea centralis (the fovea receives its blood supply from the choroid). A common age-related disease of the macula lutea is macular degeneration, which may gradually lead to blindness.

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Regions of the Head

6. Orbit & Eye

Eye: Lens & Cornea

Fig. 6.36 Position of the lens and cornea Histological section through the cornea, lens, and suspensory apparatus of the lens. The normal lens is clear, transparent, and only 4 mm thick. It is suspended in the hyaloid fossa of the vitreous body. The lens is attached by rows of fibrils (zonular fibers) to the ciliary muscle, whose contractions alter the shape and focal length of the lens. Thus, the lens is a dynamic structure that can change its shape in response to visual requirements. The anterior chamber of the eye is situated in front of the lens, and the posterior chamber is located between the iris and the anterior epithelium of the lens. The lens, like the vitreous body, is devoid of nerves and blood vessels and is composed of elongated epithelial cells (lens fibers).

Anterior chamber

Cornea

Posterior chamber

Iris Canal of Schlemm

Scleral spur Ocular conjunctiva Ciliary muscle Sclera

Pars plana

Pars plicata

Ciliary body

Zonular fibers

Lens

Pupil

Epithelium of ciliary body

Trabecular meshwork

Iris

Lens Pupil

Ciliary body, pars plicata Ciliary body, pars plana

Fig. 6.37 Lens and ciliary body Posterior view. The curvature of the lens is regulated by the muscle fibers of the annular ciliary body. The ciliary body lies between the ora serrata and the root of the iris and consists of a relatively flat part (pars plana) and a part that is raised into folds (pars plicata). The latter part is ridged by approximately 70 to 80 radially oriented ciliary processes, which surround the lens like a halo when viewed from behind. The ciliary processes contain large capillaries, and their epithelium secretes the aqueous humor. Very fine zonular fibers extend from the basal layer of the ciliary processes to the equator of the lens. These fibers and the spaces between them constitute the suspensory apparatus of the lens, called the zonule. Most of the ciliary body is occupied by

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Sclera Choroid Retina, optical part

Zonular fibers Ciliary processes

Ciliary muscle

the ciliary muscle, a smooth muscle composed of meridional, radial, and circular fibers. It arises mainly from the scleral spur (a reinforcing ring of sclera just below the canal of Schlemm), and it attaches to structures including the Bruch membrane of the choroid and the inner surface of the sclera. When the

Ora serrata

ciliary muscle contracts, it pulls the choroid forward and relaxes the zonular fibers. As these fibers become lax, the intrinsic resilience of the lens causes it to assume the more convex relaxed shape that is necessary for near vision. This is the basic mechanism of visual accommodation.

Regions of the Head

6. Orbit & Eye

Ciliary muscle relaxed, zonular fibers tense, lens flattened Equator

Light rays in distant accommodation

Lens

Lens capsule

Anterior pole

Posterior pole Light rays in near accommodation

A

B

Axis

Fig. 6.38 Reference lines and dynamics of the lens A Principal reference lines of the lens: The lens has an anterior and posterior pole, an axis passing between the poles, and an equator. The lens has a biconvex shape with a greater radius of curvature posteriorly (16 mm) than anteriorly (10 mm). Its function is to transmit light rays and make fine adjustments in refraction. Its refractive power ranges from 10 to 20 diopters, depending on the state of accommodation. The cornea has a considerably higher refractive power of 43 diopters.

Embryonic nucleus

B Light refraction and dynamics of the lens: • Upper half of diagram: fine adjustment of the eye for far vision. Parallel light rays arrive from a distant source, and the lens is flattened. • Lower half of diagram: For near vision (accommodation to objects less than 5 m from the eye), the lens assumes a more rounded shape. This is effected by contraction of the ciliary muscle (parasympathetic innervation from the oculomotor nerve), causing the zonular fibers to relax and allowing the lens to assume a more rounded shape because of its intrinsic resilience.

Stratified nonkeratinized squamous epithelium

External view of lens capsule

Fetal nucleus

Ciliary muscle contracted, zonular fibers lax, lens more rounded

Basement membrane Bowman membrane

Cortex Epithelium Capsule Stroma

A

Infantile nucleus

Adult nucleus

B

Fig. 6.39 Growth of the lens and zones of discontinuity A Anterior view. B Lateral view. The lens continues to grow throughout life, doing so in a manner opposite to that of other epithelial structures (i.e., the youngest cells are at the surface of the lens, whereas the oldest cells are deeper). Due to the constant proliferation of epithelial cells, which are all firmly incorporated in the lens capsule, the tissue of the lens becomes increasingly dense with age. A slit-lamp examination will demonstrate zones of varying cell density (zones of discontinuity). The zone of highest cell density, the embryonic nucleus, is at the center of the lens. With further growth, it becomes surrounded by the fetal nucleus. The infantile nucleus develops after birth, and finally the adult nucleus begins to form during the third decade of life. These zones are the basis for the morphological classification of cataracts, a structural alteration in the lens, causing opacity, that is more or less normal in old age (present in 10% of all 80-year-olds).

Descemet membrane Endothelium

Fig. 6.40 Structure of the cornea The cornea is covered externally by stratified, nonkeratinized squamous epithelium whose basal lamina borders on the anterior limiting lamina (Bowman membrane). The stroma (substantia propria) makes up approximately 90% of the corneal thickness and is bounded on its deep surface by the posterior limiting lamina (Descemet membrane). Beneath is a single layer of corneal endothelium. The cornea does have a nerve supply (for corneal reflexes), but it is not vascularized and therefore has an immunologically privileged status: normally, a corneal transplant can be performed without fear of a host rejection response.

129

Regions of the Head

6. Orbit & Eye

Eye: Iris & Ocular Chambers

Cornea

Iris

Anterior chamber

Pupillary sphincter Pupillary dilator

Chamber angle

Canal of Schlemm

Ciliary muscle

Ocular conjunctiva

Ciliary body

Zonular fibers Posterior chamber

Pupil

Fig. 6.41 Iris and chambers of the eye Transverse section through the anterior segment of the eye, superior view. The iris, the choroid, and the ciliary body at the periphery of the iris are part of the uveal tract. In the iris, the pigments are formed that determine eye color. The iris is an optical diaphragm with a central aperture, the pupil, placed in front of the lens. The pupil is 1 to 8 mm in diameter; it constricts on contraction of the pupillary sphincter (parasympathetic innervation via the oculomotor nerve and ciliary ganglion)

Sclera

Lens

and dilates on contraction of the pupillary dilator (sympathetic innervation from the superior cervical ganglion via the internal carotid plexus). Together, the iris and lens separate the anterior chamber of the eye from the posterior chamber. The posterior chamber behind the iris is bounded posteriorly by the vitreous body, centrally by the lens, and laterally by the ciliary body. The anterior chamber is bounded anteriorly by the cornea and posteriorly by the iris and lens.

Table 6.7 Changes in pupil size: causes

A

B

Fig. 6.42 Pupil size A Normal pupil size. B Maximum constriction (miosis). C Maximum dilation (mydriasis). The regulation of pupil size is aided by the two intraocular muscles, the pupillary sphincter and pupillary dilator. The pupillary sphincter (parasympathetic innervation) narrows the pupil, and the pupillary dilator (sympathetic inner vation) enlarges the pupil. Pupil size is normally adjusted in response to incident light and serves mainly to optimize visual acuity.

130

C

Normally, the pupils are circular in shape and equal in size (3 to 5 mm). Various influences may cause the pupil size to vary over a range from 1.5 mm (miosis) to 8 mm (mydriasis). A greater than 1 mm discrepancy of pupil size between the right and left eyes is called anisocoria. Mild anisocoria is physiological in some individuals. Pupillary reflexes such as convergence and the consensual light response are described on p. 138.

Pupil constriction (parasympathetic)

Pupil dilation (sympathetic)

Light

Darkness

Sleep, fatigue

Pain, excitement

Miotic agents: • Parasympathomimetics (e.g., tear gas, VX and sarin, Alzheimer’s drugs such as rivastigmine) • Sympatholytics (e.g., antihypertensives)

Mydriatic agents: • Parasympatholytics (e.g., atropine) • Sympathomimetics (e.g., epinephrine)

Horner syndrome (also causes ptosis and narrowing of palpebral fissure)

Oculomotor palsy

General anesthesia, morphine

Migraine attack, glaucoma attack

Regions of the Head

Cornea

Pupillary sphincter

Pupillary dilator

Lesser arterial circle of iris Iris stroma

Greater arterial circle of iris

Trabecular meshwork with Fontana spaces

Two layers of pigmented iris epithelium

6. Orbit & Eye

Fig. 6.43 Structure of the iris The basic structural framework of the iris is the vascularized stroma, which is bounded on its deep surface by two layers of pigmented iris epithelium. The loose, collagen-containing stroma of the iris contains outer and inner vascular circles (greater and lesser arterial circles), which are interconnected by small anastomotic arteries. The pupillary sphincter is an annular muscle located in the stroma bordering the pupil. The radially disposed pupillary dilator is not located in the stroma; rather, it is composed of numerous myofibrils in the iris epithelium (myoepithelium). The stroma of the iris is permeated by pigmented connective tissue cells (melanocytes). When heavily pigmented, these melanocytes of the anterior border zone of the stroma render the iris brown or “black.” Otherwise, the characteristics of the underlying stroma and epithelium determine eye color, in a manner that is not fully understood.

Anterior chamber

Cornea

Canal of Schlemm Conjunctiva

Scleral spur Episcleral veins

A

Sclera Zonular fibers Ciliary body

Chamber angle

Posterior chamber

Iris

Lens

Fig. 6.44 Normal drainage of aqueous humor The aqueous humor (approximately 0.3 mL per eye) is an important determinant of the intraocular pressure. It is produced by the nonpigmented ciliary epithelium of the ciliary processes in the posterior chamber (approximately 0.15 mL/hour) and passes through the pupil into the anterior chamber of the eye. The aqueous humor seeps through the spaces of the trabecular meshwork (Fontana spaces) in the chamber angle and enters the canal of Schlemm (venous sinus of the sclera), through which it drains to the episcleral veins. The draining aqueous humor flows toward the chamber angle along a pressure gradient (intraocular pressure = 15 mm Hg, pressure in the episcleral veins = 9 mm Hg) and must surmount a physiological resistance at two sites: • Pupillary resistance (between the iris and lens) • Trabecular resistance (narrow spaces in the trabecular meshwork)

B

Fig. 6.45 Obstruction of aqueous drainage and glaucoma Normal function of the optical system requires normal intraocular pressure (15 mm Hg in adults). This maintains a smooth curvature of the corneal surface and helps keep the photoreceptor cells in contact with the pigment epithelium. Obstruction of the normal drainage of aqueous humor causes an increase in intraocular pressure. This constricts the optic nerve at the lamina cribrosa, where it emerges from the eyeball through the sclera. Such constriction eventually leads to blindness. There are two types of glaucoma: A Acute (closed-angle) glaucoma: The chamber angle is obstructed by iris tissue. Aqueous fluid cannot drain into the anterior chamber and pushes portions of the iris upward, blocking the chamber angle. This type of glaucoma often develops quickly. B Chronic (open-angle) glaucoma: The chamber angle is open, but drainage through the trabecular meshwork is impaired. Ninety percent of all glaucomas are primary chronic open-angle glaucomas. This is increasingly prevalent after 40 years of age. Treatment options include parasympathomimetics (to induce sustained contraction of the ciliary muscle and pupillary sphincter), prostaglandin analogues (to improve aqueous drainage), and beta-adrenergic agonists (to decrease production of aqueous humor).

Approximately 85% of the aqueous humor flows through the trabecular meshwork into the canal of Schlemm. Only 15% drains through the uveoscleral vascular system into the vortical veins (uveoscleral drainage route).

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Regions of the Head

6. Orbit & Eye

Eye: Retina

Nonvisual retina

Optic part of retina

Macula lutea

Fig. 6.46 Overview of the retina The retina is the third, innermost layer of the eyeball. It consists mainly of a photosensitive optic part and a smaller, nonphotosensitive forward prolongation called the nonvisual retina. The optic part of the retina (yellow) varies in thickness. It overlies the pigment epithelium of the uveal tract and is pressed against it by the intraocular pressure. The optic part of the retina ends at a jagged margin, the ora serrata, which is where the nonvisual retina begins. The site on the retina where visual acuity is highest is the fovea centralis, a small depression at the center of a yellowish area, the macula lutea. The optic part of the retina is particularly thin at this site; it is thickest at the point where the optic nerve emerges from the eyeball at the lamina cribrosa.

Sclera Uveal tract Fovea centralis

Optic nerve (CN II)

Optic disk Ora serrata

Cornea

Ocular conjunctiva Iris

Ciliary body

Ora serrata

Iridial part of retina Ciliary part of retina

Neural layer

Nonvisual retina

Pigmented layer Sclera

Optic part of retina

Fig. 6.47 Parts of the retina The posterior surface of the iris bears a double layer of pigment epithelium, the iridial part of the retina. Just peripheral to it is the ciliary part of the retina, also formed by a double layer of epithelium (one of which is pigmented) and covering the posterior surface of the ciliary body. The iridial and ciliary parts of the retina together constitute the

132

nonvisual retina —the portion of the retina that is not sensitive to light. The nonvisual retina ends at a jagged line, the ora serrata, where the light-sensitive optic part of the retina begins. Consistent with the development of the retina from the embryonic optic cup, two layers can be distinguished within the optic part: • An outer layer nearer the sclera: the pigmented layer, consisting of a single layer of pigmented retinal epithelium. • An inner layer nearer the vitreous body: the neural layer, comprising a system of receptor cells, interneurons, and ganglion cells.

Regions of the Head

Inner limiting membrane Incident light

Blood vessels

10. Inner limiting membrane

7. Inner plexiform layer

Amacrine cells

6. Nuclei of bipolar cells (inner nuclear layer)

Second neurons (bipolar cells)

5. Outer plexiform layer

Horizontal cell

Outer limiting membrane

4. Nuclei of photoreceptor cells (outer nuclear layer) 3. Outer limiting membrane

Pigment epithelium

2. Processes of photoreceptor cells

First neurons (photoreceptors)

Müller cells Bruch membrane

A

9. Nerve fiber layer 8. Nuclei of ganglion cells

Third neurons (ganglion cells)

Excitation

6. Orbit & Eye

Choroid

B

Fig. 6.48 Structure of the retina A Retinal neurons of the visual pathway. B Anatomical layers of the retina. Light passes through all the layers of the retina to be received by the photoreceptors on the outermost surface of the retina. Sensory information is then transmitted via three retinal neurons of the visual pathway to the optic disk: • First neurons (pink): Photoreceptor cells (light-sensitive sensory cells) that transform light stimuli (photons) into electrochemical signals. The two types of photoreceptors are rods and cones, named for the shape of their receptor segment. The retina contains 100 million to 125 million rods, which are responsible for twilight and night vision, but only about 6 million to 7 million cones. Different cones are specialized for the perception of red, green, and blue. The processes and nuclei of the first neurons compose anatomical layers 2 to 4 (see B). • Second neurons (yellow): Bipolar cells that receive impulses from the photoreceptors and relay them to the ganglion cells. These neurons compose anatomical layers 5 to 7.

Bruch membrane

Choroid

Second neurons (bipolar cells)

First neurons (photoreceptors)

1. Pigment epithelium

• Third neurons (green): Retinal ganglion cells whose axons converge at the optic disk to form the optic nerve (CN II) and reach the lateral geniculate and superior colliculus. These neurons compose anatomical layers 8 to 10. There are approximately 1 million retinal ganglion axons per eye. Support cells: Müller cells (blue) are glial cells that span the neural layer radially from the inner to the outer limiting membranes, creating a supporting framework for the neurons. In addition to the vertical connections, horizontal and amacrine cells (gray) function as interneurons that establish lateral connections. Impulses transmitted by the receptor cells are thereby processed and organized within the retina (signal convergence). Pigment epithelium: The outer layer of the retina (the pigment epithelium, brown) is attached to the Bruch membrane, which contains elastic fibers and collagen fibrils and mediates the exchange of substances between the adjacent choroid (choriocapillaris) and the photoreceptor cells. Note: The photoreceptors are in contact with the pigment epithelium but are not attached to it. The retina may become detached (if untreated, this leads to blindness).

Fovea centralis

Optic disk

Ganglion cells Inner nuclear layer

Lamina cribrosa Central retinal artery

Third neurons (ganglion cells)

Meninges

Outer nuclear layer

Subarachnoid space

Fig. 6.49 Optic disk (“blind spot”) and lamina cribrosa The unmyelinated axons of the third neurons (retinal ganglion cells) pass to a collecting point at the posterior pole of the eye. There they unite to form the optic nerve and leave the retina through numerous perforations in the sclera (lamina cribrosa). (Note: The optic disk has no photoreceptors and is therefore the physiological blind spot.) In the optic nerve, these axons are myelinated by oligodendrocytes. The optic nerve (CN II) is an extension of the diencephalon and therefore has all the coverings of the brain (dura mater, arachnoid, and pia mater). It is surrounded by a subarachnoid space that contains cerebrospinal fluid (CSF) and communicates with the subarachnoid spaces of the brain and spinal cord.

Pigment epithelium Blood vessels

Bruch membrane

Choroid

Fig. 6.50 Macula lutea and fovea centralis Temporal to the optic disk is the macula lutea. At its center is a funnelshaped depression approximately 1.5 mm in diameter, the fovea centralis, which is the site of maximum visual acuity. At this site the inner retinal layers are heaped toward the margin of the depression, so that the cells of the photoreceptors (just cones, no rods) are directly exposed to the incident light. This arrangement significantly reduces scattering of the light rays.

133

Regions of the Head

6. Orbit & Eye

Visual System (I): Overview & Geniculate Part

Optic nerve

Lateral ventricle

Optic tract

Optic nerve

Lateral geniculate body Optic radiation for lower visual field

Incident light

Third neuron: ganglion cells Second neuron: bipolar cells Impulse conduction

Striate area

A

Optic chiasm

Anterior temporal lobe

Optic radiation for upper visual field

Fig. 6.51 Overview of the visual pathway Left lateral view. The visual pathway extends from the eye, an anterior prolongation of the diencephalon, back to the occipital pole. Thus, it encompasses almost the entire longitudinal axis of the brain. The principal stations are as follows: Retina: The first three neurons of the visual pathway (B): • First neuron: photoreceptor rods and cones, located on the deep retinal surface opposite the direction of the incoming light (“inversion of the retina”). • Second neuron: bipolar cells. • Third neuron: ganglion cells whose axons are collected to form the optic nerve. Optic nerve (CN II), optic chiasm, and optic tract: This neural portion of the visual pathway is part of the central nervous system and is surrounded by meninges. Thus, the optic nerve is actually a tract rather than a true nerve. The optic nerves join below the base of the diencephalon to form the optic chiasm, which then divides into the two optic tracts. Each of these tracts divides in turn into a lateral and medial root.

B

First neuron: photoreceptor rods and cones

C

Stria of Gennari

Lateral geniculate body: Ninety percent of the axons of the third neuron (= 90 % of the optic nerve fibers) terminate in the lateral geniculate body on neurons that project to the striate area (visual cortex, see below). This is the geniculate part of the visual pathway. It is concerned with conscious visual perception and is conveyed by the lateral root of the optic tract. The remaining 10% of the third-neuron axons in the visual pathway do not terminate in the lateral geniculate body. This is the nongeniculate part of the visual pathway (medial root, see Fig. 6.56), and its signals are not consciously perceived. Optic radiation and visual cortex (striate area): The optic radiation begins in the lateral geniculate body, forms a band that winds around the inferior and posterior horns of the lateral ventricles, and terminates in the visual cortex or striate area (= Brodmann area 17). Located in the occipital lobe, the visual cortex can be grossly identified by a prominent stripe of white matter in the otherwise gray cerebral cortex (the stria of Gennari, see C). This white stripe runs parallel to the brain surface and is shown in the inset, where the gray matter of the visual cortex is shaded light red.

Nasal visual field of right eye Left half of visual field Right half of visual field

Temporal visual field of right eye Temporal retina Nasal retina

Fig. 6.52 Representation of each visual field in the contralateral visual cortex Superior view. The light rays in the nasal part of each visual field are projected to the temporal half of the retina, and those from the temporal part are projected to the nasal half. Because of this arrangement, the left half of the visual field projects to the visual cortex of the right occipital pole, and the right half projects to the visual cortex of the left occipital pole. For clarity, each visual field in the diagram is divided into two halves. Note: The axonal fibers from the nasal half of each retina cross to the opposite side at the optic chiasm and then travel with the uncrossed fibers from the temporal half of each retina.

Optic nerve (CN II) Optic chiasm Optic tract Lateral geniculate body Visual cortex (striate area)

134

Regions of the Head

Macular visual field

6. Orbit & Eye

Blind spot

Visual field

Fovea centralis Representation of visual field as determined by perimetry

Temporal crescent 1

Blind spot 2

Fig. 6.54 Informal visual field examination with the confrontation test The visual field examination is an essential step in the examination of lesions of the visual pathway (see Fig. 6.55). The confrontation test is an informal test in which the examiner (with an intact visual field) and the patient sit face-toface, cover one eye, and each fixes their gaze on the other’s open eye, creating identical visual axes. The examiner then moves his or her index finger from the outer edge of the visual field toward the center until the patient signals that he or she can see the finger. With this test the examiner can make a gross assessment as to the presence and approximate location of a possible visual field defect. The precise location and extent of a visual field defect can be determined by perimetry, in which points of light replace the examiner’s finger. The results of the test are entered in charts that resemble the small diagrams in Fig. 6.53.

3

4 5 6

7

Optic nerve

8

Optic chiasm Optic tract

Lateral geniculate body

Fig. 6.53 Geniculate part of visual pathway: topographic organization The visual field is divided into four quadrants: upper temporal, upper nasal, lower nasal, and lower temporal. The lower nasal quadrant is indented by the nose. The representation of this subdivision is continued into the visual cortex. Note: Only the left visual hemifield (blue) is shown here (compare to Fig. 6.52). 1 Visual hemifield: Each visual hemifield is divided into three zones (indicated by color shading): • Fovea centralis: The smallest and darkest zone is at the center of the visual field. It corresponds to the fovea centralis, the point of maximum visual acuity on the retina. The fovea centralis has a high receptor density; accordingly, a great many axons pass centrally from its receptors. It is therefore represented by a disproportionately large area in the visual cortex. • Macular visual field: The largest zone in the visual hemisphere; it also contains the blind spot. • Temporal crescent: The temporal, monocular part of the visual field. This corresponds to more peripheral portions of the retina that contain fewer receptors and therefore fewer axons, resulting in a smaller representational area in the visual cortex. 2 Retinal projection: All light that reaches the retina must pass through the narrow pupil, which functions like the aperture of a

9

camera. Up/down and nasal/temporal are therefore reversed when the image is projected on the retina. 3,4 Optic nerve: In the distal part of the optic nerve, the fibers that represent the macular visual field initially occupy a lateral position (3), then move increasingly toward the center of the nerve (4). 5 Optic chiasm: While traversing the optic chiasm, the fibers of the nasal retina of the optic nerve cross the midline to the opposite side. 6 Start of the optic tract: Fibers from the corresponding halves of the retinas unite (e.g., right halves of the left and right retinas in the right optic tract). The impulses from the left visual field (right retinal half) will therefore terminate in the right striate area. 7 End of the optic tract: Fibers are collected to form a wedge before entering the lateral geniculate body. 8 Lateral geniculate body: Macular fibers occupy almost half of the wedge. After the fibers are relayed to the fourth neuron, they project to the posterior end of the occipital pole (= visual cortex). 9 Visual cortex: There exists a point-to-point (retinotopic) correlation between the number of axons in the retina and the number of axons in the visual cortex (e.g., the central part of the visual field is represented by the largest area in the visual cortex, due to the large number of axons concentrated in the fovea centralis). The central lower half of the visual field is represented by a large area on the occipital pole above the calcarine sulcus; the central upper half of the visual field is represented below the sulcus.

135

Regions of the Head

6. Orbit & Eye

Visual System (II): Lesions & Nongeniculate Part

Temporal

Nasal

Right visual field

Left visual field

Nasal

Temporal

1

1

2

2

3

3 1 2

4

4

3 5

6

5

5

4

7

7

6

7

Fig. 6.55 Visual field defects and lesions of the visual pathway Circles represent the perceived visual disturbances (scotomas, or areas of darkness) in the left and right eyes. These characteristic visual field defects (anopias) result from lesions at specific sites along the visual pathway. Lesion sites are illustrated in the left visual pathway as red wedges. The nature of the visual field defect often points to the location of the lesion. Note: Lesions past the optic chiasm will all be homonymous (same visual field in both eyes). 1 Unilateral optic nerve lesion: Blindness (amaurosis) in the affected eye. 2 Lesion of optic chiasm: Bitemporal hemianopia (think of a horse wearing blinders). Only fibers from the nasal portions of the retina (representing the temporal visual field) cross in the optic chiasm. 3 Unilateral optic tract lesion: Contralateral homonymous hemianopia. The lesion interrupts fibers from the temporal portion of the retina on the ipsilateral side and nasal portions of the retina on the contralateral side. The patient therefore has visual impairment of the same visual hemisphere in both eyes.

136

6

4 Unilateral lesion of the optic radiation in the anterior temporal lobe: Contralateral upper quadrantanopia (“pie in the sky” deficit). Lesions in the anterior temporal lobe affect only those fibers winding under the inferior horn of the lateral ventricle (see Fig. 6.51). These fibers represent only the upper half of the visual field (in this case the nasal portion). 5 Unilateral lesion of the optic radiation in the parietal lobe: Contralateral lower quadrantanopia. Fibers from the lower half of the visual field course superior to the lateral ventricle in the parietal lobe. 6 Occipital lobe lesion: Homonymous hemianopia. The lesion affects the optic radiations from both the upper and lower visual fields. However, as the optic radiation fans out widely before entering the visual cortex, foveal vision is often spared. These lesions are most commonly due to intracerebral hemorrhage; the visual field defects vary considerably with the size of the hemorrhage. 7 Occipital pole lesion (confined to cortical area): Homonymous hemianopic central scotoma. The cortical areas of the occipital pole represent the macula.

Regions of the Head

Suprachiasmatic nucleus

6. Orbit & Eye

Visual cortex (striate area)

Pulvinar of thalamus

Superior colliculus

Optic radiation Pretectal area Lateral geniculate body

Terminal nuclei

Reticular formation

Fig. 6.56 Nongeniculate part of the visual pathway Approximately 10% of the axons of the optic nerve do not terminate on neurons in the lateral geniculate body for projection to the visual cortex. They continue along the medial root of the optic tract, forming the nongeniculate part of the visual pathway. The information from these fibers is not processed at a conscious level but plays an important role in the unconscious regulation of various vision-related processes and in visually mediated reflexes (e.g., the afferent limb of the pupillary light reflex). Axons from the nongeniculate part of the visual pathway terminate in the following regions: • Axons to the superior colliculus transmit kinetic information that is necessary for tracking moving objects by unconscious eye and head movements (retinotectal system). • Axons to the pretectal area transmit afferents for pupillary responses and accommodation reflexes (retinopretectal system). Subdivision

Afferent fibers

Efferent fibers

Optic nerve (CN II)

Oculomotor nerve (CN III) Trigeminal nerve (CN V)

Vestibulocochlear nerve (CN VIII)

Pupillary reflex Vestibuloocular reflex

Facial nerve (CN VII) Corneal reflex

• •

•

•

into specific nuclei has not yet been accomplished in humans, and so the term “area” is used. Axons to the suprachiasmatic nucleus of the hypothalamus influence circadian rhythms. Axons to the thalamic nuclei (optic tract) in the tegmentum of the mesencephalon and to the vestibular nuclei transmit afferent fibers for optokinetic nystagmus (= jerky, physiological eye movements during the tracking of fast-moving objects). This has also been called the “accessory visual system.” Axons to the pulvinar of the thalamus form the visual association cortex for oculomotor function (neurons are relayed in the superior colliculus). Axons to the parvocellular nucleus of the reticular formation function during arousal.

Fig. 6.57 Brainstem reflexes Brainstem reflexes are important in the examination of comatose patients. Loss of all brainstem reflexes is considered evidence of brain death. Three of these reflexes are described below: Pupillary reflex: The pupillary reflex relies on the nongeniculate parts of the visual pathway (see Fig. 6.59). The afferent fibers for this reflex come from the optic nerve, which is an extension of the diencephalon. The efferents for the pupillary reflex come from the accessory nucleus of the oculomotor nerve (CN III), which is located in the brainstem. Loss of the pupillary reflex may signify a lesion of the diencephalon (interbrain) or mesencephalon (midbrain). Vestibulo-ocular reflex: Irrigating the ear canal with cold water in a normal individual evokes nystagmus that beats toward the opposite side (afferent fibers are conveyed in the vestibulocochlear nerve [CN VIII], efferent fibers in the oculomotor nerve [CN III]). When the vestibulo-ocular reflex is absent in a comatose patient, it is considered a poor sign because this reflex is the most reliable clinical test of brainstem function. Corneal reflex: This reflex is not mediated by the visual pathway. The afferent fibers for the reflex (elicited by stimulation of the cornea, as by touching it with a sterile cotton wisp) are conveyed in the trigeminal nerve (CN V) and the efferent fibers (contraction of the orbicularis oculi in response to corneal irritation) in the facial nerve (CN VII). The relay center for the corneal reflex is located in the pontine region of the brainstem.

137

Regions of the Head

6. Orbit & Eye

Visual System (III): Reflexes

Ciliaris Pupillary sphincter Medial rectus Short ciliary nerves

Ciliary ganglion

Optic nerve Optic tract

Oculomotor nerve

Perlia’s nucleus

Lateral geniculate body

Nucleus of oculomotor nerve (medial rectus)

Pretectal area

Area 19 (secondary visual cortex)

Edinger-Westphal nuclei

Area 17 (primary visual cortex) Area 18

Fig. 6.58 Pathways for convergence and accommodation When the distance between the eyes and an object decreases, three processes must occur in order to produce a sharp, three-dimensional visual impression (the first two are simultaneous): 1. Convergence (red): The visual axes of the eyes move closer together. The two medial rectus muscles contract to move the ocular axis medially. This keeps the image of the approaching object on the fovea centralis. 2. Accommodation: The lenses adjust their focal length. The curvature of the lens is increased to keep the image of the object sharply focused on the retina. The ciliary muscle contracts, which relaxes the tension on the lenticular fibers. The intrinsic pressure of the lens then causes it to assume a more rounded shape. (Note: The lens is flattened by the contraction of the lenticular fibers, which are attached to the ciliary muscle.) 3. Pupillary constriction: The pupil is constricted by the pupillary sphincter to increase visual acuity. Convergence and accommodation may be conscious (fixing the gaze on a near object) or unconscious (fixing the gaze on an approaching automobile). Pathways: The pathways can be broken into three components: 1. Geniculate visual pathway (purple): Axons of the first neurons (photoreceptors) and second neurons (bipolar cells) relay sensory information to the third neurons (retinal ganglion cells), which course in the optic nerve (CN II) to the lateral geniculate body. There they syn-

138

apse with the fourth neuron, whose axons project to the primary visual cortex (area 17). 2. Visual cortexes to cranial nerve nuclei: Interneurons (black) connect the primary (area 17) and secondary (area 19) visual cortexes. Synaptic relays (red) connect area 19 to the pretectal area and ultimately Perlia’s nucleus (yellow), located between the two EdingerWestphal (visceral oculomotor) nuclei (green). 3. Cranial nerves: At Perlia’s nucleus, the pathway for convergence diverges with the pathways for accommodation and pupillary constriction: • Convergence: Neurons relay impulses to the somatomotor nucleus of the oculomotor nerve, whose axons pass directly to the medial rectus muscle via the oculomotor nerve (CN III). • Accommodation and pupillary constriction: Neurons relay impulses to the Edinger-Westphal nucleus, whose preganglionic parasympathetic axons project to the ciliary ganglion. After synapsing in the ciliary ganglion, the postganglionic axons pass either to the ciliary muscle (accommodation) or the pupillary sphincter (pupillary constriction) via the short ciliary nerves. Note: The pupillary sphincter light response is abolished in tertiary syphilis, while accommodation (ciliary muscle) and convergence (medial rectus) are preserved. This phenomenon, called an Argyll Robertson pupil, indicates that the connections to the ciliary and pupillary sphincter muscles are mediated by different tracts, although the anatomy of these tracts is not yet fully understood.

Regions of the Head

6. Orbit & Eye

Pupillary sphincter

Short ciliary nerves Ciliary ganglion Optic nerve Oculomotor nerve (parasympathetic portion)

Optic tract

Lateral geniculate body

Visceral oculomotor (Edinger-Westphal) nuclei

Medial geniculate body

Fig. 6.59 Pupillary light reflex The pupillary light reflex enables the eye to adapt to varying levels of brightness. When a large amount of light enters the eye (e.g., beam of a headlight), the pupil constricts to protect the photoreceptors in the retina; when the light fades, the pupil dilates. This reflexive pathway takes place without conscious input via the nongeniculate part of the visual pathway. The reflex can be broken into components: 1. Afferent limb: The first (photoreceptor) and second (bipolar) neurons relay sensory information to the third (retinal ganglion) neurons, which combine to form the optic nerve (CN II). Most third neurons (purple) synapse at the lateral geniculate body (geniculate part of the visual pathway). The third neurons responsible for the light reflex (blue) synapse at the pretectal area in the medial root of the optic tract (nongeniculate part of the visual pathway). Fourth neurons from the pretectal area pass to the parasympathetic Edinger-Westphal nuclei. Note: Because both nuclei are innervated, a consensual light response can occur (contraction of one pupil will cause contraction of the other). 2. Efferent limb: Fifth neurons from the Edinger-Westphal nuclei (preganglionic parasympathetic neurons) synapse in the ciliary ganglion. Sixth neurons (postganglionic parasympathetic neurons) pass to the pupillary sphincter via the short ciliary nerves. Loss of light response: Because fourth neurons from the pretectal area pass to both Edinger-Westphal nuclei, a consensual light response can occur (contraction of one pupil will cause contraction of the other). The light response must therefore be tested both directly and indirectly:

Pretectal area

• Direct light response: Tested by covering both eyes of the conscious, cooperative patient and then uncovering one eye. After a short latency period, the pupil of the light-exposed eye will contract. • Indirect light response: Tested by placing the examiner’s hand on the bridge of the patient’s nose, shading one eye from the beam of a flashlight while shining it into the other eye. The object is to test whether shining the light into one eye will cause the pupil of the shaded eye to contract as well (consensual light response). Lesions can occur all along the pathway for the pupillary light reflex. The direct and indirect light responses can be used to determine the level: • Unilateral optic nerve lesion: This produces blindness on the affected side. If the patient is unconscious or uncooperative, the light responses can determine the lesion, as the afferent limb of the pupillary light reflex is lost. Affected side: No direct light response and no consensual light response on the opposite side. Unaffected side: Direct light response and consensual light response on the opposite (affected) side. Because the efferent limb of the reflex is not mediated by the optic nerve, the functional afferent limb can bypass the impaired afferent limb. • Lesion of the parasympathetic Edinger-Westphal nucleus or the ciliary ganglion: The efferent limb of the pupillary light reflex is lost. Affected side: No direct or indirect pupillary light response on the opposite side. Unaffected side: Direct light response, no indirect light response on the opposite (affected) side. • Lesion of the optic radiation or visual cortex (geniculate part of the visual pathway): Intact pupillary reflex (direct and indirect light response on both sides).

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Regions of the Head

6. Orbit & Eye

Visual System (IV): Coordination of Eye Movement

Rostral interstitial nucleus of medial longitudinal fasciculus (riMLF)

Nucleus of oculomotor nerve Nucleus of trochlear nerve

Mesencephalic reticular formation (MRF)

Medial longitudinal fasciculus (MLF)

Paramedian pontine reticular formation (PPRF)

Nucleus of abducent nerve

Nucleus prepositus hypoglossi

riMLF A

III

IV

PPRF

B

Fig. 6.60 Oculomotor nuclei and connections in the brainstem A Midsagittal section viewed from left side. B Circuit diagram showing the supranuclear organization of eye movements. The extraocular muscles receive motor innervation from the oculomotor (CN III), trochlear (CN IV), and abducent (CN VI) nerves. The concerted movement of the extraocular muscles allows for shifting of gaze, the swift movement of the visual axis toward the intended target. These rapid, precise, “ballistic” eye movements are called saccades. They are preprogrammed and, once initiated, cannot be altered until the end of the saccadic movement. The nuclei of CN III, IV, and VI (red) are involved in these saccadic movements. They are interconnected for this purpose by the medial longitudinal fasciculus (MLF, blue). Because these complex movements involve all the extraocular muscles and their associated nerves, the activity of the nuclei must be coordinated at a higher, or supranuclear, level. For example, gazing to the right requires four concerted movements:

140

• • • •

PPRF

VI

Contract right lateral rectus (CN VI nucleus activated) Relax right medial rectus (CN III nucleus inhibited) Relax left lateral rectus (CN VI nucleus inhibited) Contract left medial rectus (CN III nucleus activated)

These conjugate eye movements are coordinated by premotor nuclei (purple) in the mesencephalic reticular formation (green). Horizontal gaze movements are programmed in the nuclear region of the paramedian pontine reticular formation (PPRF). Vertical gaze movements are programmed in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). Both gaze centers establish bilateral connections with the nuclei of CN III, IV, and VI. The tonic signals for maintaining the new eye position originate from the nucleus prepositus hypoglossi.

Regions of the Head

6. Orbit & Eye

Nucleus of oculomotor nerve (CN III) Nucleus of trochlear nerve (CN IV)

Corticonuclear fibers

Cerebral aqueduct Medial longitudinal fasciculus

Corticospinal tract

Nucleus of abducent nerve (CN VI)

Right

Left

Internuclear ophthalmoplegia (red arrows: abducting nystagmus)

Gaze to the right

Convergence A Anterior view. Left Medial rectus (not activated)

Right

Lateral rectus (intact)

Oculomotor nerve (CN III)

Abducent nerve (CN VI)

Medial longitudinal fasciculus

Nucleus of oculomotor nerve

Fig. 6.61 Course of the MLF in the brainstem Midsagittal section viewed from the left side. The MLF runs anterior to the cerebral aqueduct on both sides and continues from the mesencephalon to the cervical spinal cord. It transmits fibers for the coordination of conjugate eye movements. A lesion of the MLF results in internuclear ophthalmoplegia (see Fig. 6.62).

Fig. 6.62 Internuclear ophthalmoplegia The MLF interconnects the oculomotor nuclei and also connects them with the opposite side. When this “information highway” is interrupted, internuclear ophthalmoplegia develops. This type of lesion most commonly occurs between the nuclei of the abducent and the oculomotor nerves. It may be unilateral or bilateral. Typical causes are multiple sclerosis and diminished blood flow. The lesion is manifested by the loss of conjugate eye movements. With a lesion of the left MLF, as shown here, the left medial rectus muscle is no longer activated during gaze to the right. The eye cannot be moved inward on the side of the lesion (loss of the medial rectus), and the opposite eye goes into an abducting nystagmus (lateral rectus is intact and innervated by the abducent nerve). Reflex movements such as convergence are not impaired, as there is no peripheral or nuclear lesion, and this reaction is not mediated by the MLF.

Nucleus of trochlear nerve

Area 8 (frontal gaze center) Lesion

Nucleus of abducent nerve

B Superior view.

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Regions of the Head

7. Nose & Nasal Cavity

Nose: Nasal Skeleton

Nasomaxillary suture

Major alar cartilage, lateral crus

Glabella Nasion

Major alar cartilage, medial crus

Nasal bone Frontal process of maxilla

Naris

Lateral nasal cartilage

Nasal ala

Septal cartilage

Major alar cartilage

Anterior nasal spine Minor alar cartilages

Fig. 7.1 Skeleton of the external nose Left lateral view. The skeleton of the nose is composed of bone, cartilage, and connective tissue. Its upper portion is bony and frequently involved in midfacial fractures, whereas its lower, distal portion is cartilaginous and therefore more elastic and less susceptible to injury. The proximal lower portion of the nostrils (alae) is composed of connective tissue with small embedded pieces of cartilage. The lateral nasal cartilage is a winglike lateral expansion of the cartilaginous part of the nasal septum rather than a separate piece of cartilage.

Frontal bone

Ethmoid bone

Sphenoid bone

Fig. 7.2 Nasal cartilage Inferior view. Viewed from below, each of the major alar cartilages is seen to consist of a medial and lateral crus. This view also displays the two nares, which open into the nasal cavities. The right and left nasal cavities are separated by the nasal septum, whose inferior cartilaginous portion is just visible in the diagram.

Frontal bone

Ethmoid bone, perpendicular plate

Sphenoid bone

Nasal bone

Nasal bone Occipital bone

Lacrimal bone

Occipital bone

Septal cartilage

Vomer Inferior nasal concha Incisive canal

Major alar cartilage Palatine bone Maxilla

Fig. 7.3 Bones of the lateral wall of the right nasal cavity Left lateral view. The lateral wall of the right nasal cavity is formed by six bones: the maxilla, nasal bone, ethmoid bone, inferior nasal concha, palatine bone, and sphenoid bone. Of the nasal concha, only the inferior is a separate bone; the middle and superior conchae are parts of the ethmoid bone.

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Palatine bone Maxilla

Fig. 7.4 Bones of the nasal septum Parasagittal section. The nasal septum is formed by six bones. The ethmoid and vomer bones are the major components of the septum. The sphenoid bone, palatine bone, maxilla, and nasal bone (roof of the septum) contribute only small bony projections to the nasal septum.

Regions of the Head

Anterior cranial fossa

Cribriform plate

7. Nose & Nasal Cavity

Superior meatus

Frontal sinus Crista galli

Sphenoid bone, lesser wing

Frontal bone

Middle cranial fossa

Nasal bone

Hypophyseal fossa

Lacrimal bone Sphenoid sinus

Frontal process of maxilla

Superior concha (ethmoid bone) Body of sphenoid bone

Anterior nasal aperture

Pterygoid process, medial plate Choana (posterior nasal aperture) Middle meatus Pterygoid process, lateral plate Inferior concha (independent bone) Palatine process of maxilla

Palatine bone, horizontal plate Inferior meatus

Middle concha (ethmoid bone)

Fig. 7.5 Lateral wall of the right nasal cavity Medial view. Air enters the bony nasal cavity through the anterior nasal aperture and travels through the three nasal passages: the superior meatus, middle meatus, and inferior meatus, which are the spaces infero-

Anterior cranial fossa

lateral to the superior, middle, and inferior conchae, respectively. Air leaves the nose through the choanae (posterior nasal apertures), entering the nasopharynx.

Cribriform plate

Crista galli Sphenoid sinus

Frontal sinus Nasal bone

Hypophyseal fossa

Ethmoid bone, perpendicular plate

Sphenoid crest Vomer

Septal cartilage

Choana

Major alar cartilage, medial crus

Posterior process Nasal crest

Palatine bone, horizontal plate

Incisive canal

Oral cavity

Palatine process of maxilla

Fig. 7.6 Nasal septum Parasagittal section viewed from the left side. The left lateral wall of the nasal cavity has been removed with the adjacent bones. The nasal septum consists of an anterior septal cartilage and a posterior bony part composed of several bones. The posterior process of the carti-

laginous septum extends deep into the bony septum. Deviations of the nasal septum are common and may involve the cartilaginous part of the septum, the bony part, or both. Cases in which the septal deviation is sufficient to cause obstruction of nasal breathing can be surgically corrected.

143

Regions of the Head

7. Nose & Nasal Cavity

Nose: Paranasal Sinuses

Frontal sinus

Ethmoid air cells

Frontal sinus

Ethmoid air cells

Age 20 Age 12 Age 8 Age 1

Age 4

Age 4

Age 1

Age 8 Age 12 Age 20 Age 60+ Maxillary sinus

A

B

Maxillary sinus

Sphenoid sinus

Fig. 7.7 Projection of the paranasal sinuses onto the skull A Anterior view. B Lateral view. The paranasal sinuses are air-filled cavities that reduce the weight of the skull. They are subject to inflammation that may cause pain over the affected sinus (e.g., frontal headache due to frontal sinusitis). Knowing the location and sensory supply of the sinuses is helpful in making the correct diagnosis.

Anterior cranial fossa

Cribriform plate

Fig. 7.8 Pneumatization of the maxillary and frontal sinuses Anterior view. The frontal and maxillary sinuses develop gradually during the course of cranial growth (pneumatization), unlike the ethmoid air cells, which are already pneumatized at birth. As a result, sinusitis in children is most likely to involve the ethmoid air cells (with risk of orbital penetration: red, swollen eye).

Orifices of posterior ethmoid air cells

Sphenoethmoidal recess

Frontal sinus

Superior nasal concha (cut)

Crista galli Frontal bone

Hypophyseal fossa

Nasal bone

Sphenoid sinus

Frontonasal duct Sphenopalatine foramen

Ethmoid bulla

Sphenoid bone

Lacrimal bone Uncinate process Frontal process of maxilla Semilunar hiatus Inferior nasal concha (cut)

Pterygoid process, medial plate

Opening of nasolacrimal canal Palatine process of maxilla A

Oral cavity

Maxillary hiatus

Palatine bone, perpendicular plate

Fig. 7.9 Lateral wall of the right nasal cavity Left lateral view of midline section with nasal conchae removed to display the openings of the nasolacrimal duct and paranasal sinuses. A Opened nasal wall. B Drainage of the paranasal sinuses. See Table 7.1.

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Cut edge of middle nasal concha (ethmoid bone)

B

Regions of the Head

Anterior cranial fossa

Cribriform plate

Crista galli

Frontal sinus

7. Nose & Nasal Cavity

Ethmoid bone, perpendicular plate Superior meatus and concha

Ethmoid bone, orbital plate

Nasal septum

Nasal cavity

Orbit Middle meatus and concha

Middle ethmoid air cells

Ostium of maxillary sinus

Maxilla

Uncinate process

Inferior meatus

Maxillary sinus

Inferior concha

Vomer

Fig. 7.10 Bony structure of the paranasal sinuses Anterior view. The central structure of the paranasal sinuses is the ethmoid bone (red). Its cribriform plate forms a portion of the anterior skull base. The frontal and maxillary sinuses are grouped around the ethmoid bone. The inferior, middle, and superior meatuses of the nasal cavity are bounded by the accordingly named conchae. The bony ostium of the maxillary sinus opens into the middle meatus, lateral to the middle concha. Below the middle concha and above the maxillary sinus ostium is the ethmoid bulla, which con-

Table 7.1 Drainage of the paranasal sinuses and nasolacrimal duct Structure

Nasal passage

Nasolacrimal duct (red) via nasolacrimal canal

Inferior meatus

Frontal sinus (yellow) via frontonasal duct

Middle meatus

Palatine process of maxilla

tains the middle ethmoid air cells. At its anterior margin is a bony hook, the uncinate process, which bounds the maxillary sinus ostium anteriorly. The middle concha is a useful landmark in surgical procedures on the maxillary sinus and anterior ethmoid. The lateral wall separating the ethmoid bone from the orbit is the paper-thin orbital plate (= lamina papyracea). Inflammatory processes and tumors may penetrate this thin plate in either direction. Note: The maxilla forms the floor of the orbit and roof of the maxillary sinus. In addition, roots of the maxillary dentition may project into the maxillary sinus.

Maxillary sinus Mucosal folds on the middle turbinate

Septum Cavernous sinus

Sphenoid sinus Pituitary gland

Internal carotid artery

Fig. 7.11 Nasal cavity and paranasal sinuses Transverse section viewed from above. The mucosal surface anatomy has been left intact to show how narrow the nasal passages are. Even relatively mild swelling of the mucosa may obstruct the nasal cavity, impeding aeration of the paranasal sinuses. The pituitary gland, located behind the sphenoid sinus in the hypophyseal fossa, is accessible via transnasal surgical procedures.

Frontal sinus Orbit Nasal cavity Ethmoid air cells Middle concha

Nasal septum Maxillary sinus

Maxillary sinus (orange)

Inferior concha

Anterior and middle ethmoid air cells (green) Posterior ethmoid air cells (green)

Superior meatus

Sphenoid sinus (blue)

Sphenoethmoid recess

Fig. 7.12 Osteomeatal unit (complex) Coronal section. The osteomeatal unit (complex) is that part of the middle meatus into which the frontal and maxillary sinuses drain along with the anterior and middle ethmoid air cells. When the mucosa (ciliated respiratory epithelium) in the ethmoid air cells (green) becomes swollen due to inflammation (sinusitis), it blocks the flow of secretions from the frontal sinus (yellow) and maxillary sinus

(orange) in the osteomeatal unit (red). Because of this blockage, microorganisms also become trapped in the other sinuses, where they may incite an inflammation. Thus, whereas the anatomical focus of the disease lies in the ethmoid air cells, inflammatory symptoms are also manifested in the frontal and maxillary sinuses. In patients with chronic sinusitis, the narrow sites can be surgically widened to establish an effective drainage route.

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Regions of the Head

7. Nose & Nasal Cavity

Nasal Cavity

Crista galli

Ethmoid air cells

Orbit Vitreous body

Ethmoid bulla

Sclera

Perpendicular plate of ethmoid bone

Middle nasal concha

Infraorbital nerve

Maxilla

Maxillary sinus

Cartilaginous nasal septum

Inferior nasal concha

Vomer

Inferior nasal meatus Root of maxillary tooth

Palatine process of the maxilla

Alveolar process

Tongue

A

Oral cavity

Anterior ethmoid air cells Perpendicular plate of ethmoid bone

Lens Vitreous body

Medial rectus

Orbit

Lateral rectus Optic nerve Posterior ethmoid air cells

Temporalis

Sphenoid sinus

Internal carotid artery

Telencephalon, temporal lobe

Dorsum sellae

B

Fig. 7.13 Overview of the nose and paranasal sinuses A Coronal section, anterior view. B Transverse section, superior view. The nasal cavities and paranasal sinuses are arranged in pairs. The left and right nasal cavities are separated by the nasal septum and have an approximately triangular shape. Below the base of the triangle is the oral cavity. Note the relations of the infraorbital nerve and maxillary dentition to the maxillary sinus. The following paired paranasal sinuses are shown in the drawings:

146

• • • •

Frontal sinus Ethmoid air cells (ethmoid sinus*) Maxillary sinus Sphenoid sinus

The interior of each sinus is lined with ciliated respiratory epithelium (see p. 150). * The term ethmoid sinus has been dropped from the latest anatomical nomenclature, although it is still widely used by medical practitioners.

Regions of the Head

Sphenoid sinus

7. Nose & Nasal Cavity

Hypophyseal (pituitary) fossa Dorsum sellae

Frontal sinus

Clivus Pharyngeal tonsil

Nasal septum

Choana Torus tubarius Pharyngeal orifice of pharyngotympanic (auditory) tube

Incisive canal

Dens of axis Maxilla

Hard palate

Incisive foramen

Atlas (anterior arch)

Soft palate, palatine septum

Upper lip

A

Sphenoid sinus

Superior nasal concha

Sphenoethmoid recess

Middle nasal concha

Superior meatus Middle meatus

Pharyngeal tonsil Torus tubarius

Inferior nasal concha

Salpingopharyngeal fold

Limen nasi Nasal vestibule B

Inferior meatus

Pharyngeal recess

Pharyngeal orifice of pharyngotympanic (auditory) tube

Pharyngeal tonsil

Basilar part of occipital bone Middle nasal concha

Pharyngeal recess

Vomer

Choana (“posterior naris”)

Inferior nasal concha Soft palate

Palatopharyngeal arch Uvula

Tongue base with lingual tonsil C

Palatine tonsil Epiglottis

Fig. 7.14 Mucosa of the nasal cavity A Mucosa of the nasal septum, parasagittal section viewed from the left side. B Mucosa of the right lateral nasal wall, viewed from the left side. C Posterior view through the choanae into the nasal cavity. Although the medial wall of the nasal cavity is smooth, its lateral wall is raised into folds by the three conchae (superior, middle, and inferior concha), which increase the surface area of the nasal cavity, enabling it to warm and humidify the inspired air more efficiently. They also create turbulence, mixing olfactory stimulants (see p. 148 for olfactory nerve). The choanae (posterior nasal apertures) (C) are the posterior openings by which the nasal cavity communicates with the nasopharynx. Note the close proximity of the choanae to the pharyngotympanic (auditory) tube and pharyngeal tonsil.

147

Regions of the Head

7. Nose & Nasal Cavity

Nasal Cavity: Neurovascular Supply

Olfactory bulb

Cribriform plate

Olfactory tract (CN I)

Anterior ethmoidal artery (from ophthalmic artery)

Sphenoid sinus Basilar artery Medial superior posterior nasal branches (from CN V2)

Olfactory fibers (from CN V1) Anterior septal branches (from CN V1)

Posterior septal branches (from sphenopalatine artery)

Medial nasal branches (from CN V1)

Torus tubarius

Kiesselbach’s area

Choana

Septal branches of superior labial artery Incisive canal (with nasopalatine nerve and greater palatine artery)

Nasopalatine nerve (from CN V2) Incisive foramen

Fig. 7.15 Neurovasculature of the nasal septum Parasagittal section, left lateral view. The nasal septum is supplied anterosuperiorly by CN V1 and posteroinferiorly by CN V2. It receives blood primarily from branches of the ophthalmic and maxillary arteries, with contribution from the facial artery (septal branches of the superior labial artery).

Olfactory bulb (CN I) and olfactory fibers

Superior nasal concha

Posterior ethmoidal artery (from ophthalmic artery)

Posterosuperior nasal branches

Anterior ethmoidal artery (from ophthalmic artery) Middle nasal concha

Pterygopalatine ganglion

Posteroinferior nasal branches and lateral posterior nasal arteries (descending palatine artery)

Descending palatine artery and nerve Greater and lesser palatine nerves

Inferior nasal concha Incisive canal (with nasopalatine nerve and greater palatine artery ) Greater palatine artery and nerve

Fig. 7.16 Neurovasculature of the lateral nasal wall Left medial view of right lateral nasal wall. The pterygopalatine ganglion (located in the pterygopalatine fossa but exposed here) is an important relay in the parasympathetic nervous system. The CN V2 nerve fibers passing through it pass to the small nasal glands of the nasal con-

148

Lesser palatine artery and nerve

Uvula

chae, along with palatine glands. The anterosuperior portion of the lateral nasal wall is supplied by branches of the ophthalmic artery and CN V1. Note: Olfactory fibers (CN I) pass through the cribriform plate to the olfactory mucosa at the level of the superior concha.

Regions of the Head

Note: The ophthalmic artery arises from the internal carotid artery and travels with the optic nerve (CN II), entering the orbit via the optic canal. Within the orbit it gives off the ethmoidal branches, which enter the nasal cavity via the ethmoid bone.

Fig. 7.17 Arteries of the nasal septum Left lateral view. The vessels of the nasal septum arise from branches of the external and internal carotid arteries. The anterior part of the septum contains a highly vascularized area called Kiesselbach’s area, which is supplied by vessels from both major arteries. This area is the most common site of significant nosebleed due to anastomoses.

Posterior ethmoidal artery

7. Nose & Nasal Cavity

Ophthalmic artery

Sphenopalatine artery via sphenopalatine foramen

Anterior ethmoidal artery Anterior septal branches

Maxillary artery Internal carotid artery

Kiesselbach’s area Nasal branch of greater palatine artery

Posterior septal branches

Septal branch of superior labial artery (facial artery) Frontal sinus

External carotid artery

Greater palatine artery

Cribriform plate

Descending palatine artery

Olfactory bulb (CN I)

Anterior ethmoidal nerve (CN V1)

Fig. 7.18 Nerves of the nasal septum Left mesial view of lateral septum. The nasal septum receives its general sensory innervation from branches of the trigeminal nerve (CN V). The anterosuperior part of the septum is supplied by branches of the ophthalmic division (CN V1) and the rest by branches of the maxillary division (CN V2). Bundles of olfactory nerve fibers (CN I) arise from receptors in the olfactory mucosa on the superior part of the septum, pass through the cribriform plate, and enter the olfactory bulb.

Olfactory fibers (CN I)

CN V2

Medial nasal branches (CN V1)

CN V1 Trigeminal ganglion (CN V) CN V3 Pterygopalatine ganglion in pterygopalatine fossa

Medial superior posterior nasal branches (CN V2) Vomer

Nasopalatine nerve (CN V2)

Posterior ethmoidal artery Anterior ethmoidal artery

Anterior ethmoidal nerve (CN V1)

Ophthalmic artery

Sphenopalatine Zygomatic foramen (opened) process of maxilla

Cribriform plate

Middle nasal concha

Sphenopalatine artery Descending palatine artery (gives rise to greater and lesser palatine arteries)

Lateral superior posterior nasal branches (CN V2)

External nasal branch

Pterygopalatine ganglion

Maxillary artery

Posteroinferior nasal branches (from desending palatine nerve)

Internal carotid artery Alar branches of lateral nasal artery

External carotid artery Greater palatine artery

Lateral posterior nasal arteries

Fig. 7.19 Arteries of the right lateral nasal wall Left mesial view of lateral nasal wall. The nasal wall is supplied primarily by branches of the ophthalmic artery (anterosuperiorly) and maxillary artery (posteroinferiorly), with contributions from the facial artery (alar branches of the lateral nasal artery).

Sphenoid sinus

Lesser palatine nerves

Lateral nasal branches Internal nasal branches

Inferior nasal concha

Greater palatine nerve

Fig. 7.20 Nerves of the right lateral nasal wall Left mesial view of lateral nasal wall. The nasal wall derives its sensory innervation from branches of the ophthalmic division (CN V1) and the maxillary division (CN V2). Receptor neurons in the olfactory mucosa send their axons in the olfactory nerve (CN I) to the olfactory bulb.

149

Regions of the Head

7. Nose & Nasal Cavity

Nose & Paranasal Sinuses: Histology & Clinical Anatomy

Middle nasal concha

Kinociliabearing epithelial cells

Pseudostratified ciliated epithelium (“respiratory epithelium”)

Semilunar hiatus

Goblet cells

Uncinate process Nasal septum, vomer

Maxillary sinus Inferior nasal concha with decongested mucosa

Congested mucosa of the inferior concha

Fig. 7.21 Functional states of the nasal mucosa Coronal section, anterior view. The function of the nasal mucosa is to warm and humidify the inspired air and mix olfactory stimulants. This is accomplished by an increase of blood flow through the mucosa, placing it in a congested (swollen) state. The mucous membranes are not simultaneously congested on both sides, but undergo a normal cycle of congestion and decongestion that lasts approximately six hours (the right side is decongested in the drawing). Examination of the nasal cavity can be facilitated by first administering a decongestant to shrink the mucosa.

Frontal sinus

Fibrous lamina propria

Ethmoid sinus

Fig. 7.22 Histology of the nasal mucosa The surface of the pseudostratified respiratory epithelium of the nasal mucosa consists of kinocilia-bearing cells and goblet cells, which secrete their mucus into a watery film on the epithelial surface. Serous and seromucous glands are embedded in the connective tissue and also release secretions into the superficial fluid film. The directional fluid flow produced by the cilia is an important component of the nonspecific immune response. If coordinated beating of the cilia is impaired, the patient will suffer chronic recurring infections of the respiratory tract.

Ostium

Sphenoid sinus

Posterior wall of frontal sinus

Choanae

Nasopharynx Maxillary sinus

Fig. 7.23 Normal drainage of secretions from the paranasal sinus Left lateral view. The beating cilia propel the mucous blanket over the cilia and through the choana into the nasopharynx, where it is swallowed.

150

A

Medial wall of maxillary sinus

Ostium

B

Ethmoid infundibulum

Fig. 7.24 Ciliary beating and fluid flow in the right maxillary and frontal sinuses Schematic coronal sections of the right maxillary sinus (A) and frontal sinus (B), anterior view. Beating of the cilia produces a flow of fluid in the paranasal sinuses that is always directed toward the sinus ostium. This clears the sinus of particles and microorganisms that are trapped in the mucous layer. If the ostium is obstructed due to swelling of the mucosa, inflammation may develop in the affected sinus (sinusitis). This occurs most commonly in the osteomeatal complex of the middle meatus.

Regions of the Head

7. Nose & Nasal Cavity

Trocar

Endoscope

I

Fig. 7.26 Endoscopy of the maxillary sinus Anterior view. The maxillary sinus is not accessible to direct inspection and must therefore be examined with an endoscope. To enter the maxillary sinus, the examiner pierces the thin bony wall below the inferior concha with a trocar and advances the endoscope through the opening. The scope can then be angled and rotated to inspect all of the mucosal surfaces.

A

Anterior and posterior ethmoidal arteries

II

Ophthalmic artery

Kiesselbach’s area

Sphenopalatine artery Maxillary artery Internal carotid artery External carotid artery

A

Middle concha

Pharyngeal tonsil

Choana

Posterior margin of septum

Pharyngeal orifice of eustachian tube

Inferior concha

Ophthalmic artery

Angular artery

Orbit

Soft palate

Base of tongue

Facial artery B

Anterior and posterior ethmoidal arteries

Uvula

Fig. 7.25 Anterior and posterior rhinoscopy A Anterior rhinoscopy is a procedure for inspection of the nasal cavity. Two different positions (I, II) are used to ensure that all of the anterior nasal cavity is examined. B In posterior rhinoscopy, the choanae and pharyngeal tonsil are accessible to clinical examination. The rhinoscope can be angled and rotated to demonstrate the structures shown in the composite image. Today the rhinoscope is frequently replaced by an endoscope.

B

Infraorbital foramen

Fig. 7.27 Sites of potential arterial ligation for the treatment of severe nosebleed If a severe nosebleed cannot be controlled with ordinary intranasal packing, it may be necessary to ligate relatively large arterial vessels. The following arteries may be ligated due to the rich aterial anastomoses in the blood supply to the nasal cavity: • Maxillary artery or sphenopalatine artery (A) • Both ethmoidal arteries in the orbit (B)

151

Regions of the Head

7. Nose & Nasal Cavity

Olfactory System (Smell)

Medullary stria of thalamus Longitudinal striae

Interpeduncular nucleus

Medial olfactory stria

Habenular nuclei Tegmental nucleus

Olfactory bulb

Uncus, with amygdala below

Olfactory fibers

Olfactory bulb

Reticular formation Dorsal longitudinal fasciculus Lateral olfactory stria A

Olfactory mucosa

• Some of the axons of the olfactory tract run in the lateral olfactory stria to the olfactory centers: the amygdala, semilunar gyrus, and ambient gyrus. The prepiriform area (Brodmann area 28) is considered to be the primary olfactory cortex in the strict sense. It contains the third neurons of the olfactory pathway. Note: The prepiriform area is shaded in B, lying at the junction of the basal side of the frontal lobe and the medial side of the temporal lobe. • Other axons of the olfactory tract run in the medial olfactory stria to nuclei in the septal (subcallosal) area, which is part of the limbic system, and to the olfactory tubercle, a small elevation in the anterior perforated substance. • Yet other axons of the olfactory tract terminate in the anterior olfactory nucleus, where the fibers that cross to the opposite side branch off and are relayed. This nucleus is located in the olfactory trigone, which lies between the two olfactory striae and in front of the anterior perforated substance.

152

Prepiriform area

Medial olfactory stria

Prepiriform area

Fig. 7.28 Olfactory system: olfactory mucosa and central connections Olfactory tract viewed in midsagittal section (A) and from below (B). The olfactory mucosa is located in the roof of the nasal cavity. The olfactory cells (= primary sensory cells) are bipolar neurons. Their peripheral receptor-bearing processes terminate in the epithelium of the nasal mucosa, and their central processes pass to the olfactory bulb. The olfactory bulb, where the second neurons of the olfactory pathway (mitral and tufted cells) are located, is considered an extension of the telencephalon. The axons of these second neurons pass centrally as the olfactory tract. In front of the anterior perforated substance, the olfactory tract widens to form the olfactory trigone and splits into the lateral and medial olfactory striae.

Olfactory tract

Olfactory trigone

Lateral olfactory stria

Amygdala (deep to brain surface)

Ambient gyrus B

Semilunar gyrus

Diagonal stria

Anterior perforated substance

Note: None of these three tracts are routed through the thalamus. Thus, the olfactory system is the only sensory system that is not relayed in the thalamus before reaching the cortex. There is, however, an indirect route from the primary olfactory cortex to the neocortex passing through the thalamus and terminating in the basal forebrain. The olfactory signals are further analyzed in these basal portions of the forebrain (not shown). The olfactory system is linked to other brain areas well beyond the primary olfactory cortical areas, with the result that olfactory stimuli can evoke complex emotional and behavioral responses. Noxious smells induce nausea, and appetizing smells evoke watering of the mouth. Presumably these sensations are processed by the hypothalamus, thalamus, and limbic system via connections established mainly by the medial forebrain bundle and the medullary striae of the thalamus. The medial forebrain bundle distributes axons to the following structures: • • • •

Hypothalamic nuclei Reticular formation Salivatory nuclei Dorsal vagal nucleus

The axons that run in the medullary striae of the thalamus terminate in the habenular nuclei. This tract also continues to the brainstem, where it stimulates salivation in response to smell.

Regions of the Head

Olfactory fibers

7. Nose & Nasal Cavity

Olfactory bulb

Connective tissue

Cribriform plate

Basal cells Light cells

Submucosa

Dark cells

Basal cell

Olfactory cell

Supporting cell Olfactory cilia

A

Bowman gland

Fig. 7.29 Olfactory mucosa and vomeronasal (Jacobson’s) organ (VNO) The olfactory mucosa occupies an area of approximately 2 cm2 on the roof of each nasal cavity, and 107 primary sensory cells are concentrated in each of these areas (A). At the molecular level, the olfactory receptor proteins are located in the cilia of the sensory cells (B). Each sensory cell has only one specialized receptor protein that mediates signal transduction when an odorant molecule binds to it. Although humans are microsmatic, having a sense of smell that is feeble compared with other mammals, the olfactory receptor proteins still make up 2 % of the human genome. This underscores the importance of olfac tion in humans. The primary olfactory sensory cells have a life span of approximately 60 days and regenerate from the basal cells (lifelong division of neurons). The bundled central processes (axons) from hundreds of olfactory cells form olfactory fibers (A) that pass through the cribriform plate of the ethmoid bone and terminate in the olfactory bulb, which lies above the cribriform plate. The VNO (C) is located on both sides of the anterior nasal septum. It is an accessory olfactory organ and is generally considered vestigial in adult humans. However, it responds to steroids and evokes subconscious reactions in subjects (possibly influences the choice of a mate). Mate selection in many animal species is known to be mediated by olfactory impulses that are perceived in the VNO.

Axons Submucous gland Submucosa

Olfactory cells Bowman gland

Microvilli Cilia with receptor proteins

B

C

Mucus–water film

To/from opposite side Olfactory tract

Anterior olfactory nucleus

Olfactory bulb

Granule cell

Mitral cell

Apical dendrite Olfactory glomerulus

Periglomerular cells

Fig. 7.30 Synaptic patterns in an olfactory bulb Specialized neurons in the olfactory bulb, called mitral cells, form apical dendrites that receive synaptic contact from the axons of thousands of primary sensory cells. The dendrite plus the synapses make up the olfactory glomeruli. Axons from sensory cells with the same receptor protein form glomeruli with only one or a small number of mitral cells. The basal axons of the mitral cells form the olfactory tract. The axons that run in the olfactory tract project primarily to the olfactory cortex but are also distributed to other nuclei in the central nervous system. The axon collaterals of the mitral cells pass to granule cells: both granule cells and periglomerular cells inhibit the activity of the mitral cells, causing less sensory information to reach higher centers. These inhibitory processes are believed to heighten olfactory contrast, which aids in the more accurate perception of smells. The tufted cells, which also project to the primary olfactory cortex, are not shown.

