Head and Neck Anatomy
January 17, 2017 | Author: Mobarobber | Category: N/A
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2021MSC – Head and Neck Anatomy
Contents 1. Embryology ......................................................................................................................................... 6 1.1. Introduction ................................................................................................................................. 6 1.2. The Germ Layers .......................................................................................................................... 6 1.3. Formation of the Mesoderm ....................................................................................................... 7 1.4. Development of the Nervous System .......................................................................................... 7 1.5. The Ectomesenchyme .................................................................................................................. 8 1.6. Facial Development ..................................................................................................................... 9 1.6.1. The Stomodeum and Oral Cavity .......................................................................................... 9 1.6.2. The Neck.............................................................................................................................. 10 1.6.3. The Branchial Arches........................................................................................................... 10 1.6.4. The First Branchial Arch ...................................................................................................... 11 1.6.5. 2nd Branchial Arch ............................................................................................................... 11 1.6.6. 3rd Branchial Arch ................................................................................................................ 11 1.6.7. 4th and 6th Arches ................................................................................................................ 12 1.7. Formation of the Face ................................................................................................................ 12 1.7.1. Formation of the Palate ...................................................................................................... 13 1.7.2. Formation of the Tongue .................................................................................................... 14 1.7.3. Formation of the Mandible ................................................................................................. 14 1.7.4. Formation of the Maxilla .................................................................................................... 15 1.8. Congenital Defects ..................................................................................................................... 15 2. Osteology of the Skull and Cervical Vertebrae ................................................................................. 16 2.1. Introduction ............................................................................................................................... 16 2.2. The Skull ..................................................................................................................................... 16 2.3. Single Bones ............................................................................................................................... 17 2.3.1. The Frontal Bone ................................................................................................................. 17 2.3.2. The Occipital Bone .............................................................................................................. 18 2.3.3. The Ethmoid Bone ............................................................................................................... 20 2.3.4. The Sphenoid Bone ............................................................................................................. 21 2.4. Paired Bone ................................................................................................................................ 23 2.4.1. Parietal Bones ..................................................................................................................... 23 2.4.2. Temporal Bones .................................................................................................................. 23 2.4.3. Maxillae ............................................................................................................................... 25 Page | 1
2021MSC – Head and Neck Anatomy 2.4.4. The Zygomatic Bones .......................................................................................................... 26 2.4.5. The Mandible (THE BIG ONE FOR US) ................................................................................. 26 2.4.6. The Palate ........................................................................................................................... 28 2.4.7. The Hyoid Bone ................................................................................................................... 28 2.5. The Vertebral Column ................................................................................................................ 29 2.5.1. C1 a.k.a. Atlas....................................................................................................................... 30 2.5.2. C2 a.k.a. Axis ........................................................................................................................ 30 3. Temporomandibular Joint (TMJ)....................................................................................................... 31 3.1. The Articular Disc (Meniscus) .................................................................................................... 32 3.2. Ligaments ................................................................................................................................... 32 3.2.1. Accessory Ligaments ........................................................................................................... 32 3.2.2. Ligaments of the Joint ......................................................................................................... 33 3.3. Innervation ................................................................................................................................. 33 3.4. Blood Supply .............................................................................................................................. 33 3.5. Movements of the Mandible at the TMJ ................................................................................... 34 3.6. Ligaments and their Functions ................................................................................................... 34 4. Muscles of Mastication ..................................................................................................................... 36 4.1. Summary of the Main Muscles .................................................................................................. 37 4.2. Accessory Muscles ..................................................................................................................... 38 4.2.1. The Digastric Muscle ........................................................................................................... 38 4.3.1. Mylohyoid Muscle ............................................................................................................... 39 5. Muscles of Facial Expression ............................................................................................................. 40 5.1. Facial Structure .......................................................................................................................... 40 5.2. Muscles of the Lips and Cheeks ................................................................................................. 40 5.2.1. Deep Layer .......................................................................................................................... 40 5.2.2. Superficial Layer .................................................................................................................. 41 5.3. Muscles of the Orbit and Eyelid ................................................................................................. 43 5.4. Muscles of the Scalp .................................................................................................................. 43 6. Lymphatic Drainage .......................................................................................................................... 44 6.1. Lymphatic Capillaries ................................................................................................................. 44 6.2. Lymphatic Nodules..................................................................................................................... 45 6.3. Lymph Nodes ............................................................................................................................. 46 6.3.1. Nodes of the Head and Neck .............................................................................................. 46 7. Arterial Supply to the Head and Neck ............................................................................................... 49 Page | 2
2021MSC – Head and Neck Anatomy 7.1. The Aortic Arch .......................................................................................................................... 50 7.2. The Vertebral Artery .................................................................................................................. 50 7.3. The Carotid Arteries ................................................................................................................... 51 7.3.1. The External Carotid Artery ................................................................................................ 52 7.3.2. Internal Carotid Artery ........................................................................................................ 58 7.3.3. Circle of Willis...................................................................................................................... 59 8. Venous Drainage ............................................................................................................................... 61 8.1. The Cavernous Sinus .................................................................................................................. 62 8.2. Veins........................................................................................................................................... 63 8.3. The Pterygoid Plexus .................................................................................................................. 64 8.4. Surgical Plasticity........................................................................................................................ 65 8.5. Blood Supply to the PDL ............................................................................................................. 65 9. The Neck............................................................................................................................................ 66 9.1. Fasciae of the Neck .................................................................................................................... 66 9.2. Triangles of the Neck ................................................................................................................. 68 10. General Nervous System ................................................................................................................. 70 10.1. CNS ........................................................................................................................................... 71 10.1.1. The Spinal Cord ................................................................................................................. 72 11. Autonomic/Visceral Nervous System.............................................................................................. 75 11.1. Afferent Pathways.................................................................................................................... 75 11.2. Efferent Pathways .................................................................................................................... 75 11.3. The Sympathetic System .......................................................................................................... 76 11.3.1. Sympathetic Nervous System – Cranial Part ..................................................................... 77 11.4. Parasympathetic System .......................................................................................................... 78 11.4.1. The Facial Nerve ................................................................................................................ 78 11.4.2. Glossopharyngeal Nerve (IX)............................................................................................. 79 12. VII, IX, XII and the Cervical Plexus ................................................................................................... 80 12.1. The Facial Nerve (VII) ............................................................................................................... 80 12.1.1. Course of the Facial Nerve ................................................................................................ 80 12.1.2. The Facial Nerve’s Main Trunk (continued) ...................................................................... 83 12.1.3. Clinical Considerations: Paralysis ...................................................................................... 84 12.2. The Glossopharyngeal Nerve (IX) ............................................................................................. 85 12.2.1. Course of IX ....................................................................................................................... 85 12.3. The Vagus Nerve (X) ................................................................................................................. 87 Page | 3
2021MSC – Head and Neck Anatomy 12.4. The Hypoglossal Nerve (XII) ..................................................................................................... 88 12.5. The Cervical Plexus................................................................................................................... 88 12.5.1. Superficial Ascending Branches ........................................................................................ 90 12.5.2. Superficial Descending Branches ...................................................................................... 90 12.5.3. Deep Branches .................................................................................................................. 91 13. The Trigeminal Nerve (V1 and V2) ................................................................................................... 92 13.1. V in general .............................................................................................................................. 92 13.1.1. Cutaneous Distribution ..................................................................................................... 92 13.1.2. Central Connections .......................................................................................................... 93 13.2. V1: The Ophthalmic Division..................................................................................................... 94 13.2.1. Course ............................................................................................................................... 94 13.2.2. Frontal Nerve .................................................................................................................... 95 13.2.3. Lacrimal Nerve .................................................................................................................. 95 13.2.3. Nasociliary Nerve ............................................................................................................. 95 13.3. The Maxillary Division (V2) ....................................................................................................... 96 13.3.1. Course ............................................................................................................................... 96 13.3.2. The Branches ..................................................................................................................... 96 13.3.3. Branches of the Maxillary Nerve from a Lateral View and Associated Structures ........... 99 13.4. Nerve Supply of the Upper Teeth .......................................................................................... 100 14. The Mandibular Division of the Trigeminal Nerve (V3) ................................................................. 101 14.1. Course .................................................................................................................................... 101 14.2. Branches of the Posterior Division......................................................................................... 102 14.2.1. Auriculotemporal Nerve ................................................................................................. 102 14.2.2. Inferior Dental Nerve (VERY IMPORTANT)...................................................................... 102 14.2.3. Nerve to the Mylohyoid .................................................................................................. 103 14.2.4. The Lingual Nerve ........................................................................................................... 103 14.3. Branches of the Anterior Division .......................................................................................... 104 14.3.1. The Buccal Nerve (aka Long Buccal Nerve) ..................................................................... 104 14.4. A Nice Visual Summary of the Branches ................................................................................ 104 15. Brainstem and Nuclei .................................................................................................................... 105 15.1. The Reticular Formation ........................................................................................................ 105 15.2. The Midbrain .......................................................................................................................... 106 15.3. The Pons ................................................................................................................................. 107 15.4. The Medulla Oblongata ......................................................................................................... 108 Page | 4
2021MSC – Head and Neck Anatomy 15.5. The Trigeminal Nerve (V) ....................................................................................................... 109 15.5.1. Mesencephalic Nucleus .................................................................................................. 110 15.5.2. Chief Sensory Nucleus ..................................................................................................... 110 15.5.3. Nucleus of the Spinal Tract ............................................................................................. 110 15.5.4. The Tract of the Spinal Nucleus ...................................................................................... 110 15.5.5. The Motor Part................................................................................................................ 111 15.6. The Facial Nerve (VII) ............................................................................................................. 111 15.7. Glossopharyngeal Nerve ........................................................................................................ 111 16. Clinical Case Studies ...................................................................................................................... 112 16.1. Cavernous Sinus Thrombosis ................................................................................................. 112 16.2. Designing a Periodontal Flap ................................................................................................. 113 16.3. Bell’s Palsy .............................................................................................................................. 113 16.4. Ludwig’s Angina ..................................................................................................................... 114 16.5. Principles for Injecting Local Anaesthesia.............................................................................. 115
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2021MSC – Head and Neck Anatomy 1. Embryology 1.1. Introduction -
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The most important thing to take note of first is that almost nothing in the body is formed for no reason. Every structure will have some form of function or purpose that it will fulfil. Similarly, formation of the skull is attempted by minimising material and maintenance. o It is interesting to note that many spaces and septa within the head actually serve to add strength against longitudinal forces In a way, we are getting something for nothing. o The face is however, vulnerable to horizontal damage. The neck needs to be overengineered in order to protect it. o It is structure such that no matter what position it is in, the bones will not disrupt any existing nerves or blood vessels. The key to anatomy is to logically link how, where and why structures are where they are. o There is always a correlation between function and structure. o It is also important to note that soft tissues such as blood vessels, nerves and muscles form before the bone and therefore, formation of bone accommodates and facilitates these structures E.g. Foramena
1.2. The Germ Layers -
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The developing embryo forms a three-layered plate shape structure that is made up three germ layers being: o Ectoderm o Mesoderm o Endoderm The ectoderm and endoderm develop first with the mesoderm developing in the third week. The mesoderm gives rise to connective tissue which gives structure, form and reparative capabilities to our body.