Olfactory fibers

153

Regions of the Head

8. Temporal Bone & Ear

Temporal Bone

Parietal bone

Fig. 8.1 Temporal bone in the skull Left lateral view. The temporal bone is a major component of the base of the skull. It forms the capsule for the auditory and vestibular apparatus and bears the articular fossa of the temporomandibular joint (TMJ).

Temporal bone Occipital bone

Zygomatic bone

Sphenoid bone, greater wing Petrous pyramid

Mandibular fossa Squamous part

Styloid process

Squamous part

Tympanic part Tympanic part

B

A

Fig. 8.2 Parts of the left temporal bone A Left lateral view. B Inferior view. The temporal bone develops from four centers that fuse to form a single bone: • The squamous part, or temporal squama (light green), bears the articular fossa of the TMJ (mandibular fossa).

Chorda tympani

Facial nerve (CN VII)

Sigmoid sinus

Tympanic membrane Pharyngotympanic (auditory) tube Internal carotid artery Internal jugular vein

154

Petromastoid part

Petromastoid part

Mastoid process

• The petromastoid part, or petrous bone (pale green), contains the auditory and vestibular apparatus. • The tympanic part (darker green) forms large portions of the external auditory canal. • The styloid part (styloid process) develops from cartilage derived from the second branchial arch. It is a site of muscle attachment.

Mastoid air cells

Fig. 8.3 Clinically important relations in the temporal bone Left lateral view with projected structures. The petrous part of the temporal bone contains the tympanic cavity of the middle ear (see Fig. 8.15). The middle ear communicates with the nasopharynx via the pharyngotympanic (auditory) tube. During chronic suppurative otitis media, an inflammation of the middle ear, pathogenic bacteria from the nasopharynx may spread to the tympanic cavity and then to surrounding structures. Bacterial spread upward (through the roof of the tympanic cavity into the middle cranial fossa) may incite meningitis or a cerebral abscess of the temporal lobe. Invasion of the mastoid air cells may cause mastoiditis; invasion of the sigmoid sinus may cause sinus thrombosis. Passage into the facial nerve canal may cause facial paralysis. Bacteria may even pass through the mastoid air cells and into the overlying cerebrospinal fluid (CSF) spaces.

Regions of the Head

8. Temporal Bone & Ear

Postglenoid tubercle

Zygomatic process

Temporal surface

External acoustic opening Articular tubercle

Mastoid foramen

Mandibular fossa (TMJ)

External acoustic meatus

Petrotympanic fissure

Tympanomastoid fissure Styloid process

A

Zygomatic process

Petrous pyramid

Mastoid process Articular tubercle Groove for middle meningeal artery

Mandibular fossa Arcuate eminence

Carotid canal

External acoustic opening

Styloid process

Groove for superior petrosal sinus

Mastoid process

Jugular fossa (forms jugular foramen with occipital bone)

Petrous ridge

Mastoid (digastric) notch

Stylomastoid foramen Occipital groove

Zygomatic process

Mastoid foramen

B

Internal acoustic meatus Mastoid foramen

Petrous apex Carotid canal Bony canal for pharyngotympanic tube

C

Groove for sigmoid sinus

Styloid process

Fig. 8.4 Left temporal bone A Lateral view. The mandibular fossa articulates with the head of the mandible via an articular disk (TMJ). The external acoustic meatus is the opening of the external auditory canal, which communicates with the tympanic cavity (middle ear) within the petrous part via the intervening tympanic membrane. The mastoid part contains a mastoid foramen that conducts an emissary vein from the scalp to the sigmoid sinus (see C). The chorda tympani and anterior tympanic DUWHU\SDVVWKURXJKWKHPHGLDOSDUWRIWKHSHWURW\PSDQLFÀVVXUHWR enter the tympanic cavity. B Inferior view. The facial nerve (CN VII) emerges from the base of the skull via the stylomastoid foramen. The jugular fossa of the tem-

poral bone combines with the jugular process of the occipital bone to form the jugular foramen (containing the jugular bulb proximal to the internal jugular vein). C Medial view. The internal acoustic meatus conveys the facial (CN VII) and vestibulocochlear (CN VIII) nerves, along with the labyrinthine artery and vein. Note: The arcuate eminence marks the position of the anterior semicircular canal. A bony canal within the petrous part of the temporal bone connects the pharyngotympanic (auditory) tube to the nasopharynx (see Fig. 8.5). The petrous pyramid separates the posterior and middle cranial fossa.

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Regions of the Head

8. Temporal Bone & Ear

Ear: Overview & External Ear

External acoustic meatus

Arcuate eminence

Posterior semicircular canal

Lateral semicircular canal

Anterior semicircular canal Vestibule Vestibular root Cochlear root

Vestibulocochlear nerve (CN VIII)

Petrous apex Cochlea Malleus, head Temporal bone, petrous part Stapes Tensor tympani Tympanic cavity

Incus

External auditory canal

Pharyngotympanic (auditory) tube

Tympanic membrane

Styloid process

Mastoid process

External ear

A

Inner ear

Fig. 8.5 Auditory and vestibular apparatus in situ A Coronal section through the right ear, anterior view. B Auditory apparatus: external ear (yellow), middle ear (blue), and inner ear (green). The auditory and vestibular apparatus are located deep in the petrous part of the temporal bone. The auditory apparatus consists of the external ear, middle ear, and inner ear. Sound waves are captured by the auricle and travel through the external auditory canal to the tympanic membrane (the lateral boundary of the middle ear). The sound waves set the tympanic membrane into motion, and these mechanical vibrations are transmitted by the chain of auditory ossicles in the middle ear to the oval window, which leads into the inner ear. The ossicular chain induces vibrations in the membrane covering the oval window, and these in turn cause a fluid column in the inner ear to vibrate, setting receptor cells in motion. The transformation of sound waves into electrical impulses takes place in the inner ear, which is the actual organ of hearing. The external ear and middle ear, on the other hand, constitute the sound conduction apparatus. The organ of balance is the vestibular apparatus, which is also located in the auditory apparatus. It contains the semicircular canals for the perception of angular acceleration (rotational head movements) and the saccule and utricle for the perception of linear acceleration. Diseases of the vestibular apparatus produce dizziness (vertigo).

156

Middle ear

B

Regions of the Head

8. Temporal Bone & Ear

Crura of antihelix

Scaphoid fossa

Posterior auricular artery

Triangular fossa

Parietal branch Frontal branch

Cymba conchae External auditory canal

Helix

Superficial temporal artery

Tragus Intertragic incisure Antihelix

Antitragus Concha

Perforating branches

Anterior auricular arteries

Earlobe

Transverse facial artery

Fig. 8.6 Right auricle The auricle of the ear encloses a cartilaginous framework (auricular cartilage) that forms a funnel-shaped receptor for acoustic vibrations.

Maxillary artery Posterior auricular artery A

External carotid artery

Auricularis superior Helicis major Helicis minor

Auricularis posterior

External auditory canal

Antitragus

Tragus

Perforating branches Auricularis posterior

Anastomotic arcades

A

Posterior auricular artery Auricularis superior

Obliquus auriculae

Auricularis anterior

Transversus auriculae

External auditory canal

Insertions of auricularis posterior

B

Fig. 8.7 Cartilage and muscles of the auricle A Lateral view of the external surface. B Medial view of the posterior surface of the right ear. The skin (removed here) is closely applied to the elastic cartilage of the auricle (light blue). The muscles of the ear are classified as muscles of facial expression and, like the other members of this group, are supplied by the facial nerve (CN VII). Prominent in other mammals, the auricular muscles are vestigial in humans, with no significant function.

B

External carotid artery

Fig. 8.8 Arterial supply of the auricle Lateral view (A) and posterior view (B) of right auricle. The proximal and medial portions of the laterally directed anterior surface of the ear are supplied by the anterior auricular arteries, which arise from the superficial temporal artery. The other parts of the auricle are supplied by branches of the posterior auricular artery, which arises from the external carotid artery. These vessels are linked by extensive anastomoses, so operations on the external ear are unlikely to compromise the auricular blood supply. The copious blood flow through the auricle contributes to temperature regulation: dilation of the vessels helps dissipate heat through the skin. The lack of insulating fat predisposes the ear to frostbite, which is particularly common in the upper third of the auricle. The auricular arteries have corresponding veins that drain to the superficial temporal vein.

157

Regions of the Head

8. Temporal Bone & Ear

External Ear

Posterior zone

Anterior zone

External auditory canal

Superficial parotid lymph nodes

Mastoid lymph nodes (retroauricular)

Parotid fascia

Lower zone

Deep parotid lymph nodes Internal jugular vein

Fig. 8.9 Auricle and external auditory canal: lymphatic drainage Right ear, oblique lateral view. The lymphatic drainage of the ear is divided into three zones, all of which drain directly or indirectly into the deep cervical lymph nodes along the internal jugular vein. The lower zone drains directly into the deep cervical lymph nodes. The anterior zone first drains into the parotid lymph nodes, the posterior zone into the mastoid lymph nodes.

Parotid gland

Deep cervical lymph nodes

Facial nerve (CN VII)

Trigeminal nerve (CN V) via auriculotemporal nerve

Trigeminal nerve (CN V) via auriculotemporal nerve

Vagus nerve (CN X)

Vagus nerve (CN X)

Facial nerve (CN VII)

A

Cervical plexus via lesser occipital and great auricular nerves

Fig. 8.10 Sensory innervation of the auricle Right ear, lateral view (A) and posterior view (B). The auricular region has a complex nerve supply because, developmentally, it is located at the boundary between the cranial nerves (pharyngeal arch nerves) and branches of the cervical plexus. Three cranial nerves contribute to the innervation of the auricle: • Trigeminal nerve (CN V) • Facial nerve (CN VII; the skin area that receives sensory innervation from the facial nerve is not precisely known) • Vagus nerve (CN X)

158

B

Cervical plexus via lesser occipital and great auricular nerves

Two branches of the cervical plexus are involved: • Lesser occipital nerve (C 2) • Great auricular nerve (C 2, C 3) Note: Because the vagus nerve contributes to the innervation of the external auditory canal (auricular branch, see below), mechanical cleaning of the ear canal (by inserting an aural speculum or by irrigating the ear) may evoke coughing and nausea. The auricular branch of the vagus nerve passes through the mastoid canaliculus and through a space between the mastoid process and the tympanic part of the temporal bone (tympanomastoid fissure, see p. 155) to the external ear and external auditory canal.

Regions of the Head

8. Temporal Bone & Ear

Temporal bone, tympanic part

Malleus Sebaceous and cerumen glands

Incus Lateral ligament of malleus

Bony part of external auditory canal

Stapes Handle (manubrium)

Cartilaginous part of external auditory canal

Tympanic membrane

Fig. 8.11 External auditory canal, tympanic membrane, and tympanic cavity Right ear, coronal section, anterior view. The tympanic membrane (eardrum) separates the external auditory canal from the tympanic cavity of the middle ear. The external auditory canal is an S-shaped tunnel that is approximately 3 cm long with an average diameter of 0.6 cm. The outer third of the ear canal is cartilaginous. The inner two thirds of the canal are osseous, the wall being formed by the tympanic part

of the temporal bone. The cartilaginous part in particular bears numerous sebaceous and cerumen glands beneath the keratinized stratified squamous epithelium. The cerumen glands produce a watery secretion that combines with the sebum and sloughed epithelial cells to form a protective barrier (cerumen, “earwax”) that screens out foreign bodies and keeps the epithelium from drying out. If the cerumen absorbs water (e.g., after swimming), it may obstruct the ear canal (cerumen impaction), temporarily causing a partial loss of hearing.

Tympanic membrane

Malleolar prominence

Tympanic incisure

Posterior malleolar fold

Pars flaccida Anterior malleolar fold

Incus Stapes A

B

IV

I

Umbo

Head of mandible

Tympanic bone

C

Fig. 8.12 Curvature of the external auditory canal Right ear, anterior view (A) and transverse section (B). The external auditory canal is most curved in its cartilaginous portion. When the tympanic membrane is inspected with an otoscope, the auricle should be pulled backward and upward in order to straighten the cartilaginous part of the ear canal so that the speculum of the otoscope can be introduced (C). Note the proximity of the cartilaginous anterior wall of the external auditory canal to the TMJ. This allows the examiner to palpate movements of the mandibular head by inserting the small finger into the outer part of the ear canal.

Pars tensa Malleolar stria

III

II

Cone of light

Fig. 8.13 Tympanic membrane Right tympanic membrane, lateral view. The healthy tympanic membrane has a pearly gray color and an oval shape with an average surface area of approximately 75 mm2. It consists of a lax portion, the pars flaccida (Shrapnell membrane), and a larger taut portion, the pars tensa, which is drawn inward at its center to form the umbo (“navel”). The umbo marks the lower tip of the handle (manubrium) of the malleus, which is attached to the tympanic membrane all along its length. It is visible through the pars tensa as a light-colored streak (malleolar stria). The tympanic membrane is divided into four quadrants in a clockwise direction: anterosuperior (I), anteroinferior (II), posteroinferior (III), posterosuperior (IV). The boundary lines of the quadrants are the malleolar stria and a line intersecting it perpendicularly at the umbo. The quadrants of the tympanic membrane are clinically important because they are used in describing the location of lesions. A triangular area of reflected light can be seen in the anteroinferior quadrant of a normal tympanic membrane. The location of this “cone of light” is helpful in evaluating the tension of the tympanic membrane.

159

Regions of the Head

8. Temporal Bone & Ear

Middle Ear (I): Tympanic Cavity & Pharyngotympanic Tube

Pharyngotympanic (auditory) tube Tympanic cavity Internal carotid artery

Malleus

Cochlea

Incus Anterior semicircular canal

Facial nerve Cochlear nerve

External auditory canal

Vestibular nerve

Lateral semicircular canal

Vestibule Cochlear aqueduct

Mastoid air cells

Endolymphatic sac

Auricle

Posterior semicircular canal

Sigmoid sinus

Aditus (inlet) to mastoid antrum Malleus Incus Chorda tympani (CN VII) Tensor tympani Auriculotemporal nerve (CN V3)

Lesser petrosal nerve (from tympanic plexus) Facial nerve (CN VII) Prominence of lateral semicircular canal Prominence of facial canal Stapes

Tendon of insertion of stapedius

Auricular branch of posterior auricular nerve (CN VII)

Tympanic membrane

Auricular branch via mastoid canaliculus (CN X)

External auditory canal

Fig. 8.15 Walls of the tympanic cavity Anterior view with the anterior wall removed. The tympanic cavity is a slightly oblique space that is bounded by six walls: • Lateral (membranous) wall: boundary with the external ear; formed largely by the tympanic membrane. • Medial (labyrinthine) wall: boundary with the inner ear; formed largely by the promontory, or the bony eminence, overlying the basal turn of the cochlea. • Inferior (jugular) wall: forms the floor of the tympanic cavity and borders on the bulb of the jugular vein.

160

Fig. 8.14 Middle ear and associated structures Right petrous bone, superior view. The middle ear (light blue) is located within the petrous part of the temporal bone between the external ear (yellow) and inner ear (green). The tympanic cavity of the middle ear contains the chain of auditory ossicles, of which the malleus (hammer) and incus (anvil) are visible here. The tympanic cavity communicates anteriorly with the nasopharynx via the pharyngotympanic (auditory) tube and posteriorly with the mastoid air cells. Infections can spread from the nasopharynx to the mastoid air cells by this route.

Promontory Tympanic plexus

Tympanic nerve (from CN IX) via tympanic canaliculus

• Posterior (mastoid) wall: borders on the air cells of the mastoid process, communicating with the cells through the aditus (inlet) of the mastoid antrum. • Superior (tegmental) wall: forms the roof of the tympanic cavity. • Anterior (carotid) wall (removed here): includes the opening to the pharyngotympanic (auditory) tube and borders on the carotid canal. The lateral side of the tympanic membrane is innervated by three cranial nerves: CN V (auriculotemporal nerve [branch of CN V3]), CN VII (posterior auricular nerve; pathway uncertain), and CN X (auricular branch). The medial side of the tympanic membrane is innervated by CN IX (tympanic branch).

Regions of the Head

Anterior semicircular canal

Roof of tympanic cavity (tegmen tympani)

Geniculate ganglion

Posterior semicircular canal

8. Temporal Bone & Ear

Facial nerve (CN VII) Opening for tendon of tensor tympani

Lateral semicircular canal

Greater petrosal nerve Lesser petrosal nerve

Oval window (fenestra vestibuli)

Semicanal of tensor tympani

Facial nerve canal

Internal carotid artery

Sigmoid sinus

Pharyngotympanic (auditory) tube

Promontory

Internal carotid artery with internal carotid plexus

Posterior wall of tympanic cavity

Anterior wall of tympanic cavity

Mastoid air cells Chorda tympani

Floor of tympanic cavity Facial nerve (CN VII)

Round window (fenestra cochleae)

Tympanic plexus

Fig. 8.16 Nerves in the petrous bone Oblique sagittal section showing the medial wall of the tympanic cavity (see Fig. 8.15). The tympanic nerve branches from CN IX as it passes through the jugular foramen, and conveys sensory and preganglionic paraV\PSDWKHWLFÀEHUVLQWRWKHW\PSDQLFFDYLW\E\SDVVLQJWKURXJKWKHW\PSDQLF FDQDOLFXOXV 7KH ÀEHUV IURP WKH W\PSDQLF SOH[XV SURYLGH VHQVRU\ innervation to the tympanic cavity (including the medial surface of the tympanic membrane), mastoid air cells, and part of the pharyngotympanic tube. Note: The lateral surface of the tympanic membrane receives sensory innervation from branches of CN V3, CN VII, and CN X (see Fig. 8.15). 7KH SUHJDQJOLRQLF SDUDV\PSDWKHWLF ÀEHUV RI WKH W\PSDQLF QHUYH DUH UHIRUPHGIURPWKHW\PSDQLFSOH[XVDVWKHOHVVHUSHWURVDOQHUYH7KHVH À  EHUV V\QDSVH LQ WKH RWLF JDQJOLRQ WKH SRVWJDQJOLRQLF SDUDV\PSDWKHWLFÀEHUVWUDYHOZLWKWKHDXULFXORWHPSRUDOQHUYHDEUDQFKRI&193) to supply the parotid gland.

Internal jugular vein

Tympanic nerve (CN IX) entering tympanic canaliculus

,Q WKH IDFLDO FDQDO WKH IDFLDO QHUYH &1 9,,  JLYHV R̥ D QXPEHU RI branches: the greater petrosal nerve, the nerve to the stapedius, the chorda tympani, and an auricular branch. The greater petrosal nerve DQGWKHFKRUGDW\PSDQLERWKFDUU\WDVWHÀEHUVDQGSUHJDQJOLRQLFSDUDV\PSDWKHWLF ÀEHUV 7KH JUHDWHU SHWURVDO QHUYH MRLQV ZLWK WKH GHHS petrosal nerve (postganglionic sympathetic) to form the nerve of the pterygoid canal (vidian nerve). The preganglionic parasympathetic À  EHUV LQ WKH QHUYH RI WKH SWHU\JRLG FDQDO V\QDSVH DW WKH SWHU\JRSDODWLQH JDQJOLRQ 7KH SRVWJDQJOLRQLF SDUDV\PSDWKHWLF ÀEHUV DUH WKHQ GLVWULEXWHG E\ EUDQFKHV RI WKH PD[LOODU\ QHUYH WR WKH ODFULPDO JODQG palatine glands, superior labial glands, and mucosa of the paranasal VLQXVHVDQGQDVDOFDYLW\7KHSUHJDQJOLRQLFSDUDV\PSDWKHWLFÀEHUVRI the chorda tympani synapse at the submandibular ganglion, and the SRVWJDQJOLRQLFÀEHUVDUHGLVWULEXWHGWRWKHVXEPDQGLEXODUDQGVXEOLQgual glands.

Internal carotid artery Pharyngotympanic tube, bony part

Sphenoid sinus

Tympanic membrane

Superior meatus

Pharyngeal tonsil

Middle meatus

Levator veli palatini Pharyngotympanic tube, cartilaginous part

Inferior meatus

Pharyngeal orifice of pharyngotympanic tube Pharyngotympanic tube, membranous lamina Tensor veli palatini

Fig. 8.17 Pharyngotympanic (auditory) tube Medial view of right nasal cavity. The pharyngotympanic tube creates DQRSHQFKDQQHOEHWZHHQWKHPLGGOHHDUDQGQDVRSKDU\Q[$LUSDVVLQJ through the tube serves to equalize the air pressure on the two sides of the tympanic membrane. This equalization is essential for maintaining normal tympanic membrane mobility, necessary for normal hearing. One third of the tube is bony (in the petrous bone). The cartilaginous WZR WKLUGV FRQWLQXH WRZDUG WKH QDVRSKDU\Q[ H[SDQGLQJ WR IRUP D

Salpingopharyngeus

KRRNKDPXOXV WKDWLVDWWDFKHGWRDPHPEUDQRXVODPLQD7KHÀEHUVRI WKHWHQVRUYHOLSDODWLQLDULVHIURPWKLVODPLQDZKHQWKH\WHQVHWKHVRIW SDODWH GXULQJ VZDOORZLQJ  WKHVH ÀEHUV RSHQ WKH SKDU\QJRW\PSDQLF tube. The tube is also opened by the salpingopharyngeus and levator veli palatini. The tube is lined with ciliated respiratory epithelium: the FLOLD EHDW WRZDUG WKH SKDU\Q[ LQKLELWLQJ WKH SDVVDJH RI PLFURRUJDQisms into the middle ear.

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Regions of the Head

8. Temporal Bone & Ear

Middle Ear (II): Auditory Ossicles & Tympanic Cavity

Head of malleus

Articular surface for incus

Neck

Neck Lateral process

Lateral process

Malleus Incus Stapes

Handle A

Anterior process

B

Body of incus

Tympanic membrane

Tympanic cavity

Body Articular surface for malleus

Short process

C

A Short process Long process

D

Pyramidal eminence

Oval window with annular stapedial ligament

Stapedius tendon

Lenticular process

Head of stapes

B

C

Neck

Posterior crus

Malleus

Anterior crus

E

Incudomalleolar joint F

Base

Incus

Axis of movement

Oval window

Head of malleus Neck of malleus

Short process

Anterior process

Body of incus Incudostapedial joint

Handle

Posterior crus

G

Anterior crus Base of stapes

Fig. 8.18 Auditory ossicles Auditory ossicles of the left ear. The ossicular chain (G) of the middle ear establishes an articular connection between the tympanic membrane and the oval window. It consists of three small bones: • Malleus (“hammer”): A Posterior view. B Anterior view. • Incus (“anvil”): C Medial view. D Anterolateral view. • Stapes (“stirrup”): E Superior view. F Medial view. Note the synovial joint articulations between the malleus and incus (incudomalleolar joint) and the incus and stapes (incudostapedial joint).

162

Oval window with annular stapedial ligament

D

Stapes

Fig. 8.19 Function of the ossicular chain Anterior view. A Sound waves (periodic pressure fluctuations in the air) set the tympanic membrane into vibration. The ossicular chain transmits the vibrations of the tympanic membrane (and thus the sound waves) to the oval window, which in turn communicates them to an aqueous medium (perilymph). Although sound waves encounter very little resistance in air, they encounter considerably higher impedance when they reach the fluid interface of the inner ear. The sound waves must therefore be amplified (“impedance matching”). The difference in surface area between the tympanic membrane and oval window increases the sound pressure by a factor of 17. This is augmented by the 1.3-fold mechanical advantage of the lever action of the ossicular chain. Thus, in passing from the tympanic membrane to the inner ear, the sound pressure is amplified by a factor of 22. If the ossicular chain fails to transform the sound pressure between the tympanic membrane and stapes base (footplate), the patient will experience conductive hearing loss of magnitude approximately 20 dB. B, C Sound waves impinging on the tympanic membrane induce motion in the ossicular chain, causing a tilting movement of the stapes (B normal position, C tilted position). The movements of the stapes base against the membrane of the oval window (stapedial membrane) induce corresponding waves in the fluid column in the inner ear. D The movements of the ossicular chain are essentially rocking movements (the dashed line indicates the axis of the movements, the arrows indicate their direction). Two muscles affect the mobility of the ossicular chain: the tensor tympani and the stapedius (see Fig. 8.20).

Regions of the Head

Posterior ligament of incus

Incus

8. Temporal Bone & Ear

Superior ligament of incus and superior ligament of malleus Incudomalleolar joint

Annular stapedial ligament

Malleus Tendon of tensor tympani

Stapedial footplate

Tensor tympani

Incudostapedial joint

Internal carotid artery

Pyramidal eminence

Petrotympanic fissure

Stapedius with nerve to the stapedius (CN VII)

Anterior ligament of malleus

Stylomastoid artery

Chorda tympani (CN VII)

Facial nerve

Posterior tympanic artery

Chorda tympani (CN VII)

Tympanic membrane, lateral surface

Fig. 8.20 Ossicular chain in the tympanic cavity Lateral view of the right ear. The joints and their stabilizing ligaments can be seen with the two muscles of the middle ear—the stapedius and tensor tympani. The stapedius (innervated by the stapedial branch of the facial nerve) inserts on the stapes. When it contracts, it stiffens the sound conduction apparatus and dampens sound transmission to the inner ear. This filtering function is believed to be particularly important at high sound frequencies (“high-pass filter”). When sound is transmitted into the middle ear through a probe placed in the external ear canal,

Anterior process of malleus

one can measure the action of the stapedius (stapedius reflex test) by measuring the change in acoustic impedance (i.e., the amplification of the sound waves). Contraction of the tensor tympani (innervated by the trigeminal nerve via the medial pterygoid nerve) stiffens the tympanic membrane, thereby reducing the transmission of sound. Both muscles undergo a reflex contraction in response to loud acoustic stimuli. Note: The chorda tympani passes through the middle ear without a bony covering (making it susceptible to injury during otological surgery).

Incus

Superior malleolar fold Chorda tympani Stapedius tendon Malleolar stria Umbo

Anterior tympanic artery

Epitympanum

Malleus Lateral ligament of malleus Superior recess of tympanic membrane Malleolar prominence Tympanic membrane

Fig. 8.21 Mucosal lining of the tympanic cavity Posterolateral view with the tympanic membrane partially removed. The tympanic cavity and the structures it contains (ossicular chain, tendons, nerves) are covered with mucosa. The epithelium consists mainly of a simple squamous type, with areas of ciliated columnar cells and goblet cells. Because the tympanic cavity communicates directly with the respiratory tract (nasopharynx) through the pharyngotympanic tube, it can also be interpreted as a specialized paranasal sinus. Like the sinuses, it is susceptible to frequent infections (otitis media).

Incus

Stapes

Tendon of tensor tympani

Malleus External auditory canal Tympanic membrane

Mesotympanum Hypotympanum Pharyngotympanic tube

Fig. 8.22 Clinically important levels of the tympanic cavity The tympanic cavity is divided into three levels in relation to the tympanic membrane: • Epitympanum (epitympanic recess, attic) above the tympanic membrane • Mesotympanum medial to the tympanic membrane • Hypotympanum (hypotympanic recess) below the tympanic membrane The epitympanum communicates with the mastoid air cells, and the hypotympanum communicates with the pharyngotympanic tube.

163

Regions of the Head

8. Temporal Bone & Ear

Inner Ear

Posterior semicircular duct

Lateral semicircular duct

Anterior semicircular duct

Anterior semicircular canal

Internal acoustic meatus

Temporal bone, petrous part

Dura mater Endolymphatic sac

Cochlea

Ampullary crests

45°

Endolymphatic duct

Lateral semicircular canal

90°

Utricle Macula of utricle Oval window

45°

Macula of saccule

Stapes

Saccule

Round window

A

Anterior semicircular canal

Posterior semicircular canal

Facial nerve, vestibulocochlear nerve

Cochlea Posterior semicircular canal

Ductus reuniens

Anterior semicircular canal

Cochlear aqueduct Scala tympani

Helicotrema

Scala vestibuli

Temporal bone, squamous part

Cochlear duct

Vestibule

Fig. 8.23 Inner ear The inner ear, embedded within the petrous part of the temporal bone, is formed by a membranous labyrinth, which floats within a similarly shaped bony labyrinth, loosely attached by connective tissue fibers. Membranous labyrinth (blue): The membranous labyrinth is filled with endolymph. This endolymphatic space (blue) communicates with the endolymphatic sac, an epidural pouch on the posterior surface of the petrous bone via the endolymphatic duct. Note: The auditory and vestibular endolymphatic spaces are connected by the ductus reuniens. Bony labyrinth (beige): The bony labyrinth is filled with perilymph. This perilymphatic space (beige) is connected to the subarachnoid space by the cochlear aqueduct (perilymphatic duct), which ends at the posterior surface of the petrous part of the temporal bone, inferior to the internal acoustic meatus. The inner ear contains the auditory apparatus (hearing) and the vestibular apparatus (balance). Auditory apparatus (see pp. 170–171): The sensory epithelium of the auditory apparatus (organ of Corti) is found in the cochlea. The cochlea consists of the membranous cochlear duct and bony cochlear labyrinth. Vestibular apparatus (see pp. 174–175): The sensory epithelium of the vestibular apparatus is found in the saccule, the utricle, and the three membranous semicircular ducts. The saccule and utricle are enclosed in the bony vestibule, and the ducts are enclosed in bony semicircular canals.

164

Cochlea Canthomeatal plane

30°

Lateral semicircular canal B Mastoid process

External acoustic meatus

Fig. 8.24 Projection of the inner ear onto the bony skull A Superior view of the petrous part of the temporal bone. B Right lateral view of the squamous part of the temporal bone. The apex of the cochlea is directed anteriorly and laterally—not upward as one might intuitively expect. The bony semicircular canals are oriented at an approximately 45-degree angle to the cardinal body planes (coronal, transverse, and sagittal). It is important to know this arrangement when interpreting thin-slice CT scans of the petrous bone. Note: The location of the semicircular canals is of clinical importance in thermal function tests of the vestibular apparatus. The lateral (horizontal) semicircular canal is directed 30 degrees forward and upward. If the head of the supine patient is elevated by 30 degrees, the horizontal semicircular canal will assume a vertical alignment. Because warm fluids tend to rise, irrigating the auditory canal with warm (44° C) or cool (30° C) water (relative to the normal body temperature) can induce a thermal current in the endolymph of the semicircular canal, causing the patient to manifest vestibular nystagmus (jerky eye movements, vestibulo-ocular reflex). Because head movements always stimulate both vestibular apparatuses, caloric testing is the only method of separately testing the function of each vestibular apparatus (important in the diagnosis of unexplained vertigo).

Regions of the Head

Anterior semicircular duct

Anterior ampullary nerve

Vestibulocochlear nerve (CN VIII), vestibular part Facial nerve (CN VII)

Vestibular aqueduct

Vestibular ganglion, inferior part

Dura mater

Cochlear communicating branch

Endolymphatic sac

Nervus intermedius (CN VII)

Lateral ampullary nerve

Vestibulocochlear nerve (CN VIII), cochlear part

Common crus

Saccular nerve

Utricular nerve

Posterior ampullary nerve

Lateral semicircular duct

Modiolus Spiral ganglion of cochlea

Posterior semicircular duct Posterior ampulla

Oval window

Round window

Fig. 8.25 Innervation of the membranous labyrinth 5LJKW HDU DQWHULRU YLHZ $̥HUHQW LPSXOVHV IURP WKH YHVWLEXODU DQG DXGLWRU\PHPEUDQRXVODE\ULQWKVDUHUHOD\HGYLDGHQWULWLFSURFHVVHVWR FHOOERGLHVLQWKHvestibularDQGspiral gangliaUHVSHFWLYHO\7KHFHQWUDO SURFHVVHVRIWKHYHVWLEXODUDQGVSLUDOJDQJOLDIRUPWKHYHVWLEXODUDQG F RFKOHDU SDUWV RI WKH YHVWLEXORFRFKOHDU QHUYH &1 9,,,  UHVSHFWLYHO\ &19,,,UHOD\VD̥HUHQWLPSXOVHVWRWKHEUDLQVWHPWKURXJKWKHLQWHUQDO DFRXVWLF PHDWXV DQG FHUHEHOORSRQWLQH DQJOH Vestibular ganglion: 7KH

Greater petrosal nerve

Geniculate ganglion

Transverse crest Facial nerve

FHOOERGLHVRID̥HUHQWQHXURQVELSRODUJDQJOLRQFHOOV LQWKHVXSHULRU SDUWRIWKHYHVWLEXODUJDQJOLRQUHFHLYHD̥HUHQWLPSXOVHVIURPWKHDQ WHULRUDQGODWHUDOVHPLFLUFXODUFDQDOVDQGWKHVDFFXOHFHOOERGLHVLQWKH LQIHULRUSDUWUHFHLYHD̥HUHQWLPSXOVHVIURPWKHSRVWHULRUVHPLFLUFXODU FDQDODQGXWULFOHSpiral ganglia:/RFDWHGLQWKHFHQWUDOERQ\FRUHRIWKH FRFKOHDPRGLROXV WKHFHOOERGLHVRIELSRODUJDQJOLRQFHOOVLQWKHVSLUDO JDQJOLDUHFHLYHD̥HUHQWLPSXOVHVIURPWKHDXGLWRU\DSSDUDWXVYLDWKHLU GHQWULWLFSURFHVVHV

Fig. 8.26 Cranial nerves in the right internal acoustic meatus 3RVWHULRUREOLTXHYLHZRIWKHIXQGXVRIWKHLQWHUQDODFRXVWLFPHDWXV7KH DSSUR[LPDWHO\FPORQJLQWHUQDODXGLWRU\FDQDOEHJLQVDWWKHLQWHUQDO DFRXVWLFPHDWXVRQWKHSRVWHULRUZDOORIWKHSHWURXVERQH,WFRQWDLQV ‡ 9HVWLEXORFRFKOHDU QHUYH &1 9,,,  ZLWK LWV FRFKOHDU DQG YHVWLEXODU SDUWV ‡ )DFLDOQHUYH&19,, DORQJZLWKLWVSDUDV\PSDWKHWLFDQGWDVWHÀEHUV QHUYXVLQWHUPHGLXV ‡ /DE\ULQWKLQHDUWHU\DQGYHLQQRWVKRZQ

Nervus intermedius

*LYHQ WKH FORVH SUR[LPLW\ RI WKH YHVWLEXORFRFKOHDU QHUYH DQG IDFLDO QHUYHLQWKHERQ\FDQDODWXPRURIWKHYHVWLEXORFRFKOHDUQHUYHacoustic neuroma PD\H[HUWSUHVVXUHRQWKHIDFLDOQHUYHOHDGLQJWRSHULSK HUDOIDFLDOSDUDO\VLV$FRXVWLFQHXURPDLVDEHQLJQWXPRUWKDWRULJLQDWHV IURPWKH6FKZDQQFHOOVRIYHVWLEXODUÀEHUVVRLWZRXOGEHPRUHDFFX UDWH WR FDOO LW D vestibular schwannoma 7XPRU JURZWK DOZD\V EHJLQV LQWKHLQWHUQDODXGLWRU\FDQDODVWKHWXPRUHQODUJHVLWPD\JURZLQWR WKHFHUHEHOORSRQWLQHDQJOH $FXWHXQLODWHUDOLQQHUHDUG\VIXQFWLRQZLWK KHDULQJ ORVV VXGGHQ VHQVRULQHXUDO KHDULQJ ORVV  RIWHQ DFFRPSDQLHG E\WLQQLWXVW\SLFDOO\UHÁHFWVDQXQGHUO\LQJYDVFXODUGLVWXUEDQFHYDVR VSDVPRIWKHODE\ULQWKLQHDUWHU\FDXVLQJGHFUHDVHGEORRGÁRZ 

Internal carotid artery

Cochlear nerve Vestibular nerve

Vestibular ganglion, superior part

8. Temporal Bone & Ear

Posterior SacculoUtriculoampullary nerve ampullary nerve ampullary nerve

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Regions of the Head

8. Temporal Bone & Ear

Arteries & Veins of the Ear The structures of the external and middle ear are supplied primarily by branches of the external carotid artery. (Note: The caroticotympanic arteries arise from the internal carotid artery.) The inner ear is supplied by the labyrinthine artery, which arises from the basilar artery. Venous drainage of the auricle is to the superficial temporal vein (via auricular veins), whereas drainage of the external ear is to the external jugular and maxillary veins and the pterygoid plexus. The veins of the tympanic cavity drain to the pterygoid plexus and superior petrosal sinus; the inner ear drains to the labyrinthine vein, which empties into the superior petrosal or transverse sinuses.

Table 8.1 Arteries of the ear Artery

Origin

Distribution

Caroticotympanic aa.

Internal carotid a.

Pharyngotympanic (auditory) tube and anterior wall of tympanic cavity

Stylomastoid a.

Posterior auricular a. or occipital a.

Tympanic cavity, mastoid air cells and antrum, stapedius muscle, stapes

Inferior tympanic a.

Ascending pharyngeal a.

Medial wall of tympanic cavity, promontory

Deep auricular a.

Maxillary a.

External surface of tympanic membrane

Posterior tympanic a.

Stylomastoid a.

Chorda tympani, tympanic membrane, malleus

Superior tympanic a.

Middle meningeal a.

Tensor tympani, roof of tympanic cavity, stapes

Anterior tympanic a.

Maxillary a.

Tympanic membrane, mastoid antrum, malleus, incus

Tubal a.

Ascending pharyngeal a.

Pharyngotympanic tube and anterior tympanic cavity

Tympanic branches

A. of pterygoid canal

Tympanic cavity and pharyngotympanic tube

(Superficial) petrosal a.

Middle meningeal a.

Facial n. in facial canal and tympanic cavity

Note: The arteries supplying the tympanic cavity and its contents form a rich arterial anastomotic network within the middle ear. The venous drainage of the middle ear is primarily into the pterygoid plexus of veins located in the infratemporal fossa or into dural venous sinuses. Subarcuate artery

Ascending branch of superficial petrosal artery Labyrinthine artery

Descending branch of superficial petrosal artery

Facial nerve (CN VII) Superficial petrosal artery with greater petrosal nerve Superior tympanic artery with lesser petrosal nerve

Anterior crural artery

Internal carotid artery

Posterior crural artery Stylomastoid artery, posterior tympanic branch Branches to stapedius (stapedial branch)

Incudostapedial joint (incus removed)

Pharyngotympanic (auditory) tube Tensor tympani with superior tympanic artery

Facial nerve (CN VII) Stylomastoid artery

Tendon of tensor tympani (cut) Caroticotympanic arteries Mastoid artery

Posterior tympanic artery (from stylomastoid artery)

Deep auricular artery

Fig. 8.27 Arteries of the tympanic cavity and mastoid air cells Right petrous bone, anterior view. The malleus, incus, chorda tympani, and anterior tympanic artery have been removed (see Fig. 8.28).

166

Inferior tympanic artery

Tubal artery

Regions of the Head

8. Temporal Bone & Ear

Tegmen tympani Incus

Mastoid antrum

Superior tympanic artery (from middle meningeal artery) Facial nerve (CN VII)

Tensor tympani

Stapedial branch

Anterior tympanic artery

Incudostapedial joint (stapes removed)

Handle of malleus

Chorda tympani (CN VII) Posterior tympanic artery

Pharyngotympanic (auditory) tube

Stylomastoid artery

Deep auricular artery

Tympanic membrane

Fig. 8.28 Arteries of the ossicular chain and tympanic membrane Medial view of the right tympanic membrane. This region receives most of its blood supply from the anterior tympanic artery. With inflam-

Vestibular artery

Inferior tympanic artery

mation of the tympanic membrane, the arteries may become so dilated that their course in the tympanic membrane can be seen, as illustrated here.

Vestibular ganglion, superior part

Vestibular nerve (CN VIII) Facial nerve (CN VII)

Vein of vestibular aqueduct

Labyrinthine artery and veins

Nervus intermedius (CN VII) Cochlear nerve (CN VIII) Common cochlear artery Cochlear veins Vestibulocochlear artery Cochlear artery proper

Vein of round window Vein of cochlear aqueduct

Fig. 8.29 Arteries and veins of the inner ear Right anterior view. The labyrinth receives its arterial blood supply from the labyrinthine (internal auditory) artery, which generally arises

directly from the basilar artery, but may arise from the anterior inferior cerebellar artery. Venous blood drains to the labyrinthine vein and into the inferior petrosal sinus or the transverse sinuses.

167

Regions of the Head

8. Temporal Bone & Ear

Vestibulocochlear Nerve (CN VIII)

Superior vestibular nucleus

Medial vestibular nucleus

Lateral vestibular nucleus

A

Fig. 8.30 Nuclei of the vestibulocochlear nerve (CN VIII) Cross sections through the upper medulla oblongata. A Vestibular nuclei. Four nuclear complexes are distinguished: • • • •

Superior vestibular nucleus (of Bechterew) Lateral vestibular nucleus (of Deiters) Medial vestibular nucleus (of Schwalbe) Inferior vestibular nucleus (of Roller): does not appear in a cross section at this level

Most of the axons from the vestibular ganglion terminate in these four nuclei, but a smaller number pass directly through the inferior cerebellar peduncle into the cerebellum. The vestibular nuclei appear as eminences on the floor of the rhomboid fossa. B Cochlear nuclei. Two nuclear complexes are distinguished:

Posterior cochlear nucleus Anterior cochlear nucleus

• Anterior cochlear nucleus • Posterior cochlear nucleus Both nuclei are located lateral to the vestibular nuclei. Note: The nuclei of CN VIII extend from the pons into the medulla oblongata.

B

Table 8.2 Vestibulocochlear nerve (CN VIII): overview Fibers: Special somatic afferent fibers (yellow) Structure and function: CN VIII consists anatomically and functionally of two components: • Vestibular root: Transmits impulses from the vestibular apparatus. • Cochlear root: Transmits impulses from the auditory apparatus. These roots are surrounded by a common connective tissue sheath. They pass from the inner ear through the internal acoustic meatus to the cerebellopontine angle, where they enter the brain. Nuclei and distribution: • Vestibular root: The vestibular ganglion contains bipolar ganglion cells whose central processes pass to the four vestibular nuclei on the floor of the rhomboid fossa of the medulla oblongata. Their peripheral processes begin at the sensory cells of the semicircular canals, saccule, and utricle. • Cochlear root: The spiral ganglion contains bipolar ganglion cells whose central processes pass to the two cochlear nuclei, which are lateral to the vestibular nuclei in the rhomboid fossa. Their peripheral processes begin at the hair cells of the organ of Corti. Lesions: Every thorough physical examination should include a rapid assessment of both nerve components (hearing and balance tests). • Vestibular root lesion: Dizziness. • Cochlear root lesion: Hearing loss (ranging to deafness).

168

Cerebellopontine angle Acoustic neuroma (vestibular schwannoma)

Fig. 8.31 Acoustic neuroma in the cerebellopontine angle Acoustic neuromas (more accurately, vestibular schwannomas) are benign tumors of the cerebellopontine angle arising from the Schwann cells of the vestibular root of CN VIII. As they grow, they compress and displace the adjacent structures and cause slowly progressive hearing loss and gait ataxia. Large tumors can impair the egress of CSF from the fourth ventricle, causing hydrocephalus and symptomatic intracranial hypertension (vomiting, impairment of consciousness).

Regions of the Head

8. Temporal Bone & Ear

Vestibular ganglion, superior part Vestibular root of CN VIII

Anterior ampullary nerve Lateral ampullary nerve

Cochlear root of CN VIII

Utricular nerve

Vestibular ganglion, inferior part Saccular nerve

Spiral ganglia Posterior ampullary nerve

Fig. 8.32 Vestibular ganglion and cochlear ganglion (spiral ganglia) The vestibular root and cochlear root still exist as separate structures in the petrous part of the temporal bone.

Flocculus of cerebellum Direct fibers to cerebellum

Anterior cochlear nucleus Posterior cochlear nucleus

Superior vestibular nucleus

Vestibulocochlear nerve (CN VIII) Vestibular root

Medial vestibular nucleus

Vestibular ganglion

Lateral vestibular nucleus

Semicircular canals

Inferior vestibular nucleus A

Utricle and saccule

Fig. 8.33 Nuclei of the vestibulocochlear nerve in the brainstem Anterior view of the medulla oblongata and pons. A Vestibular part: The vestibular ganglion contains bipolar sensory cells whose peripheral (dendritic) processes pass to the semicircular canals, saccule, and utricle. Their axons travel as the vestibular root to the four vestibular nuclei on the floor of the rhomboid fossa. The vestibular organ processes information concerning orientation in space. An acute lesion of the vestibular organ is manifested clinically by dizziness (vertigo).

Cochlear root B

Cochlea with spiral ganglia

Vestibulocochlear nerve (CN VIII)

B Cochlear part: The spiral ganglia form a band of nerve cells that follows the course of the bony core of the cochlea. It contains bipolar sensory cells whose peripheral (dendritic) processes pass to the hair cells of the organ of Corti. Their central processes unite on the floor of the internal auditory canal to form the cochlear root and are distributed to the two nuclei that are posterior to the vestibular nuclei.

169

Regions of the Head

8. Temporal Bone & Ear

Auditory Apparatus

Modiolus

Greater petrosal nerve

Lesser petrosal nerve

Scala vestibuli

Helicotrema

Cochlear nerve (CN VIII)

Tympanic cavity

A

Spiral ligament

Bony spiral lamina B

Petrous bone

Tectorial membrane

Spiral ganglion

Chorda tympani (CN VII)

Internal acoustic meatus

Stria vascularis

Cochlear nerve (CN VIII)

Facial nerve (CN VII) Vestibular nerve (CN VIII)

Cochlear duct

Limbus of spiral lamina

Geniculate ganglion

Cochlea

Vestibular (Reissner) membrane

Organ of Corti

Scala tympani

Basilar membrane

Semicircular canals Vestibular (Reissner) membrane

Scala vestibuli

Spiral ligament

Nuel space Inner hair cell

Spiral limbus

Cochlear duct

Bony spiral lamina

Stria vascularis Tectorial membrane Outer hair cells

Spiral ganglion

Basilar membrane

Fig. 8.34 Location and structure of the cochlea A Cross section through the cochlea in the petrous bone. B The three compartments of the cochlear canal. C Cochlear turn with sensory apparatus. The bony canal of the cochlea (spiral canal) is approximately 30 to 35 mm long in the adult. It makes two and a half turns around its bony axis, the modiolus, which is permeated by branched cavities and contains the spiral ganJOLRQSHULNDU\DRIWKHD̥HUHQWQHXURQV 7KH base of the cochlea is directed toward the internal acoustic meatus (A). A cross section through the cochlear canal displays three membranous compartments arranged in three levels (B). The upper and lower compartments, the scala vestibuli and scala tympani, each contain perilymph; the middle level, the cochlear duct (scala media), contains endolymph. The perilymphatic spaces are interconnected at the apex by the helicotrema, and the endolymphatic space ends blindly at the apex. The cochlear duct, which is triangular in cross section, is separated from the scala vestibuli by the vestibular (Reissner) membrane and from the scala tympani by the basilar membrane. The basilar membrane represents a bony projection of the modiolus (spiral lamina) and

Internal spiral sulcus

Corti tunnel

Bony wall

Scala tympani

C

widens steadily from the base of the cochlea to the apex. High frequencies (up to 20,000 Hz) are perceived by the narrow portions of the basilar membrane, whereas low frequencies (down to about 200 Hz) are perceived by its broader portions (tonotopic organization). The basilar membrane and bony spiral lamina WKXVIRUPWKHÁRRURIWKHFRFKOHDUGXFWXSRQ which the actual organ of hearing, the organ of Corti, is located. This organ consists of a system of sensory cells and supporting cells FRYHUHG E\ DQ DFHOOXODU JHODWLQRXV ÁDS WKH tectorial membrane. The sensory cells (inner and outer hair cells) are the receptors of the organ of Corti (C). These cells bear approximately 50 to 100 stereocilia, and on their apical surface synapse on their basal side with the HQGLQJVRID̥HUHQWDQGH̥HUHQWQHXURQV7KH\

have the ability to transform mechanical energy into electrochemical potentials. A magniÀHGFURVVVHFWLRQDOYLHZRIDFRFKOHDUWXUQC) also reveals the stria vascularis, a layer of vascularized epithelium in which the endolymph LV IRUPHG 7KLV HQGRO\PSK ÀOOV WKH PHPEUDnous labyrinth (appearing here as the cochlear duct, which is part of the labyrinth). The organ of Corti is located on the basilar membrane. It transforms the energy of the acoustic traveling wave into electrical impulses, which are then carried to the brain by the cochlear nerve. The principal cell of signal transduction is the inner hair cell. The function of the basilar membrane is to transmit acoustic waves to the inner hair cell, which transforms them into impulses that are received and relayed by the cochlear ganglion.

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Regions of the Head

Malleus

8. Temporal Bone & Ear

Incus

Stapes

Oval window

Scala vestibuli

Traveling wave

Stapes Annular stapedial ligament Oval window Round window

Round window

Basilar membrane

Basilar membrane

Tympanic membrane

A

Fig. 8.35 Sound conduction during hearing A Sound conduction from the middle ear to the inner ear: Sound waves in the air deflect the tympanic membrane, whose vibrations are conducted by the ossicular chain to the oval window. The sound pressure induces motion of the oval window membrane, whose vibrations are, in turn, transmitted through the perilymph to the basilar membrane of the inner ear (see B). The round window equalizes pressures between the middle and inner ear.

Inner hair cells

Tectorial membrane

Scala tympani

B

B Formation of a traveling wave in the cochlea: The sound wave begins at the oval window and travels up the scala vestibuli to the apex of the cochlea (“traveling wave”). The amplitude of the traveling wave gradually increases as a function of the sound frequency and reaches a maximum value at particular sites (shown greatly exaggerated in the drawing). These are the sites where the receptors of the organ of Corti are stimulated and signal transduction occurs. To understand this process, one must first grasp the structure of the organ of Corti (the actual organ of hearing), which is depicted in Fig. 8.36.

Shearing of the stereocilia

Stereocilia

Membrane deflection

A

Afferent cochlear nerve fibers

Outer hair cells

Basilar membrane

Fig. 8.36 Organ of Corti at rest (A) and deflected by a traveling wave (B) The traveling wave is generated by vibrations of the oval window membrane. At each site that is associated with a particular sound frequency, the traveling wave causes a maximum deflection of the basilar membrane and thus of the tectorial membrane, setting up shearing movements between the two membranes. These shearing movements cause

B

the stereocilia on the outer hair cells to bend. In response, the hair cells actively change their length, thereby increasing the local amplitude of the traveling wave. This additionally bends the stereocilia of the inner hair cells, stimulating the release of glutamate at their basal pole. The release of this substance generates an excitatory potential on the afferent nerve fibers, which is transmitted to the brain.

171

Regions of the Head

8. Temporal Bone & Ear

Auditory Pathway

Lateral sulcus Transverse temporal gyri

Area 41, transverse temporal gyri

Acoustic radiation

Nucleus of medial geniculate body Inferior collicular nucleus Commissure of inferior colliculi

Transverse temporal gyri

Lateral lemniscus 200 Hz

Posterior cochlear nucleus

Nuclei of lateral lemniscus

20,000 Hz (20 kHz) Medullary striae

Corti organ

Superior olivary nucleus

Spiral ganglion

Nucleus of trapezoid body

Fig. 8.37 Afferent auditory pathway of the left ear The receptors of the auditory pathway are the inner hair cells of the organ of Corti. Because they lack neural processes, they are called secondary sensory cells. They are located in the cochlear duct of the basilar membrane and are studded with stereocilia, which are exposed to shearing forces from the tectorial membrane in response to a traveling wave. This causes bowing of the stereocilia (see Fig. 8.36). These bowing movements act as a stimulus to evoke cascades of neural signals. Dendritic processes of the bipolar neurons in the spiral ganglion pick up the stimulus. The bipolar neurons then transmit impulses via their axons, which are collected to form the cochlear nerve, to the anterior and posterior cochlear nuclei. In these nuclei the signals are relayed to the second neuron of the auditory pathway. Information from the cochlear nuclei is then transmitted via four to six nuclei to the primary auditory cortex, where the auditory information is consciously perceived (analogous to the visual cortex). The primary auditory cortex is located in the transverse temporal gyri (Heschl gyri, Brodmann area 41). The auditory pathway thus contains the following key stations:

172

Cochlear duct

Anterior cochlear nucleus

• • • • • • • •

Inner hair cells

Cochlear nerve (CN VIII)

Inner hair cells in the organ of Corti Spiral ganglion Anterior and posterior cochlear nuclei Nucleus of the trapezoid body and superior olivary nucleus Nucleus of the lateral lemniscus Inferior collicular nucleus Nucleus of the medial geniculate body Primary auditory cortex in the temporal lobe (transverse temporal gyri = Heschl gyri or Brodmann area 41)

The individual parts of the cochlea are correlated with specific areas in the auditory cortex and its relay stations. This is known as the tonotopic organization of the auditory pathway. This organizational principle is similar to that in the visual pathway. Binaural processing of the auditory information (= stereo hearing) first occurs at the level of the superior olivary nucleus. At all further stages of the auditory pathway there are also interconnections between the right and left sides of the auditory pathway (for clarity, these are not shown here). A cochlea that has ceased to function can sometimes be replaced with a cochlear implant.

Regions of the Head

Cochlear nerve (CN VIII)

8. Temporal Bone & Ear

Facial nucleus

Facial nerve (CN VII)

Cochlear nucleus

Superior olive with superior olivary nucleus

Facial nucleus

Cochlea Stapes Tympanic membrane Stapedial nerve Stapedius muscle

Fig. 8.38 The stapedius reflex When the volume of an acoustic signal reaches a certain threshold, the stapedius reflex triggers a contraction of the stapedius muscle. This reflex can be utilized to test hearing without the patient’s cooperation (“objective” auditory testing). The test is done by introducing a sonic probe into the ear canal and presenting a test noise to the tympanic membrane. When the noise volume reaches a certain threshold, it

evokes the stapedius reflex, and the tympanic membrane stiffens. The change in the resistance of the tympanic membrane is then measured and recorded. The afferent limb of this reflex is in the cochlear nerve. Information is conveyed to the facial nucleus on each side by way of the superior olivary nucleus. The efferent limb of this reflex is formed by branchiomotor (visceromotor) fibers of the facial nerve.

Inner hair cell

Outer hair cell

Lateral olivocochlear bundle

Medial olivocochlear bundle Lateral neuron Medial neuron

Type I ganglion cell Type II ganglion cell Superior olive

Cochlear nerve

Fig. 8.39 Efferent fibers from the olive to the Corti organ Besides the afferent fibers from the organ of Corti, which form the vestibulocochlear nerve, there are also efferent fibers (red) that pass to the organ of Corti in the inner ear and are concerned with the active preprocessing of sound (“cochlear amplifier”) and acoustic protection. The efferent fibers arise from neurons that are located in either the lateral or medial part of the superior olive and project from there to the cochlea (lateral or medial olivocochlear bundle). The fibers of the

lateral neurons pass uncrossed to the dendrites of the inner hair cells, whereas the fibers of the medial neurons cross to the opposite side and terminate at the base of the outer hair cells, whose activity they influence. When stimulated, the outer hair cells can actively amplify the traveling wave. This increases the sensitivity of the inner hair cells (the actual receptor cells). The activity of the efferents from the olive can be recorded as otoacoustic emissions (OAE). This test can be used to screen for hearing abnormalities in newborns.

173

Regions of the Head

8. Temporal Bone & Ear

Vestibular Apparatus

Fig. 8.40 Structure of the vestibular apparatus The vestibular apparatus is the organ of balance. It consists of the membranous semicircular ducts, which contain sensory ridges (ampullary crests) in their dilated portions (ampullae), and of the saccule and utricle with their macular organs. The sensory organs in the semicircular ducts respond to angular acceleration; the macular organs, which have an approximately vertical and horizontal orientation, respond to horizontal (utricular macula) and vertical (saccular macula) linear acceleration, as well as to gravitational forces.

Fig. 8.41 Structure of the ampulla and ampullary crest Cross section through the ampulla of a semicircular canal. Each canal has a bulbous expansion at one end (ampulla) that is traversed by a connective tissue ridge with sensory epithelium (ampullary crest). Extending above the ampullary crest is a gelatinous cupula, which is attached to the roof of the ampulla. Each of the sensory cells of the ampullary crest (approximately 7000 in all) bears on its apical pole one long kinocilium and approximately 80 shorter stereocilia, which project into the cupula. When the head is rotated in the plane of a particular semicircular canal, the inertial lag of the endolymph causes a deflection of the cupula, which in turn causes a bowing of the stereocilia. The sensory cells are either depolarized (excitation) or hyperpolarized (inhibition), depending on the direction of ciliary displacement.

Fig. 8.42 Structure of the utricular and saccular maculae The maculae are thickened oval areas in the epithelial lining of the utricle and saccule, each averaging 2 mm in diameter and containing arrays of sensory and supporting cells. Like the sensory cells of the ampullary crest, the sensory cells of the macular organs bear specialized stereocilia, which project into an otolithic membrane. The latter consists of a gelatinous layer, similar to the cupula, but it has calcium carbonate crystals or otoliths (statoliths) embedded in its surface. With their high specific gravity, these crystals exert traction on the gelatinous mass in response to linear acceleration, and this induces shearing movements of the cilia. The sensory cells are either depolarized or hyperpolarized by the movement, depending on the orientation of the cilia. There are two distinct categories of vestibular hair cells (type I and type II); type I cells (light red) are goblet shaped.

174

Ampullary crest with anterior ampullary nerve

Anterior semicircular canal

Vestibular ganglion, superior part

Anterior semicircular duct

Vestibular ganglion, inferior part

Ampullary crest with lateral ampullary nerve

Utricle Endolymphatic sac

Utricular macula with utricular nerve Saccular macula with saccular nerve

Lateral semicircular duct

Saccule

Posterior semicircular duct

Endolymphatic duct

Ampullary crest with posterior ampullary nerve

Semicircular canal

Ductus reuniens

Ampulla Cupula Cilia of sensory cells Supporting cell Sensory cell

Ampullary crest

Otoliths

Otolithic membrane

Stereocilia of type II hair cells Stereocilia of type I hair cells Type II hair cell Type I hair cell

Basement membrane Supporting cell

Afferent nerve fiber

Regions of the Head

Fig. 8.43 Stimulus transduction in the vestibular sensory cells Each of the sensory cells of the maculae and ampullary crest bears on its apical surface one long kinocilium and approximately 80 stereocilia of graduated lengths, forming an array that resembles a pipe organ. This arrangement results in a polar differentiation of the sensory cells. The cilia are straight while in a resting state. When the stereocilia are deflected toward the kinocilium, the sensory cell depolarizes, and the frequency of action potentials (discharge rate of impulses) is increased (right side of diagram). When the stereocilia are deflected away from the kinocilium, the cell hyperpolarizes, and the discharge rate is decreased (left side of diagram). This mechanism regulates the release of the transmitter glutamate at the basal pole of the sensory cell, thereby controlling the activation of the afferent nerve fiber (depolarization stimulates glutamate release, and hyperpolarization inhibits it). In this way the brain receives information on the magnitude and direction of movements and changes of position.

Kinocilium

Stereocilia

8. Temporal Bone & Ear

Sensory cell

Time

Afferent nerve fiber

Anterior ampulla Lateral ampulla Macula of utricle Macula of saccule

Posterior ampulla Cochlear duct

Fig. 8.44 Specialized orientations of the stereocilia in the vestibular apparatus (ampullary crest and maculae) Because the stimulation of the sensory cells by deflection of the stereocilia away from or toward the kinocilium is what initiates signal transduction, the spatial orientation of the cilia must be specialized to ensure that every position in space and every movement of the head stimulates or inhibits certain receptors. The ciliary arrangement shown here ensures that every direction in space will correlate with the maximum sensitivity of a particular receptor field. The arrows indicate the polarity of the cilia (i.e., each of the arrowheads points in the direction of the kinocilium in that particular field). Note that the sensory cells show an opposite, reciprocal arrangement in the sensory fields of the utricle and saccule.

Fig. 8.45 Interaction of contralateral semicircular canals during head rotation When the head rotates to the right (red arrow), the endolymph flows to the left because of its inertial mass (solid blue arrow, taking the head as the reference point). Owing to the alignment of the stereocilia, the left and right semicircular canals are stimulated in opposite fashion. On the right side, the stereocilia are deflected toward the kinocilium (dotted arrow; the discharge rate increases). On the left side, the stereocilia are deflected away from the kinocilium (dotted arrow; the discharge rate decreases). This arrangement heightens the sensitivity to stimuli by increasing the stimulus contrast between the two sides. In other words, the difference between the decreased firing rate on one side and the increased firing rate on the other side enhances the perception of the kinetic stimulus.

175

Regions of the Head

8. Temporal Bone & Ear

Vestibular System

Nucleus of posterior commissure (Darkschewitsch nucleus) Interstitial nucleus (Cajal nucleus)

Red nucleus

Nucleus of oculomotor nerve (CN III) Nucleus of trochlear nerve (CN IV)

Globose nucleus

Uncinate fasciculus

Fastigial nucleus

Vestibular nuclei

Nucleus of abducent nerve (CN VI)

Vestibulocerebellar fibers

Flocculonodular lobe

Vestibulocochlear nerve (CN VIII)

Vestibular ganglion (CN VIII)

Ampullary crest

Reticular formation Dorsal motor nucleus (CN X)

Utricle

Nucleus of accessory nerve (CN XI)

Saccule

Medial longitudinal fasciculus Lateral vestibulospinal tract Reticulospinal tract To sacral cord To cervical cord

Fig. 8.46 Central connections of the vestibular nerve (CN VIII) Three systems are involved in the regulation of human balance: • Vestibular system • Proprioceptive system • Visual system The peripheral receptors of the vestibular system are located in the membranous labyrinth, which consists of the utricle and saccule and the ampullae of the three semicircular ducts. The maculae of the utricle and saccule respond to linear acceleration, and the semicircular duct organs in the ampullary crests respond to angular (rotational) acceleration. Like the hair cells of the inner ear, the receptors of the vestibular system are secondary sensory cells. The basal portions of the secondary sensory cells are surrounded by dendritic processes of bipo-

176

lar neurons. Their perikarya are located in the vestibular ganglion. The axons from these neurons form the vestibular nerve and terminate in the four vestibular nuclei. Besides input from the vestibular apparatus, these nuclei also receive sensory input (see Fig. 8.47). The vestibular nuclei show a topographical organization (see Fig. 8.48) and distribute their efferent fibers to three targets: • Motor neurons in the spinal cord via the lateral vestibulospinal tract. These motor neurons help to maintain an upright stance, mainly by increasing the tone of extensor muscles. • Flocculonodular lobe of the cerebellum (archicerebellum) via vestibulocerebellar fibers. • Ipsilateral and contralateral oculomotor nuclei via the ascending part of the medial longitudinal fasciculus.

Regions of the Head

Hypothalamus

Cortex

8. Temporal Bone & Ear

Thalamus Brainstem

Medial rectus

Fig. 8.47 Role of the vestibular nuclei in the maintenance of balance The vestibular nuclei receive afferent input from the vestibular system, proprioceptive system (position sense, muscles, and joints), and visual system. They then distribute efferent fibers to nuclei that control the motor systems important for balance. These nuclei are located in the: • Spinal cord (motor support) • Cerebellum (fine control of motor function) • Brainstem (oculomotor nuclei for oculomotor function) Efferents from the vestibular nuclei are also distributed to the following regions:

Eye

• Thalamus and cortex (spatial sense) • Hypothalamus (autonomic regulation: vomiting in response to vertigo)

Labyrinth

Vestibular nuclei

Cerebellum

Note: Acute failure of the vestibular system is manifested by rotary vertigo.

Spinal cord

Proprioception

Nucleus of trochlear nerve (CN IV)

Nucleus of oculomotor nerve (CN III) Medial longitudinal fasciculus

Nucleus of abducent nerve (CN VI)

Cerebellum

Inferior cerebellar peduncle Vestibulocerebellar fibers

Superior vestibular nucleus

Vestibular nerve (CN VIII)

Lateral vestibular nucleus Inferior vestibular nucleus Medial vestibular nucleus Medial longitudinal fasciculus

Lateral vestibulospinal tract

Fig. 8.48 Vestibular nuclei: topographic organization and central connections Four nuclei are distinguished:

• Afferent fibers from the ampullary crests of the semicircular canals terminate in the superior vestibular nucleus, the upper part of the inferior vestibular nucleus, and the lateral vestibular nucleus.

• • • •

The efferent fibers from the lateral vestibular nucleus pass to the lateral vestibulospinal tract. This tract extends to the sacral part of the spinal cord, its axons terminating on motor neurons. Functionally, it is concerned with keeping the body upright, chiefly by increasing the tone of the extensor muscles. The vestibulocerebellar fibers from the other three nuclei act through the cerebellum to modulate muscular tone. All four vestibular nuclei distribute ipsilateral and contralateral axons via the medial longitudinal fasciculus to the three motor nuclei of the nerves to the extraocular muscles (i.e., the nuclei of the oculomotor [CN III], trochlear [CN IV], and abducent [CN VI] nerves).

Superior vestibular nucleus (of Bechterew) Lateral vestibular nucleus (of Deiters) Medial vestibular nucleus (of Schwalbe) Inferior vestibular nucleus (of Roller)

The vestibular system has a topographic organization: • Afferent fibers of the saccular macula terminate in the inferior vestibular nucleus and lateral vestibular nucleus. • Afferent fibers of the utricular macula terminate in the medial part of the inferior vestibular nucleus, the lateral part of the medial vestibular nucleus, and the lateral vestibular nucleus.

177

Regions of the Head

9. Oral Cavity & Perioral Regions

Oral Cavity: Overview

Philtrum Nasolabial crease

Upper lip

Oral fissure

Angle of mouth

Lower lip

Fig. 9.1 Lips and labial creases Anterior view. The upper and lower lips meet at the angle of the mouth. The oral fissure opens into the oral cavity. Changes in the lips noted on visual inspection may yield important diagnostic clues: Blue lips (cyanosis) suggest a disease of the heart, lung, or both, and deep nasolabial creases may reflect chronic diseases of the digestive tract.

Fig. 9.2 Oral cavity Anterior view. The dental arches (with the alveolar processes of the maxilla and mandible) subdivide the oral cavity into two parts: • Oral vestibule: portion outside the dental arches, bounded on one side by the lips/cheek and on the other by the dental arches. • Oral cavity proper: region within the dental arches, bounded posteriorly by the palatoglossal arch. The oral cavity is lined by oral mucosa, which is divided into lining, masticatory, and gingival mucosa. The mucosal lining consists of nonkeratinized, stratified squamous epithelium that is moistened by secretions from the salivary glands. The keratinized, stratified squamous epithelium of the skin blends with the nonkeratinized, stratified squamous epithelium of the oral cavity at the vermilion border of the lip. The masticatory mucosa is orthokeratinized to withstand masticatory stress. The gingiva that supports the teeth is keratinized.

Upper lip Frenulum of upper lip Oral vestibule

Hard palate

Palatoglossal arch

Soft palate

Palatopharyngeal arch

Uvula Palatine tonsil

Faucial isthmus

Dorsum of tongue

Oral cavity proper

Oral vestibule

Frenulum of lower lip Lower lip

Nasal septum

Hard palate

Torus tubarius

Airway

Oral cavity proper

Foodway

Soft palate

Superior labial vestibule

Uvula Nasopharynx

Upper lip Lower lip

Oropharynx

Tongue Hyoid bone

Mandible Mylohyoid A

Geniohyoid

Fig. 9.3 Organization and boundaries of the oral cavity Midsagittal section, left lateral view. The oral cavity is located below the nasal cavity and anterior to the pharynx. The inferior boundary of the oral cavity proper is formed by mylohyoid muscle. The roof of the oral cavity is formed by the hard palate in its anterior two thirds and

178

Laryngopharynx

Epiglottis B

by the soft palate (velum) in its posterior third. The uvula hangs from the soft palate between the oral cavity and pharynx. The midportion of the pharynx (oropharynx) is the area in which the airway and foodway intersect (B).

Regions of the Head

Fig. 9.4 Maxillary and mandibular arches A Maxilla. Inferior view. B Mandible. Superior view. There are three basic types of teeth — incisiform (incisors), caniniform (canines), and molariform (premolars and molars) — that perform cutting, piercing, and grinding actions, respectively. Each half of the maxilla and mandible contains the following sets of teeth: • Anterior teeth: two incisors and one canine tooth. • Posterior (postcanine) teeth: two premolars and three molars.

9. Oral Cavity & Perioral Regions

Incisive fossa

Incisors

Interalveolar septum

Canine

Premolars

Incisive suture

Median palatine suture

Each tooth is given an identification code to describe the specific location of dental lesions such as caries (see p. 180).

Molars

Greater palatine foramen

A Transverse palatine suture

Posterior nasal spine

Lesser palatine foramen

Head (condyle) of mandible Pterygoid fovea

Coronoid process

Molars

Angle of mandible

Mental (genial) spines

Premolars

Interalveolar septum

Canine Incisors

B

179

Regions of the Head

9. Oral Cavity & Perioral Regions

Permanent Teeth

1

2

3

4

5

6

32 31

7

9

8

10

11

12 13

14

15

16

17 18

30

29

28

27

26

25

Fig. 9.5 Coding the permanent teeth In the United States, the permanent teeth are numbered sequentially, not assigned to quadrants. Progressing in a clockwise fashion (from the perspective of the viewer), the teeth of the upper arc are numbered

24

23

22

21

20

19

1 to 16, and those of the lower are considered 17 to 32. Note: The third upper molar (wisdom tooth) on the patient’s right is considered 1.

Labial

Mesial Distal

Buccal

Lingual

Palatal

Buccal

Distal

Mesial Labial A

Fig. 9.6 Designation of tooth surfaces A Inferior view of the maxillary dental arch. B Superior view of the mandibular dental arch. The mesial and distal tooth surfaces are those closest to and farthest from the midline, respectively. The term labial is

180

B

used for incisors and canine teeth, and buccal is used for premolar and molar teeth. Palatal denotes the inside surface of maxillary teeth, and lingual denotes the inside surface of mandibular teeth. These designations are used to describe the precise location of small carious lesions.

Regions of the Head

Maxillary sinus

Nasal septum

Orbit

9. Oral Cavity & Perioral Regions

Articular tubercle

Mandibular (glenoid) fossa Condylar process 1

16

17 32 Third molar (wisdom tooth)

Mandibular angle

31

Mandibular canal

30 29

28

27

26

25

Fig. 9.7 Dental panoramic tomogram The dental panoramic tomogram (DPT) is a survey radiograph that allows a preliminary assessment of the temporomandibular joints, maxillary sinuses, maxilla, mandible, and dental status (carious lesions, location of the wisdom teeth). It is based on the principle of conventional tomography in which the x-ray tube and film are moved about the plane of interest to blur out the shadows of structures outside the sectional plane. The plane of interest in the DPT is shaped like a parabola, conforming to the shape of the jaws. In the case shown here, all four wisdom teeth (third molars) should be extracted: teeth 1, 16, and

Bite guide of scanner

17 are not fully erupted, and tooth 32 is horizontally impacted (cannot erupt). If the DPT raises suspicion of caries or root disease, it should be followed with spot radiographs so that specific regions of interest can be evaluated at higher resolution. (Tomogram courtesy of Prof. Dr. U. J. Rother, director of the Department of Diagnostic Radiology, Center for Dentistry and Oromaxillofacial Surgery, Eppendorf University Medical Center, Hamburg, Germany.) Note: The upper incisors are broader than the lower incisors, leading to a “cusp-and-fissure” type of occlusion (see p. 183).

181

Regions of the Head

9. Oral Cavity & Perioral Regions

Structure of the Teeth

Neck (cementoenamel junction)

Cusp of tooth

Enamel

Crown

Crown Root

Dentine

Pulp chamber

A Neck

Fig. 9.8 Parts of the tooth A Individual tooth (mandibular molar). B Cross section of a tooth (mandibular incisor). The teeth consist of an enamel-covered crown that meets the cementum-covered roots at the neck (cervical margin). The body of the tooth is primarily dentine.

Gingival margin Cementum

Periodontal ligament Root Alveolar bone Apex of root Apical foramen B

Table 9.1 Structures of the tooth Protective coverings: These hard, avascular layers of tissue protect the underlying body of the tooth. They meet at the cervical margin (neck, cementoenamel junction).

Enamel: Hard, translucent covering of the crown of the tooth. Maximum thickness (2.5 mm) occurs over the cusps. The enamel covering meets the cementum at the neck (cervical margin, cementoenamel junction). Failure to do so exposes the underlying dentine, which has extremely sensitive pain responses.

Body of the tooth: The tooth is primarily composed of dentine, which is supported by the vascularized dental pulp.

Dentine: Tough tissue composing the majority of the body of the tooth. It consists of extensive networks of tubules (intratubular dentine) surrounded by peritubular dentine. The tubules connect the underlying dental pulp to the overlying tissue. Exposed dentine is extremely sensitive due to extensive innervation via the dental pulp.

Cementum: Bonelike covering of the dental roots, lacking neurovascular structures.

Dental pulp: Located in the pulp chamber, the dental pulp is a well-vascularized layer of loose connective tissue. Neurovascular structures enter the apical foramen at the apex of the root. The dental pulp receives sympathetic innervation from the superior cervical ganglion and sensory innervation from the trigeminal ganglion (CN V). Periodontium: The tooth is anchored and supported by the periodontium, which consists of several tissue types. Note: The cementum is also considered part of the periodontium.

Periodontal ligament: Dense connective tissue fibers that connect the cementum of the roots in the osseous socket to the alveolar bone. Alveolar bone (alveolar processes of maxilla and mandible): The portion of the maxilla or mandible in which the dental roots are embedded are considered the alveolar processes (the more proximal portion of the bones are considered the body). Gingiva: The attached gingivae bind the alveolar periosteum to the teeth; the free gingiva composes the 1 mm tissue radius surrounding the neck of the tooth. A mucosogingival line marks the boundary between the keratinized gingivae of the mandibular arch and the nonkeratinized lingual mucosa. The palatal mucosa is masticatory (orthokeratinized), so no visual distinction can be made with the gingiva of the maxillary arch. Third molars (wisdom teeth) often erupt through the mucosogingival line. The oral mucosa cannot support the tooth, and food can become trapped in the regions lacking attached gingiva.

182

Regions of the Head

Fig. 9.9 Periodontium The tooth is anchored in the alveolus by a special type of syndesmosis (gomphosis). The periodontium, the all-encompassing term for the tissues that collectively invest and support the tooth, consists of: • • • •

9. Oral Cavity & Perioral Regions

Gingiva

Cementum Periodontal ligament Alveolar wall of alveolar bone Gingiva

Sharpey fibers

The Sharpey fibers are collagenous fibers that pass obliquely downward from the alveolar bone and insert into the cementum of the tooth. This downward obliquity of the fibers transforms masticatory pressures on the dental arch into tensile stresses acting on the fibers and anchored bone (pressure would otherwise lead to bone atrophy).

Fig. 9.10 Connective tissue fibers in the gingiva Many of the tough collagenous fiber bundles in the connective tissue core of the gingiva above the alveolar bone are arranged in a screwlike pattern around the tooth, further strengthening its attachment.

Alveolar wall

Cementum A

B

Decussating interdental fibers Interdental papilla Circular fibers

Premolars

Molars

Canine Incisors Occlusal planes

A

B

Fig. 9.11 Occlusal plane and dental arches A Occlusal plane. The maxilla and mandible present a symmetrical arrangement of teeth. The occlusal plane (formed when the mouth is closed) often forms a superiorly open arch (von Spee curve, red). B Cusp-and-fissure dentition. With the mouth closed (occlusal position), the maxillary teeth are apposed to their mandibular counterparts. They are offset relative to one another so that the cusps of

C

one tooth fit into the fissures of the two opposing teeth (cusp-andfissure dentition, blue). Because of this arrangement, every tooth comes into contact with two opposing teeth. This offset results from the slightly greater width of the maxillary incisors. C Dental arches. The teeth of the maxilla (green) and mandible (blue) are arranged in superior and inferior arches. The superior dental arch forms a semi-ellipse, and the inferior arch is shaped like a parabola.

183

Regions of the Head

9. Oral Cavity & Perioral Regions

Incisors, Canines & Premolars Central incisors

Root (flattened mesiodistally)

Incisal edge Labial

Distal

Palatal

Labial

A

Distal

Palatal

B

Labial

Distal

C

Fig. 9.12 Incisors A Central maxillary incisor (9). B Lateral maxillary incisor (10). C Mandibular incisors (23–26).

Table 9.2 Incisors and canines Tooth

Crown

Surfaces

Root(s)

Incisors: The incisors have a sharp-edged crown for biting off bits of food. The palatal surface often bears a blind pit (foramen cecum), a site of predilection for dental caries. The maxillary incisors are considerably larger than the mandibular incisors. This results in cusp-and-fissure dentition (see Fig. 9.11).

Maxillary

Central incisor (8, 9); see Fig. 9.12A Lateral incisor (7, 10); see Fig. 9.12B

Mandibular

Roughly trapezoidal in the labial view; contains an incisal edge with 3 tubercles (mamelons)

Central incisor (25, 24); see Fig. 9.12C

Labial: Convex Palatal: Concavoconvex

1 rounded root

Labial: Convex Lingual: Concavoconvex

1 root, slightly flattened

Lateral incisor (26, 23) see Fig. 9.12C Canines: These teeth (also known as cuspids or eyeteeth) are developed for piercing and gripping food. The crown is thicker mesially than distally and has greater curvature (arrow, Fig. 9.13A).

Maxillary (upper) canine (6, 11); see Fig. 9.13A

Roughly trapezoidal with 1 labial cusp

Mandibular (lower) canine (27, 22); see Fig. 9.13B

Labial: Convex Lingual: Concavoconvex

Labial

Distal

Palatal

Fig. 9.13 Canines (cuspids) A Maxillary canine (11). B Mandibular canine (22).

184

1 root, the longest of the teeth (note: mandibular canines are occasionally bifid)

Labial cusp

Labial cusp A

Labial: Convex Palatal: Concavoconvex

Occlusal

B

Labial

Distal

Lingual

Regions of the Head

Buccal root

9. Oral Cavity & Perioral Regions

Palatal root

Longitudinal groove

Mesiodistal fissure Palatal cusp

Buccal cusp A

Buccal

Distal

Occlusal

Buccal cusp

B

Buccal

Distal

Occlusal Buccal cusp

Mesial occlusal pit

Mesiodistal fissure

Distal occlusal pit

C

Buccal

Distal

Occlusal

D

Buccal

Distal

Occlusal

Fig. 9.14 Premolars (bicuspids) A First maxillary premolar (12). B Second maxillary premolar (13). C First mandibular premolar (21). D Second mandibular premolar (20).

Table 9.3 Premolars The premolars represent a transitional form between the incisors and molars. Like the molars, they have cusps and fissures, indicating that their primary function is the grinding of food rather than biting or tearing. Tooth

Maxillary

1st premolar (5, 12); see Fig. 9.14A

Crown

Surfaces

Root(s)

2 cusps (1 buccal, 1 palatal, separated by a mesodistal fissure)

Buccal, distal, palatal/lingual, and mesial: All convex, slightly flattened. The mesial surface often bears a small pit that is difficult to clean and vulnerable to caries.

The only premolar with 2 roots (1 buccal, 1 palatal)

2nd premolar (4, 13); see Fig. 9.14B

Mandibular

1st premolar (28, 21); see Fig. 9.14C

2 cusps (1 tall buccal cusp connected to 1 smaller lingual cusp); the ridge between the cusps creates a mesial and a distal occlusal pit

2nd premolar (29, 20); see Fig. 9.14D

3 cusps (1 tall buccal cusp separated from 2 smaller lingual cusps by a mesiodistal fissure)

Occlusal: The occlusal surfaces of the maxillary premolars tend to be more oval (less circular or square) than the mandibular premolars.

1 root divided by a longitudinal groove and containing 2 root canals 1 root (occasionally bifid)

1 root

185

Regions of the Head

9. Oral Cavity & Perioral Regions

Molars

Table 9.4 Molars Most of the molars have three roots to withstand the greater masticatory pressures in the molar region. Because the molars crush and grind food, they have a crown with a plateau. The fissures between the cusps are a frequent site of caries formation in adolescents. Note: The roots of the third molars (wisdom teeth, which erupt after 16 years of age, if at all) are commonly fused together, particularly in the upper third molar. The mandibular third molars erupt anterosuperiorly, and the maxillary third molars erupt posteroinferiorly. Impactions are therefore most common in mandibular wisdom teeth. Tooth

Maxillary

Mandibular

186

Crown

Surfaces

Root(s)

1st molar (3, 14); see Fig. 9.15A

4 cusps (1 at each corner of its occlusal surface); a ridge connects the mesiopalatal and distobuccal cusps

Buccal, distal, palatal/lingual, and mesial: All convex, slightly flattened.

3 roots (2 buccal and 1 palatal)

2nd molar (2, 15); see Fig. 9.16A

4 cusps (though the distopalatal cusp is often small or absent)

Occlusal: Rhomboid

3 roots (2 buccal and 1 palatal), occasionally fused

3rd molar (wisdom tooth, 1, 16); see Fig. 9.17A

3 cusps (no distopalatal)

1st molar (30, 19); see Fig. 9.15B

5 cusps (3 buccal and 2 lingual), all of which are separated by fissures

2nd molar (31, 18); see Fig. 9.16B

4 cusps (2 buccal and 2 lingual)

3rd molar (wisdom tooth, 32, 17); see Fig. 9.17B

May resemble either the 1st or 2nd molar

3 roots (2 buccal and 1 palatal), often fused

Buccal, distal, palatal/lingual, and mesial: All convex, slightly flattened.

2 roots (1 mesial and 1 distal); widely spaced 2 roots (1 mesial and 1 distal)

Occlusal: Rectangular 2 roots, often fused

Regions of the Head

Distobuccal cusp

Palatal root

9. Oral Cavity & Perioral Regions

Palatal root

Mesiopalatal cusp

Distopalatal cusp

A

Buccal

Distal

Palatal

Occlusal

A

Buccal

Distal

Palatal

Occlusal

B

Buccal

Distal

Lingual

Occlusal

B

Buccal

Distal

Lingual

Occlusal

Fig. 9.15 First molars A Maxillary first molar (14). B Mandibular first molar (19). Note: The term lingual is used for the mandibular teeth, the term palatal for the maxillary.

Fig. 9.16 Second molars A Maxillary second molar (15). B Mandibular second molar (18).

Palatal root (fused with buccal roots)

A

Buccal

Distal

Palatal

Occlusal

B

Buccal

Distal

Lingual

Occlusal

Fig. 9.17 Third molars (wisdom teeth) A Maxillary third molar (16). B Mandibular third molar (17).

187

Regions of the Head

9. Oral Cavity & Perioral Regions

Deciduous Teeth

Birth

6 months

1 year

A

B

C

D

E 2½ years

Fig. 9.18 Deciduous teeth Left side. The deciduous dentition (baby teeth) consists of only 20 teeth. Each of the four quadrants contains the following teeth: A Central incisor (first incisor). B Lateral incisor (second incisor). C Canine (cuspid). D First molar (6-yr molar). E Second molar (12-yr molar).

4 years

To distinguish the deciduous teeth from the permanent teeth, they are coded with letters. The upper arch is labeled A to J, the lower is labeled K to T. 6 years

Table 9.5 Eruption of the teeth The eruptions of the deciduous and permanent teeth are called the first and second dentitions, respectively. Types of teeth are ordered by the time of eruption; individual teeth are listed from left to right (viewer’s perspective). Type of tooth

Tooth

8 years

Time of eruption

First dentition (deciduous teeth)

Central incisor

E, F

P, O

6–8 months

Lateral incisor

D, G

Q, N

8–12 months

First molar

B, I

S, L

12–16 months

Canine

C, H

R, M

15–20 months

Second molar

A, J

T, K

20–40 months 12 years

Second dentition (permanent teeth)

First molar

3, 14

30, 19

6–8 years (“6-yr molar”)

Central incisor

8, 9

25, 24

6–9 years

Lateral incisor

7, 10

26, 23

7–10 years

First premolar

5, 12

28, 21

9–13 years

Canine

6, 11

27, 22

9–14 years

Second premolar

4, 13

29, 20

11–14 years

Second molar

2, 15

31, 18

10–14 years (“12-yr molar”)

Third molar

1, 16

32, 17

16–30 years (“wisdom tooth”)

188

10 years

Fig. 9.19 Eruption pattern of the deciduous and permanent teeth Left maxillary teeth. Deciduous teeth (black), permanent teeth (red). Eruption times can be used to diagnose growth delays in children.

Regions of the Head

A B T

C

S

R

D Q

E P

O

N

M

Infraorbital foramen

I J

H

G

F

9. Oral Cavity & Perioral Regions

L

K Anterior nasal spine

Fig. 9.20 Coding the deciduous teeth The upper right molar is considered A. The lettering then proceeds clockwise along the upper arc and back across the lower.

Fig. 9.21 Dentition of a 6-year-old child Anterior (A,B) and left lateral (C,D) views of maxillary (A,C) and mandibular (B,D) teeth. The anterior bony plate over the roots of the deciduous teeth has been removed to display the underlying permanent tooth buds (blue). At 6 years of age, all the deciduous teeth have erupted and are still present, along with the first permanent tooth, the first molar.

Second permanent premolar

Intermaxillary suture

First permanent premolar

Second deciduous molar

Permanent canine

First deciduous molar Permanent lateral incisor

A

Permanent central incisor

Deciduous lateral incisor

Deciduous canine

Deciduous canine Deciduous Deciduous central incisor lateral incisor

First deciduous molar

Second deciduous molar First permanent molar Second permanent molar Second permanent premolar

B

First permanent premolar Mental foramen

Permanent central incisor

Permanent lateral incisor

Permanent canine

Permanent canine Second permanent molar Second permanent premolar

Permanent lateral incisor First permanent premolar Deciduous central incisor

C

Deciduous Deciduous lateral incisor canine

First deciduous molar

Second deciduous molar

First permanent molar

Second deciduous molar First deciduous molar

First permanent molar

Deciduous canine Deciduous lateral incisor Permanent central incisor Second permanent molar

Permanent lateral incisor

D

Second permanent premolar Permanent canine

First permanent premolar

189

Regions of the Head

9. Oral Cavity & Perioral Regions

Hard Palate

Alveolar process of maxilla Palatine process of maxilla (floor of nasal cavity)

Floor of maxillary sinus (palatine and alveolar processes)

Palatine bone, horizontal plate

Palatine bone, perpendicular plate Palatine bone, pyramidal process

A

Fig. 9.22 Hard palate in the skull base Inferior view.

Maxilla, zygomatic process

Lateral pterygoid plate of sphenoid bone Medial pterygoid plate of sphenoid bone

Incisive fossa Maxilla, alveolar process

Maxilla, palatine process (roof of oral cavity) Choanae

Fig. 9.23 Bones of the hard palate A,C Superior view. The upper part of the PD[LOOD LV UHPRYHG 7KH ÁRRU RI WKH QDVDO cavity (A) and the roof of the oral cavity (B) are formed by the union of the palatine processes of two maxillary bones with the horizontal plates of two palatine bones. Cleft palate results from a failed fusion of the palatine processes at the median palatine suture. B,D Inferior view. The nasal cavity communicates with the nasopharynx via the choanae, which begin at the posterior border of the hard palate. The two nasal cavities communicate with the oral cavity via the incisive canals (D), which combine and emerge at the incisive foramen (E). C,E Oblique posterior view. This view illustrates the close anatomical relationship between the oral and nasal cavities. Note: The pyramidal process of the palatine bone is integrated into the lateral plate of the pterygoid process of the sphenoid bone. The palatine margin of the vomer articulates with the hard palate along the nasal crest.

Palatine bone, horizontal plate

Sphenoid bone

Palatine bone, pyramidal process Vomer

B

Maxilla, zygomatic process

Middle nasal concha (ethmoid bone) Inferior nasal concha

Choana Sphenoid bone, lateral pterygoid plate

Vomer

Palatine bone, pyramidal process C

Maxilla, alveolar process

Palatine bone, horizontal plate Maxilla, palatine process Incisive fossa (opening of incisive canal)

190

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Regions of the Head

9. Oral Cavity & Perioral Regions

Anterior nasal spine (cut)

Incisive canal

Maxillary sinus

Nasal crest (cut)

Palatine process of maxilla Palatine bone, perpendicular plate

Transverse palatine suture Greater palatine canal

Palatine bone, pyramidal process

Pterygoid process, medial plate (sphenoid bone)

Pterygoid process, lateral plate (sphenoid bone)

Palatine bone, posterior nasal spine

D

Incisive foramen (opening of incisive canal)

Palatine process of maxilla

Transverse palatine suture

Median (intermaxillary) palatine suture

Greater palatine foramen

Lesser palatine foramen

Inferior orbital fissure

Pterygoid process, medial plate

Pyramidal process of palatine bone

Pterygoid fossa

Choana Posterior nasal spine

Pterygoid process, lateral plate Vomer

E

Anterior clinoid process

Foramen ovale

Septum of sphenoid sinus

Optic canal

Superior orbital fissure

Ostium of sphenoid sinus

Middle concha

Pterygoid fossa

Ethmoid bone, perpendicular plate

Inferior orbital fissure

Inferior concha

Choana

Pterygoid process, lateral plate

Vomer Median palatine suture F

Pterygoid canal

Pterygoid process, medial plate Incisive foramen

Palatine process of maxilla

191

Regions of the Head

9. Oral Cavity & Perioral Regions

Mandible & Hyoid Bone

Head (condyle) of mandible

Condylar process Coronoid process

Oblique line

Ramus of mandible

Head (condyle) of mandible Alveolar part of mandible Body of mandible

Alveoli (tooth sockets)

Coronoid process

Mental protuberance

A

Lingula

Mandibular notch Coronoid process

Mandibular foramen Mylohyoid groove

Head (condyle) of mandible Pterygoid fovea

Mylohyoid line

Condylar process Mandibular foramen

Superior and inferior genial (mental) spines

B Submandibular fossa

Digastric fossa

Ramus of mandible Alveolar part Mental tubercle

C

Angle

Mental foramen

Oblique line

Fig. 9.24 Mandible A Anterior view. B Posterior view. C Oblique left lateral view. The mandibular teeth are embedded in the alveolar processes of the mandible that run along the superior border of the body of the mandible. The vertical ramus joins the body of the mandible at the mandibular angle. The ramus contains a coronoid process (site of attachment of the temporalis) and a condylar process that are separated by the mandibular notch. The convex surface of the condylar process (the head of

192

the mandible) articulates via an articular disk with the mandibular (glenoid) fossa of the temporal bone at the temporomandibular joint (see p. 194). The depression on the anteromedial side of the condylar process (pterygoid fovea) is a site of attachment of the lateral pterygoid. The inferior alveolar nerve (a branch of CN V3) enters the mandibular foramen and runs through the mandibular canal in the body of the mandible, exiting the mental foramen as the mental nerve.

Regions of the Head

9. Oral Cavity & Perioral Regions

A

B

C

Fig. 9.25 Age-related changes in the mandible The structure of the mandible is greatly influenced by the alveolar processes of the teeth. Because the angle of the mandible adapts to changes in the alveolar process, the angle between the body and ramus also varies with age-related changes in the dentition. The angle measures approximately 150 degrees at birth, and approximately 120 to 130 degrees in adults, decreasing to 140 degrees in the edentulous mandible of old age. A At birth the mandible is without teeth, and the alveolar part has not yet formed. B In children the mandible bears the deciduous teeth. The alveolar part is still relatively poorly developed because the deciduous teeth are considerably smaller than the permanent teeth.

Lesser horn

A

D

C In adults the mandible bears the permanent teeth, and the alveolar part of the bone is fully developed. D Old age is characterized by an edentulous mandible with resorption of the alveolar process. Note: The resorption of the alveolar process with advanced age leads to a change in the position of the mental foramen (which is normally located below the second premolar tooth, as in C). This change must be taken into account in surgery or dissections involving the mental nerve.

Greater horn

Body

Lesser horn

B

Greater horn

Body

Lesser horn

Greater horn

C

Fig. 9.26 Hyoid bone A Anterior view. B Posterior view. C Oblique left lateral view. The hyoid bone is suspended by muscles and ligaments between the oral

floor and the larynx. The greater horn and body of the hyoid bone are palpable in the neck. The physiological movement of the hyoid bone can be palpated during swallowing.

193

Regions of the Head

9. Oral Cavity & Perioral Regions

Temporomandibular Joint (TMJ)

Zygomatic process of temporal bone

Articular tubercle Mandibular fossa of TMJ

Petrotympanic fissure

Postglenoid tubercle

Styloid process

External acoustic meatus (auditory canal)

Mastoid process

Atlantooccipital joint

Fig. 9.27 Mandibular fossa of the TMJ Inferior view of skull base. The head (condyle) of the mandible articulates with the mandibular fossa of the temporal bone via an articular disk. The mandibular fossa is a depression in the squamous part of the temporal bone, bounded by an articular tubercle and a postglenoid

tubercle. Unlike other articular surfaces, the mandibular fossa is covered by fibrocartilage, not hyaline cartilage. As a result, it is not as clearly delineated on the skull (compare to the atlanto-occipital joints). The external auditory canal lies just posterior to the mandibular fossa. Trauma to the mandible may damage the auditory canal.

Head (condyle) of mandible

Joint capsule

Pterygoid fovea

Neck of mandible

Coronoid process Neck of mandible

Lingula Mandibular foramen

A

B

Stylomandibular ligament

Mylohyoid groove

Fig. 9.28 Head of the mandible in the TMJ A Anterior view. B Posterior view. The head (condyle) of the mandible is markedly smaller than the mandibular fossa and has a cylindrical shape. Both factors increase the mobility of the mandibular head, allowing rotational movements about a vertical axis.

194

Lateral ligament

Fig. 9.29 Ligaments of the lateral TMJ Left lateral view. The TMJ is surrounded by a relatively lax capsule that permits physiological dislocation during jaw opening. The joint is stabilized by three ligaments: lateral, stylomandibular, and sphenomandibular (see also Fig. 9.30). The strongest of these ligaments is the lateral ligament, which stretches over and blends with the joint capsule.

Regions of the Head

9. Oral Cavity & Perioral Regions

Articular tubercle

Pterygoid process, lateral plate

Articular disk Pterygospinous ligament

Postglenoid tubercle

Mandibular notch

Joint capsule

Sphenomandibular ligament

Head (condyle) of mandible

Stylomandibular ligament

Stylomandibular ligament

Pterygoid process, medial plate

Fig. 9.30 Ligaments of the medial TMJ Left medial view. Note the sphenomandibular ligament. The variable pterygospinous ligament is also present.

Fig. 9.31 Opened TMJ Left lateral view. The TMJ capsule begins at the articular tubercle and extends posteriorly to the petrotympanic fissure (see Fig. 9.27). Interposed between the mandibular head and fossa is the fibrocartilaginous articular disk, which is attached to the joint capsule on all sides.

Posterior division Auriculotemporal nerve

Mandibular nerve (CN V3) Anterior division Deep temporal nerve, posterior branch Masseteric nerve

Fig. 9.32 Dislocation of the TMJ The head of the mandible may slide past the articular tubercle when the mouth is opened, dislocating the TMJ. This may result from heavy yawning or a blow to the opened mandible. When the joint dislocates, the mandible becomes locked in a protruded position and can no longer be closed. This condition is easily diagnosed clinically and is reduced by pressing on the mandibular row of teeth.

Fig. 9.33 Sensory innervation of the TMJ capsule Superior view. The TMJ capsule is supplied by articular branches arising from three nerves from the mandibular division of the trigeminal nerve (CN V3): • Auriculotemporal nerve • Deep temporal nerve, posterior branch • Masseteric nerve

195

Regions of the Head

9. Oral Cavity & Perioral Regions

Temporomandibular Joint (TMJ): Biomechanics

Retrusion

Transverse axis through head of mandible (axis of rotation)

150°

A

Head of mandible

B

Median plane

Protrusion

Axis of rotation

Axis of rotation

Resting condyle Swinging condyle

Balance side (mediotrusion)

Working side (laterotrusion) Working side

C

Bennett angle

Fig. 9.34 Movements of the mandible in the TMJ Superior view. Most of the movements in the TMJ are complex motions that have three main components: • Rotation (opening and closing the mouth) • Translation (protrusion and retrusion of the mandible) • Grinding movements during mastication A Rotation. The axis for joint rotation runs transversely through both heads of the mandible. The two axes intersect at an angle of approximately 150 degrees (range of 110 to 180 degrees between individuals). During this movement the TMJ acts as a hinge joint (abduction/depression and adduction/elevation of the mandible). In humans, pure rotation in the TMJ usually occurs only during sleep with the mouth slightly open (aperture angle up to approximately 15 degrees). When the mouth is opened past 15 degrees, rotation is combined with translation (gliding) of the mandibular head.

196

Balance side

D

B Translation. In this movement the mandible is advanced (protruded) and retracted (retruded). The axes for this movement are parallel to the median axes through the center of the mandibular heads. C Grinding movements in the left TMJ. In describing these lateral movements, a distinction is made between the “resting condyle” and the “swinging condyle.” The resting condyle on the left working side rotates about an almost vertical axis through the head of the mandible (also a rotational axis), whereas the swinging condyle on the right balance side swings forward and inward in a translational movement. The lateral excursion of the mandible is measured in degrees and is called the Bennett angle. During this movement the mandible moves in laterotrusion on the working side and in mediotrusion on the balance side. D Grinding movements in the right TMJ. Here, the right TMJ is the working side. The right resting condyle rotates about an almost vertical axis, and the left condyle on the balance side swings forward and inward.

Regions of the Head

Lateral pterygoid muscle, superior head

9. Oral Cavity & Perioral Regions

Articular tubercle Mandibular fossa Articular disk Head of mandible Joint capsule Lateral pterygoid muscle, inferior head

A

Lateral pterygoid muscle, superior head Articular disk Head of mandible Joint capsule Lateral pterygoid muscle, inferior head

15°

Axis of rotation

B Lateral pterygoid muscle, superior head

Mandibular fossa Articular disk Joint capsule Lateral pterygoid muscle, inferior head

>15°

C

Fig. 9.35 Movements of the TMJ Left lateral view. Each drawing shows the left TMJ, including the articular disk and capsule and the lateral pterygoid muscle. Each schematic diagram at right shows the corresponding axis of joint movement. The muscle, capsule, and disk form a functionally coordinated musculodisco-capsular system and work closely together when the mouth is opened and closed. Note: The space between the muscle heads is greatly exaggerated for clarity.

A Mouth closed. When the mouth is in a closed position, the head of the mandible rests against the mandibular fossa of the temporal bone with the intervening articular disk. B Mouth opened to 15 degrees. Up to 15 degrees of abduction, the head of the mandible remains in the mandibular fossa. C Mouth opened past 15 degrees. At this point the head of the mandible glides forward onto the articular tubercle. The joint axis that runs transversely through the mandibular head is shifted forward. The articular disk is pulled forward by the superior part of the lateral pterygoid muscle, and the head of the mandible is drawn forward by the inferior part of that muscle.

197

Regions of the Head

9. Oral Cavity & Perioral Regions

Muscles of Mastication: Overview The muscles of mastication are derived from the first branchial arch and are located at various depths in the parotid and infratemporal regions of the face. They attach to the mandible and receive their motor

innervation from the mandibular division of the trigeminal nerve (CN V3). The muscles of the oral floor (mylohyoid and geniohyoid) are found on pp. 178, 203.

Table 9.6 Masseter and temporalis muscles Muscle

Masseter

Origin

Insertion

Innervation*

Action

① Superficial head

Zygomatic bone (maxillary process) and zygomatic arch (lateral aspect of anterior ⅔)

Mandibular angle and ramus (lower posterior lateral surface)

Masseteric n. (anterior division of CN V3)

Elevates mandible; also assists in protraction, retraction, and side-to-side motion

Middle head

Zygomatic arch (medial aspect of anterior ⅔)

Mandibular ramus (central part)

Zygomatic arch (deep surface of posterior ⅓)

Mandibular ramus (upper portion) and lateral side of coronoid process

Temporal fascia

Coronoid process of mandible (apex and medial and anterior surfaces)

Deep temporal nn. (anterior division of CN V3)

Vertical (anterior) fibers: Elevate mandible Horizontal (posterior) fibers: Retract (retrude) mandible Unilateral: Lateral movement of mandible (chewing)

②

Temporalis

Deep head

③ Superficial head ④

Deep head

Temporal fossa (inferior temporal line)

*The muscles of mastication are innervated by motor branches of the mandibular nerve (CN V3), the 3rd division of the trigeminal nerve (CN V).

⑤

④ ③

①

⑥

⑦ ②

⑧

Fig. 9.36 Masseter

Fig. 9.37 Temporalis

Fig. 9.38 Pterygoids

Table 9.7 Lateral and medial pterygoid muscles Muscle

Lateral pterygoid

Medial pterygoid

198

Origin

Insertion

Innervation

Action

Mandibular n. (CN V3) via lateral pterygoid n. (from anterior division of CN V3)

Bilateral: Protrudes mandible (pulls articular disk forward) Unilateral: Lateral movements of mandible (chewing)

Mandibular n. (CN V3) via medial pterygoid n. (from trunk of CN V3)

Raises (adducts) mandible

⑤

Superior head

Greater wing of sphenoid bone (infratemporal crest)

Mandible (pterygoid fovea) and temporomandibular joint (articular disk)

⑥

Inferior head

Lateral pterygoid plate (lateral surface)

Mandible (pterygoid fovea and condylar process)

⑦

Superficial head

Maxilla (maxillary tuberosity) and palatine bone (pyramidal process)

Pterygoid tuberosity on medial surface of the mandibular angle

⑧

Deep head

Medial surface of lateral pterygoid plate and pterygoid fossa

Regions of the Head

Zygomatic arch

Frontal bone

9. Oral Cavity & Perioral Regions

Parietal bone

Masseter, deep head

Temporalis

Superior temporal line

External acoustic meatus Mastoid process Zygomatic arch

Joint capsule

Temporalis

Styloid process A

Masseter, superficial head

Lateral ligament Superior temporal line

Fig. 9.39 Temporalis and masseter Left lateral view. A Superficial dissection. B Deep dissection. The masseter and zygomatic arch have been partially removed to show the full extent of the temporalis. The temporalis is the most powerful muscle of mastication, doing approximately half the work. It works with the masseter (consisting of a superficial and a deep part) to elevate the mandible and close the mouth. Note: A small portion of the lateral pterygoid is visible in B.

Joint capsule Lateral ligament Lateral pterygoid B

Coronoid process

Masseter

199

Regions of the Head

9. Oral Cavity & Perioral Regions

Muscles of Mastication: Deep Muscles

Lateral pterygoid, superior head (cut)

Temporalis (cut)

Articular disk

Lateral pterygoid, superior and inferior heads

Lateral pterygoid, inferior head (cut) Medial pterygoid, deep head

Medial pterygoid, superficial and deep heads

Lateral plate, pterygoid process (sphenoid bone)

Masseter (cut) B

A

Fig. 9.40 Lateral and medial pterygoid muscles Left lateral views. A The coronoid process of the mandible has been removed here along with the lower part of the temporalis so that both pterygoid muscles can be seen. B Here the temporalis has been completely removed, and the superior and inferior heads of the lateral pterygoid have been windowed. The lateral pterygoid initiates mouth opening, which is then continued by the digastric and the suprahyoid muscles, along with gravity.

Medial pterygoid, superficial head

With the temporomandibular joint opened, we can see that fibers from the lateral pterygoid blend with the articular disk. The lateral pterygoid functions as the guide muscle of the temporomandibular joint. Because both its superior and inferior heads are active during all movements, its actions are more complex than those of the other muscles of mastication. The medial pterygoid runs almost perpendicular to the lateral pterygoid and contributes to the formation of a muscular sling, along with the masseter, that partially encompasses the mandible (see Fig. 9.41).

Mandibular fossa, articular surface

Temporalis

Lateral pterygoid, superior head

Articular disk Head of mandible, articular surface

Lateral pterygoid, inferior head

Lateral pterygoid, inferior head, in pterygoid fovea

Masseter, deep part

Coronoid process (with temporalis)

Medial pterygoid, deep head

Fig. 9.41 Masticatory muscular sling Oblique posterior view. The masseter and medial pterygoid form a muscular sling in which the mandible is suspended. By combining the actions of both muscles into a functional unit, this sling enables powerful closure of the jaws.

200

Masseter, superficial part Mandibular angle

Pterygoid process, medial plate

Regions of the Head

9. Oral Cavity & Perioral Regions

Superior sagittal sinus

Falx cerebri

Frontal lobe

Inferior sagittal sinus

Temporal fascia Temporal lobe

Dura mater

Ethmoid air cells

Optic nerve (CN II)

Sphenoid sinus

Temporalis, superficial and deep heads

Zygomatic arch

Lateral pterygoid, superior head

Pterygoid process, lateral plate Nasopharynx

Masseter, deep head

Parotid gland

Lateral pterygoid, inferior head Medial pterygoid, deep and superficial heads

Oropharynx

Masseter, superficial head

Tongue

Inferior alveolar nerve (CN V3) in mandibular canal

Mandible

Lingual septum Hyoglossus

Submandibular gland

Platysma

Geniohyoid muscle

Digastric muscle, anterior belly

Mylohyoid muscle

Fig. 9.42 Muscles of mastication, coronal section at the level of the sphenoid sinus Posterior view.

201

Regions of the Head

9. Oral Cavity & Perioral Regions

Suprahyoid Muscles The suprahyoid and infrahyoid muscles attach to the hyoid bone inferiorly and superiorly, respectively. The infrahyoid muscles depress the

hyoid during phonation and swallowing. They are discussed with the suprahyoid muscles and larynx in the neck (see p. 255).

②

④

1b

③ ③

④

1a

1a

② 1b

A

Mylohyoid raphe

B

Fig. 9.43 Suprahyoid muscles: schematic A Left lateral view. B Superior view.

Table 9.8 Suprahyoid muscles Muscle

Origin

Insertion

Innervation

Action

Mylohyoid n. (from CN V3)

Elevates hyoid bone (during swallowing); assists in depressing mandible

Suprahyoid muscles: The suprahyoid muscles are also considered accessory muscles of mastication.

Digastric

1a

Anterior belly

Mandible (digastric fossa)

1b

Posterior belly

Temporal bone (mastoid notch, medial to mastoid process)

Hyoid bone (body)

Via an intermediate tendon with a fibrous loop

Facial n. (CN VII)

②

Stylohyoid

Temporal bone (styloid process)

Via a split tendon

③

Mylohyoid

Mandible (mylohyoid line)

Via median tendon of insertion (mylohyoid raphe)

Mylohyoid n. (from CN V3)

Tightens and elevates oral floor; draws hyoid bone forward (during swallowing); assists in opening mandible and moving it side to side (mastication)

④

Geniohyoid

Mandible (inferior genial [mental] spine)

Body of hyoid bone

Ventral ramus of C1

Draws hyoid bone forward (during swallowing); assists in opening mandible

202

Regions of the Head

9. Oral Cavity & Perioral Regions

Styloid process Mastoid process Digastric (posterior belly) Hyoglossus Mylohyoid

Stylohyoid Digastric (intermediate tendon)

Digastric (anterior belly)

Connective tissue sling Infrahyoid muscles (sternohyoid, thyrohyoid, and omohyoid)

Hyoid bone

A

Sublingual fold

Sublingual papilla

Oral mucosa

Genioglossus (cut)

Geniohyoid

Mylohyoid

Hyoid bone B

Hyoglossus Stylohyoid

Fig. 9.44 Suprahyoid muscles A Left lateral view. B Superior view.

203

Regions of the Head

9. Oral Cavity & Perioral Regions

Lingual Muscles There are two sets of lingual muscles: extrinsic and intrinsic. The extrinsic muscles, which are attached to specific bony sites outside the tongue, move the tongue as a whole. The intrinsic muscles, which have

no attachments to skeletal structures, alter the shape of the tongue. With the exception of the palatoglossus, the lingual muscles are supplied by the hypoglossal nerve (CN XII).

Table 9.9 Muscles of the tongue Muscle

Origin

Insertion

Innervation

Action

Inferior fibers: Hyoid body (anterosuperior surface)

Hypoglossal n. (CN XII)

Protrusion of the tongue

Extrinsic lingual muscles

Genioglossus

Mandible (superior genial [mental] spine via an intermediate tendon); more posteriorly the two genioglossi are separated by the lingual septum

Bilaterally: Makes dorsum concave Unilaterally: Deviation to opposite side

Intermediate fibers: Posterior tongue Superior fibers: Ventral surface of tongue (mix with intrinsic muscles)

Hyoglossus

Hyoid bone (greater cornu and anterior body)

Lateral tongue, between styloglossus and inferior longitudinal muscle

Depresses the tongue

Styloglossus

Styloid process of temporal bone (anterolateral aspect of apex) and stylomandibular ligament

Longitudinal part: Dorsolateral tongue (mix with inferior longitudinal muscle)

Superior and posterior movement of the tongue

Oblique part: Mix with fibers of the hyoglossus Palatoglossus

Palatine aponeurosis (oral surface)

Lateral tongue to dorsum and fibers of the transverse muscle

Vagus n. (CN X) via the pharyngeal plexus

Elevates the root of the tongue; closes the oropharyngeal isthmus by contracting the palatoglossal arch

Superior longitudinal muscle

Thin layer of muscle inferior to the dorsal mucosa; fibers run anterolaterally from the epiglottis and median lingual septum

Hypoglossal n. (CN XII)

Shortens tongue; makes dorsum concave (pulls apex and lateral margin upward)

Inferior longitudinal muscle

Thin layer of muscle superior to the genioglossus and hyoglossus; fibers run anteriorly from the root to the apex of the tongue

Shortens tongue; makes dorsum convex (pulls apex down)

Transverse muscle

Fibers run laterally from the lingual septum to the lateral tongue

Narrows tongue; elongates tongue

Vertical muscle

In the anterior tongue, fibers run inferiorly from the dorsum of the tongue to its ventral surface

Widens and flattens tongue

Intrinsic lingual muscles

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Dorsum of tongue Palatoglossus (cut)

Styloid process

Apex of tongue

Stylomandibular ligament Stylopharyngeus Styloglossus Middle pharyngeal constrictor Hyoglossus

Mandible

Hyoid bone A

Genioglossus

Geniohyoid

Lingual aponeurosis

Inferior pharyngeal constrictor

Fig. 9.45 Extrinsic and intrinsic lingual muscles A Left lateral view. B Anterior view of coronal section.

Lingual mucosa

Superior longitudinal muscle Vertical muscle of tongue

Lingual septum

Transverse muscle of tongue

Inferior longitudinal muscle Hyoglossus Genioglossus

Sublingual gland Mylohyoid

B Geniohyoid

Fig. 9.46 Unilateral hypoglossal nerve palsy Active protrusion of the tongue with an intact hypoglossal nerve (A) and with a unilateral hypoglossal nerve lesion (B). When the hypoglossal nerve is damaged on one side, the genioglossus muscle is paralyzed on the affected side. As a result, the healthy (innervated) genioglossus on the opposite side dominates the tongue across the midline toward the affected side. When the tongue is protruded, therefore, it deviates toward the paralyzed side.

Anterior belly of digastric

Paralyzed genioglossus on affected side

A

Apex of tongue

B

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Regions of the Head

9. Oral Cavity & Perioral Regions

Lingual Mucosa

Palatopharyngeal arch

Epiglottis

Fig. 9.47 Surface anatomy of the lingual mucosa Superior view. The tongue is endowed with a very powerful muscular body, making possible its motor functions in mastication, swallowing, and speaking. However, its equally important sensory functions LQFOXGLQJ WDVWH DQG ÀQH WDFWLOH GLVFULPLQDWLRQ  DUH PDGH SRVVLEOH E\ the specialized mucosal coat covering the dorsum of the tongue. The SDUWVRIWKHWRQJXHFDQEHGLVFXVVHGDVDURRWDYHQWUDOLQIHULRU VXUface, an apex, and a dorsal surface. The V-shaped furrow on the dorsum VXOFXVWHUPLQDOLV GLYLGHVWKHGRUVDOVXUIDFHLQWRDQRUDOSRUWLRQFRPSULVLQJWKHDQWHULRUWZRWKLUGV DQGDSKDU\QJHDOSRUWLRQFRPSULVLQJ WKHSRVWHULRURQHWKLUG 

Lingual tonsil

Foramen cecum Palatine tonsil Palatoglossal arch

Posterior (pharyngeal) part

Sulcus terminalis

Dorsum

See detail in Fig. 9.48A

Anterior (oral) part

Median furrow

Apex

Filiform papillae

Vallate papilla

Fungiform papilla Papilla Nonkeratinized, stratified squamous epithelium Lingual aponeurosis

Sulcus Wall of papilla Taste buds

Lingual muscles

Excretory duct of a serous gland Keratinized squamous epithelium on tips of papillae

A

B

Foliate papillae

Tip of papilla (partially covered by keratinized epithelium)

Taste buds

Connective tissue core

C

Serous glands (von Ebner glands)

Excretory duct of gland

D

Fig. 9.48 Papillae of the tongue The mucosa of the anterior dorsum is composed of numerous papillae (A DQGWKHFRQQHFWLYHWLVVXHEHWZHHQWKHPXFRVDOVXUIDFHDQGPXVculature contains many small salivary glands. The papillae are divided into four morphologically distinct types (see Table 9.10 

Serous gland

E

‡ &LUFXPYDOODWHB (QFLUFOHGDQGFRQWDLQLQJWDVWHEXGV ‡ )XQJLIRUP C  0XVKURRPVKDSHG DQG FRQWDLQLQJ PHFKDQLFDO DQG thermal receptors and taste buds. ‡ )LOLIRUPD 7KUHDGVKDSHGDQGVHQVLWLYHWRWDFWLOHVWLPXOLWKHRQO\ OLQJXDOSDSLOODHZLWKRXWWDVWHEXGV  ‡ )ROLDWHE &RQWDLQLQJWDVWHEXGV

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9. Oral Cavity & Perioral Regions

Table 9.10 Regions and structures of the tongue Region

Structures

Anterior (oral, presulcal) portion of the tongue

The anterior ⅔ of the tongue contains the apex and the majority of the dorsum. It is tethered to the oral floor by the lingual frenulum. • Mucosa: ◦ Dorsal lingual mucosa: This portion (with no underlying submucosa) contains numerous papillae. ◦ Ventral mucosa: Covered with the same smooth (nonkeratinized, stratified squamous epithelial) mucosa that lines the oral floor and gums. • Innervation: The anterior portion is derived from the first (mandibular) arch and is therefore innervated by the lingual nerve, a branch of the mandibular nerve (CN V3).

Median furrow (midline septum): The furrow running anteriorly down the midline of the tongue; this corresponds to the position of the lingual septum. Note: Muscle fibers do not cross the lingual septum. Papillae (Fig. 9.48A): The dorsal mucosa, which has no submucosa, is covered with nipplelike projections (papillae) that increase the surface area of the tongue. There are four types, all of which occur in the presulcal but not postsulcal portion of the tongue. • Circumvallate (Fig. 9.48B): Encircled by a wall and containing abundant taste buds. • Fungiform (Fig. 9.48C): Mushroom-shaped papillae located on the lateral margin of the posterior oral portion near the palatoglossal arches. These have mechanical receptors, thermal receptors, and taste buds. • Filiform (Fig. 9.48D): Thread-shaped papillae that are sensitive to tactile stimuli. These are the only papillae that do not contain taste buds. • Foliate (Fig. 9.48E): Located near the sulcus terminalis, these contain numerous taste buds.

Sulcus terminalis

The sulcus terminalis is the V-shaped furrow that divides the tongue functionally and anatomically into an anterior and a posterior portion.

Foramen cecum: The embryonic remnant of the passage of the thyroid gland that migrates from the dorsum of the tongue during development. The foramen cecum is located at the convergence of the sulci terminalis.

Posterior (pharyngeal, postsulcal) portion of the tongue

The base of the tongue is located posterior to the palatoglossal arches and sulcus terminalis. • Mucosa: The same mucosa that lines the palatine tonsils, pharyngeal walls, and epiglottis. The pharyngeal portion of the tongue does not contain papillae. • Innervation: The posterior portion is innervated by the glossopharyngeal nerve (CN IX).

Lingual tonsils: The submucosa of the posterior portion contains embedded lymph nodes known as the lingual tonsils, which create the uneven surface of the posterior portion. Oropharynx: The region posterior to the palatoglossal arch. The oropharynx, which contains the palatine tonsils, communicates with the oral cavity via the oropharyngeal isthmus (defined by the palatoglossal arches).

Glossoepiglottic folds and epiglottic valleculae: The (nonkeratinized, stratified squamous) mucosal covering of the posterior tongue and pharyngeal walls is reflected onto the anterior aspect of the epiglottis, forming one median and two lateral glossoepiglottic folds. The median glossoepiglottic fold is flanked by two depressions, the epiglottic valleculae.

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Pharynx & Tonsils

Fig. 9.49 Waldeyer’s ring Posterior view of the opened pharynx. Waldeyer’s ring is composed of immunocompetent lymphatic tissue (tonsils and lymph follicles). The tonsils are “immunological sentinels” surrounding the passageways from the mouth and nasal cavity to the pharynx. The lymph follicles are distributed over all of the epithelium, showing marked regional variations. Waldeyer’s ring consists of the following structures: • Unpaired pharyngeal tonsil on the roof of the pharynx • Paired palatine tonsils in the oropharynx • Lingual tonsil, the lymph nodes embedded in the postsulcal portion of the tongue • Paired tubal tonsils (tonsillae tubariae), which may be thought of as lateral extensions of the pharyngeal tonsil • Paired lateral bands in the salpingopharyngeal fold

Roof of pharynx (sphenoid and occipital bones)

Pharyngeal tonsil Nasal conchae

Tubal tonsil

Soft palate Uvula Palatine tonsil

Lymphatic tissue of lateral bands (salpingopharyngeal fold)

Palatopharyngeal arch Lingual tonsil (postsulcal portion of tongue) Epiglottis

Soft palate

Palatine tonsil

Palatoglossal arch Tonsillar fossa Uvula

Palatopharyngeal arch

Palatoglossal arch

Palatine tonsil

A

Fig. 9.50 Palatine tonsils: location and abnormal enlargement Anterior view of the oral cavity. The palatine tonsils occupy a shallow recess on each side, the tonsillar fossa, which is located between the anterior and posterior pillars (palatoglossal arch and palatopharyngeal arch). The palatine tonsil is examined clinically by placing a tongue

208

Tonsillar fossa

Enlarged palatine tonsil

B

C

depressor on the anterior pillar and displacing the tonsil from its fossa while a second instrument depresses the tongue (B). Severe enlargement of the palatine tonsil (due to viral or bacterial infection, as in tonsillitis) may significantly narrow the outlet of the oral cavity, causing difficulty in swallowing (dysphagia, C).

Regions of the Head

Choana

9. Oral Cavity & Perioral Regions

Sphenoid sinus Roof of pharynx (sphenoid and occipital bones)

Nasal septum

Pharyngeal tonsil

Torus tubarius

Pharyngeal orifice of pharyngotympanic tube

Choana

Pharyngeal recess Anterior arch of axis (C1)

Enlarged pharyngeal tonsil

Dens of axis (C2)

Soft palate

Salpingopharyngeal fold Uvula A

B

evoke a heightened immune response in the lymphatic tissue, causing “adenoids” or “polyps.”) The enlarged pharyngeal tonsil blocks the choanae, obstructing the nasal airway and forcing the child to breathe through the mouth. Because the mouth is then constantly open during respiration at rest, an experienced examiner can quickly diagnose the adenoidal condition by visual inspection.

Fig. 9.51 Pharyngeal tonsil: location and abnormal enlargement Sagittal section through the roof of the pharynx. Located on the roof of the pharynx, the unpaired pharyngeal tonsil can be examined by means of posterior rhinoscopy. It is particularly well developed in (small) children and begins to regress at 6 or 7 years of age. An enlarged pharyngeal tonsil is very common in preschool-aged children (B). (Chronic recurrent nasopharyngeal infections at this age often

Epithelium

Lymphocytes

Respiratory epithelium

Crypts

Nonkeratinized, stratified squamous epithelium

Crypts Secondary follicles Connective tissue capsule

A

Lymph follicles

B

Secondary follicles

Fig. 9.52 Histology of the lymphatic tissue of the oral cavity and pharynx Because of the close anatomical relationship between the epithelium and lymphatic tissue, the lymphatic tissue of Waldeyer’s ring is also designated lymphoepithelial tissue. A Lymphoepithelial tissue. Lymphatic tissue, both organized and diffusely distributed, is found in the lamina propria of all mucous membranes and is known as mucosa-associated lymphatic tissue (MALT). The epithelium acquires a looser texture, with abundant lymphocytes and macrophages. Besides the well-defined tonsils, smaller collections of lymph follicles may be found in the lateral

C

Remnants of sloughed epithelial cells

bands (salpingopharyngeal folds). They extend almost vertically from the lateral wall to the posterior wall of the oropharynx and nasopharynx. B Pharyngeal tonsil. The mucosal surface of the pharyngeal tonsil is raised into ridges that greatly increase its surface area. The ridges and intervening crypts are lined by ciliated respiratory epithelium. C Palatine tonsil. The surface area of the palatine tonsil is increased by deep depressions in the mucosal surface (creating an active surface area as large as 300 cm2). The mucosa is covered by nonkeratinized, stratified squamous epithelium.

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Pharynx: Divisions & Contents Sphenoid bone Sigmoid sinus Pharyngeal tonsil

Middle nasal turbinate

Pharyngeal recess

Nasal septum

Choanae

Inferior nasal turbinate

Stylohyoid Digastric muscle, posterior belly

Salpingopharyngeal fold

Masseter

Soft palate

Faucial (oropharyngeal) isthmus, posterior border

Uvula

Medial pterygoid Palatine tonsil

Palatopharyngeal arch

Aryepiglottic fold

Root of tongue

Laryngeal inlet

Epiglottis

Cuneiform tubercle Corniculate tubercle

Piriform recess

Pharyngeal raphe (cut)

Thyroid gland

Trachea Esophagus

A

Fig. 9.53 Pharyngeal mucosa and musculature Posterior view. A Mucosal lining. B Internal musculature. The muscular posterior wall of the pharynx has been divided along the mid-

line (pharyngeal raphe) and spread open to demonstrate its mucosal anatomy.

Table 9.11 Levels of the pharynx The anterior portion of the muscular pharyngeal tube communicates with three cavities (nasal, oral, and laryngeal). The three anterior openings divide the pharynx into three parts with corresponding vertebral levels. Region

Level

Description

Communications

Nasopharynx (Epipharynx)

C1

Upper portion, lying between the roof (formed by sphenoid and occipital bones) and the soft palate

Nasal cavity

Via choanae

Tympanic cavity

Via pharyngotympanic tube

Oropharynx (Mesopharynx)

C2–C3

Middle portion, lying between the uvula and the epiglottis

Oral cavity

Via oropharyngeal isthmus (formed by the palatoglossal arch)

Laryngopharynx (Hypopharynx)

C4–C6

Lower portion, lying between the epiglottis and the inferior border of the cricoid cartilage

Larynx

Via laryngeal inlet

Esophagus

Via cricopharyngeus (pharyngeal sphincter)

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Levator veli palatini

Tensor veli palatini

Styloid process Stylohyoid Superior pharyngeal constrictor

Digastric, posterior belly Masseter, superficial and deep heads

Salpingopharyngeus Pharyngeal elevators

Uvular muscle

Palatopharyngeus

Medial pterygoid Angle of mandible

Stylopharyngeus

Middle pharyngeal constrictor

Oblique arytenoid

Transverse arytenoid Inferior pharyngeal constrictor Posterior cricoarytenoid

Circular muscle fibers of esophagus

B

Fig. 9.54 Posterior rhinoscopy The nasopharynx can be visually inspected by posterior rhinoscopy.

Pharyngeal tonsil

A Technique of holding the tongue blade and mirror. The angulation of the mirror is continually adjusted to permit complete inspection of the nasopharynx. B Composite posterior rhinoscopic image acquired at various mirror DQJOHV 7KH SKDU\QJRW\PSDQLF DXGLWRU\  WXEH RULÀFH DQG SKDU\QJHDOWRQVLOFDQEHLGHQWLÀHG

Pharyngotympanic tube orifice Nasal septum

A

B

Uvula

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Muscles of the Soft Palate & Pharynx The soft palate is the aponeurotic and muscular region hanging from the hard palate at the posterior portion of the oral cavity. It separates the nasopharynx from the oropharynx. During swallowing, it can be tensed to further restrict the communication between the cavities. The palatoglossus restricts the communication between the oral cavity and phar-

ynx. The pharyngeal muscles elevate and constrict the pharynx (see Table 9.12, Table 9.13, and Fig. 9.56). Though several muscles originate on the pharyngotympanic (auditory) tube, only the tensor veli SDODWLQLSOD\VDVLJQLÀFDQWUROHLQLWVRSHQLQJ

Roof of pharynx (sphenoid and occipital bones)

Pharyngeal tonsil Cartilaginous part of pharyngotympanic (auditory) tube

Levator veli palatini Salpingopharyngeus

Tubal orifice Tensor veli palatini

Superior pharyngeal constrictor

Medial plate of pterygoid process (sphenoid bone)

Uvular muscle Palatopharyngeus A

Pterygoid hamulus

Masticatory mucosa lining hard palate

Palatine bone (posterior portion of hard palate)

Palatine aponeurosis

Pterygoid hamulus

Musculus uvulae

Lateral plate of pterygoid process (sphenoid bone)

Uvula

Tensor veli palatini Soft palate

Levator veli palatini Pharyngeal tubercle (occipital bone)

Carotid canal

B

Fig. 9.55 Muscles of the soft palate and pharyngotympanic tube A Posterior view. B Inferior view.

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Table 9.12 Muscles of the soft palate and pharyngeal elevators Muscle

Origin

Insertion

Innervation

Action

Tensor veli palatini

Sphenoid bone (scaphoid fossa of pterygoid process and medial aspect of the spine); it is connected to the anterolateral membranous wall of the pharyngotympanic (auditory) tube

Palatine aponeurosis and palatine bone (horizontal plate) via a tendon that is redirected medially by the pterygoid hamulus

N. to medial pterygoid (CN V3)

Bilaterally: Tenses anterior portion of the soft palate and flattens its arch, separating the nasopharynx from the oropharynx. Opens pharyngotympanic (auditory) tube. Unilaterally: Deviates soft palate laterally.

Levator veli palatini

Vaginal process and petrous part of temporal bone (via a tendon, anterior to the carotid canal); it is connected to the inferior portion of the cartilaginous pharyngotympanic tube

Palatine aponeurosis (the two levators combine to form a muscular sling)

Vagus n. (CN X) via pharyngeal plexus

Bilaterally: Pulls the posterior portion of the soft palate superoposteriorly, separating the nasopharynx from the oropharynx.

Musculus uvulae

Palatine bone (posterior nasal spine) and palatine aponeurosis (superior surface)

Mucosa of the uvula

Pulls the uvula posterosuperiorly, separating the nasopharynx from the oropharynx.

Palatoglossus (palatoglossal arch)

Palatine aponeurosis (oral surface)

Lateral tongue to dorsum or intrinsic transverse muscle

Pulls the root of the tongue superiorly and approximates the palatoglossal arch, separating the oral cavity from the oropharynx.

Palatopharyngeus (palatopharyngeal arch)

Palatine aponeurosis (superior surface) and posterior border of palatine bone

Thyroid cartilage (posterior border) or lateral pharynx

Bilaterally: Elevates the pharynx anteromedially.

Salpingopharyngeus

Cartilaginous pharyngotympanic tube (inferior surface)

Along salpingopharyngeal fold to palatopharyngeus

Bilaterally: Elevates the pharynx; may also open the pharyngotympanic tube.

Stylopharyngeus

Styloid process (medial surface of base)

Lateral pharynx, mixing with pharyngeal constrictors, palatopharyngeus, and thyroid cartilage (posterior border)

Glossopharyngeal n. (CN IX)

Bilaterally: Elevates the pharynx and larynx.

Table 9.13 Pharyngeal constrictors Muscle

Superior pharyngeal constrictor

Middle pharyngeal constrictor

Inferior pharyngeal constrictor

Origin

Insertion

Innervation

Action

Pterygopharyngeus

Pterygoid hamulus (occasionally to the medial pterygoid plate)

Vagus n. (CN X) via pharyngeal plexus

Constricts the upper pharynx

Buccopharyngeus

Pterygomandibular raphe

Mylopharyngeus

Mylohyoid line of mandible

Glossopharyngeus

Lateral tongue

Occipital bone (pharyngeal tubercle of basilar part, via median pharyngeal raphe)

Chondropharyngeus

Hyoid (lesser cornu) and stylohyoid ligament

Ceratopharyngeus

Hyoid (greater cornu)

Thyropharyngeus

Thyroid lamina and hyoid bone (inferior cornu)

Cricopharyngeus

Cricoid cartilage (lateral margin)

Constricts the middle pharynx

Constricts the lower pharynx

Recurrent laryngeal n. (CN X) and/or external laryngeal n.

Sphincter at intersection of laryngopharynx and esophagus

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Muscles of the Pharynx

Levator veli palatini

Tensor veli palatini

Pharyngobasilar fascia

Superior pharyngeal constrictor Stylohyoid Buccinator Styloglossus Digastric muscle, posterior belly Stylopharyngeus Hyoglossus

Mylohyoid

Middle pharyngeal constrictor Thyrohyoid membrane

Digastric muscle, anterior belly

Inferior pharyngeal constrictor

Sternohyoid Thyrohyoid Straight part Cricothyroid Oblique part Tensor veli palatini

Levator veli palatini Esophagus Trachea

1st gap A

Pterygopharyngeal part Buccopharyngeal part Mylopharyngeal part

Superior pharyngeal constrictor

Glossopharyngeal part Chondropharyngeal part

2nd gap

Ceratopharyngeal part

Hyoid bone

Thyropharyngeal part

3rd gap

Cricothyroid

B

214

Straight part Oblique part Trachea

Cricopharyngeal part 4th gap Esophagus

Table 9.14 Pharyngeal gaps Gap

Transmitted structures

1st gap

Pharyngotympanic tube

Middle pharyngeal constrictor

Levator veli palatini 2nd gap

Stylopharyngeus (inserts on larynx) Glossopharyngeal n. (CN IX)

Inferior pharyngeal constrictor

3rd gap

Internal laryngeal n. Superior laryngeal a. and v.

4th gap

Recurrent laryngeal n. Inferior laryngeal a.

Regions of the Head

Pharyngobasilar fascia

Superior pharyngeal constrictor

Masseter muscle, deep part

Digastric muscle, posterior belly

Masseter muscle, superficial part

Stylohyoid

9. Oral Cavity & Perioral Regions

Fig. 9.56 Pharyngeal musculature Left lateral (A) and posterior (C) view of the pharyngeal muscles. B Left lateral view of pharyngeal constrictors. The pharynx is a muscular tube composed of three pharyngeal constrictors (Table 9.13) and three longitudinal pharyngeal elevators (Table 9.12). The striated muscles of the pharynx attach to the skull base and pharyngeal raphe and are continuous with the esophagus at the level of the cricoid cartilage (C6 vertebral body). The cricopharyngeus is continuous across the midline and acts as a pharyngeal sphincter. When the constrictors are relaxed, it is constricted and vice versa. It therefore has a separate innervation (recurrent laryngeal nerve and/or external laryngeal nerve, and generally not pharyngeal plexus).

Medial pterygoid

Stylopharyngeus Middle pharyngeal constrictor

Hyoid bone, greater horn

Thyropharyngeus (inferior pharyngeal constrictor)

Pharyngeal raphe

Thyroid gland Cricopharyngeus (inferior pharyngeal constrictor)

Oblique part

Killian triangle (dehiscence)

Fundiform part

Laimer triangle

C

Fundiform part of cricopharyngeus

Esophagus A

Vomer

Foramen ovale

Medial plate of pterygoid process

Foramen lacerum Body of sphenoid bone

Carotid canal

Cricopharyngeus

B

Zenker diverticulum

Fig. 9.58 Development of diverticula A Posterior view. B Left lateral view. The cricopharyngeal part of the inferior pharyngeal constrictor is divided into an oblique and a fundiform part. Between them is an area of muscular weakness known as the Killian triangle (or dehiscence). This weak spot may allow the mucosa of the hypopharynx to bulge outward through the fundiform part (B), producing a saclike protrusion (Zenker or pharyngoesophageal diverticulum). The collection of food residues may gradually expand the sac, increasing the risk of obstructing the esophageal lumen. Zenker diverticula are most common in middle-aged and elderly individuals. Symptoms include the regurgitation of trapped food residues. In older patients who are not optimal surgical candidates, treatment consists of dividing the fundiform part of the inferior constrictor endoscopically. Note: Diverticula that develop in the Laimer triangle are considerably rarer.

Fig. 9.57 Pharyngobasilar fascia at the base of the skull Inferior view. The pharyngeal musculature arises from the base of the skull by a thick sheet of connective tissue, the pharyngobasilar fascia (shown in red). The pharyngobasilar fascia ensures that the nasopharynx is always open.