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2021MSC – Head and Neck Anatomy 1.3. Formation of the Mesoderm -
Formation of the mesoderm begins at week 3 with the development of a structure called the primitive streak
Figure 1 Formation of the primitive streak at Week 3
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Cells from the ectoderm migrate towards the primitive streak and form a cavity beneath it. They then spread between the ectoderm and endoderm to form the middle third layer. o This process continues until the mesoderm fully separates the ecto and endoderm except at the head and tail ends. Note that although the head end of the embryo has no mesoderm but we still have mesodermal structures in our head. o To understand where the mesoderm for the head comes from, the formation of the nervous system needs to be looked at.
1.4. Development of the Nervous System -
Development of the nervous system begins at the head end of the embryo. It starts off as a thickening in the ectoderm in this area. This thickening is called the Neural Plate. The margins of the neural plate then thicken resulting in the margins being raised called Neural Folds. Between the neural folds is the neural groove. Neural folds continue to develop towards each other until they meet leading to the formation of the neural tube. o The neural tube will eventually form the ventricles and central canal of the nervous system.
Figure 2 Progression from the Neural Plate
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2021MSC – Head and Neck Anatomy -
In the diagram above, note the structures that form alongside the growing folds. These are called Neural Crests When the neural tube forms, the neural crest cells separate from the remainder to form a group of cells on their own.
1.5. The Ectomesenchyme -
There is debate over whether or not the neural crest cells are derivatives of the developing nervous cells or a completely distinct group themselves o For this reason they are sometimes referred to as the Fourth Germ Layer
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Embryonic connective tissues derived from the Neural Crest Cells are termed Ectomesenchyme to distinguish them from cells of the actual mesoderm produced at the primitive streak. It reflects the ectodermal origin of Neural Crest Cells but their mesodermal functions. The significance of this is that skull and facial bones form in a different manner to other bones in the body due to the fact that they are ectomesenchyme in origin. o Bones of the face and cranium (except the base of the skull) are formed via intramembranous ossification as opposed to endochondral ossification of most other bones.
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The Neural Crest Cells are essential to the development of the embryo as they migrate extensively around the body and give rise to components of the PNS such as: o Sensory Ganglia, Sympathetic neurons, Schwann Cells, Meninges and Pigment Cells Furthermore, they also give rise to the embryonic connective tissues of the facial region and the cartilages of each branchial arch.
Note that the head and neck muscles are not ectomesenchyme in origin.
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2021MSC – Head and Neck Anatomy 1.6. Facial Development -
The face develops from five embryonic tissue masses or processes. They all arise from rapid multiplication of neural crest cells. o Frontonasal Process o Maxillary Processes (paired) o Mandibular processes (paired)
Figure 3 Processes of the developing face
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These serve as the starting points for facial development.
1.6.1. The Stomodeum and Oral Cavity
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The developing mouth is termed the stomodeum or stomatodeum It appears during the fourth week of development as a depression in the embryonic surface. o It is at that this point where facial features start being worked out. o The floor of this depression pushes against the developing GIT. The two are separated by the buccopharyngeal membrane and represents the meeting of ectoderm and endoderm. This buccopharyngeal membrane will eventually break down to allow the stomodeum to open directly into the primitive pharynx. Eventually the stomodeum will give rise to the oral cavity. o At first it is lined by oral ectoderm which gives rise to the teeth before finally becoming the oral epithelium. At the sides of the stomodeum, its space becomes limited with the formation of the first pair of branchial arches which give rise to the lower part of the face.
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2021MSC – Head and Neck Anatomy 1.6.2. The Neck
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Development of the neck begins at the same time as development of the face, being in the fourth week of embryonic life. It arises from the branchial arches and the primitive pharynx which is part of the digestive tube. o The caudal part of the primitive pharynx forms the oesophagus and a ventral outgrowth leads to formation of the larynx and trachea. The buccopharyngeal membrane eventually breaks allowing for communication between the oral cavity and the pharynx.
1.6.3. The Branchial Arches
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The branchial arches are bulges on the embryo found beneath the developing brain. Overall there are six branchial arches but the fifth one is lost. Each branchial arch develops into different structures and each contain a portion of primitive striated muscle, some nervous tissue from neural crest cells, some vascular tissue and a bar of cartilage in its mesodermal core. o Because of this, each arch contains its own major nervous and blood supply Each branchial is covered externally by ectoderm and internally by endoderm and support the lateral walls of the pharynx. o The central component is either mesoderm or ectomesenchyme. Damage to any of these arches will cause defects in the structures they specifically give rise to.
Figure 4 Branchial Arches, Clefts and Pouches
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2021MSC – Head and Neck Anatomy 1.6.4. The First Branchial Arch
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Also referred to as the mandibular arch o Forms the mandible, maxilla, muscles of mastication and the mandibular division of the trigeminal nerve. o The cartilage found at the centre of this arch is called Meckel’s Cartilage This structure gives rise to the incus, malleus, sphenomandibular ligament and the lingual. Bones of the mandible and maxilla do not form from this. All facial muscles will be innervated by motor neurons of the mandibular division of the trigeminal nerve. o The nerve migrates with the muscles. The muscle tissue will develop into: o Muscles of mastication o Mylohyoid Muscle o Anterior belly of the digastric muscle The artery of the first arch does not survive. First branchial pouch becomes the auditory tube and middle ear First branchial cleft becomes the external auditory meatus and the tympanic membrane
1.6.5. 2nd Branchial Arch
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Also called the Hyoid Arch Cartilage is called Reichert’s Cartilage o Stapes o Styloid Process of the Temporal Bone o Stylohyoid Ligament The muscle tissue forms the muscles of facial expression o And Stapedius muscle, stylohoid muscle and the posterior belly of digastric It’s nerve is the Facial Nerve (VII) Artery of the second branch also degenerates. 2nd Pouch becomes the tonsillar fossa which develops into the palatine tonsil.
1.6.6. 3rd Branchial Arch
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Artery becomes the Common Carotid and contributes to the proximal part of the internal carotid Cartilage of the 3rd arch contributes to the hyoid bone Muscle becomes the stylopharyngeus muscle Nerve becomes the Glossopharyngeal Nerve (IX)
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2021MSC – Head and Neck Anatomy 1.6.7. 4th and 6th Arches
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These two arches fuse. Their cartilages contribute to most of the laryngeal cartilages Fourth Arch: o Superior Laryngeal Branch of the Vagus Nerve o Artery becomes the arch of the Aorta on the left side Contributes to the right subclavian and brachiocephalic arteries. Sixth Arch: o Recurrent Laryngeal Branch of the Vagus Nerve o Artery contributes to the pulmonary arteries.
1.7. Formation of the Face -
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The face develops between the 24th and 38th day of gestation During the early stages, development is dominated by changes that result in the formation of the primitive nasal cavities. Eventually the nasal and oral cavities will both communicate with the pharynx but not with each other. o Palate separates them. The frontonasal process develops two nasal pits. Tissue builds up around them in a horse-shoe shape fashion to form the lateral and medial nasal processes.
The maxillary process then grows medially towards the medial and lateral nasal processes.
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2021MSC – Head and Neck Anatomy 1.7.1. Formation of the Palate
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The growth of the maxillary processes pushes the two nasal processes together and towards the midline o At the midline they fuse to create the middle part of the nose, the middle part of the upper lip and the anterior part of the maxilla and the primary palate. AKA the premaxilla o Failed fusion results in a cleft palate Palatine processes then extend out from the maxillary processes and grow towards the primary palate.