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Pharynx: Topography & Innervation

Frontal sinus Nasal septum Sphenoid sinus Torus tubarius with lymphatic tissue (tonsilla tubaria) Pharyngeal tonsil in nasopharynx Pharyngeal orifice of pharyngotympanic tube Salpingopharyngeal fold with lateral lymphatic band

Right choana

Anterior arch of atlas (C1)

Soft palate

Dens of axis (C2)

Uvula

Palatine tonsil in oropharynx

Palatoglossal arch

Lingual tonsil (on postsulcal portion of the tongue)

Genioglossus Geniohyoid

Vallecula

Mylohyoid Hyoid bone

Epiglottis

Thyrohyoid ligament

Laryngopharynx

Vestibular fold Vocal fold

Cricoid cartilage

Esophagus Thyroid gland A

Trachea

• Pharyngeal tonsil (on the roof of the nasopharynx) • Paired palatine tonsils (between the palatoglossal and palatopharyngeal arches of the oropharynx) • Lingual tonsils (covering the postsulcal portion of the tongue) • Paired tonsilla tubaria (around the pharyngeal orifice of the pharyngotympanic tube) with their inferior extensions along the salpingopharyngeal folds (lateral bands) Swelling of the tonsilla tubaria may occlude the pharyngeal orifice of the pharyngotympanic (auditory) tube, preventing the equalizing of pressure in the middle ear. The mobility of the tympanic cavity is restricted, resulting in mild hearing loss. Note: Enlargement of the pharyngeal tonsil (e.g., polyps in small children) may also obstruct the orifice of the pharyngotympanic tube.

216

Nasopharynx

Airway

Fig. 9.59 Topography of the pharynx Midsagittal section, left lateral view. The pharynx communicates with the nasal cavity, tympanic cavity, oral cavity, larynx, and esophagus. Its three anterior communications divide it into three parts: nasopharynx, oropharynx, and laryngopharynx (see Table 9.15). The extensive communications make the spread of bacteria from the pharynx a real and dangerous possibility. The inflow portions (junctions with the nasal and oral cavities) are therefore lined with lymphatic tissue (Waldeyer’s ring; see Fig. 9.49). This defense system includes:

Foodway

Oropharynx Laryngopharynx B

Table 9.15 Pharyngeal levels Region

Level

Borders

Nasopharynx

C1

Roof (sphenoid and occipital bones), choanae, and soft palate

Oropharynx

C2–C3

Uvula, palatoglossal arch, and epiglottis

Laryngopharynx

C4–C6

Epiglottis, laryngeal inlet, and cricoid cartilage (inferior border)

Regions of the Head

Epiglottic cartilage

Thyrohyoid

Epiglottic cartilage

Oral floor

Thyroid cartilage

Hyoid bone

Passavant ridge (contracted superior pharyngeal constrictor)

Soft palate

Soft palate

Oral floor

9. Oral Cavity & Perioral Regions

Thyroid cartilage

Hyoid bone

Cricoid cartilage

Thyrohyoid

Cricoid cartilage

Esophagus

B

A

Fig. 9.60 Swallowing The larynx, part of the airway, is located at the inlet to the digestive tract. During swallowing, the airway must be occluded to keep food from entering the larynx and the trachea (preventing choking). Swallowing consists of three phases: 1. Oral stage (voluntary initiation): The lingual muscles move the food EROXV WR WKH RURSKDU\QJHDO LVWKPXV ZKLFK ÀUVW H[SDQGV DQG WKHQ contracts.

 3KDU\QJHDOVWDJHUHÁH[FORVXUHRIDLUZD\ 7KHORQJLWXGLQDOSKDU\Qgeal muscles elevate the larynx. The lower airway (laryngeal inlet) is covered by the epiglottis. Meanwhile, the soft palate is tensed and HOHYDWHGDJDLQVWWKHSRVWHULRUSKDU\QJHDOZDOOVHDOLQJR̥WKHXSSHU airway.  3KDU\QJRHVRSKDJHDOVWDJHUHÁH[WUDQVSRUW 7KHFRQVWULFWRUVPRYH the food bolus to the stomach.

Corticonuclear tract

To thalamus and cortex (medial lemniscus)

Mesencephalic nucleus of trigeminal nerve (CN V)

To nucleus of reticular formation (gag and swallowing reflex)

Principal sensory (pontine) nucleus of trigeminal nerve (CN V)

Solitary nucleus Glossopharyngeal nerve (CN IX)

Sensation (pain, temperature, touch)

Nucleus ambiguus IX

From the ear (tympanic nerve)

Superior and inferior ganglia

X

Vagus nerve (CN X)

Sensation Direct motor branch to stylopharyngeus

Taste Spinal nucleus of trigeminal nerve (CN V)

Pharyngeal plexus Branchiomotor

Stylopharyngeus

Pharyngeal constrictor

General somatic sensory Special visceral sensory General visceral sensory

Larynx

Fig. 9.61 Pharyngeal plexus The pharynx receives sensory and motor innervation via the pharyngeal plexus, formed by both the glossopharyngeal (CN IX) and vagus (CN X) QHUYHVDORQJZLWKSRVWJDQJOLRQLFV\PSDWKHWLFÀEHUVIURPWKHVXSHULRU cervical ganglion. Note:2QO\WKHYDJXVQHUYHFRQWULEXWHVPRWRUÀEHUV to the plexus (the stylopharyngeus is supplied directly by CN IX).

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Regions of the Head

9. Oral Cavity & Perioral Regions

Salivary Glands

Accessory parotid gland

Fig. 9.62 Major salivary glands A Left lateral view. B Superior view. There are three major (large, paired) salivary glands: parotid, submandibular, and sublingual. They collectively produce 0.5 to 2.0 liters of saliva per day, excreted into the oral cavity via excretory ducts. The saliva keeps the oral mucosa moist. It also has digestive and protective functions: saliva contains the starch-splitting enzyme amylase and the bactericidal enzyme lysozyme.

Parotid gland

Parotid duct

1. Parotid glands: Purely serous glands (watery secretions). The parotid duct crosses superficial to the masseter, pierces the buccinator, and opens into the oral vestibule opposite the second upper molar. 2. Submandibular glands: Mixed seromucous gland. The submandibular duct opens on the sublingual papilla behind the lower incisors. 3. Sublingual glands: Predominantly mucoussecreting gland (mucoserous). The sublingual gland has many smaller excretory ducts that open on the sublingual fold or into the submandibular duct.

Buccinator Masseter A

Facial artery and vein

Sublingual fold

Submandibular gland

Sternocleidomastoid

Sublingual papilla Oral mucosa Genioglossus Sublingual gland

Geniohyoid

Submandibular duct

Mylohyoid

Submandibular gland, intraoral lobe

Lingual artery B

218

Hyoid bone

Submandibular gland, extraoral lobe Hyoglossus Stylohyoid

Regions of the Head

9. Oral Cavity & Perioral Regions

Labial glands

Submandibular gland

Palatine glands

Sublingual gland Pharyngeal glands

Fig. 9.63 Minor salivary glands In addition to the three major paired glands, 700 to 1000 minor glands secrete saliva into the oral cavity. They produce only 5 to 8 percent of the total output, but this amount suffices to keep the mouth moist when the major salivary glands are not functioning.

Intraparotid lymph nodes

Fig. 9.64 Bimanual examination of the salivary glands The two salivary glands of the mandible, the submandibular gland and sublingual gland, and the adjacent lymph nodes are grouped around the mobile oral floor and therefore must be palpated against resistance. This is done with bimanual examination.

Parotid tumor

Superficial temporal artery and vein

Facial nerve Hypoglossal nerve Submandibular lymph nodes Jugular lymph nodes

Lymph node

Parotid gland, superficial part Parotid plexus Facial nerve

Internal jugular vein Parotid gland, deep part

Fig. 9.65 Spread of malignant parotid tumors Malignant tumors of the parotid gland may invade surrounding structures directly (white arrowheads) or indirectly via regional lymph nodes (red arrowheads). They may also spread systematically (metastasize) through the vascular system.

Sternocleidomastoid

Fig. 9.66 Intraglandular course of the facial nerve in the parotid gland The facial nerve divides into branches within the parotid gland and is vulnerable during the surgical removal of parotid tumors. To preserve the facial nerve during parotidectomy, it is first necessary to locate and identify the facial nerve trunk. The best landmark for locating the nerve trunk is the tip of the cartilaginous auditory canal.

219

Regions of the Head

9. Oral Cavity & Perioral Regions

Neurovasculature of the Tongue

Deep lingual artery

Lingual nerve

Styloid process

Glossopharyngeal nerve Submandibular ganglion Dorsal lingual artery Hypoglossal nerve Hyoglossus

Mandible

Lingual artery and vein Deep lingual vein C1 fibers to thyrohyoid

A

Submental artery and vein (from facial artery and vein)

Fig. 9.67 Nerves and vessels of the tongue A Left lateral view. B View of the inferior surface of the tongue. The tongue is supplied by the lingual artery (from the maxillary artery), which divides into its terminal branches, the deep lingual artery and the sublingual artery. The lingual vein usually runs parallel to the artery but on the medial surface of the hyoglossus muscle and drains into the internal jugular vein. The anterior two thirds of the lingual mucosa receives its somatosensory innervation (sensitivity to thermal and tactile stimuli) from the lingual nerve, which is a branch of the trigeminal nerve’s mandibular division (CN V3). The lingual nerve transmits fibers from the chorda tympani of the facial nerve (CN VII), among them the afferent taste fibers for the anterior two thirds of the tongue. The chorda tympani also contains presynaptic, parasympathetic visceromotor axons that synapse in the submandibular ganglion, whose neurons in turn innervate the submandibular and sublingual glands. The palatoglossus receives its somatomotor innervation from the vagus nerve (CN X) via the pharyngeal plexus, the other lingual muscles from the hypoglossal nerve (CN XII).

220

Sublingual artery

Sublingual vein

Hyoid bone Thyrohyoid membrane

Apex of tongue

Anterior lingual glands

Frenulum Sublingual fold Sublingual papilla

B

Deep lingual artery and vein Lingual nerve Submandibular duct

Regions of the Head

9. Oral Cavity & Perioral Regions

Taste

Somatic sensation

Vagus nerve (CN X)

Vagus nerve (CN X)

Glossopharyngeal nerve (CN IX)

Glossopharyngeal nerve (CN IX)

Lingual nerve (mandibular nerve, CN V3)

Facial nerve (CN VII via chorda tympani)

Fig. 9.68 Innervation of the tongue Anterior view. Left side: Somatosensory innervation. Right side: Taste innervation. The posterior one third of the tongue (postsulcal part) primarily receives somatosensory and taste innervation from the glossopharyngeal nerve (CN IX), with additional taste sensation conveyed by the vagus

nerve (CN X). The anterior two thirds of the tongue (presulcal part) receives its somatosensory innervation (e.g., touch, pain, and temperature) from the lingual nerve (branch of CN V3) and its taste sensation from the chorda tympani branch of the facial nerve (CN VII). Disturbances of sensation in the presulcal tongue can therefore be used to determine facial or trigeminal nerve lesions.

Deep cervical lymph nodes Lingual vein Submental lymph nodes

Jugulofacial venous junction

Submandibular lymph nodes

Internal jugular vein Jugular lymph nodes A

Fig. 9.69 Lymphatic drainage of the tongue and oral floor A Left lateral view. B Anterior view. The lymphatic drainage of the tongue and oral floor is mediated by submental and submandibular groups of lymph nodes that ultimately drain into the lymph nodes along the internal jugular vein (A, jugular

B

lymph nodes). Because the lymph nodes receive drainage from both the ipsilateral and contralateral sides (B), tumor cells may become widely disseminated in this region (e.g., metastatic squamous cell carcinoma, especially on the lateral border of the tongue, frequently metastasizes to the opposite side).

221

Regions of the Head

9. Oral Cavity & Perioral Regions

Gustatory System

Ventral posteromedial nucleus of thalamus

Postcentral gyrus

Insula

Dorsal tegmental nucleus Dorsal trigeminothalamic tract Oval nucleus Facial nerve Medial parabrachial nucleus

Geniculate ganglion Inferior (petrosal) ganglion

Gustatory part

Chorda tympani

Solitary tract nucleus Dorsal vagal nucleus

Lingual nerve Inferior (nodose) ganglion

Spinal nucleus of trigeminal nerve

Vagus nerve

Epiglottis

Glossopharyngeal nerve

Fig. 9.70 Gustatory pathway The receptors for the sense of taste are the taste buds of the tongue (see Fig. 9.71). Unlike other receptor cells, the receptor cells of the taste buds are specialized epithelial cells (secondary sensory cells, as they do not have an axon). When these epithelial cells are chemically stimulated, the base of the cells releases glutamate, which stimulates the peripheral processes of afferent cranial nerves. These different cranial nerves serve different areas of the tongue. It is rare, therefore, for a complete loss of taste (ageusia) to occur. • The anterior two thirds of the tongue is supplied by the facial nerve (CN VII), the afferent fibers first passing in the lingual nerve (branch of the trigeminal nerve) and then in the chorda tympani to the geniculate ganglion of the facial nerve. • The posterior third of the tongue and the vallate papillae are supplied by the glossopharyngeal nerve (CN IX). A small area on the posterior third of the tongue is also supplied by the vagus nerve (CN X). • The epiglottis and valleculae are supplied by the vagus nerve (CN X). Peripheral processes from pseudounipolar ganglion cells (which correspond to pseudounipolar spinal ganglion cells) terminate on the taste buds. The central portions of these processes convey taste information to the gustatory part of the nucleus of the solitary tract. Thus, they function as the first afferent neuron of the gustatory pathway. Their

222

perikarya are located in the geniculate ganglion for the facial nerve, in the inferior (petrosal) ganglion for the glossopharyngeal nerve, and in the inferior (nodose) ganglion for the vagus nerve. After synapsing in the gustatory part of the nucleus of the solitary tract, the axons from the second neuron are believed to terminate in the medial parabrachial nucleus, where they are relayed to the third neuron. Most of the axons from the third neuron cross to the opposite side and pass in the dorsal trigeminothalamic tract to the contralateral ventral posteromedial nucleus of the thalamus. Some of the axons travel uncrossed in the same structures. The fourth neurons of the gustatory pathway, located in the thalamus, project to the postcentral gyrus and insular cortex, where the fifth neuron is located. Collaterals from the first and second neurons of the gustatory afferent pathway are distributed to the superior and inferior salivatory nuclei. Afferent impulses in these fibers induce the secretion of saliva during eating (“salivary reflex”). The parasympathetic preganglionic fibers exit the brainstem via cranial nerves VII and IX (see the descriptions of these cranial nerves for details). Besides this purely gustatory pathway, spicy foods may also stimulate trigeminal fibers (not shown), which contribute to the sensation of taste. Finally, olfaction (the sense of smell), too, is a major component of the sense of taste as it is subjectively perceived: patients who cannot smell (anosmosia) report that their food tastes abnormally bland.

Regions of the Head

9. Oral Cavity & Perioral Regions

Epiglottis Taste bud

Lateral glossoepiglottic fold

Vallecula

Median glossoepiglottic fold

Foramen cecum

Seromucous glands

Terminal sulcus Vallate papilla (B)

Foliate papillae (D)

B

Taste bud

Taste bud

Fungiform papillae (C)

A

C

Fig. 9.71 Organization of the taste receptors in the tongue 7KHKXPDQWRQJXHFRQWDLQVDSSUR[LPDWHO\WDVWHEXGVLQZKLFK WKH VHFRQGDU\ VHQVRU\ FHOOV IRU WDVWH SHUFHSWLRQ DUH FROOHFWHG 7KH taste buds are embedded in the epithelium of the lingual mucosa and are located on the surface expansions of the lingual mucosa — the vallate papillae (principal site, B WKHIXQJLIRUPSDSLOODHC DQGWKHIRliate papillae (D  $GGLWLRQDOO\ LVRODWHG WDVWH EXGV DUH ORFDWHG LQ WKH

Nonkeratinized squamous epithelium

Taste pore

D

PXFRXVPHPEUDQHVRIWKHVRIWSDODWHDQGSKDU\Q[7KHVXUURXQGLQJ VHURXVJODQGVRIWKHWRQJXH(EQHUJODQGV ZKLFKDUHPRVWFORVHO\DVVRFLDWHGZLWKWKHYDOODWHSDSLOODHFRQVWDQWO\ZDVKWKHWDVWHEXGVFOHDQ WRDOORZIRUQHZWDVWLQJ+XPDQVFDQSHUFHLYHÀYHEDVLFWDVWHTXDOLWLHV VZHHW VRXU VDOW\ ELWWHU DQG D ÀIWK ´VDYRU\µ TXDOLW\ FDOOHG XPDPL ZKLFKLVDFWLYDWHGE\JOXWDPDWHDWDVWHHQKDQFHU 

Light taste cell

Fig. 9.72 Microscopic structure of a taste bud Nerves induce the formation of taste buds in the oral mucosa. Axons of cranial nerves VII, IX, and X grow into the oral mucosa from the EDVDOVLGHDQGLQGXFHWKHHSLWKHOLXPWRGL̥HUHQWLDWHLQWRWKHOLJKWDQG GDUN WDVWH FHOOV   PRGLÀHG HSLWKHOLDO FHOOV  %RWK W\SHV RI WDVWH FHOO KDYH PLFURYLOOL WKDW H[WHQG WR WKH JXVWDWRU\ SRUH )RU VRXU DQG VDOW\ WKH WDVWH FHOO LV VWLPXODWHG E\ K\GURJHQ LRQV DQG RWKHU FDWLRQV 7KH RWKHU WDVWH TXDOLWLHV DUH PHGLDWHG E\ UHFHSWRU SURWHLQV WR ZKLFK WKH ORZPROHFXODUZHLJKWÁDYRUHGVXEVWDQFHVELQGGHWDLOVPD\EHIRXQG LQWH[WERRNVRISK\VLRORJ\ :KHQWKHORZPROHFXODUZHLJKWÁDYRUHG VXEVWDQFHVELQGWRWKHUHFHSWRUSURWHLQVWKH\LQGXFHVLJQDOWUDQVGXFtion that causes the release of glutamate, which excites the peripheral processes of the pseudounipolar neurons of the three cranial nerve JDQJOLD7KHWDVWHFHOOVKDYHDOLIHVSDQRIDSSUR[LPDWHO\GD\VDQG UHJHQHUDWHIURPFHOOVDWWKHEDVHRIWKHWDVWHEXGVZKLFKGL̥HUHQWLDWH into new taste cells. Note:7KHROGQRWLRQWKDWSDUWLFXODUDUHDVRIWKHWRQJXHDUHVHQVLWLYHWR VSHFLÀFWDVWHTXDOLWLHVKDVEHHQIRXQGWREHIDOVH Dark taste cell

Nerve

Basal cell

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Neck 10

Bones, Ligaments & Muscles of the Neck Vertebral Column & Vertebrae . . . . . . . . . . . . . . . . . . . . . . . . 226 Ligaments of the Vertebral Column . . . . . . . . . . . . . . . . . . . . 228 Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 Joints of the Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 Ligaments of the Cervical Spine . . . . . . . . . . . . . . . . . . . . . . . 234 Ligaments of the Craniovertebral Joints . . . . . . . . . . . . . . . . 236 Muscles of the Neck: Overview. . . . . . . . . . . . . . . . . . . . . . . . 238 Muscles of the Neck & Back (I) . . . . . . . . . . . . . . . . . . . . . . . . 240 Muscles of the Neck & Back (II). . . . . . . . . . . . . . . . . . . . . . . . 242 Muscles of the Posterior Neck . . . . . . . . . . . . . . . . . . . . . . . . 244 Intrinsic Back Muscles (I): Erector Spinae & Interspinales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 Intrinsic Back Muscles (II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 Intrinsic Back Muscles (III): Short Nuchal Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 Prevertebral & Scalene Muscles . . . . . . . . . . . . . . . . . . . . . . . 252 Suprahyoid & Infrahyoid Muscles . . . . . . . . . . . . . . . . . . . . . . 254

11

Larynx Larynx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Laryngeal Muscles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Larynx: Neurovasculature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260 Larynx: Topography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 Thyroid & Parathyroid Glands . . . . . . . . . . . . . . . . . . . . . . . . . 264

12

Neurovascular Topography of the Neck Arteries & Veins of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . 266 Lymphatics of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Cervical Plexus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Cervical Regions (Triangles) . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Cervical Fasciae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274 Posterior Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276 Lateral Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278 Anterior Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Deep Anterolateral Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282 Parapharyngeal Space (I). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284 Parapharyngeal Space (II) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286

Neck

10. Bones, Ligaments & Muscles of the Neck

Vertebral Column & Vertebrae Atlas (C1)

Dens of axis (C2)

Transverse process of atlas (C1)

Axis (C2) Vertebral bodies (of C3 and C4)

Cervical spine (C1–C7)

Thoracic spine (T1–T12)

Lumbar spine (L1–L5)

Spinous process of C7 (vertebra prominens)

Cervical (secondary)

erse Transverse sses processes nd T4) (of T3 and Thoracic (primary)

Laminae (of T5 and T6)

Costal facet of transverse process

Lumbar (secondary)

Superior and inferior costal facets (of T8) Superior and inferior articular facets (of T10)

Sacral (primary) Sacrum (fused S1–S5)

Fig. 10.1 Spinal curvature Left lateral view. The spinal (vertebral) column is divided into four regions: the cervical, thoracic, lumbar, and sacral spines. In the neonate, all regions demonstrate an anteriorly concave curvature. This single concave curvature in the neonate is referred to as the primary curvature of the vertebral column. During development, the cervical and lumbar regions of the vertebral column develop anteriorly convex curvatures. These changes are referred to as secondary curvatures. The cervical secondary curvature develops as infants begin to hold up their heads. The lumbar secondary curvatures are the result of upright bipedal locomotion. Kyphosis is a pathological condition where the thoracic primary curvature is abnormally exaggerated (hunchback, rounded back). Lordosis is a pathological condition where the secondary curvatures are exaggerated. Lordosis may occur in either the cervical or lumbar regions (swayback) of the vertebral column. Differing from the abnormal development of primary and secondary curvatures, scoliosis is an abnormal lateral deviation of the vertebral column.

226

Spinous processes (of C7 and T1)

Intervertebral disk illary Mammillary sses processes nd L2) (of L1 and

Intervertebral foramina

ular Articular ce surface rum of sacrum

Sacral crest

Sacral foramina

A

Coccyx

B

Fig. 10.2 Vertebral column A Left lateral view. B Posterior view. The vertebral column is divided into four regions: cervical, thoracic, lumbar, and sacral. Each vertebra consists of a vertebral body and vertebral (neural) arch. The vertebral bodies (with intervening intervertebral disks) form the load-bearing component of the vertebral column. The vertebral (neural) arches enclose the vertebral canal, protecting the spinal cord.

Neck

Fig. 10.3 Structure of vertebrae Left oblique posterosuperior view. Each vertebra consists of a loadbearing body and an arch that encloses the vertebral foramen. The arch is divided into the pedicle and lamina. Vertebrae have transverse and spinous processes that provide sites of attachment for muscles. Vertebrae articulate at facets on the superior and inferior articular processes. Thoracic vertebrae articulate with ribs at costal facets.

10. Bones, Ligaments & Muscles of the Neck

Vertebral foramen (VF) Superior articular process (SA)

Vertebral body (VB)

Vertebral arch

Pedicle (P)

Transverse process (T)

Lamina (L)

Spinous process (S) Inferior articular process (IA)

S

S L L

Costal facet on T

T

VF

P

VF

SA facet

SA facet

P Superior and inferior costal facets

Posterior tubercle T (with sulcus for spinal nerve)

Transverse foramen A

VB

Anterior tubercle

VB

B

S (sacral crest) SA with facet

S L

Mammillary process

VF

VF (sacral canal)

Wing

SA with facet

T P

C

Superior vertebral notch Sacral promontory

D

VB

VB (base of sacrum)

Fig. 10.4 Typical vertebrae Superior view. A Cervical vertebra (C4). B Thoracic vertebra (T6). C Lumbar vertebra (L4). D Sacrum. The vertebral bodies increase in size cranially to caudally. See Fig. 10.3 for abbreviation key.

Table 10.1 Structural elements of vertebrae Each vertebra consists of a body and an arch that enclose the vertebral foramen. The types of vertebrae can be distinguished particularly easily by examining their transverse processes. The sacrum has structures that are analogous to the other vertebrae. Vertebrae

Body (VB)

Foramen (VF)

Transverse process (T)

Spinous process (S)

Cervical vertebrae C3–C7

Small (kidney-shaped)

Large (triangular)

Transverse foramina

C3–C5: short C7: long C3–C6: bifid

Thoracic vertebrae T1–T12

Medium (heart-shaped) with costal facets

Small (circular)

Costal facets

Long

Lumbar vertebrae L1–L5

Large (kidney-shaped)

Medium (triangular)

Mammillary processes

Short and broad

Sacrum (fused S1–S5)

Large to small (decreases from base to apex)

Sacral canal (triangular)

Fused (forms wing of sacrum)

Short (median sacral crest)

227

Neck

10. Bones, Ligaments & Muscles of the Neck

Ligaments of the Vertebral Column

Fig. 10.5 Ligaments of the vertebral column The ligaments of the vertebral column bind the vertebrae to one another and enable the spine to withstand high mechanical loads and shearing stresses. The ligaments are divided into ligaments of the vertebral bodies and arches (Table 10.2).

Superior articular facet

Vertebral body

Intervertebral disk

Posterior longitudinal ligament

Anulus fibrosus Nucleus pulposus

Lamina

Intervertebral foramen

A Ligaments of the vertebral column. Left lateral view of T11–L3 with T11 and T12 sectioned midsagittally. B Ligaments of the vertebral body (anterior and posterior longitudinal ligaments, and intervertebral disk). C Ligamenta flava. D Interspinous ligaments and ligamenta flava. E Complete ligaments of the vertebral column.

Ligamenta flava

Anterior longitudinal ligament

Spinous processes Interspinous ligaments

Supraspinous ligament

Transverse process

Table 10.2 Ligaments of the vertebral column

Facet joint capsule Intertransverse ligaments

Vertebral body ligaments

Superior articular process

Anterior longitudinal ligament (along anterior surface of vertebral bodies) Posterior longitudinal ligament (along posterior surface of vertebral bodies, i.e., anterior surface of vertebral canal)

Inferior articular facet A

Intervertebral disk (between adjacent vertebral bodies; the anulus fibrosus limits rotation, and the nucleus pulposus absorbs compressive forces)

Anterior longitudinal ligament

Vertebral (neural) arch ligaments

Ligamenta flava (between laminae) Interspinous ligaments (between spinous processes) Supraspinous ligaments (along posterior border of spinous processes; in the cervical spine, the supraspinous ligament is broadened into the nuchal ligament)

Vertebral body Intervertebral disk

Posterior longitudinal ligament

Ligamenta flava C

B

Intertransverse ligaments (between transverse processes)

Lamina

Transverse process

Interspinous ligaments

Facet joint capsules (enclose the articulation between the facets of the superior and inferior articular processes of adjacent vertebrae)

Lamina Ligamenta flava Spinous process D

228

Inferior articular process Superior articular process E

Intertransverse ligament

Supraspinous ligament Spinous process

Neck

Transverse process

Intervertebral disk

Vertebral body

10. Bones, Ligaments & Muscles of the Neck

Nutrient foramina

Pedicle Posterior longitudinal ligament

Intervertebral foramen

Intervertebral disk

Vertebral body

Gap in ligamentous reinforcement of the disk

Superior articular facet

Anterior longitudinal ligament

Costal process

Fig. 10.6 Individual ligaments of the vertebral column The anterior and posterior longitudinal ligaments and ligamenta flava maintain the normal curvature of the spine.

Inferior articular process

A

A Anterior longitudinal ligament. Anterior view. The anterior longitudinal ligament runs broadly on the anterior side of the vertebral bodies from the skull base to the sacrum. Its deep collagenous fibers bind adjacent vertebral bodies together (they are firmly attached to vertebral bodies and loosely attached to intervertebral disks). Its superficial fibers span multiple vertebrae. B Posterior longitudinal ligament. Posterior view with vertebral canal windowed (vertebral arches removed). The thinner posterior longitudinal ligament descends from the clivus along the posterior surface of the vertebral bodies, passing into the sacral canal. The ligament broadens at the level of the intervertebral disk (to which it is attached by tapered lateral extensions). It narrows again while passing the vertebral body (to which it is attached at the superior and inferior margins). C Ligamenta flava and intertransverse ligaments. Anterior view with vertebral canal windowed (vertebral bodies removed). The ligamentum flavum is a thick, powerful ligament that connects adjacent laminae and reinforces the wall of the vertebral canal posterior to the intervertebral foramina. The ligament consists mainly of elastic fibers that produce the characteristic yellow color. When the spinal column is erect, the ligamenta flava are tensed, stabilizing the spine in the sagittal plane. The ligamenta flava also limit forward flexion of the spine. Note: The tips of the transverse processes are connected by interspinous ligaments that limit the rocking movements of vertebrae upon one another.

B

Spinous process

Superior articular process

Transverse process

Lamina

Intertransverse ligaments

Ligamenta flava

Facet joint capsule

Inferior articular process

Posterior longitudinal ligament

Superior articular process

Anterior longitudinal ligament Inferior articular facet C

Spinous process

229

Neck

10. Bones, Ligaments & Muscles of the Neck

Cervical Spine Posterior arch of atlas (C1) Anterior tubercle

Transverse process

Posterior tubercle

Transverse foramen

C2 (axis) Spinous process of axis (C2)

Vertebral foramen

Anterior tubercle

Posterior tubercle of atlas (C1)

C1 (atlas)

Groove for vertebral artery

Superior articular facet

A

Inferior articular facet

Transverse process

Posterior arch

Vertebral body Facet (zygapophyseal) joint

Anterior tubercle

Inferior articular process

Posterior tubercle

Superior articular process

Sulcus for spinal nerve

Dens Anterior articular facet

Posterior articular facet

Superior articular facet Spinous process

Transverse foramen Body

Intervertebral foramen

Spinous process of C7

Transverse process

B

Inferior articular facet

Lamina

C7 (vertebra prominens)

Transverse foramen

Transverse foramen

Fig. 10.7 Cervical spine (C1–C7) Left lateral view. The cervical spine consists of seven vertebrae. C1 and C2 are atypical and are discussed individually. Typical cervical vertebrae (C3–C7): Typical cervical vertebrae have relatively small, kidney-shaped bodies. The superior and inferior articular processes are broad and flat; their facets are flat and inclined at approximately 45 degrees from the horizontal. The vertebral arches enclose a large, triangular vertebral foramen. Spinal nerves emerge from the vertebral canal via the intervertebral foramina formed between the pedicles of adjacent vertebrae. The transverse processes of cervical vertebrae are furrowed to accommodate the emerging nerve (sulcus for spinal nerve). The transverse processes also consist of an anterior and a posterior portion that enclose a transverse foramen. The transverse foramina allow the vertebral artery to ascend to the base of the skull. The spinous processes of C3–C6 are short and bifid. The spinous process of C7 (vertebra prominens) is longer and thicker; it is the first spinous process that is palpable through the skin. Atlas (C1) and axis (C2): The atlas and axis are specialized for bearing the weight of the head and allowing it to move in all directions. The body of the axis contains a vertical prominence (dens) around which the atlas turns. The atlas does not have a vertebral body: it consists of an anterior and a posterior arch that allow the head to rotate in the horizontal plane.

Superior articular process

Transverse process

Superior articular facet

Body

Inferior articular process

Sulcus for spinal nerve

C

Spinous process

Inferior articular facet

Transverse foramen

Superior articular process Superior articular facet Transverse process

Body

Inferior articular process D

Spinous process

Inferior articular facet

Fig. 10.8 Left lateral view of cervical vertebrae A Atlas (C1). B Axis (C2). C Typical cervical vertebra (C4). D Vertebra prominens (C7).

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Neck

Posterior arch

10. Bones, Ligaments & Muscles of the Neck

Posterior tubercle

Vertebral foramen Superior articular facet

Superior articular facet

Anterior arch

Groove for vertebral artery

Lateral masses

Transverse process Transverse foramen Facet for dens

Transverse foramen

Anterior arch Anterior tubercle

A

Inferior articular facet

Anterior tubercle

Transverse process

A

Spinous process Vertebral foramen

Anterior articular facet

Lamina Inferior articular process

Dens

Dens

Superior articular facet

Transverse process

Transverse process

Superior articular facet

Transverse foramen Anterior articular facet

Vertebral foramen

Body

B

B

Uncinate process

Spinous process

Inferior articular facet

Superior articular process

Vertebral arch Lamina Superior articular facet

Pedicle

Posterior tubercle

Transverse process with sulcus for spinal nerve

Sulcus for spinal nerve

Transverse foramen Body

C

Uncinate process

Posterior tubercle Anterior tubercle

Transverse process

Inferior articular facet

Body Spinous process

Anterior tubercle

C

Spinous process

Uncinate process

Superior articular process

Lamina Body Vertebral foramen

Transverse foramen

Inferior articular process

Superior articular facet

Sulcus for spinal nerve

Anterior tubercle Uncinate process

Fig. 10.9 Superior view of cervical vertebrae A Atlas (C1). B Axis (C2). C Typical cervical vertebra (C4). D Vertebra prominens (C7).

Sulcus for spinal nerve

Transverse foramen

Transverse process

Body D

Transverse process

Inferior Inferior articular process articular facet Spinous process D

Fig. 10.10 Anterior view of cervical vertebrae A Atlas (C1). B Axis (C2). C Typical cervical vertebra (C4). D Vertebra prominens (C7).

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Neck

10. Bones, Ligaments & Muscles of the Neck

Joints of the Cervical Spine

Dens of axis (C2)

Atlanto-occipital joint Median atlantoaxial joint

Atlas (C1)

Lateral atlantoaxial joint

Axis (C2)

Atlantoaxial joint

Uncinate processes

Uncinate joint

Facet (zygapophyseal) joint Vertebral body

Facet (zygapophyseal) joint

Transverse process

Posterior tubercle Anterior tubercle

Intervertebral disk

Sulcus for spinal nerve

Intervertebral joint

A

B

Fig. 10.11 Joints of the cervical spine A Left lateral view. B Anterior view. C Radiograph of the cervical spine. The cervical spine has five types of joints. Two joints (intervertebral and facet) are common to all regions of the spine, and three are specialized joints of the cervical spine. Joints of the vertebral column: Adjacent vertebrae articulate at two points: vertebral bodies and articular processes. The bodies of adjacent vertebrae articulate at roughly horizontal intervertebral joints (via intervertebral disks). The articular processes of adjacent vertebrae articulate at facet (zygapophyseal) joints. In the cervical spine, the intervertebral joints are angled slightly anteroinferiorly, and the zygapophyseal joints are angled posteroinferiorly (roughly 45 degrees below horizontal). Joints of the cervical spine: There are two types of joints that are particular to the cervical spine: 1. Uncovertebral joints: Upward protrusions of the lateral margins of cervical vertebral bodies form uncinate processes. These processes may articulate with the inferolateral margin of the adjacent superior vertebra, forming uncovertebral joints. 2. Craniovertebral joints: The atlas (C1) and axis (C2) are specialized to bear the weight of the head and facilitate movement in all directions. This is made possible by craniovertebral joints (see Fig. 10.12).

C

232

Inferior articular facet

Neck

Superior nuchal line

10. Bones, Ligaments & Muscles of the Neck

External occipital protuberance Foramen magnum

Lateral mass of atlas

Occipital condyle (occipital bone) Dens of axis (C2)

Axis (C2) A

Posterior arch of atlas (with tubercle)

Median atlantoaxial joint Superior articular facet (lateral mass of axis)

Dens of axis (C2)

Fig. 10.12 Craniovertebral joints A Posterior view. B Left oblique posterosuperior view. There are five craniovertebral joints. The paired atlanto-occipital joints are articulations between the concave superior articular facets of the atlas (C1) and the convex occipital condyle of the occipital bone. These allow the head to rock back and forth in the sagittal plane. The atlantoaxial joints (two lateral and one medial) allow the atlas to rotate in the horizontal plane around the dens of the axis. The lateral atlantoaxial joints are the paired articulations between the inferior and superior articular facets of the atlas and axis, respectively. The median atlantoaxial joint is the unpaired articulation between the dens of the axis and the fovea of the atlas. Note: While only the atlanto-occipital joints are direct articulations between the cranium and vertebral column, the atlantoaxial joints are generally classified as craniovertebral joints as well.

Vertebral artery in transverse foramen

Dens

Groove for vertebral artery

Transverse process

Spinous process

B

Lateral atlantoaxial joint

C1 spinal nerve

Atlas (C1) Axis (C2) Vertebral artery Uncinate process

Transverse process

C5 spinal nerve

Spinal nerve in sulcus

C7 spinal nerve A

Lateral atlantoaxial joint

Vertebral body (C7)

Fig. 10.13 Neurovasculature of the cervical spine A Anterior view. B Superior view. The transverse processes of the cervical vertebrae are extremely important in communicating neurovascular structures. Spinal nerves arise from the spinal cord in the vertebral canal. They exit via the intervertebral foramina formed by the pedicles of adjacent vertebrae. The trans-

Spinal cord in vertebral foramen

Dorsal root Ventral root

Superior articular facet

Dorsal ramus

Spinal ganglion

White and gray rami communicantes

Ventral ramus

B

Vertebral artery in transverse foramen

Vertebral body

Transverse process Uncinate process

verse processes of cervical vertebrae contain grooves (sulci) through which the spinal nerves pass. The transverse processes also contain transverse foramina that allow the vertebral artery to ascend from the subclavian artery and enter the skull via the foramen magnum. Injury to the cervical spine can compress the neurovascular structures as they emerge and ascend from the vertebral column.

233

Neck

10. Bones, Ligaments & Muscles of the Neck

Ligaments of the Cervical Spine

Occipital bone

Superior nuchal line

External occipital protuberance

Inferior nuchal line

Posterior atlanto-occipital membrane

Mastoid process

Atlas (C1)

Opening for vertebral artery Transverse process

Fig. 10.14 Ligaments of the cervical spine A Posterior view. B Anterior view after removal of the anterior skull base. C Midsagittal section, left lateral view. The nuchal ligament is the broadened, sagittally oriented part of the supraspinous ligament that extends from the vertebra prominens (C7) to the external occipital protuberance.

Axis (C2)

Ligamenta flava

Nuchal ligament

Transverse process

Joint capsule (zygapophyseal joint)

B

A

Spinous process

Vertebra prominens (C7) A

Internal occipital protuberance Internal occipital crest

Occipital bone, basilar part

Atlanto-occipital joint (atlantooccipital capsule)

Anterior atlanto-occipital membrane

Atlas (C1)

Transverse process

Transverse foramina

Lateral atlantoaxial joint (capsule)

Axis (C2) Anterior longitudinal ligament Sulcus for spinal nerve

Intervertebral disk B

234

Zygapophyseal joint (capsule)

Posterior tubercle Anterior tubercle

Vertebra prominens (C7)

Neck

10. Bones, Ligaments & Muscles of the Neck

Internal Sella Apical ligament Hypoglossal Tectorial acoustic meatus turcica canal of the dens membrane

Sphenoid sinus Occipital bone, basilar part

External occipital protuberance

Anterior atlanto-occipital membrane

Dens of axis (C2)

Anterior arch of atlas (C1)

Transverse ligament of atlas

Longitudinal fascicles

Posterior atlanto-occipital membrane

Posterior arch of atlas

Nuchal ligament

Facet joint capsule

Ligamenta flava Vertebral arch

Intervertebral disk (nucleus pulposus)

Intervertebral foramen Spinous process

Anterior longitudinal ligament

Interspinous ligament

Posterior longitudinal ligament C

Supraspinous ligament

C7 vertebral body (vertebra prominens)

Apex of dens (C2)

Body of axis (C2)

Cerebellomedullary cistern Posterior tubercle of atlas (C1) Nuchal ligament

Posterior longitudinal ligament Vertebral body (C5) Intervertebral disk Vertebra prominens (C7)

Spinous process of C7

Supraspinous ligament Spinal cord Subarachnoid space

Fig. 10.15 Magnetic resonance image of the cervical spine Midsagittal section, left lateral view, T2-weighted TSE sequence. (From Vahlensieck M, Reiser M. MRT des Bewegungsapparates. 2nd ed. Stuttgart: Thieme; 2001.)

235

Neck

10. Bones, Ligaments & Muscles of the Neck

Ligaments of the Craniovertebral Joints

Superior nuchal line

External occipital protuberance

Atlanto-occipital capsule

Atlanto-occipital capsule

Nuchal ligament Foramen magnum

External occipital crest

External occipital protuberance

Temporal bone

Atlanto-occipital joint

Occipital bone Occipital condyle Tectorial membrane Atlas (C1) Styloid process

Transverse process Ligamenta flava

Zygapophyseal joint (capsule)

Posterior longitudinal ligament

Spinous process A

B

Atlanto-occipital capsule

Alar ligaments

Tectorial membrane

Tectorial membrane

Longitudinal fascicles

Transverse foramen

Transverse ligament of atlas Intervertebral disk

Posterior arch of atlas Lateral atlantoaxial joint

Vertebral body

Laminae (cut)

C

Posterior longitudinal ligament

Cruciform ligament of atlas Cruciform ligament of atlas

Transverse process

Fig. 10.16 Ligaments of the craniovertebral joints and cervical spine Skull and upper cervical spine, posterior view. A The posterior atlanto-occipital membrane stretches from the posterior arch of the atlas to the posterior rim of the foramen magnum. This membrane has been removed on the right side. B With the vertebral canal opened and the spinal cord removed, the tectorial membrane, a broadened expansion of the posterior longitudinal ligament, is seen to form the anterior boundary of the vertebral canal at the level of the craniovertebral joints.

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Tectorial membrane

Posterior atlanto-occipital membrane (cut)

Axis (C2)

Posterior atlanto-occipital membrane

Posterior arch of atlas

Mastoid process

Longitudinal Apical ligament fascicles of dens

Alar ligaments

Lateral mass of atlas (C1)

Dens, posterior articular surface

Transverse ligament of atlas Longitudinal fascicles

Body of axis (C2) Intervertebral disk

Intervertebral foramen D

Posterior longitudinal ligament

C With the tectorial membrane removed, the cruciform ligament of the atlas can be seen. The transverse ligament of the atlas forms the thick horizontal bar of the cross, and the longitudinal fascicles form the thinner vertical bar. D The transverse ligament of the atlas and longitudinal fascicles have been partially removed to demonstrate the paired alar ligaments, which extend from the lateral surfaces of the dens to the corresponding inner surfaces of the occipital condyles, and the unpaired apical ligament of the dens, which passes from the tip of the dens to the anterior rim of the foramen magnum.

Neck

Median atlantoaxial joint

Anterior tubercle

10. Bones, Ligaments & Muscles of the Neck

Alar ligaments (cut)

Superior articular facet

Apical ligament of dens

Transverse ligament of atlas

Transverse process Transverse foramen

Dens

Lateral mass of atlas

Vertebral foramen

Longitudinal fascicles

Groove for vertebral artery Posterior arch of atlas

Posterior tubercle of atlas

Spinous process of axis

A

Posterior atlanto-occipital membrane Alar ligaments

Tectorial membrane

Apical ligament of dens

Longitudinal fascicles

Superior articular facet

Dens

Anterior arch of atlas

Median atlantoaxial joint Anterior tubercle of atlas

Lateral atlantoaxial joint

Alar Apical ligament ligaments of dens

Body of axis

Longitudinal fascicles

Transverse process

Tectorial membrane

Superior articular facet, lateral mass of atlas

B Transverse foramen

Transverse ligament of atlas

Capsule of lateral atlantooccipital joint

Transverse process Intertransverse ligament

Groove for vertebral artery

Posterior arch of atlas Ligamenta flava

C

Fig. 10.17 Ligaments of the craniovertebral joints A Superior view of atlas (C1) and axis (C2). B Anterosuperior view of C1–C4. C Posterosuperior view of atlas (C1) and axis (C2). There are five craniovertebral joints. The paired atlanto-occipital joints are articulations between the concave superior articular facets of the atlas and the convex occipital condyles of the occipital bone. The joints are stabilized by the atlanto-occipital joint capsule and the posterior atlantooccipital membrane (the equivalent of the ligamenta flava). The paired lateral atlantoaxial and unpaired median atlantoaxial joints allow the atlas to rotate in the horizontal plane around the dens of the axis. They are stabilized by the alar ligaments, the apical ligament of the dens, and the cruciform ligament of the atlas (transverse ligament and longitudinal fascicles).

Posterior atlanto-occipital membrane

Nuchal ligament

Spinous process

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Neck

10. Bones, Ligaments & Muscles of the Neck

Muscles of the Neck: Overview Fig. 10.18 Sternocleidomastoid and trapezius A Sternocleidomastoid, right lateral view. B Trapezius, posterior view.

Table 10.3 Muscles of the neck The muscles of the neck lie at the intersection of the skull, vertebral column, and upper limb. They can therefore be classified in multiple ways based on location and function. In the pages that follow, the neck muscles are grouped as follows: Superficial neck muscles

Clavicular head

Muscles that lie superficial to the deep layer (lamina) of the deep cervical fascia and are innervated by the ventral rami of spinal nerves

Sternal head

Posterior neck muscles (intrinsic back muscles)

Muscles that insert on the cervical spine and are innervated by the dorsal rami of spinal nerves • Intrinsic back muscles (including nuchal muscles) ◦ Short nuchal/craniovertebral muscles

A

p. 239

p. 240 pp. 242, 243 p. 245

Anterior neck muscles Superior part

Middle part

Muscles that insert on the anterior cervical spine and are innervated by the ventral rami of spinal nerves • Anterior vertebral (prevertebral) muscles • Lateral vertebral muscles (scalenes)

p. 252 p. 253 p. 253

Muscles that do not insert on the cervical spine • Suprahyoid muscles • Infrahyoid muscles

p. 254 p. 255 p. 255

Inferior part

B

Fig. 10.19 Superficial neck muscles A Left lateral view. B Anterior view of sternocleidomastoid and trapezius. Unlike the rest of the neck muscles, the superficial neck muscles are located superficial to the deep cervical fascia. Platysma: The platysma, like the muscles of facial expression, is not enveloped in its own fascial sheath, but is instead directly associated with (and in parts inserted into) the skin. (Note: It is innervated by the same nerve as the muscles of facial expression, the facial nerve.) The platysma is highly variable in size — its fibers may reach from the lower face to the upper thorax. Sternocleidomastoid and trapezius: The trapezius lies between the investing and prevertebral layers of cervical fascia. The investing layer splits to enclose the sternocleidomastoid and the trapezius.

238

Deep cervical fascia Sternocleidomastoid Depressor anguli oris

Platysma

A

Trapezius

Neck

10. Bones, Ligaments & Muscles of the Neck

Table 10.4 Superficial neck muscles Muscle

Origin

Insertion

Innervation

Action

Platysma

Mandible (inferior border); skin of lower face and angle of mouth

Skin over lower neck and superior and lateral thorax

Facial n. (CN VII), cervical branch

Depresses and wrinkles skin of lower face and mouth; tenses skin of neck; aids forced depression of mandible

Sternocleidomastoid

Occipital bone (superior nuchal line); temporal bone (mastoid process)

Sternal head: sternum (manubrium)

Accessory n. (CN IX), spinal part

Unilateral: Moves chin up and out (tilts occiput to same side and rotates face to opposite side) Bilateral: Extends head; aids in respiration when head is fixed

Clavicular head: clavicle (medial ⅓) Trapezius, superior fibers*

Occipital bone; C1–C7 spinous processes

Clavicle (lateral ⅓)

Draws scapula obliquely upward; rotates glenoid cavity inferiorly

Rhomboid minor

Ligamentum nuchae (inferior part); spinous processes of C7–T1 vertebrae

Medial (vertebral) border of the scapula, superior to the intersection with the scapular spine

C4–C5 ventral rami (C5 fibers are from the dorsal scapular n.)

Scapular movements (e.g., retraction and rotation)

Levator scapulae

C1–C4 cervical vertebrae; posterior tubercles of transverse processes

Scapula, medial to superior angle

C3–C5 ventral rami (C5 fibers are from the dorsal scapular n.)

Scapular movements (e.g., elevation, retraction, and rotation)

Serratus posterior superior

Ligamentum nuchae (inferior part); spinous processes of C7–T3 vertebrae

Ribs 2–5

Ventral rami of thoracic spinal nn. (intercostal nn.)

Postulated to be an accessory muscle of respiration; assists in elevating ribs

*The middle and inferior parts are not described here.

Sternocleidomastoid

Trapezius

B

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Neck

10. Bones, Ligaments & Muscles of the Neck

Muscles of the Neck & Back (I)

Sternocleidomastoid Deep cervical fascia

Trapezius, superior part Trapezius, middle part

Rhomboideus minor Levator scapulae

Clavicle

Acromion Scapular spine

Supraspinatus

Deltoid

Rhomboideus major Infraspinatus Scapula, medial border

Teres minor Teres major

Teres major

Trapezius, inferior part

Serratus anterior Latissimus dorsi (cut)

Triceps brachii

Latissimus dorsi Serratus posterior inferior

Thoracolumbar fascia, superficial layer

External oblique Olecranon Aponeurotic origin of latissimus dorsi

Internal oblique

Lumbar triangle, internal oblique Iliac crest

Gluteus medius

Fig. 10.20 Muscles of the neck and back Posterior view with trapezius and latissimus dorsi cut on right side. The extrinsic back muscles lie superficial to the thoracolumbar and deep cervical fascia. They are muscles of the upper limb (derived from the limb buds) that have migrated to the back. The intrinsic back muscles lie within the thoracolumbar and deep cervical fascia. They are derived

240

Gluteus maximus

from epaxial muscle. Because of their different embryonic origins, the intrinsic back muscles are innervated by the dorsal rami of the spinal nerves, and the extrinsic back muscles are innervated by the ventral rami. Note: The trapezius and sternocleidomastoid are innervated by the accessory nerve (CN XI).

Neck

Sternothyroid

Sternohyoid

Trachea

Esophagus

10. Bones, Ligaments & Muscles of the Neck

Visceral cervical fascia

Omohyoid

Thyroid gland

Sternocleidomastoid Pretracheal cervical fascia

Internal jugular vein

Superficial cervical fascia

Carotid sheath

Cervical fascia

Prevertebral cervical fascia

Vagus nerve Common carotid artery

Longus colli Anterior scalene

Brachial plexus

Middle scalene

C6 vertebra

Spinal cord

Levator scapulae Intrinsic back muscles Deep nuchal fascia

Trapezius

Superficial nuchal fascia

A

Abdominal aorta

Inferior vena cava

Parietal peritoneum, transversalis fascia

Kidney

Nuchal fascia

Renal fascia, anterior layer Transverse abdominis Internal oblique External oblique Fibrous capsule

L3 vertebra

Perirenal fat Renal fascia, posterior layer

Psoas major

Latissimus dorsi Vertebral arch Serratus posterior inferior

Costal process Spinous process Intrinsic back muscles (latissimus dorsi)

B

Fig. 10.21 Fascial planes Transverse sections, superior view. A Neck at the level of the C6 vertebra. B Posterior trunk wall at the level of the L3 vertebra (with cauda equina removed from vertebral canal). The muscles of the neck and back are separated by layers of deep fascia (see p. 242). The outermost layer, the deep investing cervical fascia, encloses all muscles with the exception of the platysma (this is located in the superficial fascia, not to be confused with the superficial

Quadratus lumborum Deep layer (lamella) Superficial layer (lamella)

Thoracolumbar fascia

layer of the deep cervical fascia). The deep cervical fascia, located in the anterior neck, is continuous posteriorly with the nuchal fascia in the posterior neck. The superficial layer of the nuchal fascia is continuous inferiorly with the superficial layer (lamella) of the thoracolumbar fascia. The intrinsic muscles of the neck and back lie within the deep nuchal fascia, which is continuous with the prevertebral cervical fascia (anteriorly) and thoracolumbar fascia (inferiorly). The muscles and structures of the anterior neck are enclosed in individual fascial sheaths (i.e., the visceral fascia, pretracheal fascia, and carotid sheath).

241

Neck

10. Bones, Ligaments & Muscles of the Neck

Muscles of the Neck & Back (II)

Deep nuchal fascia

Serratus posterior superior (cut)

Semispinalis capitis

Rhomboideus major and minor (cut)

Serratus posterior superior External intercostal muscles

Trapezius (cut)

Deep nuchal fascia

Splenius capitis

Superficial layer (lamella) of thoracolumbar fascia

Splenius cervicis

Latissimus dorsi (cut)

Superficial layer (lamella) of thoracolumbar fascia

Serratus posterior inferior

Spinalis*

Internal oblique

Latissimus dorsi aponeurosis

Iliocostalis*

External oblique (cut)

External oblique

Longissimus*

External intercostal muscles

External oblique

Iliac crest External oblique (cut)

Internal oblique

Iliac crest

A

Gluteus maximus

B

Fig. 10.22 Extrinsic and intrinsic back muscles Posterior view. These dissections demonstrate the distinction between the intrinsic back muscles and the surrounding extrinsic back muscles and trunk muscles. The intrinsic back muscles lie within the deep nuchal fascia, which is continuous inferiorly with the superficial layer (lamella) of the thoracolumbar fascia. They are derived from epaxial muscles and therefore innervated by the dorsal rami of spinal nerves (see p. 246). The muscles of the trunk are derived from hypaxial muscle and therefore innervated by the ventral rami of spinal nerves. The visible trunk muscles are the abdominal muscles (internal and external obliques) and the thoracic muscles (external intercostals).

242

Gluteus maximus

A Removed: Extrinsic back muscles (with the exception of the serratus posterior and the aponeurotic origin of the latissimus dorsi on the right side). B Removed: All extrinsic back muscles and portions of the fascial covering (deep nuchal and superficial layers [lamellae] of the thoracolumbar fasciae). *The spinalis, iliocostalis, and longissimus are collectively known as the erector spinae.

Neck

Splenius capitis (cut)

Semispinalis capitis

Longissimus capitis

Splenius capitis

Iliocostalis cervicis

Splenius cervicis

10. Bones, Ligaments & Muscles of the Neck

Splenius capitis (cut)

Semispinalis capitis (cut)

Superior nuchal line Rectus capitis posterior minor

Obliquus capitis superior

Obliquus capitis inferior

Rectus capitis posterior major Longissimus capitis Iliocostalis thoracis

Spinalis cervicis

External intercostal muscles

Levatores costarum Spinalis

Interspinales cervicis

Rotatores thoracis longi Levatores costarum longi

Longissimus thoracis

Rotatores thoracis breves

External intercostal muscles

Spinalis thoracis

Iliocostalis lumborum

Levatores costarum breves

Internal oblique (cut)

Transversus abdominis

Intertransversarii medialis lumborum

Iliac crest

Twelfth rib Intertransversarii laterales lumborum

Interspinales lumborum Transversus abdominis

A

Gluteus maximus

Multifidus

Deep layer (lamella) of thoracolumbar fascia

Iliac crest

B

Fig. 10.23 Intrinsic back muscles Posterior view. These dissections reveal the layers of intrinsic back muscles. The iliocostalis, longissimus, and spinalis collectively form the erector spinae. They lie deep to the superficial layer (lamella) of the thoracolumbar fascia and cover the other intrinsic back muscles.

Transverse processes

Deep layer (lamella) of thoracolumbar fascia

Multifidus

Quadratus lumborum

Gluteus maximus

A Removed on left side: Longissimus (except cervical portion), splenii capitis and cervicis. Removed on right side: Iliocostalis. Note the deep layer (lamella) of the thoracolumbar fascia, which gives origin to the internal oblique and transversus abdominis. B Removed on left side: Iliocostalis, longissimus, and internal oblique. Removed on right side: Erector spinae, multifidus, transversus abdominis, splenius capitis, and semispinalis capitis.

243

Neck

10. Bones, Ligaments & Muscles of the Neck

Muscles of the Posterior Neck

Parietal bone

Occipital bone

External occipital protuberance Semispinalis capitis (cut)

Superior nuchal line

Sternocleidomastoid (cut) Splenius capitis (cut)

Semispinalis capitis Sternocleidomastoid Rectus capitis posterior minor Rectus capitis posterior major

Mastoid process Obliquus capitis superior Transverse process of atlas (C1) Obliquus capitis inferior Longissimus capitis

Splenius capitis Spinous process of axis (C2) Semispinalis cervicis Trapezius, descending part

Fig. 10.24 Muscles in the nuchal region Posterior view of nuchal region. As the neck is at the intersection of the trunk, head, and upper limb, its muscles can be divided according to embryonic origin, function, or location. Those muscles (extrinsic and intrinsic) located in the posterior neck are often referred to as the nuchal muscles. The nuchal muscles are further divided into short

244

Semispinalis capitis (cut)

Splenius capitis (cut) Splenius cervicis

nuchal muscles, which are intrinsic back muscles innervated by the dorsal rami of cervical spinal nerves. Based on location, the short nuchal muscles may also be referred to as suboccipital muscles. The anterior and posterior vertebral muscles collectively move the craniovertebral joints.

Neck

Trapezius (cut) Rectus capitis posterior minor

10. Bones, Ligaments & Muscles of the Neck

Superior nuchal line External occipital protuberance

Inferior nuchal line

Semispinalis capitis (cut) Sternocleidomastoid (cut)

Rectus capitis posterior major

Splenius capitis (cut)

Obliquus capitis superior

Obliquus capitis superior

Mastoid process

Longissimus capitis (cut) Transverse process of atlas

Posterior atlantooccipital membrane (with opening for vertebral artery)

Rectus capitis posterior major

Posterior arch of atlas (C1)

Obliquus capitis inferior

Spinous process of axis (C2) Interspinales cervicis

Intertransversarii cervicis

Transverse process of C7

Spinous process of C7

A

Semispinalis capitis

Rectus capitis posterior minor

Rectus capitis posterior major

Trapezius Sternocleidomastoid

Splenius capitis

Obliquus capitis superior

Longissimus capitis Obliquus capitis inferior

Intertransversarii cervicis

B

Interspinales cervicis

Fig. 10.25 Muscle attachments in the nuchal region Posterior view of skull and cervical spine (C1–C7). A Short nuchal muscles with interspinales and intertransversarii cervicis. The superficial muscles (trapezius and sternocleidomastoid, innervated by CN XI) have been cut. The intrinsic back muscles inserting on the skull (splenius, longissimus, and semispinalis capitis) have also been cut. The intrinsic back muscles are all innervated by dorsal rami of spinal nerves. The short nuchal muscles are innervated by the dorsal rami of the first spinal nerve (suboccipital nerve). B Muscle origins (red) and insertions (blue).

245

Neck

10. Bones, Ligaments & Muscles of the Neck

Intrinsic Back Muscles (I): Erector Spinae & Interspinales

①

⑩ ③

⑤

⑧ ⑥

④ ⑨

⑦

②

A

C

B

Fig. 10.26 Interspinales and erector spinae A Interspinales and spinalis. B Iliocostalis. C Longissimus.

Table 10.5 Erector spinae and interspinales Like all intrinsic back muscles, these muscles are innervated by dorsal rami of spinal nerves. The erector spinae and interspinales are innervated by lateral branches of the dorsal rami. The longissimus is innervated by spinal nerves C1–L5, the iliocostalis by C8–L1. Muscle

Interspinalis

Spinalis*

Iliocostalis*

Longissimus*

Origin

Insertion

Action

①

I. cervicis

C1–C7 (between spinous processes of adjacent vertebrae)

Extends cervical spine

②

I. lumborum

L1–L5 (between spinous processes of adjacent vertebrae

Extends lumbar spine

③

S. cervicis

C5–T2 (spinous processes)

C2–C5 (spinous processes)

④

S. thoracis

T10–L3 (spinous processes, lateral surface)

T2–T8 (spinous processes, lateral surface)

Bilateral: Extends spine Unilateral: Bends laterally to same side

⑤

I. cervicis

3rd–7th ribs

C4–C6 (transverse processes)

⑥

I. thoracis

7th–12th ribs

1st–6th ribs

⑦

I. lumborum

Sacrum; iliac crest; thoracolumbar fascia

6th–12th ribs; deep thoracolumbar fascia; upper lumbar vertebrae (transverse processes)

⑧

L. cervicis

T1–T6 (transverse processes)

C2–C5 (transverse processes)

⑨

L. thoracis

Sacrum; iliac crest; L1–L5 (spinous processes); lower thoracic vertebrae (transverse processes)

2nd–12th ribs; T1–L5 (transverse processes)

⑩

L. capitis

T1–T3 (transverse processes); C4–C7 (transverse and articular processes)

Occipital bone (mastoid process)

Bilateral: Extends head Unilateral: Flexes and rotates head to same side

*The spinalis, iliocostalis, and longissimus are collectively known as the erector spinae. Note: The iliocostalis and longissimus extend the entire spine. The spinalis acts only on the cervical and thoracic spines.

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10. Bones, Ligaments & Muscles of the Neck

Atlas (C1) Axis (C2) Interspinales cervicis

Spinous process of C7 (vertebra prominens)

Spinalis cervicis Mastoid process Longissimus capitis

Iliocostalis cervicis

Spinalis thoracis

Longissimus cervicis

Iliocostalis thoracis Interspinales lumborum

Longissimus thoracis

Sacrum Transverse processes of L1–L5

Iliocostalis lumborum Iliac crest

A

Sacrum

Fig. 10.27 Interspinales and erector spinae muscles The spinalis, iliocostalis, and longissimus are collectively known as the erector spinae. A Interspinales and spinalis. B Iliocostalis and longissimus.

B

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10. Bones, Ligaments & Muscles of the Neck

Intrinsic Back Muscles (II)

˝

˟ ˢ

˞

ˠ

˨ ˦

ˡ

˧

˩

˥

ˣ

A

A

B

Fig. 10.28 6SOHQLXVDQGVHPLVSLQDOLV A Splenius. B Semispinalis.

ˤ

B

C

Fig. 10.29 ,QWHUWUDQVYHUVDULLOHYDWRUHVFRVWDUXPPXOWLÀGXVDQGURWDWRUHV A Intertransversarii and levatores costarum. B 0  XOWLÀGXVC Rotatores.

Table 10.6 6SOHQLXVVHPLVSLQDOLVLQWHUWUDQVYHUVDULLOHYDWRUHVFRVWDUXPPXOWLÀGXVDQGURWDWRUHV All intrinsic back muscles are innervated by the dorsal rami of the spinal nerves. The splenius is innervated by spinal nerves C1–C6. Muscle

Splenius

Semispinalis

Intertransversarii

Levatores costarum

Insertion

Action

Bilateral: Extends cervical spine and head Unilateral: Flexes and rotates head to same side

˝

S. capitis

C3–T3 (spinous processes)

Occipital bone (lateral superior nuchal line; mastoid process)

˞

S. cervicis

T3–T6 (spinous processes)

C1–C2 (transverse processes)

˟

S. capitis

C2–C7 (transverse processes)

Occipital bone (between superior and inferior nuchal lines)

ˠ

S. cervicis

T1–T6 (transverse processes)

C2–C7 (spinous processes)

ˡ

S. thoracis

T6–T12 (transverse processes)

C6–T4 (spinous processes)

I. anteriores cervicis

C2–C7 (between anterior tubercles of adjacent vertebrae)

ˢ

I. posteriores cervicis

C2–C7 (between posterior tubercles of adjacent vertebrae)

ˣ

I. mediales lumborum

L1–L5 (between mammillary processes of adjacent vertebrae)

ˤ

I. laterales lumborum

L1–L5 (between transverse processes of adjacent vertebrae)

˥

L.c. brevis

C7–T11 (transverse processes)

˦

L.c. longi

˧ 0XOWLÀGXV

Rotatores

Origin

Costal angle of next lower rib Costal angle of rib to vertebrae below

Bilateral: Extends spine and head (stabilizes craniovertebral joints) Unilateral: Bends head and spine to same side, rotates to opposite side Bilateral: Stabilizes and extends spine Unilateral: Bends spine laterally to same side

Bilateral: Extends thoracic spine Unilateral: Bends thoracic spine to same side, rotates to opposite side

C2–sacrum (between transverse and spinous processes, skipping two to four vertebrae)

Bilateral: Extends spine Unilateral: Flexes spine to same side, rotates to opposite side Bilateral: Extends thoracic spine Unilateral: Rotates spine to opposite side

˨

R. brevis

T1–T12 (between transverse and spinous processes of adjacent vertebrae)

˩

R. longi

T1–T12 (between transverse and spinous processes, skipping one vertebra)

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10. Bones, Ligaments & Muscles of the Neck

Superior nuchal line

Inferior nuchal line

Semispinalis capitis

Semispinalis cervicis Spinous process of C7 (vertebra prominens)

Superior nuchal line

Semispinalis thoracis Transverse process

Mastoid process

Spinous process

Intertransversarii posteriores cervicis

Rotatores longi

Splenius capitis

Posterior tubercle Spinous process of C7 (vertebra prominens)

Rotatores brevis

Splenius cervicis

Fifth rib

Transverse processes

Multifidus

Levatores costarum brevis

Levatores costarum longi

Sacrum

Transverse process

A

Fig. 10.30 Splenius with transversospinal and intertransverse systems A 7UDQVYHUVRVSLQDO V\VWHP URWDWRUHV PXOWLÀGXV DQG VHPLVSLQDOLV  B 6SOHQLXVDQGLQWHUWUDQVYHUVHV\VWHPLQWHUWUDQVYHUVDULLDQGOHYDWRUHV FRVWDUXP 

Intertransversarii mediales lumborum

Mammillary process Intertransversarii laterales lumborum

B

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10. Bones, Ligaments & Muscles of the Neck

Intrinsic Back Muscles (III): Short Nuchal Muscles Fig. 10.31 Short nuchal muscles Posterior view. The short nuchal muscles are intrinsic back muscles that are innervated by the dorsal ramus of the first spinal nerve (suboccipital nerve). These muscles contribute to the extension of the atlanto-occipital joint and rotation about the atlantoaxial joint.

①

②

④

③

Table 10.7 Short nuchal muscles Muscle

Rectii capitis posterioris

Obliquii capitis

250

Origin

Insertion

Innervation

Action

C1 spinal nerve (suboccipital n.), dorsal ramus

Bilateral: Extends head Unilateral: Rotates head to same side

①

R.c.p. minor

C1 (posterior tubercle)

Inferior nuchal line (inner ⅓)

②

R.c.p. major

C2 (spinous process)

Inferior nuchal line (middle ⅓)

③

O.c. inferior

C2 (spinous process)

C1 (transverse process)

④

O.c. superior

C1 (transverse process)

Above the insertion of the rectus capitis posterior major

Bilateral: Extends head Unilateral: Tilts head to same side; rotates head to opposite side

Neck

Superior nuchal line

Inferior nuchal line

10. Bones, Ligaments & Muscles of the Neck

Rectus capitis posterior minor

Obliquus capitis superior Mastoid process Rectus capitis posterior major

Posterior tubercle of atlas (C1)

Transverse process of atlas (C1)

Spinous process of axis (C2)

Obliquus capitis inferior

A

Transverse process of atlas

Mastoid process

Posterior arch of atlas (C1)

External occipital protuberance

Mandible

Obliquus capitis superior

Atlas (C1)

Rectus capitis posterior minor

Axis (C2)

Rectus capitis posterior major Obliquus capitis inferior

Spinous process of axis (C2)

B

Fig. 10.32 Suboccipital muscles A Posterior view. B Left lateral view. The suboccipital muscles collectively act on the craniovertebral joints. The suboccipital muscles are the rectus capitis posterior major, rectus capitis posterior minor, obliquus capitis inferior, and obliquus capitis

superior. The dorsal ramus of the first cervical spinal nerve innervates all four suboccipital muscles. Note: The suboccipital triangle is located between the rectus capitis posterior major, the obliquus capitis superior, and the obliquus capitis inferior.

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10. Bones, Ligaments & Muscles of the Neck

Prevertebral & Scalene Muscles

⑤

①

⑥ ③ ② ④

⑧ ⑦

Fig. 10.33 Prevertebral muscles Anterior view.

⑨

Fig. 10.34 Scalene muscles Anterior view.

Table 10.8 Prevertebral and scalene muscles Muscle ①

Longus capitis

Longus colli

Rectus capitis

Scalenes

252

② Vertical (intermediate) part

Origin

Insertion

Innervation

Action

C3–C6 (anterior tubercles)

Occipital bone, basilar part

Cervical plexus, direct branches (C1–C3)

Bilateral: Flexes head Unilateral: Tilts and slightly rotates head to same side

C5–T3 (anterior surfaces of vertebral bodies)

C2–C4 (anterior surfaces)

Cervical plexus, direct branches (C2–C6)

Bilateral: Flexes cervical spine Unilateral: Tilts and slightly rotates cervical spine to same side

Ventral ramus of C1 spinal n. (suboccipital n.)

Bilateral: Flexion at atlanto-occipital joint Unilateral: Lateral flexion at atlantooccipital joint

Ventral rami of cervical spinal nn.

With ribs mobile: Inspiration (elevate upper ribs) With ribs fixed: Bend cervical spine to same side (unilateral contraction); flex cervical spine (bilateral contraction)

③

Superior oblique part

C3–C5 (anterior tubercles)

C1 (anterior tubercle)

④

Inferior oblique part

T1–T3 (anterior surfaces of vertebral bodies)

C5–C6 (anterior tubercles)

⑤

R.c. anterior

C1 (lateral mass)

Occipital bone (basilar part)

⑥

R.c. lateralis

C1 (transverse process)

Occipital bone (basilar part, lateral to occipital condyles)

⑦

S. anterior

C3–C6 (anterior tubercles)

1st rib (scalene tubercle)

⑧

S. medius

C1 and C2 (transverse processes); C3–C7 (posterior tubercles)

1st rib (posterior to groove for subclavian a.)

⑨

S. posterior

C5–C7 (posterior tubercles)

2nd rib (outer surface)

Neck

Longus capitis (cut)

10. Bones, Ligaments & Muscles of the Neck

Rectus capitis anterior

Rectus capitis lateralis

Longus capitis

Transverse process of atlas (C1) Transverse process of atlas (C2)

Superior oblique part

Vertical part

Longus colli

Inferior oblique part Scalenus medius Scalenus anterior

Scalenus medius

Scalenus posterior

Scalenus posterior

Interscalene triangle

Scalenus anterior (cut)

Groove for subclavian artery

Second rib

Scalene tubercle

Fig. 10.35 Anterior vertebral (prevertebral) and lateral vertebral muscles Anterior view. Removed on left side: Longus capitis and anterior scalene. The anterior vertebral muscles are the longus colli, longus capitis, rec-

First rib

tus capitis lateralis, and rectus capitis anterior. The lateral vertebral muscles are the anterior, middle, and posterior scalenes. The anterior and lateral vertebral muscles are innervated by the ventral rami of the cervical spinal nerves.

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10. Bones, Ligaments & Muscles of the Neck

Suprahyoid & Infrahyoid Muscles

④

⑧

3b

② ①

⑤

3a

⑥ ⑦

Fig. 10.36 Suprahyoid muscles Left lateral view.

Fig. 10.37 Infrahyoid muscles Anterior view.

Table 10.9 Suprahyoid and infrahyoid muscles Muscle

Origin

Insertion

Innervation

Action

①

Geniohyoid

Mandible (inferior genial spine)

Hyoid bone

Ventral ramus of C1 via CN XII**

Draws hyoid bone forward (during swallowing); assists in opening mandible

②

Mylohyoid

Mandible (mylohyoid line)

Hyoid bone (via median tendon of insertion, the mylohyoid raphe)

Mylohyoid n. (from CN V3)

Tightens and elevates oral floor; draws hyoid bone forward (during swallowing); assists in opening mandible and moving it side to side (mastication)

3a

Digastric, anterior belly

Mandible (digastric fossa)

3b

Digastric, posterior belly

Temporal bone (mastoid notch, medial to mastoid process)

Hyoid bone (via an intermediate tendon with a fibrous loop)

④

Stylohyoid

Temporal bone (styloid process)

Hyoid bone (via a split tendon)

⑤

Omohyoid, inferior belly

Scapula (superior border, medial to suprascapular notch)

Hyoid bone

⑥

Sternohyoid

Manubrium and sternoclavicular joint (posterior surface)

⑦

Sternothyroid

Manubrium (posterior surface)

Thyroid cartilage (oblique line)

⑧

Thyrohyoid

Thyroid cartilage (oblique line)

Hyoid bone

Facial n. (CN VII)

Elevates hyoid bone (during swallowing); assists in depressing mandible

Ansa cervicalis of cervical plexus (C1–C3)

Depresses (fixes) hyoid; draws larynx and hyoid down for phonation and terminal phases of swallowing*

Ventral ramus of C1 via CN XII

Depresses and fixes hyoid; raises the larynx during swallowing

*The omohyoid also tenses the cervical fascia (with an intermediate tendon). The intermediate tendon is attached to the clavicle, pulling the omohyoid into a more pronounced triangle. **C1 ventral ramus fibers travel with the hypoglossal nerve for part of its pathway to target muscles.

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10. Bones, Ligaments & Muscles of the Neck

Stylohyoid Digastric, posterior belly

Digastric, anterior belly

Thyrohyoid Mylohyoid

Sternohyoid

Sternothyroid

Omohyoid, superior and inferior belly

Intermediate tendon of omohyoid

Coronoid process

Geniohyoid

Mylohyoid line

A

Head of mandible Mandibular foramen

Mylohyoid

Mandibular ramus

Mylohyoid Mylohyoid raphe Hyoid bone

Thyrohyoid Thyroid cartilage Sternothyroid

B

Digastric, anterior belly

C

Lesser horn Hyoid bone (body)

Greater horn

Digastric, posterior belly Stylohyoid

Sternohyoid Omohyoid, superior and inferior belly

Fig. 10.38 Suprahyoid and infrahyoid muscles A Left lateral view. B Anterior view. C Posterosuperior view. The mylohyoid and anterior digastric are derived from the first pharyngeal arch and are therefore supplied by the trigeminal nerve (CN V). The mylohyoid nerve arises from the mandibular division of CN V before the majority of fibers enter the mandibular foramen as the inferior alveolar nerve. The stylohyoid and posterior digastric are derived from the second pharyngeal arch and are therefore supplied by the facial nerve (CN VII). The remainder of the suprahyoid and infrahyoid muscles are supplied by the ventral rami of the cervical spinal nerves. Fibers from the ventral ramus of C1 travel with the hypoglossal nerve (CN XII) to the geniohyoid and thyrohyoid. Fibers from the ventral rami of C1–C3 combine to form the ansa cervicalis, which gives off branches to the omohyoid, sternohyoid, and sternothyroid.

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11. Larynx

Larynx

Lesser horn

Hyoid bone (body)

Foramen for superior laryngeal artery and internal laryngeal nerve

Axis (C2) Laryngeal prominence

Thyroid cartilage

Cricoid cartilage

Greater horn

Thyrohyoid ligament

Atlas (C1)

Hyoid bone

Epiglottis

Superior horn Thyroid cartilage

Cricothyroid ligament

Inferior horn Cricoid cartilage

Cricotracheal ligament

Tracheal cartilage

Fig. 11.1 Location of the larynx Anterior view. The bony structures of the neck have characteristic vertebral levels (shown for upright adult male): • Hyoid bone: C3 • Thyroid cartilage (superior border): C4 • Laryngotracheal junction: C6–C7 These structures are a half vertebra higher in women and children. The thyroid cartilage is especially prominent in males, forming the laryngeal prominence (“Adam’s apple”).

Vocal ligament

Lesser horn

Vestibular ligament

Epiglottic cartilage

Greater horn Corniculate cartilage Arytenoid cartilage

Thyroid cartilage

Fig. 11.2 Larynx: overview Oblique left anterolateral view. The larynx consists of five cartilages: two external cartilages (thyroid and cricoid) and three internal cartilages (epiglottic, arytenoid, and corniculate). Elastic ligaments connect these cartilages to each other as well as to the trachea and hyoid bone. This allows laryngeal motion during swallowing. The thyroid, cricoid, and arytenoid cartilages are hyaline, and the epiglottis and corniculate cartilages are elastic fibrocartilage.

Foramen for superior laryngeal artery and internal laryngeal nerve

Thyrohyoid membrane Superior horn

Corniculate cartilage

Vocal process Cricoarytenoid joint

Median cricothyroid ligament

Cricoid cartilage

Thyroepiglottic ligament

Cricoarytenoid ligament

Inferior horn

Cricothyroid joint

Cricotracheal ligament

A

Fig. 11.3 Laryngeal cartilages and ligaments A Left medial view of sagittal section. B Posterior view. Arrows indicate movement in the various joints. The large thyroid cartilage encloses most of the other cartilages. It articulates with the cricoid cartilage inferiorly at the paired crico-

256

B

thyroid joints, allowing it to tilt relative to the cricoid cartilage. The arytenoid cartilages move during phonation: their bases can translate or rotate relative to the cricoid cartilage at the cricoarytenoid joint.

Neck

Epiglottic cartilage

11. Larynx

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A

B

Fig. 11.4 Epiglottic cartilage A Laryngeal (posteroinferior) view. B Lingual (anterosuperior) view. C Left lateral view. The elastic epiglottic cartilage regulates the entrance of material into the larynx. During breathing, it is angled posterosuperiorly, allowing air to enter the larynx and trachea. During swallowing, the larynx is elevated relative to the hyoid bone. The epiglottis assumes a more horizontal position, preventing food from entering the airway.

Articular facet for arytenoid cartilage (cricoarytenoid joint)

Lamina

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C

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Fig. 11.5 Thyroid cartilage Oblique left lateral view. The hyaline thyroid cartilage consists of two quadrilateral plates (laminae) that are joined at the anterior midline. The superior portion of this junction is the laryngeal prominence (“Adam’s apple”). The posterior ends of the laminae are prolonged forming the superior and inferior horns, which serve as anchors for ligaments.

Corniculate cartilage

Apex of arytenoid cartilage

Corniculate cartilage

Colliculus

Articular facet for thyroid cartilage (cricothyroid joint)

Posterior surface

Anterolateral surface

Vocal process

A A

B Muscular process

Vocal process

C Medial surface

Arch

Arch of cricoid cartilage

Vocal process

Muscular process

Colliculus Arch

C

Fig. 11.6 Cricoid cartilage A Posterior view. B Anterior view. C Left lateral view. The hyaline cricoid cartilage is a ring that is connected inferiorly to the highest tracheal cartilage by the cricotracheal ligament. The cricoid ring is expanded posteriorly to form a lamina. The laminae each have an upper and lower articular facet for the arytenoid cartilage (cricoarytenoid joint) and thyroid cartilage (cricothyroid joint), respectively.

Corniculate cartilage D

Muscular process

Vocal ligament

Conus elasticus

Articular facet (cricothyroid joint)

Articular facet

Median cricothyroid ligament

Thyroid cartilage

B

Articular facet (cricoarytenoid joint)

Apex of arytenoid cartilage

Lamina of cricoid cartilage

Cricoarytenoid ligament

Fig. 11.7 Arytenoid and corniculate cartilages Right cartilages. A Right lateral view. B Left lateral (medial) view. C Posterior view. D Superior view. The arytenoid cartilages alter the positions of the vocal cords during phonation. The pyramid-shaped hyaline cartilages have three surfaces (anterolateral, medial, and posterior), an apex, and a base with vocal and muscular processes. The apex articulates with the tiny corniculate cartilages, which are composed of elastic fibrocartilage.

257

Neck

11. Larynx

Laryngeal Muscles Arytenoid cartilage, vocal process

Oblique line

Vocalis

Arytenoid cartilage, muscular process

Conus elasticus

Cricothyroid

Straight part

Inferior horn of thyroid cartilage

Oblique part

Lateral cricoarytenoid

Posterior cricoarytenoid

Middle cricoarytenoid ligament

Articular facet for thyroid

B

A Arch of cricoid cartilage

Epiglottic cartilage

Thyroarytenoid muscle, thyroepiglottic part

Oblique arytenoid

Aryepiglottic fold

Aryepiglottic fold

Cuneiform tubercle

Cuneiform tubercle

Thyroarytenoid

Transverse arytenoid

Lamina of cricoid cartilage

Oblique arytenoid

Posterior cricoarytenoid

Thyroarytenoid

Corniculate tubercle

Lateral cricoarytenoid

Posterior cricoarytenoid

D C

Table 11.1 Laryngeal muscles The laryngeal muscles move the laryngeal cartilages relative to one another and affect the tension and/or position of the vocal folds. Numerous muscles move the larynx as a whole (infrahyoids, suprahyoids, pharyngeal constrictors, stylopharyngeus, etc.). Muscle

Innervation

Action

Vocal folds

Rima glottidis

Posterior cricoarytenoid

Recurrent laryngeal n.**

Rotates arytenoid cartilage outward and slightly to the side

Abducts

Opens

Lateral cricoarytenoid*

Rotates arytenoid cartilage inward

Adducts

Closes

Transverse arytenoid

Moves arytenoids toward each other

Thyroarytenoid

Rotates arytenoid cartilage inward

Relaxes

Closes

Vocalis***

Regulates tension of vocal folds

Tightens

None

Cricothyroid

External laryngeal n.

Tilts cricoid cartilage posteriorly, acting on the vocalis muscle to increase tension in the vocal folds

*The lateral cricoarytenoid is called the muscle of phonation as it initiates speech production. **Unilateral loss of the recurrent laryngeal nerve (e.g., due to nodal metastases from a hilar bronchial carcinoma of the left lung) leads to ipsilateral palsy of the posterior cricoarytenoid. This prevents complete abduction of the vocal folds, causing hoarseness. Bilateral nerve loss (e.g., due to thyroid surgery) may cause asphyxiation. ***The vocalis is derived from the inferior fibers of the thyroarytenoid muscle. These fibers connect the arytenoid cartilage with the vocal ligament.

258

Neck

11. Larynx

Cricothyroid

Vocalis

Thyroarytenoid Posterior cricoarytenoid

E

Lateral cricoarytenoid

Transverse arytenoid

A

Fig. 11.8 Laryngeal muscles A Left lateral oblique view of extrinsic laryngeal muscles. B Left lateral view of intrinsic laryngeal muscles (left thyroid lamina and epiglottis removed). C Posterior view. D Left lateral view. E Actions (arrows indicate directions of pull).

B

Fig. 11.9 Indirect laryngoscopy A Mirror examination of the larynx from the perspective of the examiner. The larynx is not accessible to direct inspection but can be viewed with the aid of a small mirror. The examiner depresses the tongue with one hand while introducing the laryngeal mirror (or endoscope) with the other hand. A Optical path: The laryngeal mirror is held in front of the uvula, directing light from the examiner’s head mirror down toward the larynx. The image seen by the examiner is shown in Fig. 11.10.

Median glossoepiglottic fold Vallecula

Root of tongue Epiglottis

Vocal fold

Epiglottic tubercle

Laryngeal ventricle

Aryepiglottic fold

Vestibular fold

C

D

E

Piriform sinus

Cuneiform tubercle

Arch of cricoid cartilage

Vocal process

A

B

Corniculate tubercle

Interarytenoid notch

Trachea

Fig. 11.10 Indirect laryngoscopy A Laryngoscopic mirror image. B Normal respiration. C Vigorous respiration. D Phonation position (vocal folds completely adducted). E Whispered speech (vocal folds slightly abducted). Indirect laryngoscopy produces a virtual image of the larynx in which the right vocal fold appears on the right side of the mirror image and anterior structures (e.g., tongue base, valleculae, and epiglottis) appear at the top of the image. The vocal folds appear as smooth-edged

bands (there are no blood vessels or submucosa below the stratified, nonkeratinized squamous epithelium of the vocal folds). They are therefore markedly lighter than the highly vascularized surrounding mucosa. The glottis can be evaluated in closed (respiratory) and opened (phonation) position by having the patient alternately inhale and sing “hee.” The clinician can then determine pathoanatomical changes (e.g., redness, swelling, and ulceration) and functional changes (e.g., to vocal fold position).

259

Neck

11. Larynx

Larynx: Neurovasculature

Epiglottis

Epiglottic cartilage

Quadrangular membrane

Thyroid cartilage

Glands Rima vestibuli

Vestibular fold Cut edges Vocal fold

Laryngeal saccule

Laryngeal ventricle

Vestibular ligament

Rima glottidis

Vocal ligament Conus elasticus

Vocalis muscle

Thyroarytenoid muscle

Ventricle

A

Vallecula

Lingual tonsil Epiglottis

Hyoid bone

Piriform recess

Hyoepiglottic ligament

Aryepiglottic fold

Thyrohyoid ligament

Cuneiform tubercle

Vestibular fold

Corniculate tubercle

Ventricle Vocal fold

Piriform recess

Laryngeal vestibule

Cricoid cartilage

Median cricothyroid ligament

Intermediate laryngeal cavity

Esophagus

Tracheal cartilage

Infraglottic cavity

Membranous wall of trachea B

Fig. 11.11 Laryngeal mucosa A Posterior view with pharynx and esophagus cut along the midline and spread open. B Left lateral view of midsagittal section. C Posterior view with laryngeal levels. The larynx lies anterior to the laryngopharynx. Air enters through the laryngeal inlet formed by the epiglottis and aryepiglottic folds. Lateral to the aryepiglottic folds are pear-shaped mucosal fossae (piriform recesses), which channel food past the larynx and into the laryngopharynx and on into the esophagus. The interior of the larynx is lined with mucous membrane that is loosely applied to its underlying tissue (except at the vocal folds). The laryngeal cavity can be further subdivided with respect to the vestibular and vocal folds (Table 11.2).

260

Fig. 11.12 Vestibular and vocal folds Coronal section. The vestibular and vocal folds are the mucosal coverings of underlying ligaments. The vocal folds (“vocal cords”) contain the vocal ligament and vocalis muscle. The fissure between the vocal folds is the rima glottidis (glottis). The vestibular folds (“false vocal cords”) are superior to the vocal folds. They contain the vestibular ligament, the free inferior end of the quadrangular membrane. The fissure between the vestibular folds is the rima vestibuli, which is broader than the rima glottidis. Note: The loose connective tissue of the laryngeal inlet may become markedly swollen (e.g., insect bite, inflammatory process), obstructing the rima vestibuli. This laryngeal edema (often incorrectly called “glottic edema”) presents clinically with dyspnea and poses an asphyxiation risk.

C

Table 11.2 Divisions of the laryngeal cavity Laryngeal level

Boundaries

I: Laryngeal vestibule (supraglottic space)

Laryngeal inlet (aditus laryngis) to vestibular folds

II: Intermediate laryngeal cavity (transglottic space)

Vestibular folds across the laryngeal ventricle (lateral evagination of mucosa) to vocal folds

III: Infraglottic cavity (subglottic space)

Vocal folds to inferior border of cricoid cartilage

Neck

11. Larynx

Vagus nerve (CN X) Superior thyroid artery

Superior laryngeal nerve

Superior laryngeal artery

Internal laryngeal nerve (sensory)

Common carotid artery

External laryngeal nerve (motor to cricothyroid)

Cricothyroid branch Inferior laryngeal artery

Cricothyroid

Inferior thyroid artery

Left recurrent laryngeal nerve

Thyrocervical trunk Right subclavian artery Vagus nerve (CN X)

Brachiocephalic trunk

Aortic arch

Left recurrent laryngeal nerve (a branch of CN X)

A

Facial vein

Superior laryngeal vein Superior thyroid vein

Middle thyroid veins

Inferior laryngeal vein

Thyroid venous plexus Internal jugular vein Inferior thyroid vein Left brachiocephalic vein B

Subclavian vein

Fig. 11.13 Laryngeal blood vessels and nerves A Arteries and nerves, anterior view. B Veins, left lateral view. Arteries: The larynx derives its blood supply primarily from the superior and inferior laryngeal arteries. The superior laryngeal artery arises from the superior thyroid artery (a branch of the external carotid artery). The inferior laryngeal artery arises from the inferior thyroid artery (a branch of the thyrocervical trunk). Nerves: The larynx is innervated by the superior laryngeal nerve and the recurrent laryngeal nerve (of the vagus nerve). The superior laryngeal nerve splits into an internal (sensory) and an external (motor) laryngeal nerve. The external laryngeal nerve innervates the cricothyroid. The remaining intrinsic laryngeal muscles receive motor innervation from the recurrent laryngeal nerve, which branches from the vagus nerve below the larynx and ascends. Note: The left recurrent laryngeal nerve wraps around the aortic arch, and the right recurrent laryngeal nerve wraps around the subclavian artery. A left-sided aortic aneurysm may cause left recurrent laryngeal nerve palsy, resulting in hoarseness (see p. 263). Veins: The larynx is drained by a superior and an inferior laryngeal vein. The superior laryngeal vein drains to the internal jugular vein (via the superior thyroid vein); the inferior laryngeal vein drains to the left brachiocephalic vein (via the thyroid venous plexus to the inferior thyroid vein).

261

Neck

11. Larynx

Larynx: Topography

Superior laryngeal nerve Internal laryngeal nerve

Hyoid bone

Superior laryngeal vein and artery

Thyrohyoid membrane

Cricothyrotomy High tracheotomy

Inferior pharyngeal constrictor (thyropharyngeal part)

Thyrohyoid

External laryngeal nerve

Oblique line

Fig. 11.15 Approaches to the larynx and trachea Midsagittal section, left lateral view. When an acute edematous obstruction of the larynx (e. g., due to an allergic reaction) poses an acute risk of asphyxiation, the following surgical approaches are available for creating an emergency airway:

Median cricothyroid ligament Straight part Cricothyroid

Oblique part Middle thyroid vein Thyroid gland

Low tracheotomy

• Division of the median cricothyroid ligament (cricothyrotomy) • Incision of the trachea (tracheotomy) at a level just below the cricoid cartilage (high tracheotomy) or just superior to the jugular notch (low tracheotomy).

Inferior thyroid artery Esophagus

A Epiglottis

Recurrent laryngeal nerve

Fig. 11.14 Topography of the larynx Left lateral view. A Superficial dissection. B Deep dissection (cricothyroid and left thyroid lamina removed with pharyngeal mucosa retracted). Neurovascular structures enter the larynx posteriorly. The larynx receives sensory and motor innervation from branches of the vagus nerve (CN X). Sensory innervation: The upper larynx (above the vocal folds) receives sensory innervation from the internal laryngeal nerve, and the infraglottic cavity receives sensory innervation from the recurrent laryngeal nerve. Motor innervation: The cricothyroid receives motor innervation from the external laryngeal nerve, and the rest of the intrinsic muscles of the larynx receive motor innervation from the recurrent laryngeal nerve.

Internal laryngeal nerve

Hyoid bone

Superior laryngeal vein and artery

Median thyrohyoid ligament

Thyroid lamina

Galen’s anastomosis (between sensory branches of internal and recurrent laryngeal nerves)

Thyroarytenoid Lateral cricothyroid

Posterior cricoarytenoid

Median cricothyroid ligament

Esophagus

Cricothyroid

Middle thyroid vein

Tracheal branches Trachea B

262

Inferior thyroid artery Recurrent laryngeal nerve

Neck

To glossopharyngeal nerve (CN IX) To superior laryngeal nerve (cricothyroid muscle)

Brainstem (medulla oblongata)

Glands

Brainstem lesion (hemorrhage, neoplasm) ① Vagus nerve roots Superior (jugular) ganglion

To recurrent laryngeal nerve

Skull base tumors ②

To accessory nerve (CN XI)

Inferior (nodose) ganglion Superior laryngeal nerve Carotid surgery ③

Internal laryngeal nerve

Vestibular fold Laryngeal ventricle (Morgagni space)

Stratified, nonkeratinized squamous epithelium

Jugular foramen

Pharyngeal branch to pharyngeal plexus

Reinke space (loose connective tissue)

Thyroarytenoid

Subglottic edema, ciliated respiratory epithelium

Vocal ligament Vocalis

Conus elasticus Vagus nerve (CN X)

External laryngeal nerve

Left common carotid artery Thyroid surgery ⑥

⑤ Aortic

aneurysm

A

a b c d

Fig. 11.17 Vocal folds Schematic coronal histologic section, posterior view. The vocal fold, which is exposed to severe mechanical stresses, is covered by nonkeratinized squamous epithelium, unlike the adjacent subglottic space, which is covered by ciliated respiratory epithelium. The mucosa of the vocal folds and subglottic space overlies loose connective tissue. Chronic irritation of the subglottic mucosa (e.g., from cigarette smoke) may cause chronic edema in the subglottic space, resulting in a harsh voice. Degenerative changes in the vocal fold mucosa may lead to thickening, loss of elasticity, and squamous cell carcinoma.

Left recurrent laryngeal nerve

Table 11.3 Vagus nerve lesions

Bronchial carcinoma ④

Lesions of the laryngeal nerves (Fig. 11.16A) may cause sensory loss or motor paralysis, which disrupts the position of the vocal folds (Fig. 11.16B).

Vagus nerve (CN X)

Level of nerve lesion and effects on vocal fold position

Sites of injury to vagus nerve or its branches

B

11. Larynx

Positions of the vocal folds a. Median or phonation position b. Paramedian position c. Intermediate position d. Lateral or respiratory position

Fig. 11.16 Vagus nerve lesions The vagus nerve (CN X) provides branchiomotor innervation to the pharyngeal and laryngeal muscles and somatic sensory innervation to the larynx. Note: The vagus nerve also conveys parasympathetic motor fibers and visceral sensory fibers to and from the thoracic and abdominal viscera. Branchiomotor innervation: The nucleus ambiguus contains the cell bodies of lower motor neurons whose branchiomotor fibers travel in CN IX, X, and XI. The nuclei of the vagus nerve are located in the middle region of the nucleus ambiguus in the brainstem (the cranial portions of the nucleus send axons via the glossopharyngeal nerve, and the caudal portions send axons via the accessory nerve). Fibers emerge from the middle portion of the nucleus ambiguus as roots and combine into CN X, which passes through the jugular foramen. Branchiomotor fibers are distributed to the pharyngeal plexus via the pharyngeal branch and the cricothyroid muscle via the external laryngeal nerve (a branch of the superior laryngeal nerve). The remaining branchiomotor fibers leave the vagus nerve as the recurrent laryngeal nerves, which ascend along the trachea to reach the larynx. Sensory innervation: General somatic sensory fibers travel from the laryngeal mucosa to the spinal nucleus of the trigeminal nerve via the vagus nerve. The cell bodies of these primary sensory neurons are located in the inferior (nodose) ganglion. Note: The superior (jugular) ganglion contains the cell bodies of viscerosensory neurons.

①

Central lesion (brainstem or higher)

E.g., due to tumor or hemorrhage. Spastic paralysis (if nucleus ambiguus is disrupted), flaccid paralysis, and muscle atrophy (if motor neurons or axons are destroyed). ②

b,c

None

b,c

Entire affected side

d

Above vocal fold

a,b

Below vocal fold

Skull base lesion*

E.g., due to nasopharyngeal tumors. Flaccid paralysis of all intrinsic and extrinsic laryngeal muscles on affected side. Glottis cannot be closed, causing severe hoarseness. ③

Sensory loss

Superior laryngeal nerve lesions*

E.g., due to carotid surgery. Hypotonicity of the cricothyroid, resulting in mild hoarseness with a weak voice, especially at high frequencies. Recurrent laryngeal nerve lesions** E.g., due to bronchial carcinoma ④ , aortic aneurysm ⑤ , or thyroid surgery ⑥ . Paralysis of all intrinsic laryngeal muscles on affected side. This results in mild hoarseness, poor tonal control, rapid voice fatigue, but not dyspnea.

*Other motor deficits include drooping of the soft palate and deviation of the uvula toward the affected side, diminished gag and cough reflexes, difficulty swallowing (dysphagia), and hypernasal speech due to deficient closure of the pharyngeal isthmus. Sensory defects include the sensation of a foreign body in the throat. **Transection of both recurrent laryngeal nerves can cause significant dyspnea and inspiratory stridor (high-pitched noise indicating obstruction), necessitating tracheotomy in acute cases.

263

Neck

11. Larynx

Thyroid & Parathyroid Glands

Middle pharyngeal constrictor

Inferior pharyngeal constrictor Thyroid cartilage

Superior thyroid artery

Pyramidal lobe Cricothyroid ligament Right lobe Isthmus of thyroid gland

Cricothyroid

Parathyroid glands, superior pair

Left lobe

Parathyroid glands, inferior pair Inferior thyroid artery

Trachea B

A

Fig. 11.18 Thyroid and parathyroid glands A Anterior view. B Posterior view. The thyroid gland consists of two laterally situated lobes and a central narrowing (isthmus). A pyramidal lobe may be found in place of the isthmus; the apex points to the embryonic origin of the thyroid at the base of the tongue (on occasion, a persistent thyroglossal duct may

>O>QEVOLFA DI>KAP

be present, connecting the pyramidal lobe with the foramen cecum of the tongue). The parathyroid glands (generally four in number) show considerable variation in number and location. Note: Because the parathyroid glands are usually contained within the thyroid capsule, there is considerable risk of inadvertently removing them during thyroid surgery.

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Fig. 11.19 Topography of the thyroid gland Transverse section through the neck at the T 1 level, superior view. The thyroid gland partially surrounds the trachea and is bordered posterolaterally by the carotid sheath. When the thyroid gland is pathologically enlarged (e. g., due to iodine-deficiency goiter), it may gradually compress and narrow the tracheal lumen, causing respiratory distress. The thyroid gland is surrounded by a fibrous capsule composed of an internal and external layer. The delicate internal layer (internal capsule, not shown here) directly invests the thyroid gland and is fused with its

264

OBSBOQB?O>I I>VBO

glandular parenchyma. Vascularized fibrous slips extend from the internal capsule into the substance of the gland, subdividing it into lobules. The internal capsule is covered by the tough external capsule, which is part of the pretracheal layer of the deep cervical fascia. This capsule invests the thyroid gland and parathyroid glands and is also called the “surgical capsule” because it must be opened to gain surgical access to the thyroid gland. Between the external and internal capsules is a potential space that is traversed by vascular branches and is occupied by the parathyroid glands.

Neck

Superior thyroid artery

Inferior thyroid artery

External carotid artery

Thyrohyoid membrane

Superior laryngeal vein

Internal carotid artery

Superior thyroid vein

Internal jugular vein

Vagus nerve (CN X)

Middle thyroid vein

Thyroid venous plexus Inferior bulb of left jugular vein

Inferior bulb of right jugular vein

Thyrocervical trunk Right recurrent laryngeal nerve

11. Larynx

Left subclavian artery

Left recurrent laryngeal nerve

Subclavian vein Thoracic duct

Right lymphatic duct Inferior thyroid vein

Left brachiocephalic vein

Right brachiocephalic vein

A

Superior vena cava B

Fig. 11.20 Blood supply and innervation of the thyroid gland Anterior view. A Arterial supply: The thyroid gland derives most of its arterial blood supply from the superior and inferior thyroid arteries. The superior thyroid artery, a branch of the external carotid artery, runs forward and downward to supply the gland. It is supplied from below by the inferior thyroid artery, which branches from the thyrocervical trunk. All of these arteries, which course on the right and left sides of the organ, must be ligated during surgical removal of the thyroid gland. In addition, a rare branch, the thyroidima, may arise from the brachiocephalic trunk or right common carotid artery to supply the gland from below.

Note: Operations on the thyroid gland carry a risk of injury to the recurrent laryngeal nerve, which is closely related to the posterior surface of the gland. Because it supplies important laryngeal muscles, unilateral injury to the nerve will cause postoperative hoarseness; bilateral injury may additionally result in dyspnea (difficulty in breathing). Prior to thyroid surgery, therefore, an otolaryngologist should confirm the integrity of the nerve supply to the laryngeal muscles and exclude any preexisting nerve lesion. B Venous drainage: The thyroid gland is drained anteroinferiorly by a well-developed thyroid venous plexus, which usually drains through the inferior thyroid vein to the left brachiocephalic vein. Blood from the thyroid gland also drains to the internal jugular vein via the superior and middle thyroid veins.

Lumen of epithelial follicle Colloid Epithelial cell, squamous to low cuboidal

Chief cell Epithelial cell, cuboidal to columnar A

B

Fig. 11.21 Histology of the thyroid gland The thyroid gland absorbs iodide from the blood and uses it to make the thyroid hormones, thyroxine (T 4, tetraiodothyronine) and triiodothyronine (T 3). These hormones are stored at extracellular sites in the gland, bound to protein, and when needed they are mobilized from the thyroid follicles and secreted into the bloodstream. A special feature of the thyroid gland is the appearance of its epithelium, which varies depending on whether it is storing hormones or releasing them into the blood. The epithelial cells are flattened or squamous when in their resting or “storage state” (A), but they are columnar when in their active or “secretory state” (B). The epithelial morphology thus indicates the current functional state of the cells. Iodine deficiency causes an enlargement of the colloidal follicular lumen, which eventually results in a gross increase in the size of the thyroid (goiter). With prolonged iodine deficiency, there is a reduction in body metabolism and concomitant lethargy, fatigue, and mental depression. Conversely, hyperactivity of the thyroid, as in Graves’ disease (an autoimmune disorder), causes a generalized metabolic acceleration, with irritability and weight loss. In the midst of the thyroid follicles are parafollicular cells (C cells), which secrete calcitonin. Calcitonin inhibits bone resorption and reduces the calcium concentration in the blood.

Connective tissue fibers Oxyphilic cell

Fig. 11.22 Histology of the parathyroid gland The principal cell type in the parathyroid gland is the chief cell, which responds directly to low blood calcium levels by secreting parathyroid hormone (PTH, parathormone). Parathyroid hormone increases calcium concentration in the blood by various means, including the stimulation of bone resorption by osteoclasts and the renal tubular reabsorption of calcium. Parathyroid hormone thus acts antagonistically against calcitonin produced by the thyroid’s C cells. Inadvertent removal of the parathyroid glands during thyroid surgery can cause a dramatic fall in serum calcium, with catastrophic consequences. Such a hypocalcemic condition causes neuromuscular irritability and, potentially, generalized fatal seizures involving respiratory muscles. Conversely, pathological hyperactivity of the parathyroid can lead to chronic hypercalcemia, often associated with bone loss (osteoporosis) and abnormal calcium deposition in the circulatory and urinary systems. Chronic hyperparathyroidism with hypertrophy of chief cells and elevated serum calcium is a common consequence of end-stage renal failure, by a mechanism not clearly established.

265

Neck

12. Neurovascular Topography of the Neck

Arteries & Veins of the Neck Fig. 12.1 Arteries of the neck Left lateral view. The structures of the neck are supplied by branches of the external carotid artery and the subclavian artery (the internal carotid artery gives off no branches in the neck). The common carotid artery is enclosed in a fascial sheath (carotid sheath) along with the jugular vein and vagus nerve. The vertebral artery ascends through the transverse foramina of the cervical vertebrae.

Vertebral artery Ascending pharyngeal artery External carotid artery

Lingual artery

Internal carotid artery

Infrahyoid branch Superior thyroid artery Superior laryngeal artery

Vertebral artery Inferior thyroid artery Ascending cervical artery

Cricothyroid branch

Common carotid artery Transverse cervical artery

Glandular branches

Suprascapular artery Thyrocervical trunk Left subclavian artery

Table 12.1 Arteries of the neck For a complete treatment of the arteries of the head and neck, see Chapter 3. Artery

Branches

Secondary branches*

External carotid a.

Superior thyroid a.

Superior laryngeal, cricothyroid, infrahyoid, and sternocleidomastoid aa.

Ascending pharyngeal a.

Pharyngeal, palatine, prevertebral, inferior tympanic, and meningeal aa.

Lingual a.

Suprahyoid, dorsal lingual, deep lingual, and sublingual aa.

Facial a.

Ascending palatine, tonsillar, glandular, and submental aa.

Occipital a.

Sternocleidomastoid, descending, mastoid, auricular, and meningeal aa.

Posterior auricular a.

Stylomastoid and auricular aa.

Superficial temporal a.

(Branching occurs on the face)

Maxillary a.

(Branches within the infratemporal fossa are listed in Table 5.1, p. 102)

Vertebral a.

Spinal aa. and muscular aa.

Thyrocervical trunk

Inferior thyroid a.

Subclavian a.

Inferior laryngeal, tracheal, esophageal, and ascending cervical aa.

Suprascapular a. Transverse cervical a. Internal thoracic a.

(Branching occurs within the thorax)

Descending (dorsal) scapular a.

(When present, it supplies the territory of the deep branch of the transverse cervical a.)

*Only branches that arise in the neck are listed here.

266

Superficial and deep branches

Neck

12. Neurovascular Topography of the Neck

Facial vein External jugular vein Superior thyroid vein

Internal jugular vein Anterior jugular vein Jugular venous arch

Middle thyroid vein

Transverse cervical vein

Inferior thyroid vein

Left brachiocephalic vein

Right brachiocephalic vein

Superior vena cava

Fig. 12.2 Veins of the neck Anterior view. The veins of the head and neck drain to the superior vena cava via the right and left brachiocephalic veins. The large internal jugular vein combines with the subclavian vein to form the brachiocephalic vein on each side. The internal jugular vein is located within

the carotid sheath. It receives blood from the anterior neck and the interior of the skull. The subclavian vein receives blood from the neck via the external and anterior jugular veins, which are located within the superficial cervical fascia. Note: The thyroid venous plexus and vertebral veins typically drain directly into the brachiocephalic veins.

Table 12.2 Veins of the neck For a complete treatment of the veins of the head and neck, see Chapter 3. Right and left brachiocephalic vv.*

Internal jugular v.

Inferior petrosal sinus, pharyngeal vv.; occipital, (common) facial, lingual, and superior and middle thyroid vv.

Subclavian v.

External jugular v.

Vertebral v.

Internal and external vertebral venous plexuses; ascending cervical (anterior vertebral) and deep cervical vv.

Inferior thyroid vv.

Thyroid venous plexus

Posterior external jugular, anterior jugular, transverse cervical, and suprascapular vv.**

*The brachiocephalic vein is formed by the joining of its two primary tributaries, the internal jugular vein and the subclavian vein. Only tributaries within the neck are listed above. **The tributaries of the external jugular vein may on occasion drain directly into the subclavian vein.

267

Neck

12. Neurovascular Topography of the Neck

Lymphatics of the Neck

A distinction is made between regional lymph nodes, which are associated with a particular organ or region and constitute their primary filtering stations, and collecting lymph nodes, which usually receive lymph from multiple regional lymph node groups. Lymph from the head and neck region, gathered in scattered regional nodes, flows through its system of deep cervical collecting lymph nodes into the right and left

Retroauricular lymph nodes

Occipital lymph node

jugular trunks, each closely associated with its corresponding internal jugular vein. The jugular trunk on the right side drains into the right lymphatic duct, which terminates at the right jugulosubclavian junction. The jugular trunk on the left side terminates at the thoracic duct, which empties into the left jugulosubclavian junction (see Fig. 12.6).

Superficial parotid lymph nodes

Mastoid lymph nodes

Fig. 12.3 Superficial cervical lymph nodes Right lateral view. Enlarged cervical lymph nodes are a common finding at physical examination. The enlargement of cervical lymph nodes may be caused by inflammation (usually a painful enlargement) or neoplasia (usually a painless enlargement) in the area drained by the nodes. The superficial cervical lymph nodes are primary drainage locations for lymph from adjacent areas or organs.

Deep parotid lymph nodes

Anterior superficial cervical lymph nodes Lateral superficial cervical lymph nodes

Fig. 12.4 Deep cervical lymph nodes Right lateral view. The deep lymph nodes in the neck consist mainly of collecting nodes. They have major clinical importance as potential sites of metastasis from head and neck tumors. Affected deep cervical lymph nodes may be surgically removed (neck dissection) or may be treated by regional irradiation. For this purpose, the American Academy of Otolaryngology—Head and Neck Surgery has grouped the deep cervical lymph nodes into six levels (Robbins 1991): I Submental and submandibular lymph nodes II – IV Deep cervical lymph nodes along the internal jugular vein (lateral jugular lymph nodes): – II Deep cervical lymph nodes (upper lateral group) – III Deep cervical lymph nodes (middle lateral group) – IV Deep cervical lymph nodes (lower lateral group) V Lymph nodes in the posterior cervical triangle VI Anterior cervical lymph nodes

268

II

I

V III

IV

VI

Neck

Occipital

Parotidauricular

12. Neurovascular Topography of the Neck

Facial

Fig. 12.5 Directions of lymphatic drainage in the neck Right lateral view. Understanding this pattern of lymphatic flow is critical to identifying the location of a potential cause of enlarged cervical lymph nodes.There are two main sites in the neck where the lymphatic pathways intersect:

Nuchal Jugulofacial venous junction Parallel to internal jugular vein Along the accessory nerve Axillary

Right lymphatic duct

Submentalsubmandibular Laryngotracheothyroidal Jugulosubclavian venous junction

• Jugulofacial venous junction: Lymphatics from the head pass obliquely downward to this site, where the lymph is redirected vertically downward in the neck. • Jugulosubclavian venous junction: The main lymphatic trunk, the thoracic duct, terminates at this central location, where lymph collected from the left side of the head and neck region is combined with lymph draining from the rest of the body. If only peripheral nodal groups are affected, this suggests a localized disease process. If the central groups (e.g., those at the venous junctions) are affected, this usually signifies an extensive disease process. Central lymph nodes can be obtained for diagnostic evaluation by prescalene biopsy.

Thoracic duct

B F B C D A

F

Fig. 12.6 Relationship of the cervical nodes to the systemic lymphatic circulation Anterior view. The cervical lymph nodes may be involved by diseases that are not primary to the head and neck region, because lymph from the entire body is channeled to the left and right jugulosubclavian junctions (red circles). This can lead to retrograde involvement of the cervical nodes. The right lymphatic duct terminates at the right jugulosubclavian junction, the thoracic duct at the left jugulosubclavian junction. Besides cranial and cervical tributaries, the lymph from thoracic lymph nodes (mediastinal and tracheobronchial) and from abdominal and caudal lymph nodes may reach the cervical nodes by way of the thoracic duct. As a result, diseases in those organs may lead to cervical lymph node enlargement. For example, gastric carcinoma may metastasize to the left supraclavicular group of lymph nodes, producing an enlarged sentinel node that suggests an abdominal tumor. Systemic lymphomas may also spread to the cervical lymph nodes by this pathway.

E

E

C

D

Fig. 12.7 Systematic palpation of the cervical lymph nodes The cervical lymph nodes are systematically palpated during the physical examination to ensure the detection of any enlarged nodes. Panel A shows the sequence in which the various nodal groups are successively palpated. The examiner usually palpates the submentalsubmandibular group first (B), including the mandibular angle (C), then proceeds along the anterior border of the sternocleidomastoid muscle (D). The supraclavicular lymph nodes are palpated next (E), followed by the lymph nodes along the accessory nerve and the nuchal group of nodes (F).

269

Neck

12. Neurovascular Topography of the Neck

Cervical Plexus The neck receives innervation from the cervical spinal nerves as well as three cranial nerves: glossopharyngeal (CN IX), vagus (CN X), and accessory (CN XI). CN IX and X innervate the pharynx and larynx;

CN XI provides motor innervation to the trapezius and sternocleidomastoid. The course and distribution of the cranial nerves are described in Chapter 4.

Fig. 12.8 Cervical spinal nerves Like all spinal nerves, the cervical spinal nerves emerge from the spinal cord as a dorsal (sensory) root and a ventral (motor) root. The roots combine to form the mixed spinal nerve, which then gives off a dorsal and a ventral ramus. Dorsal rami: Supply motor innervation to the intrinsic back muscles (epiaxial muscle) (Table 12.3). Ventral rami: Supply motor innervation to the anterolateral muscles of the neck derived from the hypaxial muscle. The ventral rami of C1–C4 supply motor innervation to the deep neck muscles (scalenes, rectii capitis anterioris) via direct branches. The ventral rami also combine to form the cervical plexus, which supplies the skin and musculature of the anterior and lateral neck.

Dorsal rootlets (sensory)

Dorsal root with spinal ganglion Spinal nerve

Dorsal ramus Ventral ramus Gray ramus communicans

Ventral root Ventral rootlets (motor)

White ramus communicans

Meningeal branch Splanchnic nerves

Sympathetic ganglion

Table 12.3 Dorsal rami of C1– C3 Dorsal ramus

Motor

Sensory

C1 (Suboccipital n.)*

Nuchal muscles (e.g., superior oblique, inferior oblique, rectus capitis posterior major, rectus capitis posterior minor, semispinalis capitis)

Meninges

C2

Greater occipital n.* (medial branch of C2)

–

C2 dermatome (posterior neck and scalp)

Lateral branch of C2

Semispinalis capitis, splenius capitis, longissimus capitis

–

Least occipital n.* (medial branch of C3)

–

C3 dermatome (posterior neck)

Lateral branch of C3

Semispinalis capitis, splenius capitis, longissimus capitis

–

C3

*The suboccipital nerve is primarily a motor nerve, whereas the greater occipital and least occipital nerves are sensory branches of C2 and C3, respectively.

Fig. 12.9 Cervical plexus The ventral rami of spinal nerves C1–C4 emerge from the intervertebral foramina along the transverse processes of the cervical vertebrae. They emerge between the anterior and posterior scalenes and give off short direct branches to the scalenes and rectii capitis anterioris before coursing anteriorly to form the cervical plexus. Motor fibers: Motor fibers from C1 course with the hypoglossal nerve (CN XII). Certain fibers continue with the nerve to innervate the thyrohyoid and geniohyoid. The remainder leave CN XII to form the superior root of the ansa cervicalis. The inferior root is formed by motor fibers from C2 and C3. The ansa cervicalis innervates the omohyoid, sternothyroid, and sternohyoid. Most motor fibers from C4 descend as the phrenic nerve, which innervates the diaphragm. Sensory fibers: The sensory fibers of C2–C4 emerge from the cervical plexus as peripheral nerves. (Note: The sensory fibers of C1 go to the meninges.) These peripheral sensory nerves emerge from Erb’s point and provide sensory innervation to the anterolateral neck.

270

To meninges (sensory) Hypoglossal nerve (CN XII)

C1

C2

C3

Superior root of ansa cervicalis (C1, motor)

C4

Inferior root of ansa cervicalis (C2–C3, motor)

C5

Ansa cervicalis Phrenic nerve (C3–C5, mixed)

Lesser occipital nerve (C2, sensory)

Great auricular nerve (C2–C3, sensory) Transverse cervical nerve (C2–C3, sensory)

Supraclavicular nerves (C3–C4, sensory)

To brachial plexus

Neck

Hyoglossus

Arc of hypoglossal nerve

Stylohyoid

12. Neurovascular Topography of the Neck

Styloglossus

Hypoglossal nerve (CN XII)

Ventral ramus of C1 C1 C2 Lingual nerve (CN V3) Genioglossus

C3

Geniohyoid branch (C1)

Thyrohyoid branch (C1) Superior root of ansa cervicalis (C1) Thyrohyoid Inferior pharyngeal constrictor Inferior root of ansa cervicalis (C2–C3)

Omohyoid, superior belly Sternohyoid Sternothyroid

Fig. 12.10 Motor nerves of the cervical plexus Left lateral view.

Ansa cervicalis

Sternocleidomastoid Parotid gland (within capsule)

Lesser occipital nerve (C2)

Great auricular nerve (C2–C3) Transverse cervical nerve (C2–C3)

Erb’s point

Platysma

Supraclavicular nerves (C3–C4)

Trapezius

Fig. 12.11 Sensory nerves of the cervical plexus Left lateral view.

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12. Neurovascular Topography of the Neck

Cervical Regions (Triangles)

Occipital region

Parietal region

˝

Submandibular triangle

Carotid triangle

Submental triangle

˞

Muscular triangle

ˠ

A Occipital triangle

Omoclavicular triangle

Lesser supraclavicular fossa B

ˠ

˟

Fig. 12.12 Cervical regions A Right lateral oblique view. B Left posterior oblique view. For descriptive purposes, the anterolateral neck is divided into an anterior and a posterior cervical triangle, separated by the sternocleido-

mastoid. The posterior portion of the neck is referred to as the nuchal region.

Table 12.4 Cervical regions Region

Subdivision

˝ Anterior cervical region (anterior cervical triangle): Bounded by the midline, mandible, and sternocleidomastoid.

Submandibular (digastric) triangle: Bounded by the mandible and the bellies of the digastric muscle. Carotid triangle: Bounded by the sternocleidomastoid, superior belly of the omohyoid, and posterior belly of the digastric. Muscular triangle: Bounded by the sternocleidomastoid, superior omohyoid, and sternohyoid. Submental triangle: Bounded by the anterior bellies of the diagastric, the hyoid bone, and the mandible.

˞

Sternocleidomastoid region: The region lying under the sternocleidomastoid muscle.

˟ Lateral cervical region (posterior cervical triangle): Bounded by the sternocleidomastoid, trapezius, and clavicle.

Omoclavicular (subclavian) triangle: Bounded by the inferior belly of the omohyoid, the clavicle, and the sternocleidomastoid. Occipital triangle: Bounded by the inferior belly of the omohyoid, the trapezius, and the clavicle.

ˠ Posterior cervical region (nuchal region): Region lying under the trapezius muscle inferior to its insertion at the superior nuchal line and superior to the vertebra prominens (C7).

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12. Neurovascular Topography of the Neck

Submandibular triangle

Digastric muscle, posterior belly

Digastric muscle, anterior belly

Sternocleidomastoid Lateral cervical region (posterior cervical triangle)

Submental triangle Carotid triangle Submandibular triangle

Trapezius

Muscular triangle

Digastric muscle, anterior belly

B Lesser supraclavicular fossa

Submental triangle Hyoid bone Sternocleidomastoid region

Carotid triangle

Clavicle

Fig. 12.13 Muscle dissection of the neck A Anterior view with the head slightly extended. B Left lateral view.

A Lateral cervical region (posterior cervical triangle)

Lesser supraclavicular fossa

Trapezius

External occipital protuberance Suprasternal notch Clavicle

Inferior border of mandible Acromion

A

Fig. 12.14 Palpable bony prominences in the neck A Anterior view. B Posterior view. Certain palpable structures define the boundaries of the neck. The superior boundaries of the neck are the

Spinous process of C7 vertebra

Tip of mastoid process

Acromion

B

inferior border of the mandible, tip of the mastoid process, and external occipital protuberance. The inferior boundaries are the suprasternal notch, clavicle, acromion, and spinous process of the C7 vertebra.

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12. Neurovascular Topography of the Neck

Cervical Fasciae Fig. 12.15 Cervical fasciae The structures of the neck are enclosed by multiple layers of cervical fasciae, sheets of connective tissue that subdivide the neck into compartments. The fascial layers are separated by interfascial spaces. There are four major fascial spaces in the neck: pretracheal, retropharyngeal, prevertebral, and carotid. These spaces are not prominent under normal conditions (the fasciae lie flat against each other). However, the spaces may provide routes for the spread of inflammatory processes (e.g., tonsillar infections in the infratemporal fossa) from regions of the head and neck into the mediastinum.

˟ Muscular pretracheal fascia

˝ Deep cervical fascia

ˠ Visceral pretracheal fascia Carotid sheath ˠ

Prevertebral fascia ˞

Deep nuchal fascia ˞

ˠ Buccopharyngeal fascia

Superficial nuchal fascia ˝

Table 12.5 Cervical fasciae and fascial spaces 'HVSLWHJHQHUDOO\EHLQJFRQWLQXRXVPDQ\RIWKHIDVFLDOOD\HUVEHDUGL̥HUHQWQDPHVLQGL̥HUHQWUHJLRQVRIWKHQHFNUHODWLYHWRWKHVWUXFWXUHVWKH\HQFORVH Layer Fascial layer

Description

Contents

6XSHUÀFLDOFHUYLFDOIDVFLDQRWVKRZQ

Subcutaneous tissue that lies deep to the skin and contains the platysma anterolaterally.

Platysma

˝ Investing layer (yellow) = Deep cervical IDVFLD6XSHUÀFLDOQXFKDOIDVFLD

Envelops the entire neck and is continuous with the nuchal ligament posteriorly.

Trapezius and (splits around the) sternocleidomastoid

˞

Prevertebral layer (purple) = Prevertebral fascia + Deep nuchal fascia

Attaches superiorly to the skull base and continues inferiorly into the superior mediastinum, merging with the anterior longitudinal ligament. Continues along the subclavian artery and brachial plexus, becoming continuous with the axillary sheath. ‡ 7  KHSUHYHUWHEUDOIDVFLDVSOLWVLQWRDQDQWHULRUDODU DQGDSRVWHULRU layer (the “danger space” is located between these layers).

Intrinsic back muscles and prevertebral muscles

Pretracheal fascia (green)

˟

Carotid sheath (blue)

Muscular portion (light green)

Infrahyoid muscles

ˠ Visceral portion (dark green): Attaches to the cricoid cartilage and is continuous posteriorly with the buccopharyngeal fascia. Continues inferiorly into the superior mediastinum, eventually PHUJLQJZLWKWKHÀEURXVSHULFDUGLXP

Thyroid gland, trachea, esophagus, and pharynx

Consisting of loose areolar tissue, the sheath extends from the base of the skull (from the external opening of the carotid canal) to the aortic arch.

Common and internal carotid arteries, internal jugular vein, and vagus nerve (CN X); in addition, &1,;&1;,DQG&1;,,EULHÁ\ pass through the most superior part of the carotid sheath.

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12. Neurovascular Topography of the Neck

Mandible (no fascial layers on face)

Parotid gland with opened capsule Deep cervical fascia

Sternocleidomastoid (cut)

Sternohyoid

Carotid sheath (cut)

Visceral pretracheal fascia

Muscular pretracheal fascia (cut) Prevertebral fascia Trapezius Clavicle Sternal and clavicular heads of sternocleidomastoid (cut)

Clavipectoral fascia

A

Superficial nuchal fascia

Nuchal ligament

Spinal cord

Deep cervical fascia Muscular pretracheal fascia

Posterior layer Anterior (alar) layer Deep nuchal fascia

Visceral pretracheal fascia

Prevertebral fascia

“Danger space” (between layers of prevertebral fascia) B Retrovisceral fascia

Fig. 12.16 Fascial relationships in the neck A $QWHULRUYLHZZLWKVNLQVXSHUÀFLDOFHUYLFDOIDVFLDDQGSODW\VPDUHPRYHGB / HIWODWHUDOYLHZRIPLGVDJLWWDOVHFWLRQ 7KHVXSHUÀFLDOFHUYLFDOIDVFLDQRWVKRZQ OLHVMXVWGHHSWRWKHVNLQDQG FRQWDLQVWKHFXWDQHRXVPXVFOHRIWKHQHFNSODW\VPD 7KHLQYHVWLQJ OD\HU FRQWDLQV WKH UHPDLQGHU RI WKH VWUXFWXUHV LQ WKH QHFN 7KH GHHS FHUYLFDO IDVFLD DWWDFKHV WR WKH LQIHULRU ERUGHU RI WKH PDQGLEOH DQG LV FRQWLQXRXVLQIHULRUO\ZLWKWKHFODYLSHFWRUDOIDVFLDDQWHULRUO\ DQGWKH VXSHUÀFLDOQXFKDOIDVFLDDQGWKHWKRUDFROXPEDUIDVFLDSRVWHULRUO\ 7KH GHHSFHUYLFDOIDVFLDVSOLWVWRHQFORVHWKHSDURWLGJODQGLQDFDSVXOHA, VZHOOLQJRIWKHSDURWLGJODQGUHVXOWVLQSDLQGXHWRFRQVWULFWLRQE\WKH FDSVXOH ,WDOVRVSOLWVWRHQFORVHWKHVWHUQRFOHLGRPDVWRLG,QWKHDQWHULRUQHFNWKHSUHWUDFKHDOOD\HUOLHVMXVWGHHSWRWKHLQYHVWLQJOD\HU,W

Retropharyngeal space (between retrovisceral and alar fasciae)

FRQVLVWVRIDPXVFXODUSRUWLRQDQGDYLVFHUDOSRUWLRQZKLFKFROOHFWLYHO\ HQFORVHWKHVWUXFWXUHVRIWKHDQWHULRUQHFNLQFOXGLQJWKHSKDU\Q[WUDFKHDDQGHVRSKDJXV7KHSRUWLRQRIWKHSUHWUDFKHDOIDVFLDSRVWHULRUWR WKHHVRSKDJXVLVNQRZQDVWKHUHWURYLVFHUDOIDVFLDB ,WLVVHSDUDWHG IURPWKHSUHYHUWHEUDOIDVFLDE\WKHUHWURSKDU\QJHDOVSDFH,QIHULRUWR WKHODU\QJHDOLQOHWWKHSUHYHUWHEUDOIDVFLDVSOLWVLQWRDQDQWHULRUDODU  DQGDSRVWHULRUOD\HUZKLFKDUHVHSDUDWHGE\WKH´GDQJHUVSDFHµ³D SRWHQWLDO URXWH IRU WKH VSUHDG RI LQIHFWLRQ IURP WKH SKDU\Q[ LQWR WKH VXSHULRUPHGLDVWLQXP:LWKWXEHUFXORXVRVWHRP\HOLWLVRIWKHFHUYLFDO VSLQH D UHWURSK\DUQJHDO DEVFHVV PD\ GHYHORS LQ WKH ´GDQJHU VSDFHµ DORQJWKHSUHYHUWHEUDOIDVFLD%RWKSUHYHUWHEUDOOD\HUVDUHFRQWLQXRXV SRVWHULRUO\ZLWKWKHGHHSQXFKDOIDVFLDNote:7KHODWHUDOO\ORFDWHGFDURWLGVKHDWKA GRHVQRWDSSHDULQWKHPLGVDJLWWDOVHFWLRQ

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12. Neurovascular Topography of the Neck

Posterior Neck Occipital region

Occipital artery and vein

Greater occipital nerve (dorsal ramus of C2) Occipital lymph nodes

Semispinalis capitis

Third occipital nerve (dorsal ramus of C3)

Lesser occipital nerve (C2) Sternocleidomastoid Splenius capitis Great auricular nerve (C2–C3) Accessory nerve (CN XI)

Posterior cutaneous branches (dorsal ramus of C6)

Fig. 12.17 Posterior cervical (nuchal) region Posterior view. Left side: Subcutaneous layer of superficial nuchal fascia. Right side: All fascia removed (superficial cervical fascia, investing layer, prevertebral layer). The posterior cervical region is bounded superiorly by the superior nuchal line (the attachment of the trapezius and sternocleidomastoid to the occipital bone) and inferiorly by the palpable spinous process of the last cervical vertebra, the vertebra prominens (C7). The posterior cervical region, like the rest of the neck, is completely enveloped in superficial fascia (left side). The investing layer of deep cervical fascia envelops the trapezius and splits to enclose the sternocleidomastoid.

276

Trapezius

Both muscles are innervated by the accessory nerve (CN XI). The deep nuchal fascia (the posterior continuation of the prevertebral fascia) lies deep to the trapezius and sternocleidomastoid and encloses the intrinsic back muscles (here: semispinalis and splenius capitis). The intrinsic back muscles receive motor and sensory innervation from the dorsal rami of the spinal nerves (see Fig. 12.20). The great auricular and lesser occipital nerves are also visible in this dissection. They are sensory nerves arising from the cervical plexus (formed by the ventral rami of C1–C4). The major artery of the occipital region is the occipital artery, a posterior branch of the external carotid artery.

Neck

Trapezius (cut)

Occipital artery

Splenius capitis (cut)

12. Neurovascular Topography of the Neck

Sternocleidomastoid (cut)

Semispinalis capitis (cut) Obliquus capitis superior Rectus capitis posterior minor Greater occipital nerve (C2)

Suboccipital nerve (C1)

Vertebral artery

Occipital artery

Rectus capitis posterior major

Great auricular nerve

Obliquus capitis inferior Spinous process of axis Third occipital nerve (C3)

Fig. 12.18 Suboccipital triangle Posterior view of right side. The suboccipital triangle is a muscular triangle lying deep to the trapezius, splenius capitis, and semispinalis capitis. It is bounded superiorly by the rectus capitis posterior major, laterally by the obliquus capitis superior, and inferiorly by the obliquus capitis inferior. A short segment of the vertebral artery runs through the deep part of the triangle after leaving the transverse foramen of the atlas. It gives off branches to the surrounding short nuchal muscles before exiting the suboccipital triangle by perforating the posterior atlanto-occipital membrane. The vertebral arteries unite intracranially to form the basilar artery, a major contributor to cerebral blood flow.

Transverse process of atlas Cervical posterior intertransversarius Longissimus capitis Semispinalis capitis

Splenius capitis

Supraorbital nerve (from CN V1) Greater occipital nerve

C2

Supraorbital nerve (from CN V1)

C3

Lesser occipital nerve

Greater occipital nerve (dorsal ramus of C2)

C4

Lesser occipital nerve (C2)

A Dorsal rami of spinal nerves B

Fig. 12.19 Sites of emergence of the occipital nerves Posterior view. The sites where the lesser and greater occipital nerves emerge from the fascia into the subcutaneous connective tissue are clinically important because they are tender to palpation in certain diseases (e. g., meningitis). The examiner tests the sensation of these nerves by pressing lightly on the circled points with the thumb. If these points (but not their surroundings) are painful, the clinician should suspect meningitis.

Great auricular nerve (C2–C3) Supraclavicular nerves (C3–C4)

Fig. 12.20 Cutaneous innervation of the posterior neck Posterior view. A Segmental innervation (dermatomes). B Peripheral cutaneous nerves. The occiput and nuchal regions derive most of their segmental innervation from the C2 and C3 spinal nerves. Of the specific cutaneous nerves, the greater occipital nerve is a dorsal ramus; the lesser occipital, great auricular, and supraclavicular nerves are branches of the cervical plexus (formed from the ventral rami of C1–C4). See p. 65 for segmental versus peripheral cutaneous innervation.

277

Neck

12. Neurovascular Topography of the Neck

Lateral Neck

Parotid gland

Fig. 12.21 Lateral neck Right lateral view. Removed: Superficial cervical fascia, platysma, and parotid capsule (investing layer). The investing layer of deep cervical fascia encloses all the structures of the neck with the exception of the platysma. (Note: The face does not have fascial layers.) It splits to enclose the parotid gland in a capsule. The capsule has been opened to show the emergence of the cervical branch of the facial nerve (CN VII) from the parotid plexus. The cervical branch provides motor innervation to the platysma. The sensory nerves of the anterolateral neck (lesser occipital, great auricular, transverse cervical, and supraclavicular) arise from the cervical plexus, formed by the ventral rami of C1–C4. They pierce the investing layer at or near the punctum nervosum (Erb’s point), midway down the posterior border of the sternocleidomastoid. Note: The transverse cervical nerve (sensory) courses deep to the external jugular vein and forms a mixed anastomosis with the cervical branch (motor) of CN VII.

278

Masseter

Lesser occipital nerve (C2) Great auricular nerve (C2–C3) Erb’s point

Facial vein External jugular vein

Lateral supraclavicular nerves (C3–C4)

Posterior border of sternocleidomastoid

Anterior border of trapezius

Anastomosis Investing layer of deep cervical fascia Transverse cervical nerve (C2–C3) Clavicle

Intermediate supraclavicular nerves (C3–C4)

Fig. 12.22 Posterior cervical triangle Right lateral view. A Investing fascia removed. B Pretracheal fascia removed. C Prevertebral fascia removed. The investing layer of deep cervical fascia splits into a superficial and a deep lamina to enclose the sternocleidomastoid and trapezius, both of which are innervated by the accessory nerve (CN XI). (Note: The accessory nerve may be injured during lymph node biopsy.) Removing the investing layer between the sternocleidomastoid and trapezius reveals the posterior cervical triangle (bounded inferiorly by the clavicle). This exposes the prevertebral fascia, which encloses the intrinsic and deep muscles of the neck. The prevertebral fascia is fused to the pretracheal fascia, which envelops the omohyoid (B). Removing the prevertebral fascia exposes the phrenic nerve (C), which arises from the cervical plexus and descends to innervate the diaphragm. The brachial plexus (C) is also visible at its point of emergence between the anterior and middle scalenes.

Facial nerve (CN VII), cervical branch of parotid plexus

Medial supraclavicular nerves (C3–C4)

Lesser occipital nerve Great auricular nerve Accessory nerve (CN XI)

External jugular vein

Erb’s point

Superficial lamina of investing layer

Superficial cervical node

Anastomosis

Superficial cervical artery

Sternocleidomastoid

Trapezius Transverse cervical nerve

Supraclavicular nerves

A

Prevertebral lamina

Superficial cervical vein

Pretracheal lamina

Deep lamina of investing layer

Neck

Lesser occipital nerve

12. Neurovascular Topography of the Neck

Parotid gland

Great auricular nerve Accessory nerve (CN XI) Lateral supraclavicular nerves

External jugular vein

Intermediate supraclavicular nerves

Sternocleidomastoid Transverse cervical and CN VII anastomosis

Trapezius

Prevertebral fascia

Transverse cervical artery and vein

Transverse cervical nerve Right subclavian vein

Omohyoid

B

Sternocleidomastoid Trapezius

Accessory nerve (CN XI) Scalenus medius Levator scapulae Scalenus posterior Transverse cervical artery and vein Omohyoid, inferior belly

Phrenic nerve (C3–C5)

Brachial plexus Scalenus anterior Suprascapular artery Right subclavian vein

C

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12. Neurovascular Topography of the Neck

Anterior Neck Mandible

Fig. 12.23 Anterior neck Anterior view. Left neck: Superficial cervical fascia removed to expose platysma. Right neck: Platysma removed to expose investing layer. The investing layer of deep cervical fascia lies just deep to the cutaneous platysma muscle, which is innervated by the cervical branch of the facial nerve (CN VII). It attaches to the inferior border of the mandible and is continuous inferiorly with the clavipectoral fascia. The investing layer splits to form a capsule around the parotid gland. Inflammation of the parotid gland (e.g., mumps) causes conspicuous facial swelling and deformity in this region (“hamster cheeks” with prominent earlobes). The investing layer also divides into a deep and a superficial lamina to enclose the sternocleidomastoid. The investing layer has been cut around the midline to expose the pretracheal layer of deep cervical fascia, which encloses the infrahyoid muscles and the viscera of the anterior neck.