Figure 5 Palatine Processes extending out from the maxillary process towards the primary palate
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Take note that it isn’t till after the formation of the secondary palate that the distinction between the oral and nasal cavities can be made clearly. o Formation of the secondary palate takes place between the 7th and 8th weeks of development and results from fusion of the palatine processes. Because the difference in formation, the primary and secondary palates have different innervations and blood supplies with the crossover occurring at the canines. o Therefore when extracting a canine, block both nerves.
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Primary Palate: o Upper incisors and anterior palate o Nerve: Incisive Branch of the Long Nasopalatine Branch of the Maxillary Division of the Trigeminal Nerve Secondary Palate: o Nerve: Greater Palatine Branch of the Maxillary Division of the Trigeminal Nerve
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2021MSC – Head and Neck Anatomy 1.7.2. Formation of the Tongue
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At the midline of the mandibular process, a mesenchymal swelling arises called the tuberculum impar. Two other swellings appear on either side of the tuberculum impar which expand rapidly and merge together with the tuberculum impar to form a large mass. o This large mass forms the anterior two thirds of the tongue. It is this reason why the anterior 2/3s of the tongue are innervated by the mandibular division of the trigeminal nerve as their sensory nerve supply. The nerve of the second branchial arch supplies the taste fibres to the anterior 2/3s
The posterior 1/3 of the tongue arises from the hypobrancheal eminence which is a large midline swelling from the third branchial arch. It is innervated by the Glossopharyngeal nerve.
1.7.3. Formation of the Mandible
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The mandible develops in the mandibular process. It is important to note that whilst it is located closely to Meckel’s Cartilage, it makes very little contribution to the formation of the mandible. The two mandibular processes fuse in the midline to the mandibular arch. o The bone of the mandible forms in the mesenchymal tissue that condenses laterally to the cartilage. The cartilage begins to disappear.
The bone forms a trough through which the inferior dental nerve runs. Page | 14
2021MSC – Head and Neck Anatomy -
The bone directly above this through forms a series of compartments for the individual teeth. It then closes over the tooth germs to form a roof over the trough.
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By 10 weeks of development, the rudimentary mandible is formed almost entirely from intramembranous ossification with little influence from Meckel’s cartilage o Still keep in mind which structures Meckel’s cartilage gives rise to. o However, there is some evidence to suggest that Meckel’s cartilage may contribute to a small extent to the formation of the mandible anterior to the mental foramen.
1.7.4. Formation of the Maxilla
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Similarly to the mandible, the maxilla develops from condensation of mesenchyme from the first branchial arch. The maxilla is also formed by intramembranous ossification Maxillary sinus forms in the 16th week.
1.8. Congenital Defects -
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Although genetic determinants are the primary actors in formation of the head, environmental factors such as drugs can also result in congenital defects. Types of environmental factors which can affect the embryo include: o Infectious agents o Ionising radiation such as X-rays o Drugs o Hormones o Nutritional Deficiencies o Stress The most common congenital defects are orofacial clefts (and cleft palates) o These result from failed fusion of the medial nasal processes and the maxillary processes.
Because of this, the affected person cannot generate the pressure to suck due to not having the seal. This defect can also be unilateral (only on one side)
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2021MSC – Head and Neck Anatomy 2. Osteology of the Skull and Cervical Vertebrae TO LEARN: -
Be able to draw both a superior and inferior view of the floor of the cranium Also be able to draw the individual bones.
2.1. Introduction -
As stated in the previous topic, always remember that structures in the skull exist for a reason and will reflect the soft tissue structures within those areas. o This will help you learn and relate the locations of different structures, both bone and soft tissue o i.e. Nerves, blood vessels etc. form first with bone then forming around them (which explains the position and existence of foramena)
2.2. The Skull -
The skull is made up of the mandible and the cranium o The reason for this separation is that the ONLY moveable joint between bones in the skull occurs between the mandible and a specific point on the cranium
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Another way to divide the bones of the skull is as follows: o Bones that make up the face (Facial Bones) The upper part is fixed to the calvaria and cannot move. The lower part is the mandible and has the ability to move. o Bones that contain the brain (Cranial Bones which together is called the Calvaria)
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It is the most highly modified and specialised region of the skeleton o It is adapted to support and contain the brain and the special senses with it as well as the opening of the GIT.
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The joints between the bones of the cranium are immovable fibrous joints called sutures o Except the mandible of course
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Sutures allow for the growth of the calvaria and facial bones and many will eventually ossify and close. o However the rate of ossification isn’t necessarily proportional to age.
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Sutures are only found the in skull.
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For the sake of identifying and describe the bones of the skull, we will look at them as Single Bones and Paired Bones Page | 16
2021MSC – Head and Neck Anatomy
2.3. Single Bones -
As per their name, single bones are not bilateral and as a result will lie close to the midline of the skull.
2.3.1. The Frontal Bone
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Overall there isn’t too much that you need to know about the frontal bone.
Anterior View Frontal Tuberosity
Glabella
Remnants of the Metopic Suture
Superciliary Arches
Zygomatic process Supraorbital Foramen/Notch Nasal Spine -
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Supraorbital Margin
Initially during development, a suture ran down the midline of the frontal bone called the metopic suture. Whilst the majority of it has ossified, remnants of it can be seen between the glabella and the nasal spine. The glabella is the flat surface between the superciliary arches. The zygomatic process articulates with the zygomatic bone.
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2021MSC – Head and Neck Anatomy
Ethmoid Notches
Zygomatic Process
Supraorbital foramen
Orbital Plates
Supraorbital Notch
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Nasal Spine
Nasal Spine
The ethmoid notches provide the roof of the nasal cavity and indicates where the ethmoid bone will fit.
2.3.2. The Occipital Bone
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Located at the back of the head One of few parts of the skull that are formed by both intramembranous and endochondral ossification o The base is mesoderm in origin and is therefore endochondrally formed The base is a primary centre involved in facial growth and is important in making orthodontic calculations o The back is ectomesenchyme in origin and is therefore formed intramembranously. Posterior View of the Occipital Bone Squamous (Broken Egg Shell) part of the Occipital Bone
External Occipital Protuberance
Superior Nuchal Line
Inferior Nuchal Line
Condylar Canal Hypoglossal Canal
Foramen Magnum Occipital Condyles
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2021MSC – Head and Neck Anatomy
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The Condylar Canal is an emissary structure meaning that it isn’t present in every single person. When it is present, an emissary vein runs through it. o Presence or lack thereof of these structures doesn’t make any difference. The Hypoglossal Nerve (cranial nerve XII) runs through the hypoglossal canal located anterior to the foramen magnum. The occipital condyles articulate with the first cervical vertebra (C1) The nuchal lines run along the back of the occipital bone and indicate the points of attachment of various muscles Inferior View of the Occipital Bone
External Occipital Crest
Condylar Canal (Emissary)
Occipital Condyles
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Jugular Process
Pharyngeal Tubercle
It is helpful to note that any structure with external in its name will have an internal equivalent
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2021MSC – Head and Neck Anatomy 2.3.3. The Ethmoid Bone
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Found deep in the skull Resembles a crucifix with banners Ethmoid bone is a contributor to the nasal septum The ethmoid bone articulates with many other bones. Posterior View of the Ethmoid Bone
Crista Galli Orbital Plate Superior Concha Middle Concha Perpendicular Plate
Superior View of the Ethmoid Bone
Crista Galli
Cribriform Plate
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Perpendicular Plate Ethmoidal Air Cells or Sinuses
The cribriform plate fits into the ethmoid notches of the frontal bone The holes in the cribriform plate allow olfactory nerves to pass through The crista galli faces anteriorly in the skull and is where the falx cerebri attaches anteriorly. o The falx cerebri is a strong, arched fold of dura mater that descends in the longitudinal fissure and divides the cerebral hemispheres
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2021MSC – Head and Neck Anatomy
Sphenoid Bone Frontal Bone Sphenoidal Crest Nasal Bone
Septal Cartilage of the bone
Vomer
Figure 6 Sites of attachment for the ethmoid bone
2.3.4. The Sphenoid Bone
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The sphenoid bone is a butterfly-shaped bone that lies posteriorly to the ethmoid bone It’s main body is hollow as it contains the sphenoid sinuses It is a complex bone with many features Posterior View of the Sphenoid Bone
Dorsum Sellae
Superior Orbital Fissures
Foramen Rotundum
Spine
Scaphoid Fossa Body Pterygoid Fossa
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Vaginal Process
Lateral Pterygoid Plate Medial Pterygoid Plate Pterygoid Hamulus
The Lesser and Greater Wings of the sphenoid bone are separated by the Superior Orbital Fissures on each side The Lateral Pterygoid Plate serves as a point for muscle attachment The medial pterygoid plate serves to support the pterygoid hamulus Nervous supply of the maxilla and palate goes through Foramen Rotundum An important ligament also attaches to the spine of the sphenoid bone Page | 21
2021MSC – Head and Neck Anatomy Superior View of the Sphenoid Bone Anterior Clinoid Process
Tuberculum Sellae
Foramen Spinosum
Hypophyseal Fossa
Spine of the Sphenoid Bone
Posterior Clinoid Process Dorsum Sellae
Carotid Sulcus
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Optic Canal
Foramen Ovale
The pituitary gland sits in the hypophyseal fossa where it is protected by a meningeal layer Foramen Ovale is found on the greater wing where the Mandibular Division of the Trigeminal Nerve runs through it.