Parotid gland with opened capsule Investing fascia

Platysma

External jugular vein

Anterior jugular vein Transverse cervical nerve

Great auricular nerve

Pretracheal layer of deep cervical fascia

Transverse cervical nerve

Deep lamina of investing fascia

Supraclavicular nerves

Sternocleidomastoid muscle, sternal head

Superior laryngeal artery Internal jugular vein

Fig. 12.24 Anterior cervical triangle Anterior view. The pretracheal fascia has been removed to expose the anterior cervical triangle, bounded by the mandible and the anterior borders of the sternocleidomastoid muscles. The infrahyoid muscles are enclosed by the muscular pretracheal fascia (removed). The thyroid gland and larynx are enclosed by the visceral pretracheal fascia (removed). The anterior cervical triangle contains neurovasculature of the larynx and thyroid gland, including the first branch of the external carotid artery (the superior thyroid artery). The internal and external laryngeal nerves (from the superior laryngeal branch of CN X) are visible. C1 motor fibers run with the hypoglossal nerve (CN XII) to the thyrohyoid and geniohyoid (not shown). Certain C1 motor fibers leave CN XII to form the superior root of the ansa cervicalis. The inferior root is formed by motor fibers from C2 and C3. The ansa cervicalis innervates the omohyoid, sternothyroid, and sternohyoid.

280

External laryngeal nerve Right common carotid artery Superior thyroid artery External jugular vein

Internal laryngeal nerve

Arch of jugular vein

Thyroid cartilage

Medial supraclavicular nerve

Hypoglossal nerve (CN XII) Nerve to the thyrohyoid (C1) Median thyrohyoid ligament Thyrohyoid Omohyoid (cut) Sternocleidomastoid Superior root of ansa cervicalis (C1) Cricothyroid Sternothyroid Sternohyoid (cut)

Inferior thyroid vein

Neck

12. Neurovascular Topography of the Neck

Superior laryngeal artery

Superior thyroid artery and vein

Thyroid cartilage

Trapezius

Accessory nerve (CN XI)

Phrenic nerve

External laryngeal nerve Cricothyroid

Brachial plexus

Anterior scalene

Ascending cervical artery

Internal jugular vein Inferior thyroid artery Inferior thyroid artery and middle thyroid vein

Suprascapular nerve

Thyrocervical trunk

Transverse cervical artery

Vagus nerve (CN X)

Suprascapular artery

Right subclavian vein

Left subclavian artery Thyrocervical trunk

Right recurrent laryngeal nerve Right brachiocephalic vein

Right brachiocephalic trunk

Inferior thyroid vein

Left recurrent laryngeal nerve

Fig. 12.25 Root of the neck (thoracic inlet) Anterior view. The root of the neck contains numerous structures, including the common carotid artery, subclavian artery, subclavian vein, internal jugular vein, inferior thyroid vein, vagus nerve, phrenic nerve,

Left common carotid artery

and recurrent laryngeal nerve. A retrosternal goiter enlarging the inferior pole of the thyroid gland can easily compress neurovascular structures at the thoracic inlet.

Inferior thyroid artery Vertebral artery Recurrent laryngeal nerve

A

B

C

Subclavian artery

Fig. 12.26 Course of the right recurrent laryngeal nerve (after von Lanz and Wachsmuth) Anterior view. The recurrent laryngeal nerve is a somatomotor and sensory branch of the vagus nerve, which innervates all the muscles of the larynx except the cricothyroid muscle. Unilateral damage to this nerve supply results in hoarseness, and bilateral damage leads to a closed glottis with severe dyspnea. The right recurrent laryngeal nerve may pass in front of (A), behind (B), or between (C), the branches of the inferior thyroid artery. Its course should be noted during operations on the thyroid gland due to its close relationship to the posterior surface of the gland. Note: The left recurrent laryngeal nerve passes around the aortic arch in proximity to the ligamentum arteriosum.

A

B

C

Fig. 12.27 Variations in the branching pattern of the right inferior thyroid artery (after Platzer) The course of the inferior thyroid artery is highly variable. It may run medially behind the vertebral artery (A), divide immediately after arising from the thyrocervical trunk (B), or arise as the first branch of the subclavian artery (C).

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Neck

12. Neurovascular Topography of the Neck

Deep Anterolateral Neck

Median thyrohyoid ligament

Thyroid cartilage

Common carotid artery

Internal jugular vein Vagus nerve (CN X)

External laryngeal nerve

Fig. 12.28 Root of the neck Anterior view of left neck. Removed: Clavicle (sternal end), first rib, manubrium sterni, and thyroid gland. The left common carotid artery has been cut to expose sympathetic ganglia and the ascent of the left recurrent laryngeal nerve from the aortic arch (where it arises from CN X). The brachial plexus can be seen emerging from the interscalene space between the anterior and middle scalenes. It courses with the subclavian artery and vein into the axilla. The phrenic nerve descends on the anterior scalene into the mediastinum, where it innervates the diaphragm. The left thoracic duct terminates at the jugulosubclavian venous junction. It receives lymph from the entire body with the exception of the right upper quadrant, which drains to the right lymphatic duct.

Accessory nerve (CN XI) Trapezius

Middle cervical ganglion

Phrenic nerve

Cricothyroid

Scalenus anterior

Sympathetic trunk

Brachial plexus

Inferior thyroid artery

Ascending cervical artery

C8 nerve root

Transverse cervical artery

Vertebral artery

Suprascapular artery

T1 nerve root

Subclavian artery

Recurrent laryngeal nerve

Transverse cervical vein

Stellate (cervicothoracic) ganglion

Subclavian vein Left common carotid artery

Thoracic duct

Digastric, posterior belly

Internal carotid artery

Internal thoracic artery

External carotid artery

Accessory nerve (CN XI)

Facial nerve (CN VII), mandibular branch

282

Submandibular gland

Internal jugular vein

Hypoglossal nerve (CN XII)

Common facial vein

Hyoid bone Internal laryngeal nerve

Sternocleidomastoid artery

Nerve to thyrohyoid (C1)

Vagus nerve (CN X)

Superior thyroid artery

Carotid body

Sternothyroid Superior root of ansa cervicalis (C1)

External jugular vein

Thyroid gland

Sternocleidomastoid

Internal jugular vein

Facial artery Lingual artery

Superior cervical ganglion

Fig. 12.29 Carotid triangle Right lateral view. The investing layer of deep cervical fascia has been removed to expose the carotid triangle, a subdivision of the anterior cervical triangle bounded by the sternocleidomastoid, superior belly of the omohyoid, and posterior belly of the digastric. The prevertebral and pretracheal fasciae have also been removed to expose the contents of the carotid triangle, which include the internal and external carotid arteries and the tributaries of the internal jugular vein. The sympathetic trunk runs between the major blood vessels along with the vagus nerve (CN X). C1 motor fibers course with the hypoglossal nerve (CN XII) to the thyrohyoid and geniohyoid. Certain C1 motor fibers leave to form the superior root of the ansa cervicalis (the inferior root is formed from C2–C3 fibers). The ansa cervicalis innervates the omohyoid, sternohyoid, and sternothyroid.

Thyrocervical trunk

Ansa cervicalis (C1–C3) Inferior root of ansa cervicalis (C2–C3)

Omohyoid

Neck

12. Neurovascular Topography of the Neck

Splenius capitis Semispinalis capitis Internal carotid artery

Facial artery and vein

External carotid artery

Hypoglossal nerve (CN XII)

Superior cervical ganglion

Sympathetic trunk

Accessory nerve (CN XI)

Omohyoid, superior belly (cut)

Scalenus medius

Carotid bifurcation with carotid body

Scalenus anterior

Superior thyroid artery

Internal jugular vein

Thyroid gland

Superficial cervical artery

Common carotid artery

Ansa cervicalis

Sternohyoid Inferior thyroid artery

Phrenic nerve

Vagus nerve (CN X)

Brachial plexus

Vertebral artery

Omohyoid muscle, inferior belly (cut)

Sternothyroid Sternocleidomastoid (cut)

Fig. 12.30 Deep lateral cervical region Right lateral view. The sternocleidomastoid region and carotid triangle have been dissected along with adjacent portions of the posterior and anterior cervical triangles. The carotid sheath has been removed in this dissection along with the cervical fasciae and omohyoid muscle to demonstrate important neurovascular structures in the neck: • • • • •

Common carotid artery with internal and external carotid arteries Superior and inferior thyroid arteries Internal jugular vein Deep cervical lymph nodes along the internal jugular vein Sympathetic trunk, including ganglia

External carotid artery Thyrolingual trunk

B

Vagus nerve (CN X) Accessory nerve (CN XI) Hypoglossal nerve (CN XII) Brachial plexus Phrenic nerve

The phrenic nerve (C3–C5) originates from the cervical plexus and the brachial plexus. The muscular landmark for locating the phrenic nerve is the scalenus anterior, along which the nerve descends in the neck. The (posterior) interscalene space is located between the scalenus anterior and medius and the first rib and is traversed by the brachial plexus and subclavian artery. The subclavian vein passes the scalenus anterior.

Linguofacial trunk

Internal carotid artery

A

• • • • •

C

D

Thyrolinguofacial trunk

E

Fig. 12.31 Variants of the carotid arteries (after Faller and Poisel-Golth) The internal carotid artery may arise from the common carotid artery posterolateral (49%, A) or anteromedial (9%, B) to the external carotid artery, or at other intermediate sites. The external carotid artery may give origin to a thyrolingual trunk (4%, C), linguofacial trunk (23%, D), or thyrolinguofacial trunk (0.6%, E).

283

Neck

12. Neurovascular Topography of the Neck

Parapharyngeal Space (I)

Occipital bone Vagus nerve (CN X) Sigmoid sinus

Pharyngobasilar fascia

Superior jugular bulb (cut)

Pharyngeal raphe

Accessory nerve (CN XI)

Occipital artery

Hypoglossal nerve (CN XII)

Superior pharyngeal constrictor

Stylopharyngeus Superior cervical ganglion

Middle pharyngeal constrictor

Glossopharyngeal nerve (CN IX)

Internal jugular vein

Superior laryngeal nerve

Sternocleidomastoid

External carotid artery Internal carotid artery Ascending pharyngeal artery

Middle cervical ganglion

Hypoglossal nerve (CN XII) Carotid body

Pharyngeal venous plexus

Sympathetic trunk Inferior pharyngeal constrictor

Superior thyroid artery Vagus nerve (CN X)

Thyroid gland Parathyroid gland Esophagus A

Fig. 12.32 Parapharyngeal space Posterior view. A Removed: Fascial layers and contents of the prevertebral fascia. B Pharynx opened along pharyngeal raphe. The common and internal carotid arteries travel with the jugular vein and vagus

Ascending pharyngeal artery

Occipital artery

Facial artery

Internal carotid artery External carotid artery A

284

B

nerve within the carotid sheath, which attaches to the skull base. The pharynx, thyroid gland, and anterior viscera are enclosed within the pretracheal fascia (the posterior portion, the buccopharyngeal fascia, lies anterior to the prevertebral fascia).

C

D

Fig. 12.33 Ascending pharyngeal artery: variants (after Tillmann, Lippert, and Pabst) Left lateral view. The main arterial vessel supplying the upper and middle pharynx is the ascending pharyngeal artery. In 70% of cases (A) it arises from the posteroinferior surface of the external carotid artery. In approximately 20% of cases it arises from the occipital artery (B). Occasionally (8%) it originates from the internal carotid artery or carotid bifurcation (C), and in 2% of cases it arises from the facial artery (D).

Neck

Choanae, of nasal cavity

Abducent nerve (CN VI)

Trochlear nerve (CN IV) and oculomotor nerve (CN III)

12. Neurovascular Topography of the Neck

Trigeminal nerve (CN V)

Vestibulocochlear nerve (CN VIII) and facial nerve (CN VII)

Middle nasal turbinate Inferior nasal turbinate

CN IX, X, and XI

Glossopharyngeal nerve (CN IX)

Occipital artery

Uvular muscle

Superior cervical ganglion

Palatopharyngeus

Salpingopharyngeus

Hypoglossal nerve (CN XII)

Accessory nerve (CN XI)

Vagus nerve (CN X)

Sternocleidomastoid

Superior laryngeal nerve

Root of tongue

Epiglottis

Vagus nerve (CN X)

Sympathetic trunk

Cuneiform tubercle

Internal laryngeal nerve Corniculate tubercle

Superior laryngeal artery and vein

Arytenoid muscle, oblique part Arytenoid muscle, transverse part

Internal jugular vein Posterior cricoarytenoid

Common carotid artery

Middle cervical ganglion Recurrent (inferior) laryngeal nerve

Inferior thyroid artery External jugular vein

Vertebral artery (cut) Left subclavian artery Right recurrent laryngeal nerve Right brachiocephalic vein

Vertebral ganglion

Brachiocephalic trunk Left recurrent laryngeal nerve Aortic arch

Vagus nerve (CN X) Superior vena cava

B

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Neck

12. Neurovascular Topography of the Neck

Parapharyngeal Space (II)

Lingual tonsil

Sublingual gland Mandible Buccinator

Masseter

Oral vestibule Submandibular ganglion Lingual nerve

Pharynx

Inferior alveolar nerve and artery

Palatine tonsil

Medial pterygoid

Parotid gland Styloid process

Styloglossus

Parotid duct

Retromandibular vein

Internal carotid artery

External carotid artery

Internal jugular vein

Retropharyngeal lymph nodes

Palatopharyngeus

Dens of axis

Fig. 12.34 Spaces in the neck Transverse section, superior view. The pharynx is enclosed by the pretracheal fascia along with the larynx and thyroid gland. The posterior portion of the pretracheal fascia that is in direct contact with the pharynx is called the buccopharyngeal fascia. The fascial space surrounding the pharynx (parapharyngeal space) is divided into a posterior (retropharyngeal) space and a lateral (lateropharyngeal) space. The

Stylopharyngeal aponeurosis

Vertebral artery

Vagus nerve

retropharyngeal space (green) lies between the anterior alar layer of the prevertebral fascia (red) and the buccopharyngeal fascia, the posterior portion of the pretracheal fascia. The lateropharyngeal space is divided by the stylopharyngeal aponeurosis into an anterior and a posterior part. The anterior part (yellow) is contained within the pretracheal fascia in the neck (this section is through the oral cavity). The posterior part (orange) is contained within the carotid sheath.

Subarachnoid space Prevertebral fascia

Orbit Jugular vein

Pretracheal layer

Cavernous sinus

From palatine tonsil

Carotid artery Palatine tonsil

Parotid gland

Space bounded by visceral fascia

①

④

Cervical soft tissues

A

Fig. 12.35 Clinical significance of the parapharyngeal space (after Becker, Naumann, and Pfaltz) Bacteria and inflammatory processes from the oral and nasal cavities (e.g., tonsillitis, dental infections) may invade the parapharyngeal space. From there, they may spread in various directions (A). Invasion of the jugular vein may lead to bacteremia and sepsis. Invasion of the subarachnoid space poses a risk of meningitis. Inflammatory processes may also track downward into the mediastinum (gravitation abscess),

286

Retropharyngeal space

Investing fascia

Parapharyngeal space

B

Mediastinum

② ③

“Danger space” (between alar and prevertebral layers)

causing mediastinitus (B). These may spread anteriorly in the spaces between the investing and muscular pretracheal layers ① or in the space within the pretracheal fascia ②. They may also spread posteriorly in the retropharyngeal space ③ between the buccopharyngeal prevertebral fascia and the alar prevertebral fascia. Infections that enter the “danger space” ④ between the alar and prevertebral layers of the prevertebral fascia may spread directly into the mediastinum.

Neck

12. Neurovascular Topography of the Neck

Foliate papilla

Vallate papilla Palatoglossus Palatine tonsil Plane of section in Fig. 12.34 Glossopharyngeal nerve (CN IX)

Lingual tonsil Vallecula

Ascending pharyngeal artery, tonsillar branches

Aryepiglottic fold Palatopharyngeus Epiglottis

Superior laryngeal artery

Cuneiform tubercle

Internal laryngeal nerve

Piriform recess

Interarytenoid notch

Corniculate tubercle

Stylopharyngeus Posterior cricoarytenoid

Thyroid gland

Inferior thyroid vein Inferior thyroid artery Right recurrent laryngeal nerve Esophagus Trachea Submucosal venous plexus

Fig. 12.36 Neurovascular structures of the parapharyngeal space Posterior view of an en bloc specimen composed of the tongue, larynx, esophagus, and thyroid gland, as it would be resected at autopsy for pathologic evaluation of the neck. This dissection clearly demonstrates the branching pattern of the neurovascular structures that occupy the plane between the pharyngeal muscles.

Note the vascular supply to the palatine tonsil and its proximity to the neurovascular bundle, which creates a risk of hemorrhage during tonsillectomy.

287

Neuroanatomy 13

Neuroanatomy Nervous System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Spinal Cord: Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Brain: Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 Brain & Meninges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 Spinal Cord & Meninges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 Cerebrospinal Fluid (CSF) Spaces . . . . . . . . . . . . . . . . . . . . . . 300 Dural Sinuses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 Arteries of the Brain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 Neurons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306

Neuroanatomy

13. Neuroanatomy

Nervous System

Encephalon

Spinal cord

Brachial plexus

Intervertebral foramina

Spinal ganglia

Spinal nerves

Lumbosacral plexus

A

Fig. 13.1 Topography of the nervous system A Posterior view. B Right lateral view. The central nervous system (CNS), consisting of the brain (encephalon) and spinal cord, is shown in pink. The peripheral nervous system (PNS), consisting of nerves and ganglia, is shown in yellow. The nerves arising from the spinal cord leave their bony canal through the intervertebral foramina and are distributed to their target structures. The spinal nerves are formed in the foramina by the union of their dorsal (poste-

290

B

rior) roots and ventral (anterior) roots (see p. 292). The small spinal ganglion in the intervertebral foramen appears as a slight swelling of the dorsal root (visible only in the posterior view; its function is described on p. 292). In the limbs, the ventral rami of the spinal nerves come together to form plexuses. These plexuses then give rise to the peripheral nerves that supply the limbs.

Neuroanatomy

13. Neuroanatomy

I

Parietal/dorsal

II III IV V VI VII

Cranial/oral Occipital/ caudal

Frontal/cranial/ oral/rostral

②

VIII XII

IX

XI

X

Basal/ventral Dorsal/ posterior

Fig. 13.2 Spinal and cranial nerves Anterior view. Thirty-one pairs of spinal nerves arise from the spinal cord. Twelve pairs of cranial nerves arise from the brain. The cranial nerve pairs are traditionally designated by Roman numerals. Note: There is a spinal contribution to the accessory nerve (CN XI).

Spinal nerves

X

①

Ventral/ anterior

Caudal

Fig. 13.3 Terms of location and direction in the CNS Midsagittal section, right lateral view. Note two important axes: ① The almost vertical brainstem axis (corresponds approximately to the body axis). ② The horizontal axis through the diencephalon and telencephalon.

Joints, skin, skeletal muscle

Skeletal muscle

Somatosensory fibers

Afferents

Viscerosensory fibers

Viscera, vessels

Somatomotor fibers

CNS

Efferents

Visceromotor fibers

Glands, smooth muscle, cardiac muscle

Fig. 13.4 Information flow in the nervous system The information encoded in nerve fibers is transmitted either to the CNS (brain and spinal cord) or from the CNS to the periphery (PNS, including the peripheral parts of the autonomic nervous system). Fibers that carry information to the CNS are called afferent fibers or afferents for short; fibers that carry signals away from the CNS are called efferent fibers or efferents.

291

Neuroanatomy

13. Neuroanatomy

Spinal Cord: Organization Roof plate

Roof plate Alar plate White matter Alar plate

Posterior (dorsal) horn

Zone of autonomic neurons

White matter

Lateral horn

Basal plate

Basal plate

Anterior (ventral) horn

Floor plate

A

Zone of autonomic neurons

Floor plate

B

Fig. 13.5 Development of the spinal cord Transverse section, superior view. A Early neural tube. B Intermediate stage. C Adult spinal cord. The spinal cord consists of white matter that encloses gray matter columns arranged about the central canal. The gray matter primarily contains the cell bodies of neurons, and the white matter primarily consists of nerve fibers (axons). Axons with the same function are collected into bundles. Within the spinal cord, these bundles are called tracts (in the periphery they are called nerves). Ascending (afferent or sensory) tracts terminate in the brain. Descending (efferent or motor) tracts pass from the brain into the spinal cord.

Central canal

C

The spinal cord develops from the neural tube. Note: Neurons do not develop from the roof or floor plates. • Posterior (dorsal) horn: Develops from basal plate (posterior neural tube, pink). It contains afferent (sensory) neurons. • Anterior (ventral) horn: Develops from the alar plate (anterior neural tube, blue). It contains efferent (motor) neurons. • Lateral horn: Develops from the intervening zone. It contains autonomic sympathetic neurons. Note: The lateral horn is present in the thoracic and upper lumbar regions of the spinal cord. C1

Dorsal horn

Dorsal rootlets

Spinal ganglia

Dorsal root with spinal ganglion

T1 Spinal nerve

Spinal cord

Dorsal ramus Ventral ramus

Ventral horn

Ventral root Ventral rootlets

A

Meningeal branch Splanchnic nerves

Gray ramus communicans White ramus communicans Sympathetic ganglion

L2 vertebra

L1

Cauda equina S1

B

Fig. 13.6 Organization of spinal cord segments A Transverse section, superior view. B Longitudinal section, posterior view with laminar (neural) arches of vertebral bodies removed. There are two main organizational principles in the spinal cord: 1. Functional organization within segments (A). In each spinal cord segment, afferent dorsal rootlets enter the cord posteriorly, and efferent ventral rootlets emerge anteriorly. The rootlets combine to form the dorsal (posterior) and ventral (anterior) roots. The dorsal and ventral roots of each spinal cord segment fuse to form a mixed spinal nerve, which carries both sensory and motor fibers. Shortly

292

after the fusion of its two roots, the spinal nerve divides into various branches. 2. Topographical organization of segments (B). The spinal cord consists of a vertical series of 31 segments. Each segment innervates a specific area. Most spinal nerves emerge inferior to their corresponding vertebra (see Fig. 13.7). The spinal cord level does not, however, correspond to the level of the vertebra. The lower end of the adult spinal cord extends only to the first lumbar vertebral body (L1). Below L1, the spinal nerve roots descend to the intervertebral foramina as the cauda equina (“horse’s tail”). At the intervertebral foramina, they join to form the spinal nerves.

Neuroanatomy

T8 L4

L3

L2

L1

T6 T7

T4 T5

13. Neuroanatomy

T2 T3

C2

T1

L5 S1

C3

S2

2 3 4

C5

S5

C3

T9

T 11

C4

T 12

C6

T 10

C5 T1

C6 C7

2 3

T1 T2

4

C7

T3

5

C8

T4

6

T5

7

T6

8

T7

9

T8

10

T9

11

T 10

12 L1

Fig. 13.8 Dermatomes Sensory innervation of the skin correlates with the sensory roots of the spinal nerves. Every spinal cord segment (except for C1) innervates a particular skin area (= dermatome). From a clinical standpoint, it is important to know the precise correlation of dermatomes

T 11

2 3 4 5

T 12 L1

with spinal cord segments so that the level of a spinal cord lesion can be determined based on the location of the affected dermatome. For example, a lesion of the C8 spinal nerve root is characterized by a loss of sensation on the ulnar (small-finger) side of the hand.

L2

L3

L4

L5

S2

S1

S3 S4 Filum terminale

C4

S4

C2

5 6 7 8

T1

S1 2 3 4 5

S3

C1

C1

S5

Fig. 13.7 Spinal cord segments Midsagittal section, viewed from the right side. The spinal cord is divided into five major regions: the cervical cord (C, pink), thoracic cord (T, blue), lumbar cord (L, green), sacral cord (S, yellow), and coccygeal cord (gray). The adult spinal cord generally extends to the level of the L1 vertebral body. The region below, known as the cauda equina (see Fig. 13.6B), provides relatively safe access for

Table 13.1 Levels of spinal cord segments Spinal cord segment

Nearest vertebral body

Nearest spinous process

C8

C6 (inferior margin) and C7 (superior margin)

C6

T6

T5

T4

T12

T10

T9

L3

T11

S1

T12

Note: These are only approximations and may differ among individuals.

introducing a spinal needle to sample CSF (lumbar puncture). Numbering of spinal cord segments. The spinal cord segments are numbered according to the exit point of their associated spinal nerve. In most cases, the spinal nerve emerges inferior to its associated vertebra (exceptions: C1–C8*). The emergence point does not necessarily correlate with the nearest skeletal element (see Table 13.1). Progressively greater

“mismatch” between segments and associated vertebrae occurs at more caudal levels. The relationship between the spinal cord segments and vertebrae can be used to assess injuries to the vertebral column (e.g., spinal fracture or cord lesions). * Note: There are only seven cervical vertebrae but eight pairs of cervical spinal nerves (C1– C8).

293

Neuroanatomy

13. Neuroanatomy

Brain: Organization

Fig. 13.9 Gross anatomy of the brain A Left lateral view with dura mater removed. B Basal (inferior) view with cervical spinal cord sectioned. The central nervous system consists of the brain and spinal cord. The brain is divided into four major parts (Fig. 13.10): telencephalon (cerebrum), diencephalon, brainstem, and cerebellum. The telencephalon (cerebrum) is the large outer portion of the brain, consisting of two hemispheres separated by a longitudinal cerebral fissure (B). The telencephalon (cerebrum) is divided macroscopically into five lobes: frontal, parietal, temporal, occipital, and central (insular). Note: The central (insular) lobe cannot be seen unless the temporal or parietal lobe is retracted at the lateral sulcus. The surface contours of the cerebrum are defined by convolutions (gyri) and depressions (sulci). The central sulcus, an important reference point on the cerebrum, separates the precentral gyrus from the postcentral gyrus. The precentral gyrus mediates voluntary motor activity, and the postcentral gyrus mediates the conscious perception of body sensation. Gyri vary considerably between individuals and may even vary between hemispheres. Sulci may be narrowed and compressed in brain edema (excessive fluid accumulation in the brain). They are enlarged in brain atrophy (e.g., Alzheimer disease), due to tissue loss from the gyri.

Central sulcus

Precentral gyrus

Parietal lobe

Postcentral gyrus

Frontal lobe Occipital lobe

Temporal lobe Lateral sulcus Brainstem

A

Frontal lobe

Temporal lobe

Cerebellum

Longitudinal cerebral fissure

Hypophysis (pituitary)

Pons

Medulla oblongata Cerebellum

B

294

Cervical cord

Neuroanatomy

13. Neuroanatomy

Telencephalon

Corpus callosum Diencephalon Mesencephalon Cerebellum

Pituitary

Pons Medulla oblongata

Fig. 13.10 Developmental organization of the brain Midsagittal section of brain (along longitudinal cerebral fissure). Medial view of right hemisphere. The brain is divided developmentally into six major parts: telencephalon (cerebrum), diencephalon, mesencephalon, pons, medulla oblongata, and cerebellum. The mesencephalon, pons,

and medulla oblongata are collectively referred to as the brainstem. The medulla oblongata, the caudal portion of the brainstem, is continuous inferiorly with the spinal cord. There is no definite anatomical boundary between them, as the brain and spinal cord are a functional unit (the central nervous system).

Table 13.2 Development of the brain Primary vesicle

Neural tube

Prosencephalon (forebrain)

Region

Structure

Telencephalon

Cerebral cortex, white matter, and basal ganglia

Diencephalon

Epithalamus (pineal), dorsal thalamus, subthalamus, and hypothalamus

Mesencephalon (midbrain)* Rhombencephalon (hindbrain)

Tectum, tegmentum, and cerebral peduncles Metencephalon

Myelencephalon

Cerebellum

Cerebellar cortex, nuclei, and peduncles

Pons*

Nuclei and fiber tracts

Medulla oblongata*

*The mesencephalon, pons, and medulla oblongata are collectively known as the brainstem.

295

Neuroanatomy

13. Neuroanatomy

Brain & Meninges

Dura mater, endosteal layer

Inner table Cranial bone

Diploë

Lateral lacuna (open)

Outer table

Arachnoid granulations

Lateral lacuna (closed)

Middle meningeal artery, anterior (frontal) branch

Superior sagittal sinus (open)

Middle meningeal artery, posterior (parietal) branch

Lateral lacuna (open) Arachnoid granulations

Ostia of bridging veins

A Confluence of the sinuses

Superior cerebral veins Branches of middle cerebral artery

Arachnoid

Cerebral surface with pia mater Bridging veins (superior cerebral veins just before they enter the superior sagittal sinus)

Dura mater

B

Fig. 13.11 Brain and meninges in situ Superior view. A The calvaria has been removed, and the superior sagit tal sinus and its lateral lacunae have been opened. B The dura mater has been removed from the left hemisphere, and the dura and arachnoid have been removed from the right hemisphere. The brain and spinal cord are covered by membranes called meninges, which form a sac filled with cerebrospinal fluid (CSF). The meninges are composed of the following three layers: • Outer layer: The dura mater (often shortened to “dura”) is a tough layer of collagenous connective tissue. It consists of two layers, an inner meningeal layer and an outer endosteal layer. The periosteal layer adheres firmly to the periosteum of the calvaria within the cranial cavity, but it is easy to separate the inner layer from the bone in this region, leaving it on the cerebrum, as illustrated here (A). • Middle layer: The arachnoid (arachnoid membrane) is a translucent membrane through which the cerebrum and the blood vessels in the subarachnoid space can be seen (B).

296

• Inner layer: The pia mater directly invests the cerebrum and lines its fissures (B). The arachnoid and pia are collectively called the leptomeninges. The space between them, called the subarachnoid space, is filled with CSF and envelops the brain. It contains the major cerebral arteries and the superficial cerebral veins, which drain chiefly through “bridging veins” into the superior sagittal sinus. The dura mater in the midline forms a double fold between the periosteal and meningeal layers that encloses the endothelium-lined superior sagittal sinus, which has been opened in the illustration. Inspection of the opened sinus reveals the arachnoid granulations (pacchionian granulations, arachnoid villi). These protrusions of the arachnoid are sites for the reabsorption of CSF. Arachnoid granulations are particularly abundant in the lateral lacunae of the superior sagittal sinus. The dissection in A shows how the middle meningeal artery is situated between the dura and calvaria. Rupture of this vessel causes blood to accumulate between the bone and dura, forming an epidural hematoma.

Neuroanatomy

Superior sagittal sinus Telencephalon, frontal lobe Lateral ventricle Telencephalon, temporal lobe Pituitary Cavernous sinus

13. Neuroanatomy

Lateral ventricle, anterior horn Interventricular foramen Third ventricle Sphenoparietal sinus Superior petrosal sinus Transverse sinus Pons

Cerebellum Basilar plexus

Inferior petrosal sinus Sigmoid sinus

Medulla oblongata

Fig. 13.12 Projection of important brain structures Anterior view. The largest structures of the cerebrum (telencephalon) are the frontal and temporal lobes. The falx cerebri separates the two cerebral hemispheres in the midline (not visible here). In the brainstem,

we can identify the pons and medulla oblongata on both sides of the midline below the telencephalon. The superior sagittal sinus and the paired sigmoid sinuses can also be seen. The anterior horns of the two lateral ventricles are projected onto the forehead.

Great cerebral vein Superior sagittal sinus Inferior sagittal sinus Interventricular foramen Third ventricle Cerebral aqueduct Cavernous sinus Superior petrosal sinus

Anterior (frontal) horn Central part Posterior (occipital) horn

Lateral ventricle

Inferior (temporal) horn Straight sinus Fourth ventricle Confluence of the sinuses Transverse sinus Occipital sinus

Inferior petrosal sinus

Fig. 13.13 Projection of important brain structures Left lateral view. The relationship of specific lobes of the cerebrum to the cranial fossae can be appreciated in this view. The frontal lobe lies in the anterior cranial fossa, the temporal lobe in the middle cranial fossa,

Sigmoid sinus

and the cerebellum in the posterior cranial fossa. The following dural venous sinuses can be identified: the superior and inferior sagittal sinus, straight sinus, transverse sinus, sigmoid sinus, cavernous sinus, superior and inferior petrosal sinus, and occipital sinus.

297

Neuroanatomy

13. Neuroanatomy

Spinal Cord & Meninges

Fig. 13.14 Spinal cord in the vertebral canal Transverse section at the level of the C4 vertebra, viewed from above. The spinal cord occupies the center of the vertebral foramen and is anchored within the subarachnoid space to the spinal dura mater by the denticulate ligament. The root sleeve, an outpouching of the dura mater in the intravertebral foramen, contains the spinal ganglion and the dorsal and ventral roots of the spinal nerve. The spinal dura mater is bounded externally by the epidural space, which contains venous plexuses, fat, and connective tissue. The epidural space extends upward as far as the foramen magnum, where the dura becomes fused to the cranial periosteum.

Posterior internal vertebral venous plexus

Epidural space Subarachnoid space

Dorsal horn

Arachnoid

Denticulate ligament

Spinal dura mater

Ventral horn Intervertebral foramen (superior notch shown)

Dorsal root Ventral root

Spinal ganglion Spinal nerve

Vertebral artery Vertebral veins

Epidural fat

Posterior internal vertebral venous plexus

Anterior internal vertebral venous plexus

Dural (thecal) sac

Root sleeve

Fatty tissue Epidural space Cauda equina

Filum terminale Spinal ganglion

Fig. 13.15 Cauda equina in the vertebral canal Transverse section at the level of the L2 vertebra, viewed from below. The spinal cord usually ends at the level of the first lumbar vertebra (L1). The space below the lower end of the spinal cord is occupied by the cauda equina and filum terminale in the dural sac, which ends at the level of the S2 vertebra. The epidural space expands at that level and contains extensive venous plexuses and fatty tissue.

298

Anterior internal vertebral venous plexus

Spinal dura mater

Neuroanatomy

13. Neuroanatomy

L1 vertebra Conus medullaris

T 12 Conus medullaris (adult)

Filum terminale

L1 Spinal ganglion

Conus medullaris (newborn)

Cauda equina (dorsal and ventral spinal roots)

Dural sac (lumbar cistern)

Spinal dura mater Spinal arachnoid

Sacral hiatus Filum terminale

Fig. 13.16 Cauda equina in the vertebral canal Posterior view. The laminae and the dorsal surface of the sacrum have been partially removed. The spinal cord in the adult terminates at approximately the level of the first lumbar vertebra (L1). The dorsal and ventral spinal nerve roots extending from the lower end of the spinal cord (conus medullaris) are known collectively as the cauda equina. During lumbar puncture at this level, a needle introduced into the subarachnoid space (lumbar cistern) normally slips past the spinal nerve roots without injuring them.

Fig. 13.17 Age-related changes of spinal cord levels Anterior view. As an individual grows, the longitudinal growth of the spinal cord increasingly lags behind that of the vertebral column. At birth the distal end of the spinal cord, the conus medullaris, is at the level of the L3 vertebral body (where lumbar puncture is contraindicated). The spinal cord of a tall adult ends at the T12/L1 level, whereas that of a short adult extends to the L2/L3 level. The dural sac always extends into the upper sacrum. It is important to consider these anatomical relationships during lumbar puncture. It is best to introduce the needle at the L3/L4 interspace (see Fig. 13.18).

Conus medullaris Cauda equina 1

Filum terminale

2

Sacral hiatus

A

B

3

Fig. 13.18 Lumbar puncture, epidural anesthesia, and lumbar anesthesia In preparation for a lumbar puncture, the patient bends far forward to separate the spinous processes of the lumbar spine. The spinal needle is usually introduced between the spinous processes of the L3 and L4 vertebrae. It is advanced through the skin and into the dural sac (lumbar cistern, see Fig. 13.17) to obtain a CSF sample. This procedure has numerous applications, including the diagnosis of meningitis. For epidural anesthesia, a catheter is placed in the epidural space without penetrating the dural sac (1). Lumbar anesthesia is induced by injecting a local anesthetic solution into the dural sac (2). Another option is to pass the needle into the epidural space through the sacral hiatus (3).

299

Neuroanatomy

13. Neuroanatomy

Cerebrospinal Fluid (CSF) Spaces

Arachnoid granulations

Choroid plexus of lateral ventricle

Choroid plexus of third ventricle Superior sagittal sinus Ambient cistern Interhemispheric cistern

Straight sinus

Interventricular foramen

Cerebral aqueduct

Confluence of the sinuses Cistern of lamina terminalis

Basal cistern

Vermian cistern Choroid plexus of fourth ventricle

Chiasmatic cistern

Cerebellomedullary cistern (cisterna magna)

Interpeduncular cistern

Median aperture

Pontomedullary cistern Central canal

Spinal cord Vertebral venous plexus Subarachnoid space Endoneural space Spinal nerve

Fig. 13.19 CSF spaces Schematized midsagittal section. Medial view of right hemisphere. The brain and spinal cord are suspended in CSF. CSF is located in the subarachnoid space enclosed by the meningeal layers surrounding the brain and spinal cord. The cerebral ventricles and subarachnoid space have a combined capacity of approximately 150 mL of CSF (80% in subarachnoid space, 20% in ventricles). This volume is completely replaced two to four times daily. CSF is produced in the choroid plexus

300

(red), present in each of the four cerebral ventricles (see Fig. 13.13). It flows from the ventricles through the median and lateral apertures (not shown) into the subarachnoid space. Most CSF drains from the subarachnoid space through the arachnoid granulations (see Fig. 13.11) and the dural sinuses. Smaller amounts drain along the proximal portions of the spinal nerves into venous plexuses or lymphatic pathways. Obstruction of CSF drainage will cause a rapid rise in intracranial pressure due to the high rate of CSF turnover.

Neuroanatomy

Posterior thalamic nucleus Pineal body

Choroid plexus of lateral ventricle

13. Neuroanatomy

Middle cerebellar peduncles Median aperture

Fornix

Taenia choroidea Taenia thalami

Taenia fornicis B

A

Lateral aperture

Bochdalek’s flower basket

Fig. 13.20 Choroid plexus A Lateral ventricles. Rear view of thalamus. B Fourth ventricle. Posterior view of partially opened rhomboid fossa (cerebellum removed). C Cerebral ventricles, superior view. The choroid plexus is formed by the ingrowth of vascular loops into the ependyma. The ependyma is firmly attached to the walls of the associ-

ated ventricles. Its lines of attachment, the taeniae, are revealed when the plexus tissue is removed with forceps (C). As the choroid plexus is adherent to the ventricular wall at only one site, it can float freely in the ventricular system. Free ends of the choroid plexus may extend through the lateral aperture into the subarachnoid space (“Bochdalek’s flower basket”).

Dural venous sinus

Ependyma Cuboidal epithelium

CSF space

C

Choroid plexus

Arachnoid granulations Fourth ventricle

Brush border Blood vessels

Subarachnoid space

Median aperture Cerebral aqueduct Lateral ventricle

Fig. 13.21 Histological section of the choroid plexus (after Kahle) The choroid plexus is a protrusion of the ventricular wall. It is often likened to a cauliflower because of its extensive surface folds. The epithelium of the choroid plexus consists of a single layer of cuboidal cells and has a brush border on its apical surface (to increase the surface area further).

Olfactory cistern

Cistern of corpus callosum

Fig. 13.22 CSF circulation The choroid plexus is present to some extent in each of the four cerebral ventricles. It produces CSF, which flows through the two lateral apertures (not shown) and median aperture into the subarachnoid space. From there, most of the CSF drains through the arachnoid granulations into the dural venous sinuses.

Cistern of lamina terminalis Chiasmatic cistern

Carotid cistern

Cistern of lateral cerebral fossa (encloses middle cerebral artery)

Interpeduncular cistern

Posterior communicating artery

Crural cistern (encloses the anterior choroidal artery)

Middle cerebral artery Ambient cistern (encloses posterior cerebral artery and superior cerebellar artery)

Trigeminal cistern Median pontine cistern

Anterior inferior cerebellar artery

Basilar artery

Flocculus

Posterior inferior cerebellar artery Vertebral artery

Third ventricle

Pontocerebellar cistern Posterior spinal cistern

Lateral cerebelloAnterior medullary cistern spinal cistern

Fig. 13.23 Subarachnoid cisterns (after Rauber and Kopsch) Basal view. The cisterns are CSF-filled expansions of the subarachnoid space. They contain the proximal portions of some cranial nerves and basal cerebral arteries (veins are not shown). When arterial bleeding occurs (as from a ruptured aneurysm), blood will seep into the subarachnoid space and enter the CSF. A ruptured intracranial aneurysm is a frequent cause of blood in the CSF.

301

Neuroanatomy

13. Neuroanatomy

Dural Sinuses

Inferior sagittal sinus

Superior sagittal sinus

Superior anastomotic vein (of Trolard) Deep middle cerebral vein

Basilar vein

Fig. 13.24 Dural sinus tributaries from the cerebral veins (after Rauber and Kopsch) Right lateral view. Venous blood collected deep within the brain drains to the dural sinuses through superficial and deep cerebral veins. The red arrows in the diagram show the principal directions of venous blood flow in the major sinuses. Because of the numerous anastomoses, the isolated occlusion of a complete sinus segment may produce no clinical symptoms.

Internal cerebral vein

Anterior cerebral vein

Great cerebral vein

Anterior intercavernous sinus Superficial middle cerebral vein

Straight sinus Confluence of the sinuses Inferior anastomotic vein (of Labbé)

Cavernous sinus Emissary vein (sphenoidal) Superior petrosal sinus Transverse sinus

Parietal emissary vein

Inferior petrosal sinus Superior jugular bulb

Great cerebral vein Inferior sagittal sinus

Superior sagittal sinus Straight sinus

Superior ophthalmic vein

Superior petrosal sinus

Angular vein

Occipital emissary vein

Inferior ophthalmic vein

Occipital vein Confluence of the sinuses

Cavernous sinus

Transverse sinus

Infraorbital vein

Posterior auricular vein

Venous plexus of foramen ovale

Sigmoid sinus

Pterygoid plexus Deep facial vein

Mastoid emissary vein

Inferior petrosal sinus

Condylar emissary vein

Maxillary vein

Superficial temporal vein

Retromandibular vein Facial vein Posterior division, retromandibular vein

External jugular vein

Fig. 13.25 Accessory drainage pathways of the dural sinuses Right lateral view. The dural sinuses have many accessory drainage pathways besides their principal drainage into the two internal jugular veins. The connections between the dural sinuses and extracranial veins mainly serve to equalize pressure and regulate temperature. These anastomoses are of clinical interest because their normal direction of blood flow may reverse (general absence of functional valves in the head and neck), allowing blood from extracranial veins to reflux into the dural sinuses. This mechanism may give rise to sinus infections that lead, in turn, to vascular occlusion (venous

302

Internal jugular vein

Anterior division, retromandibular vein

sinus thrombosis). The most important accessory drainage vessels include the following: • Emissary veins (diploic and superior scalp veins) • Superior ophthalmic vein (angular and facial veins) • Venous plexus of foramen ovale (pterygoid plexus, retromandibular vein) • Marginal sinus and basilar plexus (internal and external vertebral venous plexus)

Neuroanatomy

Sagittal suture

13. Neuroanatomy

Parietal foramen with parietal emissary vein

Superior sagittal sinus

Lambdoid suture

Confluence of the sinuses

Parietomastoid suture

Transverse sinus External occipital protuberance

Occipital foramen with occipital emissary vein

Mastoid foramen with mastoid emissary vein Venous plexus around the foramen magnum (marginal sinus) Mastoid process Venous plexus of hypoglossal nerve canal External vertebral venous plexus

Sigmoid sinus

(Posterior) condylar canal with condylar emissary vein

Occipital condyle Internal jugular vein Occipital vein

Fig. 13.26 Emissary veins Posterior view of occiput. Emissary veins establish a direct connection between the intracranial dural sinuses and extracranial veins. They run through small cranial openings such as the parietal and mastoid foramina. Emissary veins are of clinical interest because they create a potential route by which bacteria from the scalp may spread to the dura mater and incite a purulent meningitis. Only the posterior emissary veins are shown here.

303

Neuroanatomy

13. Neuroanatomy

Arteries of the Brain

Internal carotid artery, cerebral part Posterior communicating artery Internal carotid artery, petrous part Basilar artery

Posterior cerebral artery Atlas

Axis

Fig. 13.27 Arterial supply to the brain Left lateral view. The parts of the brain in the anterior and middle cranial fossae receive their blood supply from branches of the internal carotid artery; the parts of the brain in the posterior cranial fossa are supplied by branches of the vertebral and basilar arteries (the basilar artery is formed by the confluence of the two vertebral arteries). The carotid and basilar arteries are connected by a vascular ring called the circle of Willis (see Fig. 13.29). In many cases the circle of Willis allows for compensation of decreased blood flow in one vessel with increased “collateral” blood flow through another vessel (important in patients with stenotic lesions of the afferent arteries, see Fig. 13.31).

Internal carotid artery, cervical part External carotid artery Superior thyroid artery Common carotid artery

Aortic arch

Carotid bifurcation Vertebral artery

Subclavian artery

Anterior choroidal artery Anterior cerebral artery

Middle cerebral artery C1

Posterior communicating artery

(4) Cerebral part C2 Carotid siphon

Ophthalmic artery C3

C4

Petrous bone

Temporal bone

(3) Cavernous part C5 (2) Petrous part

(1) Cervical part

304

Zygomatic arch Styloid process Mastoid process

Fig. 13.28 Anatomical divisions of the internal carotid artery Anterior view of the left internal carotid artery. The internal carotid artery consists of four topographically distinct parts between the carotid bifurcation and the point where it divides into the anterior and middle cerebral arteries. The parts (separated in the figure by white disks) are: (1) Cervical part (red): Located in the lateral pharyngeal space. (2) Petrous part (yellow): Located in the carotid canal of the petrous bone. (3) Cavernous part (green): Follows an S-shaped curve in the cavernous sinus. (4) Cerebral part (purple): Located in the chiasmatic cistern of the subarachnoid space. Except for the cervical part, which generally does not give off branches, all the other parts of the internal carotid artery give off numerous branches. The intracranial parts of the internal carotid artery are subdivided into five segments (C1–C5) based on clinical criteria: • C1–C2: Supraclinoid segments, located within the cerebral part. C1 and C2 lie above the anterior clinoid process of the lesser wing of the sphenoid bone. • C3–C5: Infraclinoid segments, located within the cavernous sinus.

Neuroanatomy

Posterior communicating artery

Superior sagittal sinus Anterior cerebral artery

Posterior cerebral artery

Anterior communicating artery

Anterior inferior cerebellar artery

13. Neuroanatomy

Anterior cerebral artery

Anterior communicating artery

Middle cerebral artery

Posterior communicating artery

Internal carotid artery

Posterior cerebral artery

Basilar artery

A

Middle cerebral artery

Basilar artery

Internal carotid artery

Foramen magnum

Superior cerebellar artery

Vertebral artery Posterior spinal artery Anterior spinal artery

Pontine arteries Confluence of the sinuses

Posterior inferior cerebellar artery

Fig. 13.29 Circle of Willis Superior view. The two vertebral arteries enter the skull through the foramen magnum and unite behind the clivus to form the unpaired basilar artery. This vessel then divides into the two posterior cerebral arteries (additional vessels that normally contribute to the circle of Willis are shown in Fig. 13.30). Note: Each middle cerebral artery (MCA) is the direct continuation of the internal carotid artery on that side. Clots ejected by the left heart will frequently embolize to the MCA territory.

B

C

D

E

F

G

Fig. 13.30 Variants of the circle of Willis (after Lippert and Pabst) The vascular connections within the circle of Willis are subject to considerable variation. As a rule, the segmental hypoplasias shown here do not significantly alter the normal functions of the arterial ring. A In most cases, the circle of Willis is formed by the following arteries: the anterior, middle, and posterior cerebral arteries; the anterior and posterior communicating arteries; the internal carotid arteries; and the basilar artery. B Occasionally, the anterior communicating artery is absent. C Both anterior cerebral arteries may arise from one internal carotid artery (10% of cases). D The posterior communicating artery may be absent or hypoplastic on one side (10% of cases). E Both posterior communicating arteries may be absent or hypoplastic (10% of cases). F The posterior cerebral artery may be absent or hypoplastic on one side. G Both posterior cerebral arteries may be absent or hypoplastic. In addition, the anterior cerebral arteries may arise from a common trunk.

Middle cerebral artery Carotid siphon

Basilar artery

Carotid bifurcation

Vertebral artery Common carotid artery

Origin of vertebral artery Subclavian artery Brachiocephalic trunk

Fig. 13.31 Stenoses and occlusions of arteries supplying the brain Atherosclerotic lesions in older patients may cause the narrowing (stenosis) or complete obstruction (occlusion) of arteries that supply the brain. Stenoses most commonly occur at arterial bifurcations. The sites of predilection are shown with circles. Isolated stenoses that develop gradually may be compensated for by collateral vessels. When stenoses occur simultaneously at multiple sites, the circle of Willis cannot compensate for the diminished blood supply, and cerebral blood flow becomes impaired (varying degrees of cerebral ischemia). Note: The damage is manifested clinically in the brain, but the cause is located in the vessels that supply the brain. Because stenoses are treatable, their diagnosis has major therapeutic implications.

Subclavian artery Aortic arch

Fig. 13.32 Anatomical basis of subclavian steal syndrome “Subclavian steal” usually results from stenosis of the left subclavian artery (red circle) located proximal to the origin of the vertebral artery. This syndrome involves a stealing of blood from the vertebral artery by the subclavian artery. When the left arm is exercised, as during yard work, insufficient blood may be supplied to the arm to accommodate the increased muscular effort (the patient complains of muscle weakness). As a result, blood is “stolen” from the vertebral artery circulation, and there is a reversal of blood flow in the vertebral artery on the affected side (arrows). This leads to deficient blood flow in the basilar artery and may deprive the brain of blood, producing a feeling of lightheadedness.

305

Neuroanatomy

13. Neuroanatomy

Neurons Receptor segment

Transmission segment

Terminal segment

Soma Dendrite

Direction of transmission

Axon hillock Axon

Presynaptic terminal (bouton) Membrane potential

¸‚ˆ J

¸‚ˆ J

¸‚ˆ J

¸‚ˆ J

ˆ

ˆ

ˆ

ˆ

¨†ˆ J

¨†ˆ J

¨†ˆ J

¨†ˆ J

Excitatory postsynaptic potential (EPSP)

Inhibitory postsynaptic potential (IPSP)

Potential at the axon hillock

Fig. 13.33 Neurons (nerve cells) Neurons are the smallest functional units of the nervous system. Each neuron is composed of a cell body (soma or perikaryon) and two types of processes: dendrites and axons. The function of the neuron is reflected in the number and type of processes arising from the cell body (see Fig. 13.35). • Dendrite (receptor segment): Conducts impulses from synapse to the cell body. Depending on its function, a neuron may have multiple dendrites. Dendrites may undergo complex arborization to increase their surface area. • Axon (projecting segment): Conducts impulses to other neurons or cells (e.g., skeletal muscle). Neurons have only one axon. In the CNS, axons are generally myelinated (covered with myelin cells). The cell membranes of myelin cells are predominantly lipid (this gives white matter its fatty appearance). Myelination electrically insulates axons, increasing the speed of impulse conduction.

Action potential

Neurons communicate at synapses, the junction between the axon of one neuron and the dendrite or cell body of the other (see Fig. 13.37). Nerve impulses are propagated through waves of depolarization across cell membranes. Resting nerve cells have a membrane potential of −80 mV (higher concentration of positive ions outside the nerve cell than inside). In response to a nerve impulse, neurotransmitters are released into the synapse. These neurotransmitters bind ion channels that allow positive ions to rush into the cytoplasm. This initiates other channels to open, causing the cell membrane to become massively depolarized (+40 mV). This initiates an action potential at the axon hillock, the origin of the axon on the cell body. The action potential travels along the axon and induces the release of neurotransmitters from the presynaptic terminal at the next synapse. The action potential is therefore propagated rapidly across multiple cells, which are repolarized through the action of ion pumps. Note: Neurotransmitters may be either excitatory or inhibitory (create either an excitatory or inhibitory postsynaptic potential at the target neuron).

Dendrite

Fig. 13.34 Electron microscopy of the neuron The organelles of neurons can be resolved with an electron microscope. Neurons are rich in rough endoplasmic reticulum (protein synthesis, active metabolism). This endoplasmic reticulum (called Nissl substance under a light microscope) is easily demonstrated by light microscopy when it is stained with cationic dyes (which bind to the anionic mRNA and nRNA of the ribosomes). The distribution pattern of the Nissl substance is used in neuropathology to evaluate the functional integrity of neurons. The neurotubules and neurofilaments that are visible by electron microscopy are referred to collectively in light microscopy as neurofibrils, as they are too fine to be resolved as separate structures under the light microscope. Neurofibrils can be demonstrated in light microscopy by impregnating the nerve tissue with silver salts. This is important in neuropathology, for example, because the clumping of neurofibrils is an important histological feature of Alzheimer disease.

306

Nucleus

Nucleolus

Mitochondrion

Nuclear pore Axon hillock

Golgi apparatus

Axon

Rough endoplasmic reticulum

Neurotubules and neurofilaments

Neuroanatomy

13. Neuroanatomy

Presynaptic membrane Presynaptic terminal (bouton)

Synaptic cleft 1

Postsynaptic membrane

Vesicles with neurotransmitter

Spine

Postsynaptic membrane Synaptic cleft Presynaptic membrane A

B

C

D

E

2

F

Fig. 13.35 Basic neuron forms Neurons consist of a cell body, an axon, and one or more dendrites. The function of the neuron is reflected in its structure. Neurons A–D are efferent (motor) neurons, which convey impulses from the CNS to the periphery. Neurons E and F are afferent (sensory) neurons, which convey impulses to the CNS. A, B Multipolar neurons: Multiple dendrites with either a long (A) or short (B) axon. Alpha motor neurons of the spinal cord are the longaxon form. Interneurons in the gray matter of the brain and spinal cord are the short-axon form. C Pyramidal cell: Long axon with multiple dendrites only at the apex and base of the triangular cell body (e.g., efferent neurons of cerebral motor cortex). D Purkinje cell: Long axon with elaborately branched dendritic tree from one site on the cell body. Purkinje cells are found within the cerebellum. E Bipolar neuron: Long axon and long dendrite that arborizes in the periphery (e.g., retinal cells). F Pseudounipolar neuron: Long axon and long arborized dendrite that are not separated by the cell body. This is the traditional form of primary afferent (sensory) neurons in spinal nerves. The cell bodies of these neurons form the spinal (dorsal root) ganglion.

Fig. 13.36 Synapses in the CNS Synapses are the functional connection between two neurons. They consist of a presynaptic membrane, a synaptic cleft, and a postsynaptic membrane. In a “spine synapse” (1), the presynaptic terminal (bouton) is in contact with a specialized protuberance (spine) of the target neuron. The side-by-side synapse of an axon with the flat surface of a target neuron is called a parallel contact or bouton en passage (2). The vesicles in the presynaptic expansions contain the neurotransmitters that are released into the synaptic cleft by exocytosis when the axon fires. From there the neurotransmitters diffuse to the postsynaptic membrane, where their receptors are located. A variety of drugs and toxins act upon synaptic transmission (antidepressants, muscle relaxants, nerve gases, botulinum toxin).

Axon

Axon Axosomatic

Dendrite Axodendritic

Axoaxonal

Fig. 13.37 Synaptic patterns Axons may terminate at various sites on the target neuron and form synapses there. The synaptic patterns are described as axodendritic, axosomatic, or axoaxonal. Axodendritic synapses are the most common. The cerebral cortex consists of many small groups of neurons that are collected into functional units called columns.

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Sectional Anatomy 14

Sectional Anatomy of the Head & Neck Coronal Sections of the Head (I): Anterior . . . . . . . . . . . . . . . 310 Coronal Sections of the Head (II): Posterior . . . . . . . . . . . . . 312 Coronal MRIs of the Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . 314 Coronal MRIs of the Neck (I): Anterior . . . . . . . . . . . . . . . . . . 316 Coronal MRIs of the Neck (II) . . . . . . . . . . . . . . . . . . . . . . . . . 318 Coronal MRIs of the Neck (III): Posterior . . . . . . . . . . . . . . . . 320 Transverse Sections of the Head (I): Cranial . . . . . . . . . . . . . 322 Transverse Sections of the Head (II) . . . . . . . . . . . . . . . . . . . . 324 Transverse Sections of the Head (III): Caudal . . . . . . . . . . . . 326 Transverse Sections of the Neck (I): Cranial. . . . . . . . . . . . . . 328 Transverse Sections of the Neck (II): Caudal . . . . . . . . . . . . . 330 Transverse MRIs of the Head. . . . . . . . . . . . . . . . . . . . . . . . . . 332 Transverse MRIs of the Oral Cavity . . . . . . . . . . . . . . . . . . . . . 334 Transverse MRIs of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . 336 Sagittal Sections of the Head (I): Medial . . . . . . . . . . . . . . . . 338 Sagittal Sections of the Head (II): Lateral. . . . . . . . . . . . . . . . 340 Sagittal MRIs of the Head . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342 Sagittal MRIs of the Neck . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal Sections of the Head (I): Anterior

Anterior cranial fossa Frontal lobe of cerebrum

Levator palpebrae superioris Periorbital fat

Orbital plate of ethmoid bone

Vitreous body

Ethmoid air cells

Medial rectus Inferior rectus

Middle nasal meatus and concha

Inferior oblique Orbicularis oculi

Infraorbital nerve (from CN V2) in infraorbital canal Maxillary sinus

Cartilaginous nasal septum

Inferior nasal meatus

Inferior nasal concha

Vomer Palatine process of the maxilla

First upper molar

Greater palatine artery

Buccinator

Oral cavity

Tongue Oral vestibule

Genioglossus Geniohyoid

First lower molar

Inferior alveolar nerve, artery, and vein in mandibular canal

Mylohyoid Platysma

Fig. 14.1 Coronal section through the anterior orbital margin Anterior view. This section of the skull can be roughly subdivided into four regions: the oral cavity, the nasal cavity and sinus, the orbit, and the anterior cranial fossa. Inspecting the region in and around the oral cavity, we observe the muscles of the oral floor, the apex of the tongue, the neurovascular structures in the mandibular canal, and the first molar. The hard palate separates the oral cavity from the nasal cavity, which is divided into left and right halves by the nasal septum. The inferior and middle nasal conchae can be identified along with the laterally situated maxillary sinus. The structure bulging down into the roof of the sinus is the infraorbital canal, which transmits the infraorbital nerve (branch of the maxillary division of the trigeminal nerve, CN V2).

310

Digastric (anterior belly)

The plane of section is so far anterior that it does not cut the lateral bony walls of the orbits because of the lateral curvature of the skull. The section passes through the transparent vitreous body and three of the six extraocular muscles, which can be identified in the periorbital fat. Two additional muscles can be seen in the next deeper plane of section (Fig. 14.2). The space between the two orbits is occupied by the ethmoid cells. Note: The bony orbital plate is very thin (lamina papyracea) and may be penetrated by infection, trauma, and neoplasms. In the anterior cranial fossa, the section passes through both frontal lobes of the brain in the most anterior portions of the cerebral gray matter. Very little white matter is visible at this level.

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Superior sagittal sinus

Falx cerebri*

Frontal lobe of cerebrum

Crista galli

Olfactory bulb (CN I)

Levator palpebrae superioris

Ethmoid air cells

Superior rectus Superior oblique

Temporalis, superficial and deep heads

Lateral rectus Optic nerve (CN II)

Inferior orbital fissure

Medial rectus Inferior rectus

Infratemporal fossa

Middle nasal concha

Zygomatic arch

Inferior nasal concha

Maxillary sinus Masseter, superficial part

Masseter

Masseter, deep part Buccal nerve

Buccinator

Buccal vein

Tongue Lingual nerve, deep lingual vein Inferior alveolar nerve, artery, and vein in mandibular canal

Geniohyoid Mylohyoid Digastric (anterior belly)

Fig. 14.2 Coronal section through the retrobulbar space Anterior view. Here, the tongue is cut at a more posterior level than in Fig. 14.1 and therefore appears broader. In addition to the oral floor muscles, we see the muscles of mastication on the sides of the skull. In the orbital region we can identify the retrobulbar space with its fatty tissue, the extraocular muscles, and the optic nerve. The orbit communicates laterally with the infratemporal fossa through the inferior

orbital fissure. This section cuts through both olfactory bulbs in the anterior cranial fossa, and the superior sagittal sinus can be recognized in the midline. *Note: More posteriorly, the falx cerebri does not separate the cerebral hemispheres. Its inferior margin is nonattached, superior to the corpus callosum.

311

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal Sections of the Head (II): Posterior

Superior sagittal sinus

Falx cerebri

Frontal lobe of cerebrum

Olfactory nerve (CN I) Superior oblique

Superior rectus Lateral rectus

Temporalis

Optic nerve (CN II)

Ethmoid air cells

Medial rectus Inferior rectus

Nasal septum

Infraorbital nerve (from CN V2)

Zygomatic arch

Masseter Maxillary sinus Nasal cavity

Coronoid process Soft palate

Mandibular ramus

Buccal fat pad Medial pterygoid

Tongue

Buccinator Body of mandible

Genioglossus Lingual nerve, deep lingual artery and vein Mylohyoid

Inferior alveolar nerve, artery, and vein in mandibular canal Hyoglossus Digastric (anterior belly)

Geniohyoid

Fig. 14.3 Coronal section through the orbital apex Anterior view. The soft palate replaces the hard palate in this plane of section, and the nasal septum becomes osseous at this level. The buccal fat pad is also visible in this plane. The buccal pad is attenuated in

312

wasting diseases; this is why the cheeks are sunken in patients with end-stage cancer. This coronal section is slightly angled, producing an apparent discontinuity in the mandibular ramus on the left side of the figure (compare with the continuous ramus on the right side).

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Superior sagittal sinus Falx cerebri Lateral ventricle Corpus callosum Parietal lobe

Head of caudate nucleus Internal capsule Putamen

Temporalis Anterior cerebral artery

Optic nerve (CN II) Oculomotor nerve (CN III)

Internal carotid artery

Trochlear nerve (CN IV)

Temporal lobe

Abducent nerve (CN VI)

Pituitary

Ophthalmic division (CN V1)

Cavernous sinus Sphenoid sinus

Zygomatic arch

Septum of sphenoid sinus

Maxillary division (CN V2) Middle cranial fossa Mandibular division (CN V3) Masseter Lateral pterygoid

Nasopharynx

Lingual nerve

Lingual nerve

Inferior alveolar nerve

Inferior alveolar nerve

Mandibular ramus Medial pterygoid

Uvula Oropharynx

Palatine tonsil

Epiglottis

Laryngopharynx

Fig. 14.4 Coronal section through the pituitary Anterior view. The nasopharynx, oropharynx, and laryngopharynx can now be identified. This section cuts the epiglottis, below which is the supraglottic space. The plane cuts the mandibular ramus on both sides, and a relatively long segment of the mandibular division (CN V3) can be identified on the left side. Above the roof of the sphenoid sinuses is the pituitary (hypophysis), which lies in the hypophyseal fossa. In the cranial cavity, the plane of section passes through the middle cranial fossa.

Due to the presence of the carotid siphon (a 180-degree bend in the cavernous part of the internal carotid artery), the section cuts the internal carotid artery twice on each side. Cranial nerves can be seen passing through the cavernous sinus on their way from the middle cranial fossa to the orbit. The superior sagittal sinus appears in cross section at the attachment of the falx cerebri. At the level of the cerebrum, the plane of section passes through the parietal and temporal lobes.

313

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal MRIs of the Head

Superior sagittal sinus

Falx cerebri with superior frontal gyrus

Ethmoid air cells Roof of orbit

Levator palpebrae superioris, superior rectus, and supraorbital nerve Superior oblique with superior ophthalmic vein Lacrimal gland Eyeball Lateral rectus Periorbital fat Inferior rectus and inferior oblique

Medial rectus with ophthalmic artery Zygomatic bone

Infraorbital artery, vein, and nerve Middle and inferior nasal conchae

Maxillary sinus

Nasal septum Maxilla (alveolar process) Tongue

Depressor anguli oris

Mandibular dentition

Genioglossus

Fig. 14.5 Coronal MRI through the eyeball Anterior view. In this plane of section, the falx cerebri completely divides the cerebral hemispheres. The extraocular muscles can be used to find the orbital neurovasculature: the supraorbital nerve runs superior to the levator palpebrae superioris and superior rectus, the superior ophthalmic vein runs medial and superior to the superior oblique, and the oph-

314

Lingual nerve, deep lingual artery and vein

thalmic artery runs inferior to the medial rectus. The infraorbital canal (containing the infraorbital artery, vein, and nerve) runs inferior to the inferior rectus and oblique. The region medial to the mandibular dentition and lateral to the genioglossus contains the sublingual gland as well as the lingual nerve, deep lingual artery and vein, hypoglossal nerve (CN XII), and submandibular duct.

Sectional Anatomy

Superior frontal gyrus

Superior sagittal sinus

14. Sectional Anatomy of the Head & Neck

Frontal bone

Falx cerebri

Ethmoid air cells Cingulate gyrus Olfactory bulb (CN I) Levator palpebrae superioris and superior rectus with supraorbital nerve

Roof of orbit

Ophthalmic artery and optic nerve (CN II)

Periorbital fat

Lateral rectus

Orbital plate and medial rectus

Temporalis

Inferior rectus above infraorbital artery, vein, and nerve Nasal septum

Zygomatic bone

Maxillary sinus Masseter

Inferior nasal concha

Hard palate Maxilla (alveolar process)

Depressor anguli oris

Tongue Body of mandible

Genioglossus

Fig. 14.6 Coronal MRI through the posterior orbit Anterior view. The inferior margin of the falx cerebri is now superior to the cingulate gyrus. In the orbit, the supraorbital nerve runs with the levator palpebrae superioris and superior rectus, and the oculomotor nerve (CN III) runs lateral to the inferior rectus, which in turn runs supe-

Submandibular gland

rior to the infraorbital canal. The ophthalmic artery can be used to find the more medially located optic nerve (CN II), both of which emerge from the optic canal. Note the asymmetrical nature of the nasal cavities. The submandibular gland is more prominent in this section between the genioglossus and the body of the mandible.

315

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal MRIs of the Neck (I): Anterior

Anterior ethmoid air cells

Levator palpebrae superioris and superior rectus Sphenoid bone, lesser wing Lateral rectus Temporalis

Optic nerve (CN II) Superior oblique, medial rectus, and inferior rectus

Zygomatic bone Middle nasal concha Masseter

Maxillary sinus

Hard palate Transverse muscle of the tongue

Hypoglossus, genioglossus, and lingual septum

Longitudinal muscle of the tongue Buccinator

Mandible

Digastric, anterior belly Mylohyoid and geniohyoid Platysma

Thyrohyoid cartilage Vestibular fold Vocalis Infraglottic cavity

Glottis

Sternohyoid

Cricoid cartilage Trachea

Fig. 14.7 Coronal MRI of the lingual muscles Anterior view. This plane of section lies just posterior to the previous one and transects the extrinsic (genioglossus and hypoglossus) and intrinsic (longitudinal and transverse) lingual muscles. The muscles of

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mastication (temporalis and masseter) are visible, as are the buccinator, mylohyoid, and geniohyoid. This section cuts the larynx and trachea, revealing the vestibular fold, vocalis muscle, and cricoid cartilage.