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2021MSC – Head and Neck Anatomy 2.4. Paired Bone -
Bilateral. i.e. One on each side of the midline
2.4.1. Parietal Bones
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Separated by the sagittal suture Have the superior and inferior temporal line which denote the attachments of the temporalis muscle Can also contain an emissary structure called the parietal foramen. When it is present it holds an emissary veins which leads to increased circulation
2.4.2. Temporal Bones
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Contains the middle ear, air sinuses and a very important artery (carotid!) Made up of four major parts o Squamous (broken egg shell) o Mastoid (where the mastoid process is) o Petrous (looks like a stone) o Styloid Process External View of the Temporal Bone
Articular Tubercle Squamous Part
Articular Eminence
Zygomatic Process of the Temporal Bone Glenoid Fossa
Mastoid Part Postglenoid Tubercle
Tympanic Plate External Acoustic Meatus
Mastoid Process Styloid Process
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Sheath of the Styloid Process
A meatus is a blind canal meaning it stops before the cranium The condyle of the mandible sits in the glenoid fossa The postglenoid tubercle which divides the tympanic plate from the temporal bone Page | 23
2021MSC – Head and Neck Anatomy Inferior View of the Temporal Bone
Petrosquamous Fissure Petrotympanic Fissure Glenoid Fossa
Tegmen Tympani
Squamotympanic Fissure
Carotid Canal Opening of the Anterior Canaliculus for Chorda Tympani
Stylomastoid Foramen Digastric Notch
Occipital Groove for Occipital Artery
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The squamotympanic fissure begins internally to the postglenoid tubercle and continues to run internally. o It separates the squamous and mastoid parts of the temporal bone When the squamotympanic fissure reaches tegmen tympani (thin plate of bone that separates the cranium from the tympanic cavity), it splits off into the petrosquamous fissure (anterior) and the petrotympanic fissure (posterior) Internal View of the Temporal Bone Articulates with Parietal Bone
Articulates with Greater Wing of Sphenoid
Arcuate Eminence Sulcus for Sigmoid Sinus
Internal Acoustic Meatus Articulates with Occipital Bone -
Petrous part of the temporal bone holds the middle and inner ear Internal Acoustic Meatus: VII and VIII run through here Page | 24
2021MSC – Head and Neck Anatomy 2.4.3. Maxillae Lateral View of the Maxilla
Frontal Process
Joins with ethmoid bone
Infra-orbital Foramen
Zygomatic Process
Nasal Notch
Canine Eminence
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Maxillary Tuberosity
The frontal process joins with the maxillary process of the frontal bone via the frontomaxillary suture The alveolar processes hold the sockets of the teeth and disappear upon tooth loss. Nerves and vessels pass through infra-orbital foramen Medial view of the Maxilla
Nasolacrimal Groove
Maxillary Hiatus
Greater Palatine Canal
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Palatine Process
The maxillary hiatus contains the ostium which represents the opening into the maxillary sinus o Clinically, if it closes over, sinusitis will ensue Pain from the maxillary sinus can often be referred down to the maxillary teeth. Correct diagnosis is key. Page | 25
2021MSC – Head and Neck Anatomy 2.4.4. The Zygomatic Bones
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Not too much we need to know about this one. Found joining to the lateral sides of the maxilla and the frontal bone. o Joins to the frontal bone via the frontal process o Joins to the zygomatic process of the maxilla o The temporal process of the zygomatic bone joins with the zygomatic process of the temporal bone to form the zygomatic arch The inferior border of the temporal process provides the point of attachment for the masseter muscle The malar eminence is found on the maxilla underneath the zygomatic process and is known to cause problems when trying to apply anaesthetic and extracting teeth.
2.4.5. The Mandible (THE BIG ONE FOR US)
External View of the Mandible Mandibular Notch Coronoid Process
Condylar Head Condylar Neck/Process
Ramus of the Mandible
Angle of the mandible
Mental Foramen
Mental Protruberance
External Oblique Ridge Mental Tubercle
Body of the Mandible
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2021MSC – Head and Neck Anatomy Internal View of the Mandible
Lingula
Mandibular Foramen
Genial Tubercles Sublingual Fossa Digastric Fossa
Submandibular Fossa Mylohyoid Ridge/Line
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The mandibular foramen is the opening into which the Inferior Alveolar Nerve runs. o This is the nerve you target when anaesthetising the lower jaw.
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The lingula is a little ‘tongue’ of bone that lies over the opening of the mandibular foramen o Anaesthetic is applied just posterior to this structure Below is a table denoting the structures in the bone and their corresponding muscle/gland attachments
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Structure in the Bone
Muscle/Gland
Submandibular Fossa
Submandibular Gland
Mylohyoid Ridge
Mylohyoid Muscle
Digastric Fossa
Anterior Belly of the Digastric Muscle
Sublingual Fossa
Sublingual Gland
Genial Tubercles
Genioglossus and Geniohyoid muscles
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2021MSC – Head and Neck Anatomy 2.4.6. The Palate
Incisive Fossa Intermaxillary Suture Palatine Processes of the Maxilla
Palatomaxillary Suture
Greater Palatine Foramena
Horizontal Plates of the Palatine Bone
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Recall from embryology that the palate forms via two palatine processes developing out from the maxillary processes
2.4.7. The Hyoid Bone
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Unlike other bones of the skull, the hyoid bone isn’t directly attached to the rest of the skull or skeleton for that matter o Instead, it is suspended from the styloid processes of the temporal bone via the stylohyoid ligaments Superiorly, both bellies of the digastric muscle and the geniohyoid muscle attaches to it. Anteriorly, the mylohyoid and stylohyoid muscles attach Inferiorly, the sternohyoid muscle attaches (depresses the hyoid bone)
Figure 7 The hyoid bone and sites for muscle attachment
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2021MSC – Head and Neck Anatomy 2.5. The Vertebral Column
Body
Anterior Tubercle
Transverse Foramen
Posterior Tubercle Pedicle Superior Articular Facet
Vertebral Foramen
Lamina
Inferior Articular Process
Spinous Processes (Bifid) -
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Above is a generic image of the cervical vertebrae from a superior view. All the vertebrae will exhibit the majority of these structures if not all of them The transverse foramen provides the passage for the Vertebral Artery and Veins o Only cervical vertebrae have transverse foramen o Only C1-C6 have the vertebral artery running through o All the cervical vertebrae have multiple vertebral veins running through The spinal cord runs through the vertebral foramen Lateral View of a Typical Cervical Vertebra Anterior Tubercle
Raised lip on the upper surface of the body
Spinous Process Sulcus for the Ventral Ramus -
Posterior Tubercle
Inferior Articular Process
The raised lip on the upper surface of the body serves to limit neck movement The anterior and posterior tubercles of the transverse process act as points of attachment for muscles and ligaments When vertebra are attached (above and below), an intervertebral foramen is formed by the superior and inferior vertebral notches through which the spinal nerves emerge o The anterior and posterior tubercles lie either side of this foramen o The vertebrae are attached by strong ligaments Page | 29
2021MSC – Head and Neck Anatomy -
Only C3 – C6 follow the general pattern as described above. Therefore C1, C2 and C7 must be looked at separately o C1 and C2 have variations that allow free head movement i.e. Head can move without moving the neck with it.
2.5.1. C1 a.k.a. Atlas Anterior Tubercle Facet for Dens
Outline of Dens (from Axis)
Transverse Process Groove for the vertebral artery
Transverse Foramen Superior Articular Facet
Posterior Arch
Posterior Tubercle -
The first thing to take note of is that C1 does not have a body. The large superior articular facet is where the occipital condyles will articulate with the vertebra.
2.5.2. C2 a.k.a. Axis Dens Groove for the transverse Ligament of Atlas
Superior Articular Surface
Transverse Foramen
Inferior Articular Process
Body
Spinous Process
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Dens slots into the large space behind the anterior arch of Atlas. It is attached to Atlas via the Ligament of Atlas
o
It allows Atlas to rotate around the dens
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2021MSC – Head and Neck Anatomy 3. Temporomandibular Joint (TMJ) -
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The TMJ represents the most complex joint in the body excluding the knee. It is the site of articulation between the mandible and the cranium It is a bilateral synovial joint and plays a key role in mastication o Bilateral meaning there is one on each side of the midline Because of this, TMJ disorders must be treated on BOTH sides. It is made up of parts of the mandible and the temporal bone covered in stress-bearing fibrocartilage and surrounded by several ligaments as well as the joint capsule o The condyle of the mandible and the glenoid fossa of the temporal bone Between these two bones is a fibrous articular disc which divides the joint into two separate synovial-lined compartments Called the meniscus Glenoid Fossa (Temporal Bone)
Articulator Disc/Meniscus
Condyle
Figure 8 The TMJ
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The heads of the condyles are ‘football shaped’ and are directed at an oblique angle towards foramen magnum o Because of this shape and alignment, there is no such thing as perfect rotation of the mandible around the condyle o Any attempts to rotate the mandible about the condyles will force protrusion of the mandible as well. The condyles normally sit in the glenoid fossa, but when it is open, it sits just behind the articular tubercle o The tubercle actually serves to stop dislocation of the jaw wherever possible.