Sectional Anatomy

Nasopharynx

Vomer

Sphenoid sinus

14. Sectional Anatomy of the Head & Neck

Pharyngotympanic (auditory) tube, cartilaginous part

Temporalis

Zygomatic bone, temporal process

Sphenoid bone, greater wing Lateral pterygoid

Masseter

Medial pterygoid Levator veli palatini and peripharyngeal space

Soft palate Transverse muscle of the tongue

Mandible

Genioglossus Facial artery and platysma Epiglottic vallecula

Thyroid cartilage Thyroarytenoid

Piriform recess Laryngeal vestibule

Trachea Arytenoid cartilage

Sternocleidomastoid

Thyroid gland with inferior thyroid veins

Subclavian vein Clavicle

Fig. 14.8 Coronal MRI of the soft palate and muscles of mastication Anterior view. This section illustrates the convergence of the air- and foodways in the pharynx. The nasopharynx lies inferior to the sphenoid sinus and superior to the soft palate. It converges with the foodway in the oropharynx, located posterior to the uvula (not shown). The oropharynx continues inferiorly to the epiglottis (the epiglottis

vallecula lies anterior to this). The air- and foodways then diverge into the larynx and laryngopharynx, respectively. The laryngeal vestibule is the superior portion of the larynx, above the vocal folds. This section reveals the thyroid and arytenoid cartilage of the larynx. Compare this image to Fig. 14.9.

317

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal MRIs of the Neck (II)

Temporalis

Pharyngotympanic (auditory) tube

Sphenoid sinus

Pharyngeal tonsils

Tensor veli palatini

Lateral pterygoid

Maxillary artery and inferior alveolar nerve Zygomatic bone

Nasopharynx and soft palate Parotid gland

Levator veli palatini

Masseter

Medial pterygoid Facial artery

Mandibular ramus

Palatopharyngeus Palatine tonsil Submandibular gland

Oropharynx

Internal carotid artery

Epiglottic vallecula External carotid artery

Middle pharyngeal constrictor

Laryngeal vestibule

Common carotid artery

Sternocleidomastoid

Trachea

Thyroid gland

Subclavian vein

Internal jugular vein

Right brachiocephalic vein

Right lung

Right subclavian artery

Fig. 14.9 Coronal MRI of the great vessels Anterior view. This image clearly demonstrates the course of the great vessels in the neck. This image is also an excellent demonstration of the

318

Aorta

Brachiocephalic trunk

Left lung

structures of the oral cavity. Note the position of the pharyngeal tonsils on the roof of the nasopharynx and the extent of the palatine tonsils in the oropharynx.

Sectional Anatomy

Temporalis

Cavernous sinus

Sphenoid sinus

14. Sectional Anatomy of the Head & Neck

Nasopharynx

Internal carotid artery (syphon)

Pharyngotympanic (auditory) tube

Mandibular fossa of temporal bone

Zygomatic process

Articular disk Head of mandible Lateral pterygoid

Parotid gland

Maxillary artery Medial pterygoid Levator veli palatini Digastric (posterior belly)

Longus capitis Longus colli

Intervertebral disk

Comon carotid artery, internal jugular vein

Sternocleidomastoid External jugular vein

Vertebral body

Spinal nerve roots Anterior scalene Thyroid gland

Common carotid artery

Vertebral artery

Subclavian artery

Vertebral vein

Left lung

Right lung

Brachiocephalic trunk

Trachea

Fig. 14.10 Coronal MRI through the temporomandibular joint (TMJ) Anterior view. This image clearly demonstrates the structures of the TMJ, in particular the articular disk and mandibular head. The ramus of

Aorta

Common carotid artery

the mandible is seen medial to the parotid gland. This image shows the cervical vertebrae with intervertebral disks.

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Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Coronal MRIs of the Neck (III): Posterior

Temporalis

Atlas (C1), lateral mass

Dens of axis (C2)

Clivus

Temporal bone, petrous part

External acoustic meatus

Tympanic cavity

Occipital condyle

Parotid gland

Atlanto-occipital joint Atlantoaxial joint

Atlas (C1), transverse process

Internal jugular vein

Alar ligaments Stylohyoid Digastric

C4 and C5 spinal nerve roots

Sternocleidomastoid

Articular process of C6 Spinal cord

Middle scalene

Zygapophyseal joint

Posterior scalene Second rib

Right lung

Esophagus

Fig. 14.11 Coronal MRI through the cervical vertebrae and spinal nerves Anterior view. This image clearly shows the C1 through T2 vertebrae. The lateral masses of the atlas (C1) can be seen flanking the dens of the

320

Left lung

axis (C2). The more inferior vertebrae can be counted using the articular processes of the cervical vertebrae. The spinal nerve roots emerge between the articular processes (note for counting purposes: the C3 root emerges inferior to C2 and superior to the articular processes of C3).

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Foramen magnum

Temporal bone, petrous part Mastoid process

Atlas (C1), posterior arch

Digastric (posterior belly) and obliquus capitis superior Splenius capitis

Vertebral artery

Obliquus capitis inferior Longissimus capitis

Spinous process of C2 Sternocleidomastoid Deep cervical artery and vein

Levator scapulae

Splenius cervicis

Multifidus Trapezius

Brachial plexus Spinous process of C7

First rib Costal process

Right lung

Spinal cord

Fig. 14.12 Coronal MRI through the nuchal muscles Anterior view. This image clearly shows the relations of the muscles in the neck. Note: The elongated spinous process of the C7 vertebra (ver-

Left lung

tebra prominens) is still visible in this section. The spinal cord is visible both during its passage through the foramen magnum and more caudally, posterior to the T1 vertebral body.

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Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse Sections of the Head (I): Cranial

Crista galli Dorsal Vitreous body nasal artery

Periorbital fat

Nasal branch of facial artery

Ethmoid air cells

Superior oblique Levator palpebrae superioris Superior rectus

Superficial temporal vein

Infratemporal fossa Temporalis

Optic chiasm Optic tract (CN II)

Red nucleus Cerebral aqueduct

Third ventricle Cerebral peduncle Substantia nigra

Choroid plexus Vermis of cerebellum

Inferior sagittal sinus Lateral ventricle, occipital horn

Superior sagittal sinus

Fig. 14.13 Transverse section through the upper level of the orbits Superior view. The highest section in this series displays the muscles in the upper level of the orbit (the orbital levels are described on p. 116). The section cuts the bony crista galli in the anterior cranial fossa, flanked on each side by cells of the ethmoid sinus. The sections of the optic chiasm and adjacent optic tract are parts of the diencephalon, which sur-

322

rounds the third ventricle at the center of the section. The red nucleus and substantia nigra are visible in the mesencephalon. The pyramidal tract descends in the cerebral peduncles. The section passes through the posterior (occipital) horns of the lateral ventricles and barely cuts the vermis of the cerebellum in the midline.

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Nasal cavity Lens Vitreous body

Lacrimal gland

Optic nerve (CN II) Optic canal Internal carotid artery Oculomotor nerve (CN III) Cavernous sinus Pons

Cerebellar vermis

Nasal septum Ethmoid air cells Medial rectus Lateral rectus Infratemporal fossa Temporalis Pituitary (hypophysis) Dorsum sellae Basilar artery Interpeduncular fossa

Tentorium cerebelli Inferior sagittal sinus Lateral ventricle, occipital horn

Falx cerebri Superior sagittal sinus

Fig. 14.14 Transverse section through the optic nerve and pituitary Superior view. The optic nerve is seen just before its entry into the optic canal, indicating that the plane of section passes through the middle level of the orbit. Because the nerve completely fills the canal, growth disturbances of the bone at this level may cause pressure injury to the nerve. This plane cuts the ocular lenses and the cells of the ethmoid

labyrinth. The internal carotid artery can be identified in the middle cranial fossa, embedded in the cavernous sinus. The section cuts the oculomotor nerve on either side, which courses in the lateral wall of the cavernous sinus. The pons and cerebellar vermis are also seen. The falx cerebri and tentorium cerebelli appear as thin lines that come together at the straight sinus.

323

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse Sections of the Head (II)

Vomer (bony part of nasal septum) Nasal cavity

Cartilaginous nasal septum Inferior oblique

Vitreous body Inferior rectus Periorbital fat

Inferior orbital fissure Sphenoid bone, greater wing

Infratemporal fossa Temporalis Sphenoid sinus Cavernous sinus

Internal carotid artery

Trigeminal nerve (CN V)

Temporal bone, petrous part

Clivus

Pons

Basilar artery Trigeminal nerve (CN V)

Cerebellum

Tentorium cerebelli Straight sinus Falx cerebri Superior sagittal sinus

Fig. 14.15 Transverse section through the sphenoid sinus Superior view. This section cuts the infratemporal fossa on the lateral aspect of the skull and the temporalis muscle that lies within it. The plane passes through the lower level of the orbit, which is continuous posteriorly with the inferior orbital fissure. This section displays the anterior extension of the two greater wings of the sphenoid bone and

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the posterior extension of the two petrous parts of the temporal bones, which mark the boundary between the middle and posterior cranial fossae. The clivus is part of the posterior cranial fossa and lies in contact with the basilar artery. The pontine origin of the trigeminal nerve is visible. Note: The trigeminal nerve passes superior to the petrous portion of the temporal bone to enter the middle cranial fossa.

Sectional Anatomy

Nasal cavity

Buccal fat pad

Zygomatic arch Body of sphenoid bone Mandibular division (CN V3 )

14. Sectional Anatomy of the Head & Neck

Cartilaginous nasal septum

Maxillary sinus Infraorbital nerve (from CN V2) in infraorbital canal Temporalis Lateral pterygoid

Masseter Head of mandible Internal carotid artery

Superficial temporal artery and veins

Inferior petrosal sinus

Clivus Basilar artery Facial nerve (CN VII) Vestibulocochlear nerve (CN VIII)

Pontocerebellar cistern Vermis of cerebellum

Transverse sinus

Dentate nucleus

Posterior lobe of cerebellum Straight sinus

Falx cerebri Superior sagittal sinus

Fig. 14.16 Transverse section through the middle nasal concha Superior view. This section below the orbit passes through the infraorbital nerve and canal. Medial to the infraorbital nerve is the roof of the maxillary sinus. The zygomatic arch is visible in its entirety, with portions of the muscles of mastication (masseter, temporalis, and lateral pterygoid) and the upper part of the head of the mandible. The mandibular division (CN V3) appears in cross section in its bony canal, the

Occipital lobe

foramen ovale. The body of the sphenoid bone forms the bony center of the base of the skull. The facial and vestibulocochlear nerves emerge from the brainstem and enter the internal acoustic meatus. The dentate nucleus lies within the white matter of the cerebellum. The space around the anterior part of the cerebellum, the pontocerebellar cistern, is filled with cerebrospinal fluid in the living individual. The transverse sinus is prominent among the dural sinuses of the brain.

325

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse Sections of the Head (III): Caudal

Naris Cartilaginous nasal septum

Alar cartilage, medial crus Nasal cavity Nasal septum

Facial vein

Inferior nasal concha Choana

Medial pterygoid Masseter Buccal nerve Pharyngotympanic (auditory) tube CN V3

Lateral pterygoid and pterygoid venous plexus Masseteric nerve Nasopharynx

Auriculotemporal nerve and maxillary veins

Parotid gland Retromandibular vein

Internal carotid artery

External auditory canal

Auricular cartilage

Facial nerve (CN VII)

Glossopharyngeal nerve (CN IX), vagus nerve (CN X), and accessory spinal nerve (CN XI)

Internal jugular vein Sigmoid sinus Vertebral venous plexus

Accessory nerve (CN XI), spinal root Vertebral artery

Medulla oblongata Diploic veins

Falx cerebelli

Transverse sinus Semispinalis capitis

Fig. 14.17 Transverse section through the nasopharynx Superior view. This section passes through the external nose and portions of the cartilaginous nasal skeleton. The nasal cavities communicate with the nasopharynx through the choanae. Cartilaginous portions of the pharyngotympanic tube project into the nasopharynx. The internal jugular vein travels with the vagus nerve (CN X) and common carotid artery as a neurovascular bundle within the carotid sheath, a fascial covering that extends from the base of the skull to the arch of the aorta. Cranial nerves IX, XI, and XII also pierce the upper portion

326

of the carotid sheath. However, these neurovascular structures do not all enter and exit the skull base together. The jugular foramen consists of a neural and a venous portion. The neural portion conducts the glossopharyngeal (CN IX), vagus (CN X), and accessory spinal (CN XI) nerves, and the venous portion contains the jugular bulb, which receives blood from the sigmoid sinus. (Note: The internal jugular vein begins at the inferior portion of the jugular foramen.) The internal carotid artery enters the carotid canal, and the hypoglossal (CN XII) nerve enters the hypoglossal canal.

Sectional Anatomy

Soft palate (including tensor and levator veli palatini)

Maxilla

14. Sectional Anatomy of the Head & Neck

Mucoperiosteum of the hard palate

Lateral pterygoid plate

Levator anguli oris Buccinator Masseter

Lingual nerve Medial pterygoid

Inferior alveolar nerve

Lateral pterygoid

Atlas (C1)

Mandibular ramus

Glossopharyngeal nerve (CN IX)

Maxillary artery

Internal carotid artery

Internal jugular vein

Accessory spinal nerve (CN XI)

Facial nerve (CN VII) within parotid gland

Hypoglossal nerve (CN XII) Vagus nerve (CN X)

Occipital artery

Median atlantoaxial joint

Posterior condylar emissary vein Splenius capitis

Dens of axis (C2) Vertebral artery Transverse ligament of atlas

Occipital bone

Spinal Trapezius cord

Fig. 14.18 Transverse section through the median atlantoaxial joint Superior view. The section at this level passes through the connective tissue sheet that stretches over the bone of the hard palate. Portions of the upper pharyngeal muscles are sectioned close to their origin. The neurovascular structures in the carotid sheath are also well displayed. The dens of the axis articulates in the median atlantoaxial joint with the

Semispinalis capitis

facet for the dens on the posterior surface of the anterior arch of the atlas. The transverse ligament of the atlas that helps to stabilize this joint can also be identified. The vertebral artery and its accompanying veins are displayed in cross section, as is the spinal cord. In the occipital region, the section passes through the upper portion of the posterior neck muscles.

327

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse Sections of the Neck (I): Cranial

Arytenoid cartilage

Epiglottic cartilage

Laryngeal vestibule

Platysma

Omohyoid Thyrohyoid

Piriform recess

Thyroid cartilage

Superior thyroid vein Common carotid artery, internal jugular vein, and vagus nerve (CN X) in carotid sheath

Sternocleidomastoid Hypopharynx

C5 vertebra External jugular vein Longus colli

Accessory spinal nerve (CN XI), external branch

C4 spinal nerve

Vertebral artery

C5 spinal nerve

C6 vertebral body

C6 spinal nerve

Longissimus capitis

Levator scapulae

Longissimus cervicis

Trapezius

Splenius cervicis

Splenius capitis

Spinous process of C 7

Fig. 14.19 Transverse section at the level of the C5 vertebral body Inferior view. The internal jugular vein travels with the common carotid artery and vagus nerve in the carotid sheath. The accessory spinal nerve (CN XI) is medial to the sternocleidomastoid; more proximal to the skull base it will pierce the carotid sheath to enter the jugular fora-

328

Semispinalis cervicis

men with the internal jugular vein, as well as CN IX and X. The elongated spinous process of the C7 vertebra (vertebra prominens) is visible at this level, owing to the lordotic curvature of the neck. Note that the triangular shape of the arytenoid cartilage is clearly demonstrated in the laryngeal cross section.

Sectional Anatomy

Epiglottic cartilage Thyroid cartilage

14. Sectional Anatomy of the Head & Neck

Laryngeal vestibule

Piriform recess Inferior pharyngeal constrictor

Thyroid gland Common carotid artery

Superior thyroid artery and vein

Vagus nerve (CN X) Internal jugular vein

Scalenus anterior with phrenic nerve

External jugular vein C5 spinal nerve

Scalenus medius

C6 spinal nerve

Scalenus posterior

Vertebral artery

Longissimus capitis

C7 spinal nerve

Levator scapulae

C6 vertebra

Trapezius

Spinal cord

Serratus posterior superior Splenius cervicis

Vertebral arch of C7

Semispinalis cervicis

Rhomboid minor

Fig. 14.20 Transverse section through the C6 vertebral body Inferior view. The piriform recess can be identified at this level, and the vertebral artery is visible in its course along the vertebral body. The vagus nerve (CN X) lies in a posterior angle between the common carotid artery and internal jugular vein within the carotid sheath. The phrenic nerve, which arises from the ventral rami of cervical spinal nerves C3–C5, lies on the scalenus anterior muscle on the left side.

329

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse Sections of the Neck (II): Caudal

Arytenoid cartilage

Thyroid cartilage Sternohyoid

Superior thyroid vein

Thyrohyoid

Hypopharynx

Omohyoid

Common carotid artery, internal jugular vein, and vagus nerve (CN X) in carotid sheath

Thyroid gland Sternocleidomastoid

Longus colli

Scalenus anterior with C5 spinal nerve

C4 spinal nerve

Vertebral vein Scalenus medius

C6 spinal nerve and C6 vertebra

Vertebral artery Scalenus posterior

C7 spinal nerve and C7 vertebra Levator scapulae

Vertebral arch of T1

Trapezius

Fig. 14.21 Transverse section at the level of the C6 vertebral body Inferior view. This cross section passes through the base of the arytenoid cartilage in the larynx. The hypopharynx appears as a narrow transverse cleft behind the larynx.

Semispinalis cervicis

Splenius cervicis

Thyroid cartilage Rima glottidis Lamina of cricoid cartilage Hypopharynx Common carotid artery, internal jugular vein, and vagus nerve (CN X) C6 vertebra Vertebral artery and vein Scalenus medius Scalenus posterior Levator scapulae Trapezius

Fig. 14.22 Transverse section at the level of the C6/C7 vertebral junction Inferior view. This cross section passes through the larynx at the level of the vocal folds. The thyroid gland appears considerably smaller at this level than in subsequent views.

330

Sternohyoid Thyrohyoid Superior thyroid artery Sternocleidomastoid Thyroid gland External jugular vein C5 spinal nerve C6 spinal nerve C7 spinal nerve and C7 vertebra

C8 spinal nerve Vertebral arch of T1

Sectional Anatomy

Superior thyroid vein

14. Sectional Anatomy of the Head & Neck

Sternohyoid

Cricoid cartilage

Sternothyroid

Superior thyroid artery

Thyroid gland

Internal jugular vein, vagus nerve (CN X), and common carotid artery

Sternocleidomastoid

Phrenic nerve with scalenus anterior

Esophagus Thyrocervical trunk

External jugular vein

Inferior thyroid artery C6 spinal nerve

Vertebral artery and vein

C7 spinal nerve

Scalenus medius

C8 spinal nerve Scalenus posterior

Intervertebral disk

Second rib

T1 vertebra and spinal nerve

Transverse process of T2

Fig. 14.23 Transverse section at the level of the C7/T1 vertebral junction Inferior view. This cross section clearly displays the scalenus anterior and medius muscles and the interval between them, which is traversed by

Sternocleidomastoid

the C6–C8 roots of the brachial plexus. Note the neurovascular structures (common carotid artery, internal jugular vein, vagus nerve) that lie within the carotid sheath between the sternocleidomastoid, anterior scalene, and thyroid gland.

Anterior jugular vein

Arch of cricoid cartilage Trachea

Common carotid artery, internal jugular vein, and vagus nerve (CN X) Scalenus anterior Omohyoid

Thyroid gland

Esophagus Thyrocervical trunk

C6 spinal nerve

External jugular vein

C7 spinal nerve

Transverse cervical artery

C8 spinal nerve

Scalenus medius

First rib

Longus colli and vertebral artery

T1 vertebra Scalenus posterior Second rib

Pleural dome of left lung

Spinal cord

Serratus anterior

Third rib

Levator scapulae

Fig. 14.24 Transverse section at the level of the T1/T2 vertebral junction Inferior view. Due to the curvature of the neck in this specimen, the section also cuts the intervertebral disk between T1 and T2. This section includes the C6–C8 nerve roots of the brachial plexus and a small

section of the left pleural dome. The proximity of the pulmonary apex to the brachial plexus shows why the growth of an apical lung tumor may damage the brachial plexus roots. Note also the thyroid gland and its proximity to the trachea and neurovascular bundle in the carotid sheath.

331

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse MRIs of the Head Superior rectus

Ethmoid air cells

Frontal sinus

Eyeball

Lacrimal gland

Ophthalmic vein

Temporalis

Sphenoidal bone

Optic nerve (CN II)

Temporoparietalis

Sphenoid sinus and pituitary (hypophysis)

Internal carotid artery Dorsum sellae

Middle cerebral artery Lateral ventricle, temporal horn

Basilar artery

Pons Fourth ventricle Vermis of cerebellum

Temporal bone

Confluence of the sinuses Occipital bone with internal occipital protuberance

A Ethmoid air cells

Nasal bone

Anterior chamber of eyeball

Lens Zygomatic bone

Eyeball Medial, superior, and lateral rectus muscles

Optic nerve (CN II) in periorbital fat

Temporalis Temporal lobe

Temporoparietalis

CN V2 and CN V3 anterior to internal carotid artery

Sphenoid sinus Clivus

Basilar artery and pons

Cochlea with posterior semicircular canal

Mastoid air cells Sigmoid sinus

Internal acoustic meatus with facial (CN VII) and vestibulocochlear (CN VIII) nerves

Uvula of vermis

Fourth ventricle Vermis of cerebellum

B

Internal occipital protuberance

Fig. 14.25 Transverse MRIs through the orbit and ethmoid air cells Inferior view. A Superior orbit. This section demonstrates the relationship of the frontal and sphenoid sinuses to the orbit and nasal cavity. B Section through optic nerve (CN II). The divisions of the eye can be clearly seen along with the extraocular muscles located in the peri-

332

orbital fat. The sigmoid sinus is located posterior to the mastoid air cells and lateral to the cerebellum. This section clearly displays the internal acoustic meatus, which conducts the facial (CN VII) and vestibulocochlear (CN VIII) nerves.

Sectional Anatomy

Orbicularis oris

Middle nasal concha

14. Sectional Anatomy of the Head & Neck

Nasal septum

Nasal bone

Maxilla with infraorbital canal

Levator labii superioris

Nasolacrimal duct Maxillary sinus Temporalis Medial pterygoid between medial and lateral pterygoid plates

Masseter Lateral pterygoid

Pharyngeal recess

Head of mandible

Levator and tensor veli palatini

Mandibular (CN V3) and auriculotemporal nerves

Internal carotid artery

Internal jugular vein with CN IX, X, and XI

Longus capitis Mastoid air cells

Vertebral artery

Sigmoid sinus

Medulla oblongata Posterior lobe of cerebellum

Semispinalis capitis

Falx cerebri around superior sagittal sinus

Fig. 14.26 Transverse MRI through the orbit and nasolacrimal duct Inferior view. This section clearly demonstrates the relationships of the infraorbital canal and nasolacrimal duct to the maxillary sinus. The medial and lateral pterygoid plates can be seen flanking the medial pterygoid. The pharyngeal recess is visible, anterior to the longus

Occipital bone

Fourth ventricle

capitis. The mandibular division of the trigeminal nerve (CN V3) is lateral to the levator and tensor veli palatini and medial to the lateral pterygoid. Cranial nerves IX, X, and XI run just anteromedial to the internal jugular vein.

333

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse MRIs of the Oral Cavity Maxillary sinus

Nasal concha

Orbicularis oris

Zygomatic bone

Sphenoid bone

Sphenoid sinus

Temporalis Masseter

Articular disk

Trigeminal nerve (CN V) Head of mandible

Foramen lacerum

External acoustic meatus

Vertebral artery

Internal carotid artery

Internal jugular vein Mastoid air cells

Medulla oblongata Fourth ventricle Falx cerebri Cerebellum, posterior lobe Occipital bone

Fig. 14.27 Transverse MRI through the TMJ Inferior view. Note: The plane of this section is slightly higher than Fig. 14.26. It has been included here in order to show the articular disk of the TMJ and the full extent of the mandible.

Maxilla (alveolar process)

Orbicularis oris Levator anguli oris

Hard palate

Facial artery

Buccinator

Lateral and medial pterygoids

Temporalis Masseter Tensor and levator veli palatini

Mandibular ramus Internal carotid artery

Parotid gland

Internal jugular vein

Retromandibular vein Medulla oblongata and interpeduncular cistern

Mastoid air cells

Vertebral artery Condylar canal

Splenius capitis Tonsil of cerebellum

Semispinalis capitis

Fig. 14.28 Transverse MRI through the hard and soft palates Inferior view. This section demonstrates the relation of the mandibular ramus to the muscles of mastication in the infratemporal fossa.

334

Cisterna magna

Occipital bone

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Orbicularis oris

Genioglossus

Depressor anguli oris

Uvula and oropharynx

Mandible

Longus colli and capitis

Facial artery External carotid artery

Hypoglossus Masseter Medial pterygoid Palatine tonsils and pharyngeal muscles Internal jugular vein and common carotid artery

Retromandibular vein in parotid gland

Digastric, posterior belly

Sternocleidomastoid

Levator scapulae Body of axis (C2) Splenius capitis

Longissimus cervicis

Vertebral artery A

Semispinalis capitis

Spinal cord

Obliquus capitis inferior

Trapezius

Mandible Mentalis

Genioglossus

Depressor anguli oris Oropharynx Mylohyoid Hyoglossus

Hypopharynx

Retromandibular vein

Submandibular gland Stylohyoid and posterior digastric

External carotid artery

Epiglottis Palatopharyngeus and middle pharyngeal constrictor

External jugular vein

Internal carotid artery Vertebral artery

External jugular vein C3 vertebra (body and posterior arch)

Levator scapulae

Sternocleidomastoid Deep cervical veins Splenius capitis

B

Semispinalis capitis

Nuchal ligament

Fig. 14.29 Transverse MRIs through the mandible Inferior view. A Section through mandibular arch. This section demonstrates the relationship of the oropharynx to the soft palate (uvula) and

Spinalis cervicis

Trapezius

prevertebral muscles (longus colli and capitis). The vessels of the carotid sheath are clearly visible, along with the retromandibular vein in the parotid gland. B Section through body of mandible and hypophyarynx.

335

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Transverse MRIs of the Neck

Thyrohyoid and sternohyoid Epiglottic cartilage Laryngeal vestibule

Aryepiglottic fold Submandibular gland

Platysma

Common carotid artery

Inferior pharyngeal constrictor

Internal jugular vein Longus colli and capitis Sternocleidomastoid

External jugular vein

Vertebral artery

Longissimus capitis

Middle scalene

Spinalis cervicis

Levator scapulae

Splenius cervicis

Splenius capitis

Trapezius

Semispinalis cervicis

Semispinalis capitis

Fig. 14.30 Transverse MRI through the C4 vertebral body Inferior view. This section demonstrates the aryepiglottic fold in the laryngeal vestibule. Note the proximity of the prevertebral muscles to the pharyngeal constrictors.

Thyroid cartilage

Sternohyoid and thyrohyoid

Anterior jugular veins Platysma

Sternothyroid

Larynx

Thyroid gland

Internal jugular vein Common carotid artery

Cricoid cartilage

Scalenes

Sternocleidomastoid with external jugular vein Esophagus

Levator scapulae

Vertebral artery and vein

Spinalis cervicis Semispinalis cervicis

C7 spinal nerve root

Splenius capitis C6 vertebral body, C7 posterior arch

C7 spinous process

Fig. 14.31 Transverse MRI through the C6 vertebral body Inferior view. This section demonstrates the cricoid and thyroid cartilage of the larynx (note the change in shape of the larynx). Due to lordosis of the cervical spine, this section includes the C6 vertebral body and the C7 spinous process with posterior arch.

336

Multifidus

Trapezius

Sectional Anatomy

Sternohyoid and sternothyroid

Trachea

14. Sectional Anatomy of the Head & Neck

Anterior jugular vein

Thyroid gland with inferior thyroid artery

Esophagus Common carotid artery

Sternocleidomastoid Longus colli with vertebral artery

Internal jugular vein

Anterior scalene

External jugular vein

Middle and posterior scalene Spinal cord with C8 spinal nerve root

First rib Transverse process of T1 Serratus posterior superior Levator scapulae

Semispinalis capitis

Semispinalis cervicis

Fig. 14.32 Transverse MRI through the C7 vertebra Inferior view. This section demonstrates the relationship of the trachea to the esophagus. Note the position of the carotid sheath (containing the common carotid artery, internal jugular vein, and vagus nerve)

Rhomboid minor

Splenius capitis

Trapezius

with respect to the thyroid gland. The C8 spinal nerve root can be seen emerging from the spinal cord. Note the first rib and transverse process of the thoracic vertebra.

337

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Sagittal Sections of the Head (I): Medial

Frontal sinus

Corpus callosum

Anterior cranial fossa Olfactory bulb (CN I) Pituitary Sphenoid sinus

Clivus Transverse sinus

Choana

Foramen magnum

Nasal septum

Atlas (C1), anterior and posterior arches

Hard palate

Nuchal ligament

Soft palate

Transverse ligament of atlas

Nasopharynx Uvula

Median atlantoaxial joint

Mandible

Dens of axis (C2) C3 vertebra

Oropharynx Geniohyoid Mylohyoid Epiglottic vallecula Hyoid bone

Laryngeal cartilage

Fig. 14.33 Midsagittal section through the nasal septum Left lateral view. The anatomical structures at this level can be roughly assigned to the facial skeleton or neurocranium (cranial vault). The lowest level of the facial skeleton is formed by the oral floor muscles between the hyoid bone and mandible and the overlying skin. This section also passes through the epiglottis and the larynx below it, which are considered part of the cervical viscera. Note: The epiglottic vallecula, located in the oropharynx, is bounded by the root of the tongue and the epiglottis. The hard and soft palate with the uvula define the

338

Epiglottis

Laryngopharynx

boundary between the oral and nasal cavities. Posterior to the uvula is the oropharynx. The section includes the nasal septum, which divides the nasal cavity into two cavities (sectioned above and in front of the septum) that communicate with the nasopharynx through the choanae. Posterior to the frontal sinus is the anterior cranial fossa, which is part of the neurocranium. This section passes through the medial surface of the brain (the falx cerebri has been removed). The cut edge of the corpus callosum, the olfactory bulb, and the pituitary are also shown.

Sectional Anatomy

Caudate nucleus, head

Internal capsule

14. Sectional Anatomy of the Head & Neck

Medial segment of globus pallidus

Uncus

Lateral ventricle Posterior thalamic nuclei

Oculomotor nerve (CN III) Optic nerve (CN II)

Pontocerebellar cistern

Frontal sinus

Tentorium cerebelli

Ethmoid air cells

Cerebellum Pharyngotympanic (auditory) tube

Sphenoid sinus Middle nasal concha

Vertebral artery

Inferior nasal concha

Rectus capitis posterior minor

Palatine process, palatine sulcus

Semispinalis capitis

Maxilla

Rectus capitis posterior major

Superior labial vestibule Oral cavity

C2 spinal nerve

Palatopharyngeus

Obliquus capitis inferior

Inferior labial vestibule

Longus capitis

Tongue

Splenius capitis

Mandible Lingual nerve and deep lingual veins

C3 spinal nerve Spinalis cervicis

Anterior digastric

C4 spinal nerve

Mylohyoid Hyoid bone Epiglottic cartilage and vallecula

Laryngopharynx

Thyroid cartilage

Fig. 14.34 Sagittal section through the medial orbital wall Left lateral view. This section passes through the inferior and middle nasal conchae within the nasal cavity. Above the middle nasal concha are the ethmoid air cells. The only parts of the nasopharynx visible in this section are a small luminal area and the lateral wall, which bears

Vertebral artery

C5 spinal nerve

C6 spinal nerve

C7 spinal nerve

a section of the cartilaginous portion of the pharyngotympanic tube. The sphenoid sinus is also displayed. In the region of the cervical spine, the section cuts the vertebral artery at multiple levels. The lateral sites where the spinal nerves emerge from the intervertebral foramina are clearly displayed. Note: This section is lateral to the geniohyoid.

339

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Sagittal Sections of the Head (II): Lateral

Extreme capsule

External capsule

Claustrum

Putamen

Internal capsule Dentate gyrus

Amygdala Trigeminal ganglion (CN V) Internal carotid artery

Lateral rectus Superior rectus

Pharyngotympanic (auditory) tube

Frontal sinus

Posterior meningeal artery

CN II Procerus

CN IX, X, and XI

Inferior rectus Vitreous body CN V2 in pterygopalatine fossa

CN XII Transverse sinus

Sphenoid sinus

Condylar emissary vein

Lateral pterygoid Levator veli palatini

Rectus capitis posterior major

Medial pterygoid

Semispinalis capitis Internal carotid artery

Maxillary sinus

Obliquus capitis inferior

Palatine tonsil Orbicularis oris

Greater occipital nerve (C2)

Palatopharyngeus

Vertebral artery C3 spinal nerve

Tongue

Trapezius

Genioglossus

Splenius capitis

Mylohyoid

Retropharyngeal space

Anterior digastric Hyoid bone, lesser cornu

Submandibular gland

Hyoid bone, greater cornu

Thyroid cartilage, left lamina

Fig. 14.35 Sagittal section through the inner third of the orbit Left lateral view. This section passes through the maxillary and frontal sinuses while displaying one ethmoid air cell and the peripheral part of the sphenoid sinus. It passes through the medial portion of the internal carotid artery and submandibular gland. The pharyngeal and masticatory muscles are grouped about the cartilaginous part of the pharyn-

340

Inferior pharyngeal constrictor

gotympanic tube. The eyeball and optic nerve are cut peripherally by the section, which displays relatively long segments of the superior and inferior rectus muscles. Sectioned brain structures include the external and internal capsules and the intervening putamen. The amygdala can be identified near the base of the brain. A section of the trigeminal ganglion appears below the cerebrum.

Sectional Anatomy

Internal carotid artery

Temporal bone, petrous part

14. Sectional Anatomy of the Head & Neck

Foot of hippocampus

Internal auditory canal Choroid plexus

Lateral rectus

Facial nerve (CN VII)

Periorbital fat Levator palpebrae superioris Occipitofrontalis, frontal belly

Vestibulocochlear nerve (CN VIII)

Superior rectus Vitreous body Lens Inferior oblique Orbicularis oculi, orbital and palpebral parts Lateral pterygoid, superior and inferior parts

Transverse sinus

Temporalis

Cerebellum

Levator labii superioris

Semispinalis capitis

Maxillary sinus

Stylopharyngeus Obliquus capitis inferior Splenius cervicis

Medial pterygoid

Splenius capitis

Buccinator

Stylohyoid

Oral vestibule

Internal jugular vein Levator scapulae

Orbicularis oris Inferior alveolar nerve, artery, and vein in mandibular canal

Lymph node Body of mandible

Mylohyoid

Platysma

Submandibular gland

Fig. 14.36 Sagittal section through the approximate center of the orbit Left lateral view. Due to the obliquity of this section, the dominant structure in the oral floor region is the mandible, whereas the oral vestibule appears as a narrow slit. The buccal and masticatory muscles are prominently displayed. Much of the orbit is occupied by the eyeball,

Common carotid artery

which appears in longitudinal section. Aside from a few sections of the extraocular muscles, the orbit in this plane is filled with periorbital fat. Both the internal carotid artery and the internal jugular vein are demonstrated. Except for the foot of the hippocampus, the only visible cerebral structures are the white matter and cortex. The facial nerve and vestibulocochlear nerve can be identified in the internal auditory canal.

341

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Sagittal MRIs of the Head Pituitary (hypophysis)

Optic nerve (CN II)

Septum pellucidum

Superior sagittal sinus

Ethmoid air cells and sphenoid sinus

Corpus callosum

Straight sinus Fourth ventricle Confluence of the sinuses

Frontal sinus Nasal bone

Basilar artery

Nasopharynx

Rectus capitis posterior minor Nuchal ligament

Hard palate

Dens of axis (C2) and anterior arch of atlas (C1)

Tongue

C2/C3 intervertebral disk

A

Body of mandible

Internal carotid artery, syphon

Uvula

Oropharynx

Semispinalis capitis

Caudate nucleus, head

Thalamus Corpus callosum Superior sagittal sinus Tentorium cerebelli Frontal sinus Confluence of the sinuses Clivus

Ethmoid air cells and sphenoid sinus

Vertebral artery

Nasopharynx Atlas (C1), posterior arch

Inferior nasal concha Hard palate

Semispinalis capitis

B

Sublingual gland

Uvula

Fig. 14.37 Sagittal sections through the nasal cavity Left lateral view. A Midsagittal section through nasal septum. B Sagittal section through inferior and middle nasal conchae. These sections demonstrate the relationship of the nasopharynx to the oropharynx.

342

Oropharynx

Longus capitis

The optic nerve (CN II) is visible as the optic chiasm in A. The pituitary (hypophysis) can be seen inferior to it, just posterior to the sphenoid sinus. The syphon of the internal carotid artery is beautifully displayed in B.

Sectional Anatomy

Basal ganglia

Thalamus

14. Sectional Anatomy of the Head & Neck

Precentral gyrus

Roof of orbit Lateral ventricle

Corpus callosum Superior rectus

Lambdoid suture

Optic nerve (CN II)

Tentorium cerebelli Maxillary sinus

Transverse sinus Anterior and posterior lobes of the cerebellum

Medial pterygoid and levator veli palatini

Splenius capitis Levator labii superioris

Rectus capitis posterior major

Maxilla

Semispinalis capitis

Orbicularis oris

Obliquus capitis inferior Longus capitis

Mandible

Internal carotid artery

Mylohyoid

Digastric

Hyoglossus

Middle pharyngeal constrictor

Fig. 14.38 Sagittal section through the orbit Left lateral view. This view exposes the superior and inferior rectus muscles within the periorbital fat. The course of the optic nerve (CN II) within the orbit can be seen. Note the proximity of the maxillary dentition to the maxillary sinus. Roots of the maxillary dentition may erupt into the maxillary sinus. The major forceps of the corpus callosum can be seen just posterior to the lateral ventricle.

343

Sectional Anatomy

14. Sectional Anatomy of the Head & Neck

Sagittal MRIs of the Neck Middle nasal concha

Frontal sinus

Ethmoid air cells

Sphenoid sinus

Palatine tonsil

Superior pharyngeal constrictor

Longus colli

Dens of axis (C2) Nasopharynx Atlas (C1), posterior arch Orbicularis oris Suboccipital fat Hard and soft palates Oropharynx Longitudinal muscle of the tongue

Ligamentum flavum

Genioglossus and lingual septum

Nuchal ligament Interspinalis muscles

Mandible

C5 vertebral body

Transverse muscle of the tongue

C7 spinous process

Geniohyoid and mylohyoid Hyoid bone

Esophagus and anterior longitudinal ligament

Epiglottis Vestibular and vocal ligaments of the larynx

Lamina of cricoid cartilage

Thyroid gland

Brachiocephalic artery

Fig. 14.39 Midsagittal section Left lateral view. This section illustrates the relations between the nasal cavity and ethmoid air cells. The nasal cavity communicates posteriorly (via the choanae) with the nasopharynx, which is separated from the oral cavity by the soft palate and uvula. Inferior to the uvula, the nasopharynx and oral cavity converge in the oropharynx. Air continues

344

Trachea

T2 vertebral body

more anteriorly into the laryngopharynx and ultimately the trachea, whereas food passes into the esophagus, posterior to the lamina of the larynx. Note how closely opposed the esophagus is to the anterior surface of the vertebral bodies. This section also reveals the cervical vertebrae and ligaments.

Sectional Anatomy

Superior rectus

Inferior rectus

Lateral pterygoid

Medial pterygoid

14. Sectional Anatomy of the Head & Neck

Internal carotid artery

Internal jugular vein

Atlas (C1), transverse process

Rectus capitis posterior minor Optic nerve (CN II)

Rectus capitis posterior major

Maxillary sinus Obliquus capitis Buccinator

Semispinalis capitis

Stylohyoid

Levator scapulae

Digastric

External carotid artery

Mandible

Semispinalis cervicis

Facial vein Splenius capitis

Submandibular gland External jugular vein

Scalenus posterior

Common carotid artery Internal jugular vein

Brachial plexus

Sternocleidomastoid

Trapezius

Scalenus medius Rhomboids major and minor

Clavicle

Left subclavian vein

Left subclavian artery

Left lung

Interspinalis muscle

Multifidus

Fig. 14.40 Sagittal section through carotid bifurcation Left lateral view. This section shows the common and external carotid arteries, as well as the internal and external jugular veins. The craniovertebral joint muscles are visible along with the nuchal muscles. Note the position of the brachial plexus between the medial and posterior scalenes. The extent of the submandibular gland can be appreciated in this view.

345

Appendix References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349

References

Becker W, Naumann HH, Pfaltz CR. Otorhinolaryngology [in German]. 2nd ed. Stuttgart: Thieme; 1983

Schmidt F. Innervation of the Temporomandibular Joint [in German]. Gegenbaurs morphol. Jb. 1067:110;554-573

Faller A, Poisel S, Golth D, Faller A, Schuenke M. The Human Body [in German]. 14th ed. Stuttgart: Thieme; 2004

Tillmann B. Color Atlas of Anatomy Dental Medicine — Human Medicine [in German]. Stuttgart: Thieme; 1997

Kahle W, Frotscher M. Pocket Atlas of Anatomy [in German]. Vol. 3. 9th ed. Stuttgart: Thieme; 2005

Vahlensieck M, Reiser M. MRI of the Musculoskeletal System [in German]. 2nd ed. Stuttgart: Thieme; 2001

Lippert H, Pabst R. Arterial Variations in Man. Munich: Bergmann; 1985

Vahlensieck M, Reiser M, eds. MRI of the Musculoskeletal System [in German]. 2nd rev. ed. Berlin: Springer; 1959

Platzer W. Pocket Atlas of Anatomy [in German]. Vol. 1. Stuttgart: Thieme; 1999

von Lanz T, Wachsmuth W. Applied Anatomy [in German]. Vol. 2, Part 6 (Loeweneck H, Feifel G, eds.), Berlin: Springer; 1993

Platzer W. Topographic Anatomy Atlas [in German]. Stuttgart: Thieme; 1982

von Lanz T, Wachsmuth W. Applied Anatomy [in German]. Vol. 1, 2: Hals, Berlin: Springer; 1955

Rauber A, Kopsch F. Human Anatomy [in German]. Vol. 1–4. Stuttgart: Thieme; Vol. 1, 2: 1997; Vol. 2, 3: 1987; Vol. 4: 1988

348

Index

Note: Tabular material is indicated by a “t” following the page number.

A Abdomen muscles (internal/external obliques) of, 242 vagus nerve branches to, 91t Abducent nerve (CN VI), 66t, 72, 72t, 114t emergence from brainstem, 114 eye movement and, 140 function of, 67t Abducent nerve palsy, 72t, 113, 114t Abducting nystagmus, 141 Accessory lacrimal glands, 122 Accessory meningeal artery, 45t, 47t Accessory parotid gland, 218 Accessory spinal nerve (CN XI), 66t, 92 anterior cervical triangle and, 281 course of, 92t in deep lateral cervical region, 283 function of, 67t in lateral neck, 278 nerve lesions of, 92, 92t in nuchal region, 276 nuclei, ganglia, and fiber distribution of, 92t spinal contribution to, 291 on transverse MRI of head, 333 in transverse section of head through C5 level, 328 through nasopharynx, 326 Accessory visual system, 137 Accommodation, pathways for, 138 Acoustic neuroma, 87, 165, 168 Acromion, inferior boundary of neck and, 273 Action potential, 306 Adam’s apple. See Thyroid cartilage Afferent impulses, in gustatory pathway, 222 Afferent (motor) fibers, 54, 66t, 291 brainstem reflexes and, 137 facial nerve and, 82t Afferent nuclei, 68t, 69 Afferent tracts. See Sensory (afferent) pathways Age-related changes in cranial sutures and fontanelles, 3, 3t in mandible, 23, 192 in spinal cord segment levels, 299 Ageusia, 222 Air pressure equalization, 161 Airways, on coronal MRI of neck, 317 Alae, 142 Alar cartilage, 142 Alar ligaments, 236, 237 Alveolar arteries, 44, 45t Alveolar bone, 182, 182t Alveolar processes of teeth, 23

Alzheimer disease, neurofibrils in, 306 Amacrine cells, 133 Amaurosis, 136, 139 American Academy of Otolaryngology, deep cervical lymph node groups and, 268 Ampulla, 174 Ampullary crest, 174 Amygdala, in sagittal section of head, 340 Anastomosis arterial, in face, 97 in arterial supply to auricle, 157 Anesthesia, epidural and lumbar, 299 Angular vein, infection transmission and, 52t Anosmia, 222 Ansa cervicalis, 270, 282 Anterior auricular arteries, 157 Anterior cerebral artery, 305 Anterior cervical triangle, 272, 272t dissection of, 280–281 Anterior communicating artery, 305 Anterior cranial fossa, 310 Anterior ethmoid nerve, 76, 77t Anterior jugular vein, 50–51, 51t Anterior olfactory stria, 152 Anterior rhinoscopy, 151 Anterior tympanic artery, 44, 45t, 47t, 166, 166t Apical ligaments of the dens, 237 Aqueous humor, drainage of, 131 obstructed, glaucoma and, 131 Arachnoid, 296 Arcuate eminence, 155 Argyll Robertson pupil, 138 Arterial grooves, in calvaria, 10 Arterial supply to brain, 304 stenoses and occlusions of, 305 to thyroid gland, 265 Artery(ies). See also individually named arteries of auricle, 157 in circle of Willis, 305 of ear, 166–167, 166t of infratemporal fossa, 102–103, 102t laryngeal, 261 ligation sites for nosebleed, 151 of neck, 266, 266t of pterygoid canal, 45t, 46, 47t of right lateral nasal wall, 148, 149 superficial, of head, 99 of tongue, 220 Articular disk in temporomandibular joint, 37 on coronal MRI of neck, 319 on transverse MRI of neck, 334

349

A

Aryepiglottic fold

Aryepiglottic fold, on transverse MRI of neck, 336 Arytenoid cartilages, 256, 257 on coronal MRI of neck, 317 in transverse section of head, 328 Arytenoid muscles, 258, 258t Ascending pharyngeal artery, 41t, 43, 43t variants of, 284 Atherosclerosis, arterial supply to brain and, 305 Atlantoaxial joints, 233 median, transverse section of head through, 327 short nuchal muscles and, 250 Atlanto-occipital joints, 233 capsule of, 237 short nuchal muscles and, 250 Atlanto-occipital membrane, 237 Atlas (C1), 230 on coronal MRI of neck, 321 craniovertebral joints and, 232, 233 transverse ligament of, in transverse section of head, 327 Auditory apparatus, of ear, 156, 164, 170–171 key stations of, 172 Auditory ossicles, 156, 160, 162 Auditory pathway, 172–173 afferent, 172 efferent, 173 tonotopic organization of, 172 Auditory tube. See Pharyngotympanic (auditory) tube Auricle arterial supply of, 157 cartilage of, 157 muscles of, 157 sensory innervation of, 158 Auricular arteries, 157 Auricularis muscles, 25, 26, 27t Auriculotemporal nerve, 80, 81t, 160 TMJ capsule and, 37 Autonomic (visceral) nervous system, 54 motor pathways, 58, 62–63 parasympathetic, 63t sympathetic, 62t Axis (C2), 230 craniovertebral joints and, 232, 233 dens of on coronal MRI of neck, 321 in transverse section of head, 327 Axon bundles, in CNS and PNS, 306 Axon hillock, potential at, 306 Axons, 55, 306 in convergence and accommodation, 138 in gustatory pathway, 222 in olfactory tract, 152 in spinal cord, 292 in visual pathway geniculate part, 134 nongeniculate part, 137

B Baby teeth. See Deciduous teeth Back muscles. See also individually named muscles extrinsic, 240, 242 intrinsic, 240, 242–243, 248–249, 248t erector spinae and interspinales, 246–247, 246t

350

origins and insertions of, 38, 39 short nuchal, 250–251, 250t “Ballistic” eye movements, 140 Basilar artery, 305 in transverse section of head, 324 Basilar membrane, 170 Basilar plexus, dural sinus drainage and, 302 Bicuspids. See Premolars Bimanual examination, of salivary glands, 219 Binaural processing, 172 Bipolar cells, 133 Bipolar neuron(s), 55, 307 in afferent auditory pathway, 172 Bitemporal hemianopia, 136 Blind spot, 125, 127 lamina cribrosa and, 133 Blindness, 136, 139 Blink reflex/Blinking, 121 Blood supply/vessels. See Arterial supply; Artery(ies); individually named arteries and veins; Veins; Venous drainage Bone(s). See also individually named bones alveolar, 182, 182t in hard palate, 190–191 nasal, 5, 7, 11, 108, 142 of nasal cavity, 142 of nose, 142 of orbit, 108–109 of skull, 2, 5t anterior view, 2t, 6–7 lateral view, 4–5 posterior view, 8–9 of skull base, 12–13 Bony labyrinth, 164 Bony prominences, in neck, 273 Botulinum toxin injection, 24 Bouton en passage, 307 Brachial plexus, 279 anterior cervical triangle and, 281 in deep anterolateral neck, 282 deep lateral cervical region and, 283 on sagittal MRI of neck, 345 Brachiocephalic vein, 50, 267, 267t Brain arterial supply to, 304–305 developmental organization of, 295, 295t gross anatomy of, 294 meninges in situ and, 296 neuroanatomy of, 294–295 structures of, 297 Brainstem cranial nerve nuclei and, 63t, 168, 168t, 169 emergence of cranial nerves from, 114 oculomotor nuclei connections in, 140 structures of anterior projection, 297 lateral projection, 297 Brainstem reflexes, 137 Branchial muscle, 60t, 61 derivatives of, 61 embryonic development of, 60, 61t of head, 61t second arch, innervation of, 82, 84 Branchiomotor nuclei, cranial nerves, 68t, 69

Chorda tympanii

accessory spinal nerve, 92t facial nerve, 82t glossopharyngeal nerve, 88t trigeminal nerve, 75, 75t vagus nerve, 90t Bridging veins, in subarachnoid space, 296 Brodmann area, 134 Bruch membrane, 133 Buccal artery, 44, 45t, 47t Buccal fat pad, 312 Buccal muscles, in sagittal section of head, 341 Buccal nerve, 80, 81t Buccal tooth surface, 180 Buccinator muscle, 24, 28, 29, 29t Buccopharyngeal fascia, 274 retropharyngeal space and, 286 Buccopharyngeus muscle, 213t, 214

C Calvaria external and internal surfaces of, 10–11 layers of, 11 muscles of, 25, 26–27, 27t innervation, 27t scalp and, 11 sensitivity to trauma, 11 Canal of Schlemm, 124 Canines, 179, 184, 184t eruption patterns of, 188, 188t Cardinal directions of gaze, 113 Caroticotympanic arteries, 166, 166t Carotid arteries, variants of, 283. See also Common carotid artery; External carotid artery; Internal carotid artery Carotid bifurcation, 40 sagittal MRI of neck through, 345 Carotid canal foramen lacerum relationship to, 12 neurovascular pathways through, 94, 95t temporal bone and, 19 Carotid sheath fascia, 274, 274t Carotid triangle, in neck, 272, 272t deep anterolateral neck, 282 Cartilage of auricle, 157 of larynx, 256–257, 258t of nasal septum, 143 of nose, 142 Cartilaginous neurocranium, 2, 2t Cauda equina, 292 in vertebral canal, 298–299 Cavernous part/division, internal carotid artery, 48, 304 Cavernous sinus infection transmission and, 52t pterygoid plexus and, 53 Cementum, of tooth, 182, 182t, 183 Central lesion, vagus nerve, 263, 263t Central nervous system (CNS), 54, 290 information flow to and from, 291 location and direction in, terminology for, 291 neurons in, 55 synapses in, 307 Central paralysis, face, 84

C

Central scotoma, homonymous hemianopic, 136 Ceratopharyngeus muscle, 213t, 214 Cerebellar vermis, 323 Cerebellopontine angle, acoustic neuroma in, 87, 165, 168 Cerebral arteries, 305 Cerebral part/division, internal carotid artery, 48, 304 Cerebral veins, 302 Cerebrospinal fluid (CSF), 300–301 circulation of, 301 meninges and, 296 Cerumen glands, 159 Cervical fascia, 274, 274t deep, 241 relationships in neck, 275 Cervical lymph nodes, in neck anterior, 268 deep, 268 lymphatic drainage from ear into, 158 relationship to systemic lymphatic circulation, 269 superficial, 268 systematic palpation of, 269 Cervical part/division, internal carotid artery, 48, 304 Cervical plexus, 270 auricle and, 158 motor nerves of, 271 sensory nerves of, 99, 271 Cervical regions (triangles), 272–273, 272t anterior, 272, 272t lateral, 272, 272t deep, 283 posterior cervical, 272, 272t lymph nodes in, 268 sternocleidomastoid, 272, 272t Cervical spine (C1-C7) joints of, 232–233 ligaments of, 234–235, 236 nerves of, 270 dorsal rami, 270, 270t motor nerves, 271 sensory nerves, 99, 271 ventral rami, 270 neurovasculature of, 233 in vertebral column, 226, 230 Cervical vertebrae (C1-C7), 230–231. See also Atlas (C1); Axis (C2) on MRIs of neck coronal view, 319, 320 sagittal view, 343 transverse view, 336 structural elements of, 227, 227t transverse sections of head through C5 level, 328 C6 level, 330 Chambers, of eye, 130 Choana(e), 147 in head sections midsagittal, 338 transverse, 326 of nose, 143 Chondrocranium, bone development in, 2 Chondropharyngeus muscle, 213t, 214 Chorda tympani nerve supply to, 83, 85, 161 temporal bone and, 18, 19

351

C

Choroid

Choroid, 124 Choroid plexus, 301 histology of, 301 Ciliary beating, paranasal sinus drainage and, 150 Ciliary body, lens and, 128 Ciliary ganglion, sensory root of, 76, 77 Circle of Willis, 304, 305 variants of, 305 Circle of Zinn (and von Haller), 127 Circumvallate papillae, 206, 207t Cisterns, subarachnoid, 301 Clavicle, inferior boundary of neck and, 273 Clivus, in transverse section of head, 324 Closed-angle glaucoma, 131 CN. See Cranial nerve(s); individually named cranial nerves CNS. See Central nervous system (CNS) Cochlea, 164 location and structure of, 170 spiral ganglia in, 165 traveling wave formation in, 171 Cochlear amplifier, 173 Cochlear duct, 170 Cochlear ganglion. See Spiral ganglia Cochlear nuclei, 86t, 87, 168 Coding, of teeth, 180 Common carotid artery in deep lateral cervical region, 283 on MRIs of neck sagittal view, 345 transverse view, 335, 337 in thoracic inlet, 281 in transverse section of neck, 331 Common facial vein, 50 Communicating arteries, 305 Concha(e), 147 nasal. See Nasal concha(e) paranasal sinuses and, 145 Condylar canal, occipital bone and, 20 Cones, 133 Confrontation test, in visual field examination, 135 Conjugate eye movements, 140 Conjunctiva goblet cell distribution in, 123 structure of, 121 Conjunctival sac, 121 Connective tissue in gingiva, 183 of nose, 142 Constriction, pupil, 130t Contralateral homonymous hemianopia, 136 Contralateral quadrantanopia, upper and lower, 136 Contralateral visual cortex, visual fields in, 134 Conus medullaris, in adult vs. newborn, 299 Convergence internuclear ophthalmoplegia and, 141 pathways for, 138 Cornea, 124 position of, 128 structure of, 129 Corneal reflex, 137 Corniculate cartilage, 256, 257 Corpus callosum

352

in midsagittal section of head, 338 on sagittal MRI of head, 343 Corrugator supercilii muscle, 24, 26, 27, 27t Cortex motor, 58t, 63t primary auditory, 172 in sagittal section of head, 341 somatomotor, 84 visual. See Visual cortex Cranial bones development of, 2–3, 2t ossification of, 2, 2t Cranial fossa(e), 14 anterior, 310 in head sections midsagittal, 338 transverse, 324 Cranial nerve(s), 54, 291. See also individually named nerves in anterior coronal cross section of head, 313 convergence and accommodation and, 138 emergence from brainstem, 114 entry into orbit, 118 fiber types, 66t functions of, 67t in internal acoustic meatus, 165 motor pathways in, 58t, 59 overview of, 66, 66t parasympathetic ganglia and, 63 sensory pathways in, 56t, 57 in skeletal muscle innervation, 61t Cranial nerve lesions accessory spinal nerve, 92, 92t glossopharyngeal nerve, 88t hypoglossal nerve, 93, 93t vagus nerve, 90t Cranial nerve nuclei, 68t in brainstem, 63t, 168, 168t, 169 facial nerve, 82t glossopharyngeal nerve, 88t location of, 69 oculomotor nerve, 140 topographic arrangement of, 68 trigeminal nerve, 74t, 75, 75t vestibulocochlear nerve, 86t, 87 Cranial sutures. See Craniosynostoses Cranial vault. See Neurocranium Craniosynostoses, 8 in adult skull, 3 closure of, 3t premature, 8, 9 neonatal, 3 Craniovertebral joints, 232, 233 ligaments of, 236–237 muscles of, on sagittal MRI of neck, 345 suboccipital muscles and, 251 Cranium. See Skull Cribriform plate in skull base, 15 neurovascular pathways, 94, 95t traumatic fracture of, 15, 21 Cricoarytenoid muscles, 258, 258t Cricoid cartilage, 256, 257

Epaxial muscles

on MRIs of neck sagittal view, 343 transverse view, 336 Cricopharyngeus muscle, 213t, 215 Cricothyroid muscle, 258, 258t Cricothyrotomy, 262 Crista galli, ethmoid bone and, 21 Cruciform eminence, 20 Cruciform ligament of atlas, 236, 237 CSF. See Cerebrospinal fluid (CSF) Curvature, spinal, 226 ligaments maintaining, 229 Cusp-and-fissure dentition, 181, 183 Cuspids. See Canines Cutaneous sensory innervation, 65 dermatomes and, 293 nerve lesions and, 65 of nuchal region, 277 by peripheral nerves, 64

D “Danger space” cervical fasciae and, 275 infection and, 286 “Danger zone,” venous, infection and, 97 Deciduous teeth, 188–189 coding of, 188, 189 eruption of, 188, 188t in 6-year-old child, 188, 189 Deep auricular artery, 44, 45t, 47t, 166, 166t Deep cervical lymph nodes lymphatic drainage from ear into, 158 in neck, 268, 283 Deep petrosal nerve, 161 Deep temporal arteries, 44, 45t, 47t Deep temporal nerve, 80, 81t Dendrites, 55, 306 Dens of axis (C2) on coronal MRI of neck, 321 in transverse section of head, 327 Dental arches, 183. See also Mandibular arch; Maxillary arch Dental panoramic tomogram (DPT), 181 Dental pulp, 182, 182t Dentate nucleus, in transverse section of head, 325 Dentine, of tooth, 182, 182t Dentition first, 188, 188t. See also Deciduous teeth second, 188, 188t. See also Permanent teeth in 6-year-old child, 189 Depressor anguli oris muscle, 24, 25, 28, 29, 29t Depressor labii inferioris muscle, 24, 25, 28, 29, 29t Dermatomes, 293 Descending palatine artery, 45t, 46, 47t Descending palatine nerve, 78, 79t Desmocranium, bone development in, 2 Diencephalon, 295, 295t Digastric muscles, anterior and posterior belly, 202, 202t, 203, 254, 254t, 255 pharynx and, 214 Dilation, pupil, 130t Diploë, of calvaria, 11

E

Diploic veins, 11 Direct light response, testing for, 139 Dislocation, of TMJ, 37, 195 Distal tooth surface, 180 Diverticula, pharyngeal, 215 Dizziness. See Vertigo Dorsal horn, spinal cord, 292 Dorsomedial margin of brainstem, motor nuclei in, 58t DPT (dental panoramic tomogram), 181 Drainage of aqueous humor, 131 of dural sinuses, 302 lacrimal, obstructions to, 123 lymphatic. See Lymphatics of nasolacrimal duct, 145t of paranasal sinuses, 144, 145t, 150 venous. See Venous drainage Dura mater, 296 outpouching in intervertebral foramina, 298 Dural venous sinuses, 297 accessory drainage pathways of, 302 cerebral vein tributaries, 302 neuroanatomy of, 302–303 occipital bone groove for, 20 occiput veins and, 53

E Ear arteries of, 166–167, 166t auditory and vestibular apparatus of, 156 external, 156–159. See also Auricle inner. See Inner ear middle. See Middle ear muscles of, 26–27, 27t innervation, 27t veins of, 167 Ebner glands, 223 Edinger-Westphal nucleus, 138, 139 lesion of, 139 Efferent (motor) fibers, 54, 66t, 291 brainstem reflexes and, 137 Efferent nuclei, 68t, 69 Efferent tracts. See Motor (efferent) pathways Electrochemical potentials, 170 Electron microscopy, of neuron, 306 Embryonic development branchial muscle, 60, 61t neuronal migration and, 68 peripheral nerves, 64 somatic muscle, 60, 60t Emissary veins, 303 dural sinus drainage and, 302 of occiput, 11, 53 Enamel, of tooth, 182, 182t Endolymph, 170 Endoplasmic reticulum, 306 Endoscopy of maxillary sinus, 151 semilunar hiatus on, 21 Endotracheal ossification, 2, 2t Epaxial muscles, 242

353

E

Epicranial muscles

Epicranial muscles, 25, 26 Epidural anesthesia, 299 Epiglottic cartilage, 256, 257 Epiglottic vallecula, in midsagittal section of head, 338 Epiglottis, innervation of, 222 Epipharynx. See Nasopharynx Epitympanum, 163 EPSP (excitatory postsynaptic potential), 306 Erb’s point, 270, 271, 278 Erector spinae, 242, 243 interspinales and, 246–247, 246t Esophagus, on MRIs of neck sagittal view, 343 transverse view, 337 Ethmoid air cells, 144, 310 relationship with nasal cavity, 343 in sagittal section of head, 339, 340 transverse MRI of head through, 332 Ethmoid arteries, ligation site for, 151 Ethmoid bone, 5, 7, 14, 21, 108, 142, 190, 191 cranial nerve passage through, 67t paranasal sinuses and, 145 Eustachian tube. See Pharyngotympanic (auditory) tube Excitatory postsynaptic potential (EPSP), 306 External acoustic meatus, temporal bone and, 155 External auditory canal, 156, 159 auricle and, 158 curvature of, 159 temporal bone and, 155 External capsule, thyroid gland, 264 External carotid artery, 283 blood supply to anterior face from, 96 branches of, 40, 41, 41t. See also individually named arteries anterior, 41t, 42, 43, 43t medial, 41t, 42, 43t in neck, 266, 266t posterior, 41t, 42, 43t terminal, 41t, 46–47. See also Maxillary artery variants in, 41 in carotid triangle, 282 in deep lateral cervical region, 283 on sagittal MRI of neck, 345 External ear, 156–159. See also Auricle External jugular vein, 50–51, 51t on sagittal MRI of neck, 345 External laryngeal nerve, 91, 91t External occipital protuberance, superior boundary of neck, 273 Extracranial veins, infection and, 52t Extraocular muscles, 112 actions of, 113, 113t cranial nerves of, 72, 72t eye movement and, 140 innervation of, 112, 113t Extrinsic muscles of back, 240, 242 of eye. See Extraocular muscles of tongue, 204, 204t, 205 Eye movement, coordination of, 140–141 Eye/Eyeball blood supply to, 126–127 chambers of, 130 coronal MRI of head through, 314

354

muscles of, 26–27, 27t innervation, 27t reference lines/points of, 125 in sagittal section of head, 341 structure of, 124–125 surface anatomy of, 121 Eyelids, structure of, 121

F Face anterior, superficial neurovasculature of, 96 arterial anastomoses in, 97 cutaneous sensory innervation of, 64 venous “danger zone” in, 97 Facet joint capsules, of vertebral arch, 228 Facial artery branches of, 42, 43t external carotid artery and, 41t nasal septum and, 149 ophthalmic artery and, 40, 41 Facial expression, muscles of calvaria, 26–27, 27t ear, 26–27, 27t, 157 eye, 26–27, 27t mouth, 28–29, 29t origins and insertions of, 38 superficial anterior view, 24 lateral view, 25 Facial motor nucleus, 82t Facial nerve (CN VII), 66t, 82–85 in anterior face, 96 auricular muscles and, 157 brainstem reflexes and, 137 branches of, 83 external, 84, 85 internal, 82, 83 in lateral head, 100 course of, 83 intraglandular, in parotid gland, 219 fiber distribution in, 82t function of, 67t ganglia, 82t, 85 in head sections sagittal, 341 transverse, 325 innervation by of auricle, 158 of second branchial arch muscles, 82, 84 of tongue, 221, 222 in internal acoustic meatus, 165 nuclei of, 82t parotid plexus of, 100, 101 in petrous bone, 161 temporal bone and, 18, 155 on transverse MRI of head, 332 Facial paralysis, facial nerve lesions and, 83, 84 Facial skeleton ethmoid bone integration into, 21 in midsagittal section of head, 338 Facial skin, facial muscles and, 24

Glossopharyngeal nerve (CN IX)

Facial veins, 50, 51 False vocal cords, 260 Falx cerebri, 311, 313, 323 on coronal MRI of head, 315 ethmoid bone and, 21 Far vision/Farsightedness, 125, 129 Fascia(e) buccopharyngeal, 274, 286 cervical, 241, 274–275, 274t nuchal. See Nuchal fascia pharyngobasilar, 215 pretracheal. See Pretracheal fascia prevertebral. See Prevertebral fascia thoracolumbar, 241, 242, 243 Filiform papillae, 206, 207t Filum terminale, 293 in vertebral canal, 298–299 First molars, 186t, 187 eruption patterns of, 188, 188t Fissure palpebral, muscles of, 26–27, 27t petrotympanic. See Petrotympanic fissure superior orbital, neurovascular pathways through, 67t, 94, 95t, 118 Foliate papillae, 206, 207t Fontanelles, 3 closure of, 3t Foodways, on coronal MRI of neck, 317 Foramen(ina). See also individually named foramina intervertebral, 290, 297 jugular, 13, 20 for nerve supply to face, 6 of skull base, 15 neurovascular pathways through, 94, 95t of sphenoid bone, 16, 17 stylomastoid, 15 supraorbital, 6 Foramen cecum, 206, 207t Foramen lacerum carotid canal relationship to, 12 neurovascular pathways through, 94, 95t Foramen magnum neurovascular pathways through, 94, 95t occipital bone and, 13, 20 Foramen ovale cranial nerve passage through, 67t dural sinus drainage and, 302 neurovascular pathways through, 94, 95t pterygoid process and, 16, 17 Foramen rotundum, 16, 17 cranial nerve passage through, 67t neurovascular pathways through, 94, 95t Foramen spinosum neurovascular pathways through, 94, 95t pterygoid process and, 16, 17 Force, lines of, in facial skeleton, 7 Forebrain, 295, 295t Fornical conjunctiva, 121 Fovea centralis, 124, 132, 135 macula lutea and, 133 Fracture(s) cribriform plate, 15, 21

G

midfacial, classification of, 7 skull base fracture lines, 14 temporal bone, facial nerve lesion and, 82t, 83 Frontal bone, 5, 7, 9, 11, 14, 108, 142 Frontal crest, in calvaria, 10 Frontal nerve, 76, 77t Frontal sinus, 144, 146 ethmoid bone and, 145 fluid flow in, 150 pneumatization of, 144 on transverse MRI of head, 332 Fungiform papillae, 206, 207t