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2021MSC – Head and Neck Anatomy 3.1. The Articular Disc (Meniscus) -
It is a biconcave plate of dense fibrous connective tissue. The meniscus actually moves with the condylar head during movements The inferior surface is concave to facilitate the rounded condylar head The superior surface is convex centrally and concave laterally o The disc is thickest at the periphery and thinnest in the stress-bearing part of the joint.
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The blood supply to the meniscus is incredibly minimal. Therefore the majority of the nutrition must come from another source, in this case being the synovial fluid of the joint Little blood supply means that there will be very little healing capability and also very few nerves o Therefore, most pain at the TMJ won’t be from the disc.
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3.2. Ligaments -
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The ligaments of the TMJ need to be distinguished as either ligaments of the joint or accessory o Ligaments of the joint are directly involved in securing the joint They are always true ligaments o Accessory Ligaments aren’t directly involved in the joint and aren’t nearly as strong as ligaments of the joint. They do however play an important role in preventing extreme movements as they contain stretch receptors with automatic reflex cut-off systems Accessory ligaments can be both true and false Fascia are sheets of dense fibrous tissue that ‘groups and packages’ certain muscles and nerves, arteries and veins to separate them with lubricating fluid between.
Sphenomandibular Ligament Lateral/Triangular/ TM Ligament Stylomandibular Ligament 3.2.1. Accessory Ligaments
Fibrous Capsule
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2021MSC – Head and Neck Anatomy -
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The sphenomandibular ‘ligament’ is a false ligament and is actually just a sheet of fascia. o This ligament needs to be bypassed when injecting anaesthetic. o It is a derivative of Meckel’s cartilage o Runs between the spine of the sphenoid bone and the lingula of the mandible The stylomandibular ligament is a genuine ligament which runs between the styloid process of the temporal bone and the posterior border of the angle of the mandible Together, these two ligaments play a suspensory role in letting the mandible hang from the cranium. The stretch receptors play an important role in preventing excessive opening and protrusion of the mandible.
3.2.2. Ligaments of the Joint - The Fibrous Capsule contains stretch receptors. o Therefore, any pain from the TMJ is from here. o Overstretching will ‘sprain’ it and the pain will stop you from straining it further. i.e. overmove = pain o Together with the triangular ligament, it restricts movement - The Fibrous Capsule is reinforced both medially and laterally by bundles of collagen fibres. o Medially, there is a slight thickening of the capsular ligaments. o Laterally, it is a lot more heavily reinforced by the Lateral/Triangle/Temporomandibular Ligament
3.3. Innervation -
The joint capsule is highly sensitive due to being heavily endowed with sensory nerve endings from the Auriculotemporal branch of the mandibular division of the trigeminal nerve It also receives fibres from the Masseteric branch of the mandibular division
3.4. Blood Supply -
The blood supply to the TMJ occurs via the Maxillary Artery and branches of the Superficial Temporal Artery. Venous drainage occurs via the pterygoid plexus Lymphatic drainage is through the Buccal and Submandibular lymph nodes
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2021MSC – Head and Neck Anatomy 3.5. Movements of the Mandible at the TMJ -
The first thing to note is that there exists no such position of the mandible where it is fully relaxed o i.e. No matter what position the mandible is in, there is AT LEAST ONE MUSCLE WORKING
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Movements include depression, elevation, protrustion, retrusion and lateral movements Dislocation of the mandible occurs when the condyle slips out of position and is caught/jammed past the articular tubercle/eminence o Retrusion is limited in that the mandible can only be forcibly retruded avbout 1.5mm
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Jaw opening is a combination of depression and protrustion o Protusion cannot occur without depression as depression brings the teeth out of occlusion so they can move.
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During lateral movements, one condyle is ipsilateral and one is contralateral o The ipsilateral condyle is the one on the side the mandible is moving towards It remains in the fossa moving slightly downward and laterally o The contralateral condyle is the one on the opposite side
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Pulled forwards, down and medially
3.6. Ligaments and their Functions -
Generally, they act to limit the range of movement in a joint through their stretch receptors and pain reflexes as well as their tautness
Ligament
Function
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Limits the movements of the condyle to an arc-shape Limits movements of the contralateral side
Medial Thickening of Fibrous Capsule
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Limits depression of the mandible
Stylomandibular
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Limits depression and prevents dislocation Runs with the pterygoid fascia
Sphenomandibular
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Limits movements of the ipsilateral side
Articular Disc/Meniscus
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Limits retrusion of the mandible
Lateral Ligament
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2021MSC – Head and Neck Anatomy
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2021MSC – Head and Neck Anatomy 4. Muscles of Mastication -
Remember that bones and muscles together form a dynamic system being musculoskeletal. This means that they are responsive to each other and they will alter themselves in response to changes within each other o E.g. Muscle enlarges? Bone grows accordingly.
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Muscles of mastication are defined as any muscles immediately involved in movements of the mandible during mastication and speech.
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Main muscles include: o Masseter o Temporalis o Medial Pterygoid o Lateral Pterygoid Accessory muscles include: o Digastric muscle (anterior belly) o Mylohyoid o They do not directly move the condyle
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2021MSC – Head and Neck Anatomy 4.1. Summary of the Main Muscles
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2021MSC – Head and Neck Anatomy 4.2. Accessory Muscles -
Their function is dependent on the actions of other surrounding structures They are called accessory as they do not directly cause movement of the condyle. They are both suprahyoid muscles (i.e. above the hyoid bone)
4.2.1. The Digastric Muscle
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It is named as so because it is made up of two separate bellies. It mainly runs between the mastoid process (temporal bone) down to the mandible at the mental protuberance. o Part-way between, it becomes a tendon which passes through a pulley attached to the hyoid bone This pulley acts to separate the anterior and posterior bellies It can pull up the hyoid bone, thereby also pulling up the larynx to close it off when swallowing. The position/movement of the hyoid bone can modify the position of this pulley and also determine the function of the muscle. o The position or movement of the hyoid bone is dependent on the infrahyoid and suprahyoid muscles. o E.g. If the infrahyoid muscles are contracted, contraction of the suprahyoid will open the jaw. Aids in mastication. BUT, relaxation of the infrahyoid and contraction of the suprahyoid will only elevate the hyoid bone Swallowing! It is important to note that the two bellies can work independently of each other due to having separate nerve supplies. Belly
Origin
Path
Action
Nerve Supply
Anterior
Attaches to the digastric fossa. Found on the medial aspect of the mandible inferior to the genial tubercles.
Runs superficially down to the hyoid bone beneath the platysma muscle.
Pulls the hyoid bone forward and up. Also helps retract and depress the mandible.
Originates from first branchial arch so V3
Associated with mastication Posterior
Digastric notch of temporal bone. Found medial to the mastoid process.
Runs forward below the mandible beneath the superficial belly of the Submandibular gland down to the
Pulls the hyoid bone back and up
Mainly associated
Originates from second branchial arch and is therefore supplied by the Page | 38
2021MSC – Head and Neck Anatomy hyoid bone pulley -
with swallowing
Facial Nerve (VII)
Infrahyoid + Digastrics = opening of jaw for mastication Digastrics on their own = elevate the hyoid bone and larynx for swallowing
4.3.1. Mylohyoid Muscle
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Attaches the tongue to the mandible Forms the muscular floor of the mouth and is sometimes referred to as the oral diaphragm It controls the tongue and helps position it vertically
Anterior of Digastric (cut)
Digastric Fossa Median Raphe Mylohyoid Muscle Mylohyoid Ridge on the Mandible
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The mylohyoid muscle exists as two triangular sheets. They originate at the mylohyoid ridges of the mandible on each side. They both then travel posteriorly to attach to the hyoid bone The muscles meet at the midline in a tendinous raphe called the Median Raphe o The median raphe travels between the mandible and the hyoid bone. They are formed from the first brancheal arch and are innervated by the Lingual Nerve o The lingual nerve is the only motor branch of the posterior division of V3 Similarly to the digastric muscles, their function is dependent on the position of the mandible and hyoid bone.
Actions of the Mylohyoid Muscles: 1. If the mandible is held in position, the mylohyoid muscles elevate the hyoid bone and the tongue a. Important in the first phase of swallowing b. Elevation of the hyoid bone is important in closing off the larynx when swallowing 2. If the infrahyoid muscles are contracted, the mylohyoid muscle will aid in depression of the mandible.
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2021MSC – Head and Neck Anatomy 5. Muscles of Facial Expression 5.1. Facial Structure -
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The basic form of a person’s face is largely determined by the underlying bones of the skull. These bony structures are then covered by the soft tissue structures being mainly muscles and subcutaneous fat. These distribution of these soft tissues varies around the skull. Muscles of facial expression have been found to mainly act on areas with large amounts of subcutaneous tissue as they are more mobile and therefore play large role in facial expression. o Hence why they are called Subcutaneous Muscles of Facial Expression Below the skin, and move the skin.