G Galea aponeurotica, 24, 25, 26 Ganglion(ia) ciliary, sensory root of, 76, 77 cranial nerve parasympathetic, 63 facial nerve, 85 geniculate, 82t, 83, 161, 170, 222 inferior, 88t, 90t nodose, 222 otic, 80, 81t, 88t, 89, 89t, 161 petrosal, 222 in PNS, nerve tracts and, 55 prevertebral, 62t pseudounipolar ganglion cells, 222 pterygopalatine, 79t, 82t, 148 spinal, 290 spiral (cochlear), 86, 86t, 165, 170, 172, 173 submandibular, 80, 81t, 82t superior, 88t, 90t trigeminal, 340 vestibular, 86, 86t, 165, 174, 176 Gaps, pharyngeal, 214t Gastrulation, 60 Gaze, cardinal directions of, 113 Gaze centers, 140 Geniculate ganglion, 161, 170, 222 facial nerve and, 82t, 83 Genioglossus muscle, 204, 204t, 205 Geniohyoid muscle, 202, 202t, 203, 254, 254t, 255 Gennari, stria of, 134 Gingiva, 182, 182t connective tissue fibers in, 183 Glaucoma, acute and chronic, 131 Glenoid fossa, of TMJ, 36, 194 Glial cells, 133 Gliding movement, in TMJ, 34, 37, 196 Glomerulus, olfactory, 153 Glossoepiglottic folds, 207t Glossoepiglottic valleculae, 207t Glossopharyngeal nerve (CN IX), 66t, 88–89, 88t branches of, 89, 89t course of, 88t function of, 67t innervation by of pharynx, 213t, 217 of tongue, 220, 221, 222 nuclei, ganglia, and fiber distribution, 88t on transverse MRI of head, 333

355

G

Glossopharyngeus muscle

Glossopharyngeal nerve (CN IX) (continued) in transverse section of head, 326 Glossopharyngeus muscle, 213t, 214 Goblet cell, in conjunctiva, 123 Granular foveolae, in calvaria, 10 Granule cells, in olfactory bulb, 153 Graves’ disease, 265 Gray matter, 292 Great auricular nerve in anterior face, 96 auricle and, 158 in lateral head and neck, 99 in nuchal region, 276, 277 Great vessels, on coronal MRI of neck, 318 Greater occipital nerve, 270t in lateral head and neck, 99 in nuchal region, 277 Greater palatine foramen, neurovascular pathways through, 94, 95t Greater palatine nerve, 78, 79t Greater petrosal nerve, 83, 85, 161 hiatus of canal for, 94, 95t Grinding movements, in TMJ, 34, 196 Gustatory pathway, 222

H Habenular nuclei, 152 Hair cells in auditory apparatus/pathway inner, 170, 172, 173 outer, 170, 171, 173 vestibular, categories of, 174 Hard palate bones of, 190–191 in midsagittal section of head, 338 nasal cavity and, 147 in skull base, 190 transverse MRI of neck through, 334 Head anterior face, 96–97 arteries of. See also individually named arteries overview, 40–41 superficial, 99 coronal MRIs of through eyeball, 314 through posterior orbit, 315 coronal sections of anterior, 310–311 posterior, 312–313 lateral intermediate layer of, 100–101 sensory innervation of, 99 superficial neurovasculature of, 98 muscles of origins and insertions, 38–39 skeletal, 61t rotation of, semicircular canals during, 175 sagittal MRIs of through nasal cavity, 342 through orbit, 343 sagittal sections of

356

lateral, 340–341 medial, 338–339 transverse MRIs of through orbit and ethmoid air cells, 332 through orbit and nasolacrimal duct, 333 transverse sections of caudal, 326–327 cranial, 322–323 through middle nasal concha, 325 through optic nerve and pituitary, 323 through orbits (upper level), 322 through sphenoid sinus, 324 veins of deep, 52–53 superficial, 50–51, 51t Hearing loss of, CN VIII lesion and, 168 sound conduction during, 171 Helicotrema, 170 Hemianopia bitemporal, 136 contralateral homonymous, 136 homonymous, 136 Hindbrain, 295, 295t Hinge movement, in TMJ, 34, 37, 196 Hippocampus, in sagittal section of head, 341 Histology of choroid plexus, 301 of nasal mucosa, 150 of oral cavity and pharynx, 209 of parathyroid glands, 265 of thyroid gland, 265 of vocal folds, 263 Homonymous hemianopia, contralateral, 136 Homonymous hemianopic central scotoma, 136 Horizontal cells, 133 Horizontal gaze movements, 140 Hyaline cartilages, 257 “Hyaloid canal,” 125 Hydrocephalus, 9 Hyoglossus muscle, 204, 204t, 205 Hyoid bone, 23, 192, 256 Hypaxial muscles, 242 Hyperacusis, facial nerve lesions and, 82t, 83 Hypercalcemia, 265 Hyperopia, 125 Hyperparathyroidism, 265 Hypoglossal canal cranial nerve passage through, 67t neurovascular pathways through, 94, 95t occipital bone and, 20 Hypoglossal nerve (CN XII), 66t, 93 in carotid triangle, 282 course of, 93 in deep lateral cervical region, 283 function of, 67t lesions of, 93, 93t unilateral, 205 nuclei, ganglia, and fiber distribution of, 93, 93t in transverse section of head, 326 Hypopharynx. See Laryngopharynx

Internal jugular vein

Hypophysis. See Pituitary gland Hypothalamus, 62t Hypotympanum, 163

I Iliocostalis cervicis muscle, 245, 246t, 247 Iliocostalis lumborum muscle, 245, 246t, 247 Iliocostalis thoracis muscle, 245, 246t, 247 Impedance matching, 162 Incisive canal, neurovascular pathways through, 94, 95t Incisors, 179, 184, 184t eruption patterns of, 188, 188t Incus (anvil), 160, 162 Indirect light response, testing for, 139 Infection parapharyngeal space and, 286 temporal bone and, 154 of tympanic cavity, 163 venous anastomoses as portals for, 52t venous “danger zone” and, 97 via pharyngotympanic (auditory) tube, 18, 154 Inferior alveolar artery, 44, 45t, 47t Inferior alveolar nerve, 80, 81t Inferior ganglion, 88t, 90t Inferior longitudinal muscle, 204, 204t, 205 Inferior meatus, 143 paranasal sinus drainage and, 145t Inferior salivatory nucleus, 88t Inferior thyroid vein, 281 Inferior tympanic artery, 166, 166t Inflammation, conjunctival, 121 Infrahyoid muscles, 254–255, 254t Infranuclear paralysis, 84 Infraorbital artery, 44, 45t, 46, 47t Infraorbital canal, 310 on coronal MRI of head, 314, 315 Infraorbital foramen, 6 Infraorbital nerve, 78, 79t Infratemporal fossa blood vessels of, 102 dissection of deep, 103 superficial, 102 muscles of, 102 nerves of, 102–103, 103t pterygopalatine fossa and, 102, 105, 105t Infratrochlear nerve, 76, 77t Inhibitory postsynaptic potential (IPSP), 306 Inner ear, 156, 164–165 arteries and veins of, 167 sound conduction to, 171 Inner hair cells, 170, 172, 173 Innervation branchiomotor of laryngeal muscles, 263 of second branchial arch muscles, 82, 84 of infrahyoid muscles, 254, 254t of lacrimal gland, 85 of lingual muscles, 204, 204t, 205 of membranous labyrinth, 165

I

motor of extraocular muscles, 24 of facial muscles, 24 calvaria and ear, 27t mouth, 29t palpebral fissure and nose, 27t of larynx, 262 of muscles of mastication, 30, 30t, 198, 198t parasympathetic, of salivary glands, 82 of orbit, 117 of pharynx, 217 pharyngeal constrictor muscles, 213t pharyngeal levator muscles, 213t sensory. See also Cutaneous sensory innervation of auricle, 158 of face, 64 of larynx, 262, 263 of lateral head and neck, 99 of nuchal region, 277 peripheral, 65 segmental (radicular), 65 of temporomandibular joint, 37 of skeletal muscle, 60t of soft palate muscles, 213t of suprahyoid muscles, 202, 202t, 254, 254t of tongue, 207t, 221 Interfascial spaces, 274–275, 274t Internal acoustic meatus cranial nerves in, 67t, 165 facial nerve lesions and, 83 neurovascular pathways through, 94, 95t in skull base, 15 temporal bone and, 155 on transverse MRI of head, 332 Internal auditory canal, in sagittal section of head, 341 Internal capsule, thyroid gland, 264 Internal carotid artery, 48–49, 283, 313, 323 in carotid triangle, 282 in circle of Willis, 305 course in head, 40 in deep lateral cervical region, 283 divisions/parts of, 48, 304 foramen lacerum relationship to, 12 in head sections sagittal, 340, 341 transverse, 326 nasal septum and, 49 syphon of, in sagittal MRI of head, 342 temporal bone and, 18 Internal jugular vein, 50–51, 51t, 220 in carotid triangle, 282 in deep lateral cervical region, 283 in head sections sagittal, 341 transverse, 326 on MRIs of neck sagittal view, 345 transverse view, 335, 337 temporal bone and, 18 in thoracic inlet, 281 in transverse section of neck, 331

357

I

Internal laryngeal nerve

Internal laryngeal nerve, 91, 91t Interneurons, 55 Internuclear ophthalmoplegia, 141 Interspinales muscles cervical, 245, 246t, 247 erector spinae and, 246–247, 246t lumbar, 245, 246t, 247 Interspinous ligaments, 228 Intertransversarii cervicis muscles, 245, 248, 248t, 249 anterior, 248t posterior, 248, 248t, 249 Intertransversarii lumborum muscles, 248, 248t, 249 lateral, 248, 248t, 249 medial, 248, 248t, 249 Intertransverse ligaments, of vertebral arch, 228, 228t, 229 Intervertebral disks, 226, 228, 228t on coronal MRI of neck, 319 Intervertebral foramina, 290, 292, 297 outpouching of dura mater in, 298 Intracavernous course, of cranial nerves into orbit, 118 Intramembranous ossification, 2, 2t Intraspinous ligament, of cervical spine, 234, 235 Intrinsic muscles of back. See Back muscles, intrinsic of tongue, 204, 204t, 205 Iodine deficiency, 265 IPSP (inhibitory postsynaptic potential), 306 Iris, 124 ocular chambers and, 130 structure of, 131

J Jacobson’s organ, 153 Joints atlantoaxial. See Atlantoaxial joints atlanto-occipital. See Atlanto-occipital joints of cervical spine, 232 craniovertebral. See Craniovertebral joints of neck, 232–235 temporomandibular. See Temporomandibular joint (TMJ) of vertebral column, 232 Jugular foramen, 13, 20 cranial nerve passage through, 67t neurovascular pathways through, 94, 95t Jugular vein(s). See also Internal jugular vein infection transmission via, 286 on sagittal MRI of neck, 345 Jugulofacial venous junction, lymphatic drainage in neck, 269 Jugulosubclavian venous junction, lymphatic drainage in neck, 268–269

K Kiesselbach’s area, 49, 149 Killian triangle, 215 Krause gland, 122 Kyphosis, 226

L Labial (facial) artery, nasal septum and, 149

358

Labial creases, 178 Labial tooth surface, 180 Labyrinthine artery and veins of inner ear, 167 in internal acoustic meatus, 165 Lacrimal apparatus, 122–123 Lacrimal bone, 5, 108, 142 Lacrimal drainage, obstructions to, 123 Lacrimal fluid, mechanical propulsion of, 123 Lacrimal gland innervation of, 85 maxillary nerve and, 79t nerve supply to, 161 Lacrimal nerve, 76, 77t Laimer triangle, 215 Lambdoid suture, 8 Lamina cribrosa, 133 Laryngeal arteries, 261 Laryngeal cavity, divisions of, 260t Laryngeal nerves, 261 lesions of recurrent nerve, 263, 263t superior nerve, 263, 263t recurrent in anterior cervical triangle, 281 lesions of, 263, 263t Laryngeal veins, 261 Laryngopharynx, 216, 216t, 313 on coronal MRI of neck, 317 in transverse section of neck, 330 Laryngoscopy, indirect, 259 Laryngotracheal junction, 256 Larynx. See also Laryngeal entries blood supply to, 261 bony structures of, 256 cartilage of, 256–257 innervation of, 261 motor, 262 sensory, 262 laryngoscopic examination of, 259 ligaments of, 256 on MRIs of neck coronal view, 317 transverse view, 336 muscles of, 258–259, 258t neurovasculature of, 260–261, 260t parathyroid glands and, 264–265 surgical approaches to, 262 thyroid gland and, 264–265 topography of, 262–263 Lateral cervical triangle, 272, 272t deep, 283 Lateral geniculate body, 134, 135 Lateral head intermediate layer of, 100–101 sensory innervation of, 99 superficial neurovasculature of, 98 Lateral horn, spinal cord, 292 Lateral neck, sensory innervation of, 99 Lateral olfactory stria, 152 Lateral pterygoid artery, 45t, 47t Lateral pterygoid nerve, 80, 81t

MALT (mucosa-associated lymphatic tissue)

Lateropharyngeal space, 286 Le Fort fractures, midfacial, 7 Lens, 124 ciliary body and, 128 growth of, 129 light refraction and, 125 position of, 128 reference lines/points for, 129 Leptomeninges, 296 Lesser occipital nerve, 270t, 271 auricle and, 158 in lateral head and neck, 99 in nuchal region, 276, 277 Lesser palatine foramen, neurovascular pathways through, 94, 95t Lesser petrosal nerve, 85, 89, 89t, 161 hiatus of canal for, 94, 95t Levator anguli oris, 24, 28, 29, 29t Levator costarum breves muscle, 248, 248t, 249 Levator costarum longi muscle, 248, 248t, 249 Levator labii superioris alaeque nasi muscle, 24, 25, 27, 27t, 29t Levator labii superioris muscle, 24, 25, 26, 28, 29t on transverse MRI of head, 333 Levator scapulae muscle, 239t Levator veli palatini muscle, 212, 213t on transverse MRI of head, 333 Ligament(s). See also individually named ligaments of cervical spine, 234–235, 236 of craniovertebral joints, 236–237 of larynx, 256 of neck, 234–237 nuchal, 234, 235 periodontal, 182, 182t, 183 of temporomandibular joint, 36, 37 transverse, of atlas, 327 of vertebral column, 228–229, 228t vestibular. See Vestibular ligament vocal. See Vocal ligament Ligamenta flava of cervical spine, 234, 235 of vertebral arch, 228, 228t, 229 Light refraction, 125 Light response loss of, tests for, 139 of pupillary sphincter, 138 Limbs, peripheral nerves and, 64 Lines of force in facial skeleton, 7 in skull base, 14 Lingual artery, 41t, 43, 43t, 220 Lingual mucosa, 206 Lingual muscles, 204–205, 204t on coronal MRI of neck, 316 Lingual nerve, 80, 81t, 220, 221, 222 Lingual tonsils, 206, 207t, 216 Lingual tooth surface, 180 Lips, 178 Long ciliary nerves, 76, 77t Longissimus capitis muscle, 245, 246t, 247 Longissimus cervicis muscle, 245, 246t, 247 Longissimus thoracis muscle, 245, 246t, 247 Longitudinal ligaments of cervical spine, 234, 235

M

of vertebral bodies, 228, 228t anterior, 229, 344 posterior, 229 Longitudinal muscles, of tongue, 204, 204t, 205 Longus capitis muscle, 252, 252t, 253 on transverse MRI of neck, 335, 336 Longus colli muscle, 252, 252t, 253 on transverse MRI of neck, 335, 336 Lordosis, 226 Low transverse fracture, midfacial, 7 Lower quadrantanopia, contralateral, 136 Lumbar anesthesia, 299 Lumbar puncture, 299 Lumbar vertebra, structural elements of, 227, 227t Lung, pleural dome of, 331 Lymph nodes in neck deep, 268 regional vs. collecting, 268, 269 superficial, 268 of oral floor, 221 Lymphatics of ear, 158 of neck, 268–269 drainage directions, 269 superficial and deep, 268 of oral cavity, 209 system circulation and, cervical nodes relationship to, 269 of tongue and oral floor, 221 Lymphoepithelial tissue, histology of, 209

M Macula(e), saccular and utricular, 174 Macula lutea, 132 examination of, 127 fovea centralis and, 133 Macular visual field, 135 Magnetic resonance imaging (MRI) of cervical spine, 235 of head coronal views through eyeball, 314 through posterior orbit, 315 sagittal views through nasal cavity, 342 through orbit, 343 transverse views through orbit and ethmoid air cells, 332 through orbit and nasolacrimal duct, 333 of neck coronal views, 318–319 anterior, 316–317 posterior, 320–321 sagittal views, 344–345 transverse views through C7 vertebra, 337 through C4 vertebral body, 336 through C6 vertebral body, 336 Malleus (hammer), 160, 162 MALT (mucosa-associated lymphatic tissue), 208, 209

359

M

Mandible

Mandible, 5, 7, 9, 22–23, 192 age-related changes in, 23 fossa of, 36, 194 movements in TMJ, 34, 196 on MRIs of neck coronal view, 319 transverse view, 334 ramus of, 23, 319, 334 superior boundary of neck and, 273 transverse MRIs through, 335 in transverse section of head, 325 Mandibular arch, 179 incisors of, 184, 184t molars of, 186t, 187 premolars of, 185, 185t Mandibular division, of trigeminal nerve, 80, 81t Mandibular fossa, of TMJ, 36, 194 Mandibular nerve, 80, 81t Mandibular ramus, 23, 319, 334 Masseter muscle, 24, 30, 30t, 31, 198, 198t, 199 pharynx and, 215 Masseteric artery, 44, 45t, 47t Masseteric nerve, 80, 81t TMJ capsule and, 37 Mastication, mandibular movement in TMJ during, 34, 196 Masticatory muscles, 311 deep, 32–33, 200–201 in head sections sagittal, 340, 341 transverse, 325 innervation of, 30, 30t, 198, 198t on MRIs of neck coronal view, 316, 317 transverse view, 334 origins and insertions of, 38, 39 overview of, 30–31, 30t, 198–199, 198t at sphenoid sinus level, 33, 201 Masticatory muscular sling, 32, 200 Mastoid air cells arteries of, 166 infection transmission and, 154 temporal bone and, 18 Mastoid foramen, neurovascular pathways through, 94, 95t Mastoid lymph nodes, lymphatic drainage from ear into, 158 Mastoid process temporal bone and, 18, 19 tip of, superior boundary of neck and, 273 Maxilla, 5, 7, 9, 12, 108, 142, 190, 191 in nasal cavity anatomy, 142 pterygopalatine fossa and, 104, 104t Maxillary arch, 179 dentition and maxillary sinus relationship to, 343 incisors of, 184, 184t molars of, 186t, 187 premolars of, 185, 185t Maxillary artery, 41t, 44 ligation site for, 151 nasal septum and, 148, 149 parts/branches of, 45t, 47t right lateral nasal wall and, 148, 149 variants of, 44 Maxillary division, of trigeminal nerve, 78, 79t

360

Maxillary nerve, 78, 79t Maxillary sinus, 144, 146 bony ostium of, 145 endoscopy of, 151 fluid flow in, 150 on MRIs of head sagittal view, 343 transverse view, 333 pneumatization of, 144 Meatus external acoustic, temporal bone and, 155 internal acoustic. See Internal acoustic meatus nasal structures and, 143. See also Middle meatus; Superior meatus paranasal sinus drainage and, 145t Medial longitudinal fasciculus (MLF), 140 course in brainstem, 141 internuclear ophthalmoplegia and, 141 Medial olfactory stria, 152 Medial pterygoid artery, 45t, 47t Medial pterygoid nerve, 80, 81t Median furrow, of tongue, 207t Medulla oblongata, 297 Membrane potentials, 306 Membranous labyrinth, 164 endolymph in, 170 innervation of, 165 Membranous neurocranium, 2, 2t Meningeal nerve, 76, 77t Meninges brain and, 296–297 layers of, 296 spinal cord and, 298–299 Mental foramen, 6 resorption of alveolar process and, 23 Mental nerve, surgical considerations and, 23 Mentalis muscle, 24, 25, 28, 29, 29t Mesencephalic reticular formation, 140 Mesencephalon, 295, 295t, 322. See also Brainstem Mesial tooth surface, 180 Mesopharynx. See Oropharynx Mesotympanum, 163 Metencephalon, 295, 295t Microcephaly, 9 Midbrain, 295, 295t Middle cerebral artery, 305 Middle cranial fossa, 105, 105t Middle ear, 156, 160–163. See also Ossicular chain; Pharyngotympanic (auditory) tube; Tympanic cavity auditory ossicles in, 156, 160, 162 sound conduction from, 171 Middle meatus, 143 osteomeatal unit and, 145, 150 paranasal sinus drainage and, 145t Middle meningeal artery, 44, 45t, 46, 47t Middle meningeal nerve, 78, 79t Midline septum, of tongue, 207t Mirror examination, of larynx, 259 Mitral cells, in olfactory bulb, 153 MLF. See Medial longitudinal fasciculus (MLF) Modiolus, 170 Molars, 179 eruption patterns of, 188, 188t

Near vision/Nearsightedness

first, 186t, 187 second, 186t, 187 third. See Wisdom teeth Motor cortex, 58t, 63t Motor fibers. See also Afferent (motor) fibers carotid triangle and, 282 cervical plexus, 270 Motor neurons, 55, 58t, 59 facial paralysis and, 84 in parasympathetic pathway, 63t in sympathetic pathway, 62t Motor nuclei dorsal, 90t facial, 82t ventral horn of spinal cord, 58t Motor paralysis, facial nerve lesions and, 83 Motor (efferent) pathways, 56, 58–59, 58t fibers in, 138, 139 spinal cord development and, 292 Mouth. See also Oral cavity muscles of, 28–29, 29t innervation, 29t TMJ movements and, 35, 197 Mucosa laryngeal, 260 lingual, 206, 207t nasal, 147, 150 olfactory, 152 of oral cavity, 178 of pharynx, 210 of tongue, 206, 207t of tympanic cavity, 163 Mucosa-associated lymphatic tissue (MALT), 208, 209 Müller cells, 133 Multifidus muscle, 248, 248t, 249 Multipolar neurons, 307 Muscles. See also individually named muscles of abdomen (internal/external obliques), 242 of auricle, 157 of back. See Back muscles extraocular (extrinsic eye). See Extraocular muscles of facial expression. See Facial expression, muscles of of infratemporal fossa, 102 of larynx, 258–259, 258t lingual, 204, 204t, 205 of mastication. See Masticatory muscles motor lesions and, 64 of neck. See Neck, muscles of of nose, 26–27, 27t nuchal. See Nuchal muscles ocular, nerves supplying, 73 of pharyngotympanic tube, 212 of pharynx, 211, 212, 213t, 214–215 skeletal, development and innervation of, 60–61, 60t, 61t of skull, 24–33, 198–201 origins and insertions on, 38–39 of soft palate, 212, 213t thyrohyoid, 254, 254t, 255 of tongue, 204, 204t, 205 Muscular sling, masticatory, 32, 200 Muscular triangle, in neck, 272, 272t Musculus uvulae, 212, 213t

N

Myelencephalon, 295, 295t Mylohyoid muscle, 202, 202t, 203, 254, 254t, 255 Myopia, 125

N Nares, 142 Nasal bones, 5, 7, 11, 108, 142 Nasal cavity, 310 bones of, 142 ethmoid cells relationship to, 343 lateral wall of, 143 mucosa of, 147, 150 nerves of, 161 neurovasculature of, 148–149 olfactory mucosa in, 152 overview, 146 paranasal sinuses and, 144, 145 pneumatization of, 144 pterygopalatine fossa and, 105, 105t sagittal MRIs of head through, 342 Nasal concha(e), 142, 143 ethmoid bone and, 21 inferior, 7, 12, 142, 190, 191 in sagittal section of head, 339 transverse section of head through, 325 Nasal mucosa, 147 functional states of, 150 histology of, 150 Nasal septum arteries of, 148, 149 bones of, 142 deviations of, 143 in midsagittal section of head, 338 midsagittal section of head through, 338 nerves of, 148, 149 neurovasculature of, 148 structures of, 143 vascular supply of, 49 Nasal visual field, 134 Nasal wall, right lateral arteries of, 148, 149 nerves of, 148, 149 Nasalis muscle, 24, 25, 27, 27t Nasociliary nerve, 76, 77t Nasolacrimal duct drainage of, 145t transverse MRI of head through, 333 Nasolacrimal gland, 122 Nasopalatine nerve, 78, 79t Nasopharynx, 210t, 216, 216t, 313 on MRI of head, sagittal view, 342 on MRIs of neck coronal view, 317, 318 sagittal view, 343 posterior rhinoscopy of, 211 pterygopalatine fossa and, 105, 105t in sagittal section of head, 339 soft palate and, 212 transverse section of head through, 326 Nausea, noxious smell inducing, 152 Near vision/Nearsightedness, 125, 129

361

N

Neck

Neck anterior, 280–281. See also Anterior cervical triangle arteries of, 266, 266t cervical spine and, 230–231 deep anterolateral, 282–283 fascial relationships in, 275 joints of, 232–235 lateral, 278–279. See also Posterior cervical triangle sensory innervation of, 99 ligaments of, 234–237 lymphatics of, 268–269 MRIs of coronal views, 318–319 anterior, 316–317 posterior, 320–321 sagittal views, 344–345 transverse views through C7 vertebra, 337 through C4 vertebral body, 336 through C6 vertebral body, 336 muscles of, 238–255 dissection of, 273 fascial planes, 241 posterior neck, 244–245 prevertebral and scalene, 252–253, 252t, 336 superficial, 238, 238t, 239t suprahyoid and infrahyoid, 202–203, 202t, 254–255, 254t neurovascular topography of, 266–287 palpable bony prominences in, 23, 273 parapharyngeal space in, 284–285 posterior cervical (nuchal) region, 276–277 root of, structures in, 281 transverse sections of caudal, 330–331 cranial, 328–329 vagus nerve branches in, 91 veins of, 50–51, 51t, 267, 267t Nerve lesions abducent nerve, 72t cutaneous innervation and, 65 facial nerve, 82t, 83 motor lesions, 64 oculomotor nerve, 72t sensory loss and, 64 trigeminal nerve, 75, 75t trochlear nerve, 72t Nerves. See also individually named nerves of anterior face, 96 of infratemporal fossa, 102–103, 103t laryngeal, 261 of lateral head (intermediate layer), 101 of nasal septum, 148, 149 neurons and, 55 of orbit, 115 of petrous bone, 161 of right lateral nasal wall, 148, 149 of tongue, 220–221 Nervous system. See also Autonomic (visceral) nervous system; Central nervous system (CNS); Peripheral nervous system (PNS) information flow in, 291 neuroanatomy of, 290–291

362

neurons in, 306–307 organization of, 54–55 topography of, 290–291 Neural crest, cranial bone development from, 2t Neural tube, spinal cord development and, 60, 292 Neuroanatomy of brain arterial supply and, 304 meninges and, 296–297 organization of, 294–295 of CSF spaces, 300–301 of dural venous sinuses, 302–303 of meninges brain and, 296–297 spinal cord and, 298–299 of nervous system, 290–291 neurons and, 306–307 of spinal cord meninges and, 298–299 organization of, 292–293, 293t Neurocranium in midsagittal section of head, 338 ossification of, 2, 2t Neurofibrils, 306 Neuroma, acoustic, 87, 165, 168 Neurons, 306–307 basic forms of, 307 in CNS and PNS, 55 in convergence and accommodation, 138 in gustatory pathway, 222 nerves and, 55 in sensory (afferent) pathway, 56t types of, 55 of visual pathway, 133, 134 Neurotransmitters, 306 Neurotubules, 306 Neurovasculature of cervical spine, 233 of larynx, 260–261, 260t of lateral nasal wall, 148 of nasal septum, 148 in optic canal and superior orbital fissure, 118 of orbit, 116–117, 116t of parapharyngeal space, 287 pathways through skull base, 94, 95t superficial of anterior face, 96 of lateral head, 98 of tongue, 220–221 in transverse section of neck, 331 Nissl substance, 306 Nodose ganglion, 222 Nonvisual retina, 132 Nose cavity of. See Nasal cavity glands of, innervation, 85 histology and clinical anatomy of, 150–151 muscles of, 26–27, 27t innervation, 27t overview, 146 paranasal sinuses and, 144–145 passages of, 143

Optic nerve (CN II)

skeletal structures of, 142–143 Nosebleed, ligation sites for, 151 Nostrils, 142 Nuchal fascia, 241, 274, 274t intrinsic back muscles and, 241, 242 Nuchal ligament, 234, 235 Nuchal muscles, 244. See also individually named muscles coronal MRI through, 321 muscle attachments and, 245 origins and insertions of, 38, 39 on sagittal MRI of neck, 345 short, 250–251, 250t Nuchal region, 276–277 Nuclei afferent, 68t, 69 branchiomotor. See Branchiomotor nuclei, cranial nerves cochlear, 86t, 87, 168 cranial nerve. See Cranial nerve nuclei efferent, 68t, 69 habenular, 152 motor. See Motor nuclei nerve tracts and, 55 oculomotor, 140 parasympathetic. See Parasympathetic nuclei, cranial nerves parvocellular, axons to, 137 somatomotor. See Somatomotor nuclei, cranial nerves thalamic, axons to, 137 vestibular. See Vestibular nuclei viscerosensory. See Viscerosensory nuclei, cranial nerves Nucleus ambiguus, 88t, 90t Nucleus of the solitary tract, 90t facial nerve and, 82, 82t glossopharyngeal nerve and, 88, 88t Nucleus prepositus hypoglossi, 140 Nystagmus, abducting, 141

O OAE (otoacoustic emissions), 173 Obliquii capitis muscles, 250, 250t, 251 inferior, 250, 250t, 251 superior, 250, 250t, 251 Obliquus oculi muscles, 112, 113t Obstruction of arterial supply to brain, 305 lacrimal drainage, 123 Occipital artery, 41t, 42, 43t Occipital bone, 5, 9, 11, 12, 14, 20 fusion with sphenoid bone, 16, 17 Occipital lobe lesion, 136 Occipital nerves, of nuchal region, 276, 277 emergence sites, 277 Occipital pole lesion, 136 Occipital triangle, 272, 272t Occipital vein, 50, 51 infection transmission and, 52t Occipitofrontalis muscle frontal belly, 24, 25, 27t occipital belly, 25, 27t Occiput veins, 53 emissary veins, 11 Occlusal plane, 183

O

Occlusion, of arteries supplying brain, 305 Ocular chambers, 130 Ocular conjunctiva, 121 Ocular muscles, nerves supplying, 73 Oculomotor nerve (CN III), 66t, 72, 72t brainstem reflexes and, 137 on coronal MRI of head, 315 emergence from brainstem, 114 eye movement and, 140 function of, 67t Oculomotor nerve palsy(ies), 72t, 113, 114t Oculomotor nuclei connections in brainstem, 140 topography of, 114 Olfactory bulb, 148 in midsagittal section of head, 338 synaptic patterns in, 153 Olfactory glomerulus, 153 Olfactory mucosa, 152, 153 Olfactory nerve (CN I), 66t, 70 foramina of skull base and, 15 function of, 67t lateral nasal wall and, 148, 149 nasal septum and, 148, 149 Olfactory striae, 152 Olfactory system, 152–153 Olfactory tract, 152 Olive, in auditory pathway, 173 Omoclavicular (subclavian) triangle, in neck, 272, 272t Omohyoid, 278, 279 anterior cervical triangle and, 280 Omohyoid muscle, inferior belly, 254, 254t, 255 Open-angle glaucoma, 131 Ophthalmic artery, 49, 126 branches of, 49, 117, 126 on coronal MRI of head, 315 course of, 149 internal carotid artery and, 40, 41, 49 lateral nasal wall and, 148, 149 nasal septum and, 148, 149 Ophthalmic division, trigeminal nerve, 76, 77t Ophthalmoplegia, internuclear, 141 Ophthalmoscopic examination, of optic fundus, 127 Optic canal neurovascular pathways through, 67t, 94, 95t neurovasculature in, 118 Optic chiasm, 134, 135 lesion of, 136 in sagittal MRI of head, 342 Optic disk, 124 examination of, 125, 127 lamina cribrosa and, 133 Optic fundus, ophthalmoscopic examination of, 127 Optic nerve (CN II), 66t, 71, 124, 135 arteries of, 127 brainstem reflexes and, 137 function of, 67t on MRIs of head coronal views, 315 sagittal views, 342, 343 transverse MRI of head through, 332

363

O

Optic radiation

Optic nerve (CN II) (continued) transverse section of head through, 323 unilateral lesion of, 136, 139 in visual pathway, 134 Optic radiation, 134 lesions of, 139 in anterior temporal lobe, 136 in parietal lobe, 136 Optic tract thalamic nuclei and, 137 unilateral lesion of, 136 in visual pathway, 134, 135 Optical axis, of eyeball, 125 Optokinetic nystagmus, 137 Oral cavity, 310 glands of innervation, 85 maxillary nerve and, 79t lymphatics of, 209 organization and boundaries of, 178 overview of, 178–179 pterygopalatine fossa and, 105, 105t structures of, on coronal MRI of neck, 318 transverse MRIs of through hard and soft palates, 334 through mandible, 335 through temporomandibular joint, 334 Oral floor, lymph nodes of, 221 Oral stage, in swallowing, 217 Oral vestibule, 341 Orbicularis oculi muscle, 24, 25, 26, 27t Orbicularis oris muscle, 24, 25, 28, 29, 29t Orbit, 310 axis of, eyeball and, 125 bones of, 108–109 communications of, 110, 111t cranial nerves entry into, 118 innervation of, 117 MRIs of head through posterior orbit, coronal view, 315 sagittal view, 343 transverse view, 332, 333 nerves supplying, 115 neurovasculature, 116–117, 116t ophthalmic nerve divisions in, 76, 77t pterygopalatine fossa and, 105, 105t sagittal section of head through approximate center, 341 inner third, 340 topography of, 118–121 deep layer, 120 eyelids and conjunctiva, 121 intracavernous course of cranial nerves, 118 middle level, 119 optic canal and superior orbital fissure, neurovasculature, 118 superficial layer, 120 surface anatomy of eye, 121 upper level, 119 upper level of, transverse section of head through, 322 veins of, 117 Orbital apex, coronal section through, 312 Orbital plate, 21

364

Orbital wall, sagittal section of head through, 338 Organ of Corti, 170, 172 deflected by traveling wave, 171 efferent fibers from olive to, 173 at rest, 171 Oropharyngeal isthmus, 207t Oropharynx, 207t, 216, 216t, 313 in midsagittal section of head, 338 on MRI of head, sagittal view, 342 on MRIs of neck coronal view, 317, 318 sagittal view, 343 transverse view, 335 palatine tonsils in, 208 soft palate and, 212 Ossicular chain, 156, 162 arteries of, 167 function of, 162 motion in, 162 in tympanic cavity, 163 Ossification centers, in temporal bone, 18 of cranial bones, 2, 2t Osteomeatal unit, 145 Otic ganglion, 80, 81t, 88t, 89, 89t, 161 Otitis media, 163 Otoacoustic emissions (OAE), 173 Otoliths, 174 Outer hair cells, 170, 173 Oval window membrane, 171

P Palatal tooth surface, 180 Palatine aponeurosis, 212, 213t Palatine artery, nasal septum and, 149 Palatine bone, 9, 12, 108, 142, 190, 191 pterygopalatine fossa and, 104, 104t Palatine glands, nerve supply to, 161 Palatine nerves, 78, 79t Palatine tonsils, 147, 216 abnormal enlargement of, 208 on coronal MRI of neck, 318 histology of, 209 location of, 208 vascular supply to, 287 veins of, infection transmission and, 52t Palatoglossal arch, 206, 207t Palatoglossus muscle, 204, 204t, 205, 212, 213t Palatopharyngeal arch, 206, 207t Palatopharyngeus muscle, 206, 207t Palpation, of cervical lymph nodes in neck, 269 Palpebral conjunctiva, 121 Palpebral fissure, muscles of, 26–27, 27t innervation of, 27t Palsy(ies). See also Paralysis abducent nerve, 72t, 113, 114t oculomotor, 72t, 113, 114t trochlear nerve, 72t, 113, 114t Papillae, of tongue, 206, 207t Paralysis. See also Palsy(ies) facial, facial nerve lesions and, 83, 84

Plexuses (nerves)

sternocleidomastoid, 92, 92t trapezius muscle, 92, 92t Paramedian pontine reticular formation (PPRF), 140 Paranasal sinuses, 7, 144. See also Frontal sinus; Maxillary sinus bony structures of, 145 drainage of, 144, 145t histology and clinical anatomy of, 150–151 nasal cavity and, 145 nerve supply to, 161 overview of, 146 Parapharyngeal space clinical significance of, 286 divisions of, 286 neurovasculature of, 287 structures of, 284–285 Parasympathetic nervous system, 63 Parasympathetic nuclei, cranial nerves, 68t, 69 facial nerve, 82t glossopharyngeal nerve, 88t vagus nerve, 90t Parathormone, 265 Parathyroid glands, histology of, 265 Parathyroid hormone (PTH; parathormone), 265 Paraxial mesoderm, cranial bone development from, 2t Parietal bone, 5, 7, 9, 11, 12, 14 Parietal triangle, 272, 272t Parotid glands, 81t, 100, 218 facial nerve course in, 219 malignant tumor spread and, 219 nerves supplying, 161 on transverse MRI of neck, 335 Parotid lymph nodes, lymphatic drainage from ear into, 158 Parotid plexus, of facial nerve, 100, 101 Pars flaccida, 159 Pars tensa, 159 Parvocellular nucleus, axons to, 137 Peridontium, 182, 182t, 183 Periglomerular cells, 153 Perilymph, 162 sound conduction through, 171 Perimetry, visual field defect detection, 135 Periodontal ligament, 182, 182t, 183 Peripheral nerves, cutaneous sensory innervation by, 64 Peripheral nervous system (PNS), 54, 290 neurons in, 55 Peripheral paralysis, of face, 84 Peripheral sensory innervation, 65 cutaneous, 64 Perlia’s nucleus, 138 Permanent teeth, 180–181 coding of, 180 eruption of, 188, 188t panoramic tomogram of, 181 in 6-year-old child, 189 surface designation for, 180 Petrosal artery, 166, 166t Petrosal ganglion, 222 Petrotympanic fissure neurovascular pathways through, 94, 95t temporal bone and, 18, 19 Petrous apex, temporal bone and, 19 Petrous bone, in middle ear, 160

P

nerves of, 161 Petrous part/division, of internal carotid artery, 48, 304 Petrous pyramid, temporal bone and, 19, 155 Pharyngeal artery, 45t, 47t ascending, 41t, 43, 43t variants of, 284 Pharyngeal gaps, 214t Pharyngeal muscles constrictor muscles, 212, 213t, 214, 215 levator muscles, 212, 213t, 214 origins and insertions of, 39 in sagittal section of head, 340 Pharyngeal nerves, 78, 79t Pharyngeal plexus, 89, 89t, 91t Pharyngeal recess, on transverse MRI of head, 333 Pharyngeal stage, in swallowing, 217 Pharyngeal tonsils, 216 abnormal enlargement of, 208, 209 on coronal MRI of neck, 318 histology of, 209 location of, 208, 209 in posterior rhinoscopy, 211 Pharyngobasilar fascia, 215 Pharyngoesophageal stage, in swallowing, 217 Pharyngotympanic (auditory) tube, 18, 147, 154, 161 in head sections sagittal, 339, 340 transverse, 326 infection via, 18, 154 muscles of, 212 obstruction of, 216 in posterior rhinoscopy, 211 Pharynx, 286. See also Pharyngeal entries on coronal MRI of neck, 317 fascial space surrounding. See Parapharyngeal space innervation of, 217 levels of, 210t, 216t lymphatics of, 209 mucosa of, 210 muscles of, 211, 212, 213t, 214–215 topography of, 216 Waldeyer’s ring of, 208, 216 Phonation arytenoid cartilage movement during, 256, 257 vocal folds position during, 259 Photoreceptor cells, 133 Phrenic nerve, 279 in deep lateral cervical region, 283 in thoracic inlet, 281 “Pie in the sky” deficit, 136 Pigment epithelium, 133 “Pink eye,” 121 Pituitary gland coronal section through, 313 in midsagittal section of head, 338 in sagittal MRI of head, 342 transverse section of head through, 323 Platysma muscle, 24, 25, 28, 29t, 238, 239t Pleural dome of left lung, in transverse sections of neck, 331 Plexuses (nerves) brachial. See Brachial plexus cervical. See Cervical plexus

365

P

Plexuses (venous)

Plexuses (nerves) (continued) parotid, 100, 101 pharyngeal, 89, 89t, 90t, 217 Plexuses (venous) basilar, 302 choroid, 301 dural sinus drainage and, 302 external vertebral, infection transmission and, 52t pterygoid, 53 thyroid, 265 Pneumatization, of paranasal sinuses, 144 PNS. See Peripheral nervous system (PNS) Pons, 297, 323 Pontocerebellar cistern, in transverse section of head, 325 Posterior auricular arteries, 41t, 42, 43t, 157 Posterior auricular nerve, 84 Posterior auricular vein, 50, 51 infection transmission and, 52t Posterior cerebral artery, 305 Posterior cervical (nuchal) region, 276–277 Posterior cervical triangle dissection of, 278–279 lymph nodes in, 268 Posterior communicating artery, 305 Posterior condylar canal, neurovascular pathways through, 94, 95t Posterior ethmoid nerve, 76, 77t Posterior rhinoscopy, 151, 211 Posterior superior alveolar artery, 44, 45t, 47t Posterior superior nerves alveolar, 78, 79t nasal, 78, 79t Posterior tympanic artery, 166, 166t Postganglionic neuron in parasympathetic pathway, 63t in sympathetic pathway, 62t Potential at the axon hillock, 306 PPRF (paramedian pontine reticular formation), 140 Preganglionic neuron in parasympathetic pathway, 63t in sympathetic pathway, 62t Premolars, 179, 185, 185t eruption patterns, 188, 188t Pretectal area, axons to, 137 Pretracheal fascia, 274, 274t, 275 in parapharyngeal space, 284–287 Prevertebral fascia, 274, 274t, 278, 279 cervical, 241 retropharyngeal space and, 286 Prevertebral ganglia, 62t Prevertebral muscles, 252–253, 252t. See also individually named muscles origins and insertions of, 39 on transverse MRI of neck, 335, 336 Primary auditory cortex, 172 Procerus muscle, 24, 26, 27t Prosencephalon, 295, 295t Pseudounipolar neuron, 55, 57, 307 Pseuodunipolar ganglion cells, 222 Pterygoid arteries, 45t, 47t Pterygoid canal, 45t, 47t Pterygoid muscles, lateral and medial, 30, 30t, 32, 198, 198t, 200 Pterygoid plexus, 53

366

Pterygoid process plates, on transverse MRI of head, 333 Pterygopalatine fossa, 16, 17, 104–105 borders of, 104t communications of, 105, 105t infratemporal fossa and, 102, 105, 105t Pterygopalatine ganglion, 79t, 148 facial nerve and, 82t Pterygopharyngeus muscle, 213t, 214 PTH (parathyroid hormone), 265 Pulvinar of thalamus, axons to, 137 Pupil size, 130 changes in, 130t Pupillary constriction, 138 Pupillary light reflex, 139 pathway lesions and, 139 Pupillary reflex, 137 Pupillary resistance, 131 Pupillary sphincter light response, 138 Purkinje cell, 307 Pyramid fracture, midfacial, 7 Pyramidal cell, 307

Q Quadrantanopia, contralateral upper and lower, 136

R Ramus(rami) of cervical nerves dorsal, 99, 270, 270t in nuchal region innervation, 277 ventral, 270 mandibular angle of mandible and, 23 on MRIs of neck coronal view, 319 transverse view, 334 ventral, of spinal nerves, 290 Rectus capitis muscles, 252, 252t, 253 anterior, 252, 252t, 253 lateral, 252, 252t, 253 posterior, 250, 250t, 251 major, 250, 250t, 251 minor, 250, 250t, 251 in sagittal section of head, 340 Rectus oculi muscles, 112, 113t inferior on sagittal MRI of head, 343 in sagittal section of head, 340 lateral, in sagittal section of head, 340 in sagittal section of head, 340 superior, on sagittal MRI of head, 343 Recurrent laryngeal nerve, 91, 91t pharyngeal innervation and, 213t, 217 right, in anterior cervical triangle, 281 in thoracic inlet, 281 Red nucleus, 322 Reference lines/points of eyeball, 125 of lens, 129 Reflex(es)

Sinus(es)

brainstem, 137 pupillary light, 139 salivary, 222 stapedius, 173 Reissner membrane, vestibular, 170 Respiration, position of vocal folds during, 259 Respiratory epithelium, 150 Reticular formation, mesencephalic, 140 Retina, 124, 132–133 layers of, 132 light refraction and, 125 neurons of, 133, 134 nonvisual, 132 structure of, 133 Retinal projection, 135 Retrobulbar space, coronal section through, 311 Retromandibular vein, 50, 51 on transverse MRI of neck, 335 Retropharyngeal space, 286 Retrovisceral/retropharyngeal fascial space, 274, 274t Rhinoscopy, 151 posterior, of nasopharynx, 211 Rhombencephalon, 295, 295t Rhomboid minor muscle, 239t, 240 Rima glottidis, 260 Rima vestibuli, 260 Risorius muscle, 24, 25, 28, 29, 29t Rods, 133 Rotational movement, in TMJ, 34, 37, 196 Rotatores brevis muscle, 248, 248t, 249 Rotatores longi muscle, 248, 248t, 249 Round window, 171

S Saccades, 140 Saccule, 156 macular structure of, 174 Sacrum, structural elements of, 227, 227t Salivary glands bimanual examination of, 219 major, 218 minor, 219 Salivation, 219 afferent impulses and, 222 facial nerve lesions and, 82t, 83 stimulation of, 152 Salpingopharyngeal folds, 208, 209 Salpingopharyngeus muscle, 212, 213t Scaffolding, trigeminal nerve and, 74t autonomic, 79t Scala media, 170 Scala tympani, 170 Scala vestibuli, 170 Scalene muscles, 252–253, 252t. See also individually named muscles on MRIs of neck sagittal view, 345 transverse view, 336 in transverse sections of head, 329 of neck, 331 Scalene anterior muscle, 252, 252t, 253

S

in transverse sections of head, 252, 252t, 253 of neck, 331 Scalene medius muscle, 252, 252t, 253 on MRIs of neck sagittal view, 345 transverse view, 336 in transverse sections of head, 329 of neck, 331 Scalene posterior muscle, 252, 252t, 253 on MRI of neck, sagittal view, 345 in transverse sections of head, 329 of neck, 331 Scalp, calvaria and, 11 Schlemm, canal of, 124 Schwannoma, vestibular, 87, 165, 168 Sclera, 124 Scoliosis, 226 Scotoma, homonymous hemianopic central, 136 Sebaceous glands, in ear, 159 Second molars, 186t, 187 eruption patterns of, 188, 188t Secondary sensory cells in auditory pathway, 172 in vestibular system, 176 Segmental (radicular) sensory innervation, 65 Sella turcica, 16, 17 Semicircular canals, of ear, 156 during head rotation, 175 in thermal function tests, 164 Semilunar hiatus, 21 Semispinalis capitas muscle, 248, 249, 249t Semispinalis cervicis muscle, 248, 249, 249t Semispinalis thoracis muscle, 248, 249, 249t Senses smell, 152–153, 222 sound. See Hearing taste, 221, 222 Sensory cells, secondary in auditory pathway, 172 in vestibular system, 176 Sensory fibers, cervical plexus, 270 Sensory neurons, 55 Sensory (afferent) pathways, 56–57 spinal and cranial nerves, 56t, 57 spinal cord development and, 292 Septal cartilage, 142 Serratus posterior superior muscle, 239t Short nuchal muscles, 250–251, 250t Shrapnell membrane, 159 Sigmoid sinus, 297 infection transmission and, 52t, 154 on transverse MRI of head, 332 in transverse section of head, 326 Signal transduction, 170 Sinus(es) cavernous. See Cavernous sinus dural. See Dural venous sinuses frontal. See Frontal sinus

367

S

Sinusitis

Sinus(es) (continued) maxillary. See Maxillary sinus paranasal. See Paranasal sinuses sigmoid. See Sigmoid sinus sphenoid. See Sphenoid sinus superior sagittal. See Superior sagittal sinus transverse. See Transverse sinus venous. See Venous sinus(es) Sinusitis, 150 Skeletal muscle development and innervation of, 60, 60t of head, 61t Skull, 4–5. See also Cranial entries basal aspect of, 13 bones of, 2, 5t. See also individually named bones anterior view, 6–7 development of, 2t lateral view, 4–5 posterior view, 8–9 cranial nerve passages through, 67t inner ear projection into, 164 muscles of, 24–33, 198–201 origins and insertions on, 38–39 regional divisions of, 310 Skull base cranial fossae in, 14 ethmoid bone integration into, 21 external view of, 12–13 hard palate in, 190 internal view of, 14–15 lines of force in, 14 neurovascular pathways through, 94, 95t occipital bone integration into, 20 pharyngobasilar fascia at, 215 Skull base lesion, 263 vagus nerve, 263, 263t Smell, 152–153, 222 Soft palate, 312 in midsagittal section of head, 338 on MRIs of neck coronal view, 317 sagittal view, 343 transverse view, 335 muscles of, 212, 213t nasal cavity and, 147 transverse MRI of neck through, 334 Somatic muscle embryonic development of, 60, 60t of head, 61t Somatic sensation, tongue innervation and, 221 Somatomotor cortex, 84 Somatomotor nuclei, cranial nerves, 68t, 69 accessory spinal nerve, 92t hypoglossal nerve, 93t Somatosensory nuclei, cranial nerves, 68t, 69 trigeminal nerve, 75, 75t Sound conduction apparatus for, 156. See also Auditory apparatus, of ear during hearing, 171 Sound waves capture and transformation of, 156 conduction from middle to inner ear, 171

368

ossicular chain and, 162 traveling, 171 Speech, position of vocal folds during, 259 Sphenoid bone, 5, 7, 9, 14, 16–17, 108, 142, 190, 191 occipital bone fusion with, 16, 17 pterygopalatine fossa and, 104, 104t in transverse section of head through middle nasal concha, 325 through sphenoid sinus, 324 Sphenoid sinus, 16, 17, 144, 146, 147 on MRIs of head sagittal view, 342 transverse view, 332 muscles of mastication at level of, 33, 201 in sagittal section of head, 339, 340 transverse section of head through, 324–325 Sphenomandibular ligament, 37 Sphenopalatine artery, 45t, 46, 47t ligation site for, 151 Spinal cord development of, 292 on MRIs of neck coronal view, 321 transverse view, 337 neuroanatomy of, 292–293, 293t organization of, 292–293 parasympathetic pathways in, 63t in transverse section of head, 327 in vertebral canal, 298 Spinal cord segments, 293 levels of, 293t age-related changes in, 299 numbering of, 293, 293t organization (functional and topographical) of, 292 Spinal ganglion, 55, 290 Spinal nerves, 54 coronal MRI through, 320 intervertebral foramina and, 290, 291 motor pathways in, 58t, 59 in sagittal section of head, 339 sensory pathways in, 56t, 57 in transverse sections of neck, 331 Spinal nucleus, of CN V, 88t, 90t Spinalis cervicis muscle, 245, 246t, 247 Spinalis thoracis muscle, 245, 246t, 247 Spine. See also Vertebral entries curvature of, 226 regions of, 226 “Spine synapse,” 307 Spinous process of C7 vertebra inferior boundary of neck and, 273 on MRI of neck coronal view, 321 transverse view, 336 in transverse section of head, 328, 329 spinal cord segments and, 293t Spiral canal. See Cochlea Spiral ganglia, 86, 86t, 165, 169, 170, 172, 173 Spiral lamina, 170 Splenius capitis muscle, 248, 249, 249t Splenius cervicis muscle, 248, 249, 249t

Taste

Stapedial nerve, 83 Stapedius, 163 nerve supply to, 161, 163 Stapedius muscle contraction, 173 Stapedius reflex, 173 Stapes (stirrup), 162 Statoliths, 174 Stenosis(es) arterial supply to brain and, 305 subclavian steal syndrome and, 305 Stereocilia bowing of, 171, 172 sound transduction and, 175 specialized orientations of, 175 Sternocleidomastoid muscle, 25, 26, 238, 239, 239t anterior cervical triangle and, 280 origins and insertions of, 38, 39 posterior cervical triangle and, 278, 279 Sternocleidomastoid paralysis, 92, 92t Sternocleidomastoid triangle, 272, 272t Sternohyoid muscle, 254, 254t, 255 Stria(e) of Gennari, 134 olfactory, 152 Stria vascularis, 170 Striate area, 134. See also Visual cortex Styloglossus muscle, 204, 204t, 205 Stylohyoid muscle, 202, 202t, 203, 254, 254t, 255 Stylomastoid artery, 166, 166t Stylomastoid foramen neurovascular pathways through, 94, 95t in skull base, 15 temporal bone and, 19 Stylopharyngeal aponeurosis, 286 Stylopharyngeus muscle, 89t, 212, 213t Subarachnoid cisterns, 300–301 Subarachnoid space, 296 CSF in, 300–301 infection transmission via, 286 Subclavian artery branches in neck, 266, 266t in thoracic inlet, 281 Subclavian steal syndrome, 305 Subclavian vein, 281 Sublingual glands, 81t, 218 Submandibular ganglion, 80, 81t facial nerve and, 82t Submandibular glands, 81t, 218 on MRIs of head, coronal view, 315 of neck, sagittal view, 345 in sagittal section of head, 340 Submandibular lymph nodes, 268, 269 Submandibular triangle, 272, 272t Submental lymph nodes, 268, 269 Submental triangle, 272, 272t Suboccipital muscles, 250–251, 251t. See also individually named muscles Suboccipital nerve, 270t Suboccipital triangle, 277 Substantia nigra, 322 Sulcus terminalis, 206, 207t

T

Superficial cervical lymph nodes, in neck, 268 Superficial neck muscles, 238, 238t, 239t Superficial temporal artery, 47 auricular arteries and, 157 parts/branches of, 47t Superficial temporal vein, infection transmission and, 52t Superior colliculus, axons to, 137 Superior ganglion, 88t, 90t Superior labial glands, nerve supply to, 161 Superior laryngeal nerve, 91, 91t lesions of, 263, 263t Superior longitudinal muscle, 204, 204t, 205 Superior meatus, 143 paranasal sinus drainage and, 145t Superior ophthalmic vein, dural sinus drainage and, 302 on coronal MRI of head, 314 Superior orbital fissure, neurovascular pathways through, 67t, 94, 95t, 118 Superior sagittal sinus, 297, 311, 313 groove for, 10 infection transmission and, 52t Superior thyroid artery, 41t, 42, 43t Superior tympanic artery, 166, 166t Suprachiasmatic nucleus, axons to, 137 Supraclavicular nerves of lateral head and neck, 99 in nuchal region, 277 Suprahyoid muscles, 202–203, 202t, 254–255, 254t Supranuclear paralysis, 84 Supraorbital foramen, 6 Supraorbital nerve, 76, 77t on coronal MRI of head, 314, 315 Supraspinous ligaments of cervical spine, 234, 235 of vertebral arch, 228 Suprasternal notch, inferior boundary of neck and, 273 Supratrochlear nerve, 76, 77t Surface designation, of teeth, 180 “Surgical capsule,” thyroid gland, 264 Sutures, cranial. See Craniosynostoses Swallowing hyoid bone and, 23 phases of, 217 Sympathetic nervous system, 63 Sympathetic trunk in carotid triangle, 282 in deep lateral cervical region, 283 Synapses in CNS, 307 neurons and, 306 patterns in olfactory bulb, 153 Synaptic patterns, 307 Syndesmosis. See Craniosynostoses

T T4 (thyroxine), 265 Tables, outer and inner, of calvaria, 11 Taste, 222 facial nerve and, 85 nerve lesions, 82t, 83 mandibular nerve and, 81t

369

T

Taste buds

Taste (continued) maxillary nerve and, 79t qualities of, 223 tongue innervation and, 221, 223 Taste buds, 222, 223 facial nerve and, 85 Taste receptors, 223 Tear film, structure of, 123 Tectorial membrane, 170 Teeth alveolar processes of mandible shape influenced by, 23 resorption of, 23 coding of, 180 deciduous, 188–189, 188t permanent, 180–181 structure of, 182, 182t surface designation, 180 types of. See Canines; Incisors; Molars; Premolars Telencephalon, 295, 295t structures of, 297 Temporal bone, 5, 7, 9, 12, 14, 18–19, 154–155 clinically important relations in, 154 fractures of, facial nerve lesion and, 82t, 83 ossification centers of, 18 parts of, 154 in transverse section of head, 324 Temporal crescent, 135 Temporal nerve, posterior deep, TMJ capsule and, 37 Temporal visual field, 134 Temporalis muscle, 30, 30t, 31, 198, 198t, 199 Temporomandibular joint (TMJ) biomechanics of, 34–35, 196–197 dislocation of, 37, 195 glenoid fossa of, 36, 194 ligaments of, 36–37, 194–195 in lateral TMJ, 36, 194 in medial TMJ, 37, 195 mandible head in, 36, 194 mandibular fossa of, 36, 194 movements of, 35, 197 mandibular, 34, 196 MRIs of neck through coronal view, 319 transverse view, 334 open, 37, 195 sensory innervation of, 37, 195 Temporoparietalis muscle, 25 Tensor tympani, 163 Tensor veli palatini muscle, 212, 213t on transverse MRI of head, 333 Tentorium, 323 Tetraiodothyronine (thyroxine), 265 Thalamic nuclei, axons to, 137 Thermal function tests, of vestibular apparatus, 164 Third molars. See Wisdom teeth Thoracic inlet structures, 281 deep anterolateral, 282 Thoracic muscles (external intercostals), 242 Thoracic vertebra, structural elements of, 227, 227t Thoracolumbar fascia, 241, 242, 243 Thorax, vagus nerve branches to, 91t

370

Thyroarytenoid muscle, 258, 258t Thyroepiglottic ligament, 256 Thyrohyoid muscle, 254, 254t, 255 Thyroid arteries, 265 in deep lateral cervical region, 283 right inferior, branching patterns variations, 281 Thyroid cartilage, 256, 257 on MRIs of neck coronal view, 317 transverse view, 336 Thyroid gland, 264 histology of, 265 topography of, 264 on transverse MRI of neck, 337 in transverse sections of neck at C6/C7 level, 330 at C7/T1 level, 331 at T1/T2 level, 331 Thyroid veins, inferior, 281 Thyroid venous plexus, 265 Thyropharyngeus muscle, 213t, 214, 215 Thyroxine (T4, tetraiodothyronine), 265 Tinnitus, 165 TMJ. See Temporomandibular joint (TMJ) Tongue innervation of, 221 mucosa of, 206, 207t muscles of, 204, 204t, 205 neurovasculature of, 220–221 papillae of, 206 regions and structure of, 207t taste buds of, 85, 222, 223 unilateral hypoglossal nerve palsy of, 205 Tonotopic organization of auditory pathway, 172 in basilar membrane, 170 Tonsilla tubaria, 216 swelling of, 216 Tonsils lingual, 206, 207t, 216 palatine. See Palatine tonsils pharyngeal. See Pharyngeal tonsils Tooth. See Teeth Trabecular resistance, 131 Trachea on MRIs of neck sagittal view, 343 transverse view, 337 surgical approaches to, 262 Tracheotomy, 262 Translational movement, in TMJ, 34, 37, 196 Transverse ligament, of atlas, 327 Transverse muscle, of tongue, 204, 204t, 205 Transverse sinus infection transmission and, 52t in transverse section of head, 325 Trapezius muscle, 25, 26, 38, 238, 239, 239t anterior cervical triangle and, 281 origins and insertions of, 39 paralysis of, 92, 92t posterior cervical triangle and, 278, 279 Trauma. See also Fracture(s)

Vertebrae

calvarial table sensitivity to, 11 dislocation of TMJ, 37, 195 Traveling wave formation in cochlea, 171 organ of Corti deflected by, 171 “Tribasilar bone,” 16 Trigeminal ganglion, in sagittal section of head, 340 Trigeminal nerve (CN V), 66t, 74–75 of anterior face, 96 emergence of, 97 brainstem reflexes and, 137 divisions and distribution of, 74, 74t in infratemporal fossa, 102–103, 103t mandibular division, 80, 81t maxillary division, 78, 79t ophthalmic division, 76, 77t on transverse MRI of head, 333 in transverse section of head, 325 function of, 67t in lateral head and neck, 99 nasal septum and, 148, 149 nuclei and lesions of, 75, 75t of right lateral nasal wall, 149 in sensory innervation of auricle, 158 of face, 64 in transverse section of head, 324 Triiodothyronine (T3), 265 Trochlear nerve (CN IV), 66t, 72, 72t, 114t emergence from brainstem, 114 eye movement and, 140 function of, 67t Trochlear nerve palsy, 72t, 113, 114t Tubal artery, 166, 166t Tumors of inner ear, 165 malignant parotid, spread of, 165 Tympanic arteries, 166, 166t Tympanic cavity, 154, 159 arteries of, 166, 166t clinically important levels of, 163 communications with, 160 infection of, 163 mucosal lining of, 163 ossicular chain in, 163 temporal bone and, 155 walls of, 160 Tympanic membrane, 159 arteries of, 167 quadrants of, 159 stapedius reflex and, 173 temporal bone and, 18 Tympanic nerve, 89, 89t, 161

U Umbo, in tympanic membrane, 159 Uncinate process, 145 Uncovertebral joints, 232 Unilateral hypoglossal nerve palsy, 205 Unilateral optic nerve lesion, 136, 139 Unilateral optic radiation lesion

V

in anterior temporal lobe, 136 in parietal lobe, 136 Unilateral optic tract lesion, 136 Upper quadrantanopia, contralateral, 136 Utricle, 156 macular structure of, 174 Uvula. See also Soft palate nasal cavity and, 147 on sagittal MRI of neck, 343

V Vagus nerve (CN X), 66t, 90–91 branches of, 90, 90t in carotid triangle, 282 course of, 90t in deep lateral cervical region, 283 function of, 67t laryngeal innervation and, 261, 262 lesions of, 263, 263t nuclei, ganglia, and fiber distribution of, 90, 90t, 91 pharyngeal innervation and, 213t, 217 in sensory innervation of auricle, 158 tongue innervation and, 221, 222 on transverse MRIs of head, 333 of neck, 335, 337 in transverse section of head through C6 vertebral body, 329 through nasopharynx, 326 in transverse section of neck, 331 Vallecula(e) epiglottic, in midsagittal section of head, 338 glossoepiglottic, 207t innervation of, 222 Veins. See also individually named veins of auricle, 157 of head deep, 52–53 superficial, 50–51, 51t of infratemporal fossa, 102–103, 102t of inner ear, 167 laryngeal, 261 of neck, 50–51, 51t, 267, 267t of orbit, 117 of tongue, 220 Venous “danger zone,” in face, 97 Venous drainage of head and neck deep, 52–53 superficial, 50–51, 51t of thyroid gland, 265 Venous sinus(es). See also Dural venous sinuses infection transmission and, 52t thrombosis and, 52t, 302 Ventral horn, spinal cord, 292 motor nuclei in, 58t Ventral rami, of spinal nerves, 290 Ventricles (brain), 297 choroid plexus and, 301 Vertebra prominens, in transverse section of head, 328, 329 Vertebrae. See Vertebral body(ies)

371

V

Vertebral (neural) arch

Vertebral (neural) arch, 226 ligaments of, 228, 228t Vertebral artery, in head sections sagittal, 339 transverse, 327 Vertebral body(ies), 226 cervical. See Cervical vertebrae (C1-C7) ligaments of, 228, 228t spinal cord segments and, 293t structural elements of, 227, 227t transverse section of head through at C5 level, 328 at C6 level, 329 Vertebral canal, spinal cord in, 298 Vertebral column joints of, 232 ligaments of, 228–229, 228t regions of, 226 Vertebral junction, transverse sections of neck through C6/C7 level, 330 C7/T1 level, 331 T1/T2 level, 331 Vertical gaze movements, 140 Vertical muscle, of tongue, 204, 204t, 205 Vertigo, 156 CN VIII lesion and, 168 thermal function tests for, 164 Vestibular apparatus, of ear, 156, 164, 174–175 thermal function tests of, 164 Vestibular folds, 260 Vestibular ganglion, 86, 86t, 165, 167, 169, 174, 176 Vestibular ligament, 256, 260 on sagittal MRI of neck, 344 Vestibular nuclei, 86t, 87, 177 of CN VIII, 168 efferent fiber targets and, 176, 177 role in maintaining balance, 177 topographic organization of, 177 Vestibular Reissner membrane, 170 Vestibular schwannoma, 87, 165, 168 Vestibular sensory cells, stimulus transduction in, 175 Vestibular system, 176–177 Vestibulocochlear nerve (CN VIII), 66t, 86–87, 86t, 168–169, 168t brainstem reflexes and, 137 central connections of, 176 function of, 67t in head sections sagittal, 341 transverse, 325 in internal acoustic meatus, 165 lesions of, 168t nuclei of, 168, 168t in brainstem, 169 temporal bone and, 155 on transverse MRI of head, 332 Vestibulo-ocular reflex, 137 Viscerocranium boundaries of, 6 ossification of, 2, 2t Viscerosensory nuclei, cranial nerves, 68t, 69 glossopharyngeal nerve, 88t vagus nerve, 90t

372

Visual cortex, 134, 135 contralateral, visual fields in, 134 convergence and accommodation and, 138 lesion of, 139 Visual field(s) in contralateral visual cortex, 134 defects, 136 perimetry detection of, 135 examination of, 135 hemifields, 135 Visual pathways geniculate part, 134, 135 convergence and accommodation and, 138 topographic organization, 135 lesions of, 136, 139 nongeniculate part, 134, 137 overview of, 134 Visual perception, lateral geniculate body and, 134 Visual system. See Visual pathways Vitreous body (vitreous humor), 125 VNO (vomeronasal organ), 153 Vocal cords/folds, 260 examination of, 259 false, 260 histology of, 263 laryngeal divisions and, 260t nerve lesions affecting, 263, 263t positions of, 259, 263 Vocal ligament, 256, 258t, 260 on sagittal MRI of neck, 344 Vocalis muscle, 258, 258t, 260 Vomer, 9, 12, 142, 190, 191 Vomeronasal organ (VNO), 153

W Waldeyer’s ring, 208, 216 “Watery eyes,” 122 Whispered speech, position of vocal folds during, 259 White matter, 292 in head sections coronal, 310 sagittal, 341 transverse, 325 Wisdom teeth, 186t, 187 on dental panoramic tomogram, 181 eruption patterns of, 188, 188t Wolfring gland, 122 Wormian bones, 8

Z Zenker diverticulum, 215 Zones of discontinuity, 129 Zonular fibers, ciliary body and, 128 Zygomatic arch, in transverse section of head, 325 Zygomatic bone, 5, 7, 12, 108 Zygomatic nerve, 78, 79t zygomaticofacial nerve, 78, 79t zygomaticotemporal nerve, 78, 79t Zygomaticus muscles, 24, 25, 26, 28, 29, 29t