All muscles of facial expression are derived from the second branchial arch and are therefore all innervated by the Facial Nerve (VII) o Whilst the tongue and eyes also play a role in facial expression, their muscles aren’t regarded as muscles of facial expression. Most of the facial expression muscles have a bony origin and insert into the soft tissues of the face
5.2. Muscles of the Lips and Cheeks 5.2.1. Deep Layer
Closely related to Buccal mucous membrane
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2021MSC – Head and Neck Anatomy 5.2.2. Superficial Layer
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2021MSC – Head and Neck Anatomy
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2021MSC – Head and Neck Anatomy 5.3. Muscles of the Orbit and Eyelid
5.4. Muscles of the Scalp -
The scalp itself consists of 5 layers. From superficial to deep, these layers are (NOTE THE FIRST LETTER OF EACH LAYER ): o Skin o Connective Tissue o Aponeurosis Tendinous sheet At the sides of the skull, it unites with the temporal fascia o Loose Connective Tissue Permits movement of the aponeurosis o Periosteum
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2021MSC – Head and Neck Anatomy 6. Lymphatic Drainage -
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The lymphatic system is a vascular system which performs 3 main functions: o Removal and return of blood plasma that hasn’t been reabsorbed into the capillaries during circulation o Absorption of fats from the small intestine o Most importantly, it plays a huge role in immunity It is the body’s protective system It is made up of: o Lymphatic capillaries and vessels o Lymph Nodes situated along the vessels o Organs such as the thymus, spleen and bone marrow o Circulating immune cells All blood and lymphatic vessels are lined by endothelium o Tears In the vessels expose connective tissue which triggers the clotting cascade. 80-90% of interstitial fluid gets reabsorbed back into capillaries with the remainder being taken up into the lymphatic system. Note that lymphatic vessels run parallel with the venous system and eventually drains back into it. o The lymph vessels drain back through the right lymphatic or thoracic ducts which then drain into the subclavian vein.
6.1. Lymphatic Capillaries -
The lymphatic system is purely drainage similar to veins, i.e. there is no arterial part to the lymphatic system They begin in vascular tissues as blind-ended lymphatic capillaries o They do not exist in avascular structures They are lined by endothelium which overlap each other so form flaps for fluid to enter under hydrostatic pressure. Once the fluid is in the lumen, it cannot go back out.
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2021MSC – Head and Neck Anatomy -
Similarly to veins, lymph capillaries have valves to ensure the fluid travels in one direction; towards and through the lymph nodes on their way back to the venous circulation
6.2. Lymphatic Nodules -
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They are small masses of lymphatic tissue that are distributed strategically around the body to protect the underlying tissues, especially those at risk from penetration by microorganisms from the GIT, respiratory and urinary tracts. o Remember that GIT, respiratory and urinary tracts are regarded as ‘outside the body’ o They mainly occur in the connective tissue beneath mucous membranes. They are packed with lymphocytes. Unlike actual nodes, they do not directly connect to the lymph vessels Whilst most nodules exist as small and on their own, they are sometimes found in large clusters called Lymph Nodes o An example of these are our tonsils. o Our tonsils form a ring around the entry of the oro and nasopharynx, made up of: Pharyngeal Tonsil Two Palatine Tonsils Lingual Tonsil o This ring is referred to as Waldeyer’s Lymphatic Ring
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2021MSC – Head and Neck Anatomy 6.3. Lymph Nodes -
Lymph nodes are small, bean-shaped masses of lymphatic tissues of varying size.
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They are enclosed in a strong fibro-elastic capsule. This capsule extends down into the node forming trabeculae which partially divide the node into separate compartments. You’ll notice that lymph nodes strongly resemble the kidneys The fluid is forced through a series of channels called Lymphatic Sinuses within the node in order to get to the outgoing vessel. o These sinuses are lined by lymphocytes and macrophages to filter the fluid. Lymph nodes are scattered and positioned such that by the time the fluid is returned to the venous circulation, it has been cleaned of all impurities.
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Lymph node position is therefore important. This is because if we know the route by which a body part is drained and which nodes lie in the drainage part, we can assess those nodes via palpation for swelling and hardness. Lymph node positions around the body are divided into regions. For us, the head and neck nodes are important as we can assess them to determine the spread of infection.
6.3.1. Nodes of the Head and Neck - The nodes of the head and neck can be divided into superficial and deep nodes. The superficial ones are usually more relevant to us clinically since they are much more easily palpated. Superficial Groups: -
Pericervical Ring Nodes accompanying superficial neck veins
Deep Groups: -
Perivisceral Ring Deep Cervical Chain
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2021MSC – Head and Neck Anatomy 6.3.1.1. Pericervical Ring (Superficial)
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Found around the base of the head and neck (peri = outer; cervical = neck region) Clinically important and is made up of: o Submental Group (below the front of the chin) o Submandibular Group (near the Submandibular gland) o Parotid or Pre-Auricular Group (Anterior to the ear) o Mastoid Group (near the mastoid process) o Occipital Group (around the back of the neck.
Parotid Nodes Mastoid Nodes Occipital Nodes Submandibular Nodes
Deep Cervical Nodes
Submental Nodes
Figure 9 The above diagram shows the drainage patterns of each node group. They all eventually drain into one of the Deep Cervical Nodes. The significance of this will be demonstrated later.
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Note that the further anterior the fluid origin is, the more cervical the Deep Cervical Node it’ll drain into. o The deep cervical nodes sit on the carotid sheath and drains the whole head. This pattern is very useful in determining the origin of an infection. o E.g. Using the diagram above, if there is an infection in the bottom Deep Cervical Node, it must be from the Submental Group of nodes as they are the only ones which drain into this node.
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2021MSC – Head and Neck Anatomy 6.3.1.2. Superficial Neck Nodes (Superficial)
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The nodes which accompany the superficial neck veins are also important since they are easily palpable. They tell us about superficial and systemic infections. These lie in two chains which follow the anterior jugular vein and the external jugular vein. o Nodes following the external jugular vein are easily palpated since they lie superficially to the sternocleidomastoid.
6.3.1.3. Perivisceral Ring (Deep)
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Named due to the fact that it surrounds the viscera of the neck. The most anterior group of these nodes are named based on their position as the group ascends the neck. They are: o Pre-tracheal nodes In front of trachea o Pre-laryngeal Nodes In front of larynx o Infrahyoid Nodes Below hyoid bone The posterior group are similarly named and are as follows: o Retro-Oesophageal Nodes (behind oesophagus) o Retro-Pharyngeal Nodes (behind the pharynx)
6.3.1.4. The Deep Cervical Chain (Deep)
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Difficult to palpate as it mainly sits deep to the sternocleidomastoid. It’s upper and lower ends are defined by two major nodes, named for the muscles near which they lie. o Jugulo-digastric Node (Upper) o Jugulo-omohyoid Node (Lower) o The other nodes within this chain are not named. All of the lymph from the head and neck will eventually drain into the deep cervical chain on both sides. o However, the connections are at different points, a fact which is important in diagnosis. The deep cervical drain drains into the Right Lymphatic Duct on the right side and the Thoracic duct on the left side.
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2021MSC – Head and Neck Anatomy 7. Arterial Supply to the Head and Neck -
Some questions to think about: o The head uses 14% of the total blood supply of the body. Is this proportionate with the mass of the head? o How do we prevent vessels from being crushed when we move the neck? o How do we compensate for heat loss through radiation?
Figure 10 Overview of the major arteries to the Head and Neck. Refer to this diagram throughout this section.
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2021MSC – Head and Neck Anatomy 7.1. The Aortic Arch -
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The Aorta is the major artery that leaves the heart. Immediately after leaving, it gives off several branches that supply the heart itself, the head and neck and the upper limbs. The Brachiocephalic Artery is the first major branch of the aorta and runs upwards on the right side. o It supplies the right upper limbs and the two major branches to the head. o It gives off the right common carotid and the right subclavian arteries. The Left Common Carotid and Left Subclavian arteries branch directly from the aortic arch.
7.2. The Vertebral Artery -
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The vertebral artery branches from both subclavian arteries. o It passes upwards through the transverse foramina of all cervical vertebrae except C7 before ascending up through Foramen Magnum. It is positioned so deep that it is protected from all but the most severe and terminal sorts of trauma. o This protection is enhanced by the presence of the vertebrae. o This helps ensure that blood supply to the brain is protected against crushing during movements of the neck and due to trauma. Once it has passed through foramen magnum, it lies in the basal part of the occipital bone. o Here, it joins with the vertebral artery from the opposite side to form the Basilar Artery named because of its location. It forms an important part of the cerebral blood supply and circulation. The only branch we need to know is the Superior Cerebellar Artery which supplies the dorsal cerebellum, pons and midbrain.
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2021MSC – Head and Neck Anatomy
V2 and V3 run near this artery. Sometimes the pulsing of the artery can damage the myelin sheathes of these nerves causing Trigeminal Neuraglia
Superior Cerebellar Artery
7.3. The Carotid Arteries -
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Recall that the common carotid arteries arise from different sources on each side of the body. o On the right side, it arises as a branch of the brachiocephalic artery o On the left side, it arises directly from the aortic arch Aside from their origins, they follow the same course. They run upwards in the neck deep to the sternocleidomastoid until it reaches the level of the Larynx. o Here, it divides into two branches being the External and Internal Carotid Arteries The division can palpated just in front of the anterior border of the Sternocleidomastoid muscle. At the point where the common carotid gives off the internal carotid artery, there is a dilation called the Carotid Sinus which contains receptors to monitor blood pressure (baroreceptors) The Common and Internal Carotid Arteries are included in the fascia of the Carotid Sheath. o Also contains Internal Jugular Vein and Vagus nerve. The External Carotid Artery branches off to supply the superficial parts of the face and scalp. The Internal Carotid Artery goes intracranially to supply brain by travelling through the Carotid Canal
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2021MSC – Head and Neck Anatomy 7.3.1. The External Carotid Artery
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Branches off the Common Carotid and is not included in the Carotid Sheath. It provides the majority of the branches and therefore arterial supply to the face and scalp. o Its blood runs into a network of vessels that supply a large capillary plexus, especially over the face. o The purpose of this plexus is such that if one vessel is damaged, there will be many other alternative routes of blood supply and won’t deprive the major part of the plexus. This system is referred to as redundancy The presence of redundancy ensures that damage to a single vessel is unlikely to lead to tissue death. o This is particularly advantageous in cases of surgery. Excellent blood supply means rapid healing and reduced probability of infection. Furthermore, even though it should be avoided, cutting an artery during surgery may not always be incredibly detrimental. The External Carotid gives of several branches. o Some run posteriorly to supply the back of the head and neck. o Other branches run anteriorly to supply the front of the neck and face. o Only the Ascending Pharyngeal branch runs straight up to supply the roof of the cranium. In order of when they branch (going inferior to superior), the branches of the external carotid are: o Superior Thyroid Artery (runs anterior) o Ascending Pharyngeal Artery (deep artery that runs straight up) o Lingual Artery (runs anterior) o Facial artery (runs anterior) o Occipital artery (runs posterior) o Posterior Auricular Artery (runs posterior) Posterior Auricular Artery Occipital Artery Ascending Pharyngeal Artery
Facial Artery Lingual Artery
Internal Carotid Artery Superior Thyroid Artery External Carotid Artery Common Carotid Artery
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2021MSC – Head and Neck Anatomy -
The above image has had all structures cut away for ease of viewing. See below image to see their relation to other structures of the head and neck.
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The maxillary artery terminates by dividing into the Maxillary Artery and Superficial Temporal Artery
7.3.1.1. The Lingual Artery
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The Lingual Artery is the third artery to branch from the External Carotid Artery. It branches from the anterior aspect. It provides the main source of blood supply to the tongue, floor of the mouth, gums and lingual side of the anterior teeth.
After branching off, it forms a loop before ascending towards the tongue. o This loop serves to accommodate for mandibular movement so that the artery isn’t stretched, ruptured or crushed. Page | 53
2021MSC – Head and Neck Anatomy -
It runs deep to the superficial muscles into the tongue, deep to the hyoglossus muscle. o Because it is so deep, it is unlikely that you will damage it during procedures. During its course, before ascending up to the tongue, it gives off a branch called the sublingual artery which runs anteriorly to supply the floor of the mouth and the sublingual gland.
7.3.1.2. Facial Artery
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Also an anterior branch of the external carotid. It arises immediately superior to the lingual artery It arches up and runs deep to the body of the mandible. o Here it forms a loop between the Superficial Belly of the Submandibular Gland and the bone. (in the Submandibular fossa) This loops serves the same purpose as the loop the lingual artery performs o In this location, it can be damaged during surgery of the region. At the end of the loop, it reappears at the lower border of the mandible, crossing over at the anterior margin of the masseter. Here, a facial pulse can be palpated. Also at this point, the facial artery gives off a branch called the Submental Artery which runs forwards below the mandible and on the inferior surface of the mylohyoid muscle. o It then crosses over the chin to anastamose with the inferior labial and mental arteries. This forms a plexus for supply the lower lip and chin. o Before it reaches the chin, it also anastamoses with the sublingual and mylohyoid artery from the lingual branch. Forms a plexus to supply floor of mouth and anterior lingual gingiva.
Superior Labial Artery
Inferior Labial Artery Submental Artery
Submandibular Gland
Facial Artery
External Carotid Artery
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2021MSC – Head and Neck Anatomy -
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After giving off the Submental artery, it ascends obliquely across the face towards the medial angle of the eye. o As it passes the lower and upper lips, it gives off the inferior and superior labial branches o They both anastomose with the same artery on the other side. o The inferior labial artery forms a plexus with the mental and submental artery. Before giving off the Superior Labial Artery, the Facial Artery changes its name to Angular Artery and runs up to the medial corner of the eye giving off some lateral nasal branches which contribute to the facial plexus. At the corner, it anastamoses with a branch of the ophthalmic artery which joins orbital and facial circulations
7.3.1.3. Maxillary Artery
Figure 11 Maxillary Artery and its branches. Refer to this diagram for the branches.
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One of two terminal branches of the external carotid artery. o The other part being the Superior Temporal. Will only be mentioned in passing. Clinically, it is important to us because branches from it supply the upper and lower teeth, the palate, cheeks and gingivae. o Surgically, it is incredibly important as it gives off the middle meningeal artery that supplies the Meninges. There are many branches to this artery but the ones relevant to us are: o Middle Meningeal Artery It communicates with the intracranial circulation. o Inferior Alveolar Artery Supplies the mandible o Buccal Artery Supplies the cheeks Page | 55
2021MSC – Head and Neck Anatomy o
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Superior Dental Artery Posterior Dental Artery Palate Supplies the upper teeth o Greater Palatine Artery o Palatine Artery Palate o Infraorbital Artery o Arteries to Muscles of Mastication - It arises from the external carotid and runs to the medial side of the ramus of the mandible into the substance of the parotid gland. o It then runs obliquely to the pterygopalatine fossa where it gives of branches which correspond with the branches of V2 o Only the main branch will reach the pterygopalatine fossa.
Middle Meningeal Artery
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Supplies most of the dura mater in the cranium. Therefore, it must enter the cranial cavity and does this by passing through foramen Spinosum. The Accessory Meningeal Artery also enters via foramen ovale.
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It is important to take note of the relationship between the Auriculotemporal Nerve from V3 and the Middle Meningeal Artery
Trigeminal Ganglion Facial Nerve
Auriculotemporal Nerve Middle Meningeal Artery
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In the circled region in the image above, the Auriculotemporal Nerve is shown to split and run around the Middle Meningeal Artery as it heads towards the TMJ. The above image is also really handy when looking at the Facial and Trigeminal Nerves
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2021MSC – Head and Neck Anatomy
Inferior Alveolar Artery -
The inferior alveolar artery follows more or less the same path as the inferior alveolar nerve and slightly posterior. They both enter the mandible via the mandibular foramen. Once in the canal, it gives off the same branches as the nerve.
Buccal Artery -
Follows the same course as the Buccal nerve of V3 Supplies the tissues in the check and anastamoses with the facial and infraorbital arteries making the plexus.
Posterior Superior Dental Artery -
Equivalent of posterior superior alveolar nerve Supplies upper posterior teeth and the palate.
Palatine Artery -
Divides into smaller Lesser Palatine Arteries which supply part of the soft palate Greater Palatine Artery o Supplies palatal tissues and palatal gingivae of the teeth
Infraorbital Artery -
Gives rise to middle and anterior superior dental arteries Anastamoses with facial plexus
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2021MSC – Head and Neck Anatomy 7.3.2. Internal Carotid Artery
Course -
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Ascends into the cranium as part of the Carotid Sheath with the internal jugular vein and vagus nerve. o It enters the cranium via the carotid canal in the temporal bone. Once it has entered via the carotid canal, it follows a characteristic S-shaped course into the petrous part of the temporal bone. o The artery then leaves the carotid canal above the cartilage that plugs up foramen lacerum. It turns sharply upward and leaves a small groove in the body of the Sphenoid Bone called the Carotid Sulcus. (See osteology section to see this structure). As it ascends, it goes through the Cavernous Sinus and is separated from the venous blood of the sinus by a layer of endothelium. After it emerges from the Cavernous Sinus, it branches into its two terminal branches which are the Anterior and Middle Cerebral Arteries that both form parts of the Circle of Willis
Branches -
There are no important branches of this artery in the neck region. It does however, have several branches within the cranium. The ones important to us are: o Opthalmic Artery o Anterior Cerebral Artery o Middle Cerebral Artery o Posterior Communicating Artery o The latter 3 are part of the Circle of Willis.
Opthalmic Artery -
It enters the orbital region via the optic canal in the sphenoid bone to supply the retina of the eye and most structures in the orbit. It anastamoses with the angular artery (Facial Artery’s terminal end) at the medial corner of the eye and therefore establishes communication with the external carotid artery.
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2021MSC – Head and Neck Anatomy 7.3.3. Circle of Willis
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The Circle of Willis is effectively what creates a redundancy system for the brain via the Communicating Arteries
Internal Carotid Artery (ascending) Anterior Communicating Artery
Anterior Cerebral Artery
Middle Cerebral Artery Posterior Communicating Artery
Basilar Artery
Posterior Cerebral Artery
Vertebral Artery
Figure 12 The Circle of Willis (Inferior View)
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Up to now, we’ve established that Four Major Arteries enter the cranium. o Two Internal Carotid o Two Vertebral We also know from the previous section that the Vertebral Arteries unite at the basal part of the occipital bone to form the Basilar Artery These arteries form the main blood supply to the cerebrum
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The Basilar Artery gives off two branches, one on the left and one on the right called the Posterior Cerebral Arteries o They supply the posterior and middle cerebral structures.
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The Internal Carotid Arteries gives off its terminal branches more anteriorly in the calvaria o Anterior Cerebral Artery Anterior Cranial Fossa o Middle Cerebral Artery Middle Cranial Fossa
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2021MSC – Head and Neck Anatomy -
The Communicating Arteries serve to provide the cranial redundancy that is essential such that if there is damage, blood can still flow. o The Anterior Communicating Artery unites the two Anterior Cerebellar Arteries o The Posterior Communicating Arteries branch from the Internal Carotid Arteries and then run posteriorly to unite them with the Posterior Cerebral Arteries
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2021MSC – Head and Neck Anatomy 8. Venous Drainage -
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In the cranium, the venous system is made of both Veins and Veinous Sinuses o The Venous System of the Head and Neck does not have valves to control the direction of blood flow. CLINICALLY IMPORTANT o The sinuses are formed by folds in the Dura Mater and are lined by endothelium. They serve the same function as veins elsewhere in the body. The major sinuses you should be able to recognise are: o Superior Sagittal o Transverse o Sigmoid o Superior Petrosal o Inferior Petrosal o Cavernous o Intercavernous Joins the two cavernous sinuses o Sphenoparietal o Straight
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2021MSC – Head and Neck Anatomy -
Most of the cranial venous blood will drain through the Sigmoid Sinus which runs through the Jugular Foramen to become the Internal Jugular Vein, the sinuses are interconnected throughout the head and neck to the facial circulation and the scalp.
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Similar to the redundancy that the arterial system achieves, the Venous System of the Cranium is interconnected and this has clinical importance. o Remember that there are no valves which means that venous blood can flow in any direction that permits it. Direction of flow is dependent on the orientation of the head and gravity o This also means that infections can spread through the venous system in this manner too. Particularly look at the major connections to the Cavernous Sinus which lies centrally in the calvaria. o Cavernous Sinus Thrombosis!
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8.1. The Cavernous Sinus -
Middle and Inferior Cerebral Veins, Sphenoparietal Sinus drain into the Cavernous Sinus It drains into the Superior Petrosal Sinus and then into the Sigmoid Sinus The main driving force that pushes the blood in the cavernous sinus is the pulsing of the internal carotid which sits within the Sinus.
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Clinically, veins draining the nose, the eyes and upper lip drain directly back into the Superior Opthalmic Vein which is connected to the Cavernous Sinus. o This area is sometimes referred to as the danger triangle
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The Cavernous Sinuses Communicate: o Each other via the anterior and posterior Intercavernous Sinuses around the pituitary gland. o The Pterygoid Plexus via: Sphenoidal Emissary Vein when it is present (40% of skulls) Small veins passing through foramen ovale and the cartilage plug of foramen lacerum. o With the orbital circulation via the superior ophthalmic vein
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2021MSC – Head and Neck Anatomy 8.2. Veins -
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All blood from the subclavian veins drain back into the superior vena cava then into the right atrium of the heart. o Lymph from the thoracic duct drains into the left subclavian o Right Lymphatic Duct drains into right subclavian. Internal Jugular Vein arises from the sigmoid sinus at the inferior end of the jugular canal. o Runs with the carotid sheath with the internal and common carotid arteries and vagus nerve o It joins with the subclavian vein to form the brachiocephalic vein. o Drains the facial vein.
FUCK IT DRAW A DIAGRAM. SO MUCH EASIER THAN JUST NOTE TAKING.
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2021MSC – Head and Neck Anatomy 8.3. The Pterygoid Plexus -
Large network of veins found between the medial and lateral pterygoid muscles, and between the lateral pterygoid and temporalis muscles.
Pterygoid plexus
Internal Jugular Vein
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Deep Facial Vein
It communicates with: o The facial circulation via the deep facial vein and therefore the orbital circulation as well o Cavernous sinus via Foramen ovale Sphenoidal Emissary Foramen Foramen Lacerum o It also received branches from the dental, sphenopalatine and greater palatine veins.
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2021MSC – Head and Neck Anatomy 8.4. Surgical Plasticity -
Describes the nature of the blood supply to the region of the head and neck. When a part if removed, replaced or repaired, the supply to the region may be altered. o In addition, new vessels, whether it be arterial or venous may form o Surgeons are able to take advantage of this adaptability when planning operations to help ensure that adequate blood supply will be available to the tissues on which they will operate. This is relevant to us in the event of periodontal surgery
8.5. Blood Supply to the PDL -
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Blood supply arises from the: o Inferior Dental Branch o Posterior, Middle and Anterior Superior Dental Branches of Maxillary (Check this) Blood reaches the PDL via one of three routs o Apical Vessels through the apex of the route. o Alveolar Bone Vessels o Anastamosing Vessels from the gingival The walls of the alveolar sockets have perforations which allow vessels from the alveolar bone to enter. o The socket wall is referred to as another cribriform plate for this reason o IT IS NOT LAMINA DURA which is a radiographic feature. Knowledge of the blood supply to the PDL is important as we need to ensure that when designing a periodontal flap, we maintain an adequate blood supply so that it can live and heal. o DESIGNING A PERIODONTAL FLAP IS A CASE STUDY AND A POTENTIAL EXAM QUESTION.
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2021MSC – Head and Neck Anatomy 9. The Neck -
Always remember and relate the functions of the neck to the layout and shape. In turn, these factors determine the internal structure. The neck is often studied in transverse sections. You should be able to visualise and study the neck in terms of skeleton, muscles, fasciae and viscera o Skeleton of the neck is essentially the vertebral column and the larynx. Be able to identify the anatomical features of cervical vertebrae
9.1. Fasciae of the Neck -
Being able to draw the fasciae of the neck is key to comprehending its overall structure. Refer to the diagram below when practicing. o The purpose of the deep fasciae is to group and wrap up structures of similar function or relation with lubricating fluid between each ‘package’ to permit their movement within their groups.
Key: -
Pink Lines = Superficial Fascia Red Lines = Deep Fascia Red Round = Artery Blue Round = Vein Yellow = Muscle Green Round = Thyroid gland
Pre-vertebral Fascia
Trapezius Muscle
This portion of fascia forms the roof of the posterior triangle
Superficial Fascia
Paralaryngeal Space
Platysma Investing Layer of the Deep Cervical Fascia Retropharyngeal Space
Sternocleidomastoid Carotid Sheath Pre-Laryngeal Fascia
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Trachea Oesophagus
Posterior Triangle of the Neck
Please note that most of the structures above do occur on both sides.
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2021MSC – Head and Neck Anatomy
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The Superficial Fascia lies immediately beneath the skin and is continuous with it. o It contains the platysma muscle Therefore in dissection, removal of the superificial fascia also results in removal of the platysma The Deep Fasciae are designed to permit easy movement between groups of structures, and allows groups of muscles and viscera move independently of each other. Layers of deep fascia divide the neck into several compartments
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The deep fasciae comprise of multiple layers, the most superficial of this being the Investing Layer of the Deep Cervical Fascia o Next-deep layer to the superficial fascia and forms a continuous sheath around the entire neck o It contains the trapezius and sternocleidomastoid muscles The length of fascia between these two muscles forms the roof of the posterior triangle of the neck. o The fact these two muscles are in the investing layer means they can move independently of other muscles in the neck.
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The Carotid Sheath lies deep to the investing layer and wraps the Internal Jugular Vein, Common Carotid Artery and the Vagus Nerve o Eventually it only contains the internal carotid artery after the division of the common carotid.
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The pre-vertebral fascia separates the larynx and oesophagus from the pre-vertebral muscles; allowing these two viscera freedom of movement in this important area.
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The space left between the two structures and the pre-vertebral muscles is called the retropharyngeal space. o This is clinically important because inferiorly, it communicates with the medianastinum which is where the heart sits and thus provides a route for infections to spread. Such as infections from lower molars Infections in this area can cause problems in swallowing and breathing It can also communicate with the posterior triangle.
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The thyroid gland and larynx are anteriorly surrounded by the pre-laryngeal fascia o Wraps the thyroid glands and runs in front of the larynx/trachea o Paralaryngeal/Parapharyngeal Space lies between this and the investing layer and carotid sheath Infections in the Paralaryngeal Space can spread to the Retropharyngeal space and vice-versa.
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2021MSC – Head and Neck Anatomy 9.2. Triangles of the Neck -
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For ease of description and study, the neck is referred to as a series of triangles bordered by imaginary lines corresponding with major anatomical structures.
Triangle
Anterior Boundary
Posterior Boundary
Base
Anterior Triangle (is subdivided into more triangles.
Midline of the neck
Anterior border of Sternocleidomastoid
Lower border of the body of the mandible up to the mastoid process
Posterior Triangle
Posterior border of sternocleidomastoid
Anterior border of trapezius
Middle 1/3 of the clavicle
Important Structures
The Posterior Triangle is situated in the space between the investing layer, carotid sheath and the prevertebral fascia. o It is here that many structures are found upon dissection.
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2021MSC – Head and Neck Anatomy
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You should be able to identify: o Three scalene muscles Anterior Attaches to the anterior tubercles of the 3rd and 6th cervical vertebrae Brachial Plexus found near scalenus anterior Phrenic nerve runs over scalenus anterior to control the diaphragm Medius Attaches to posterior tubercle of C5 Posterior Posterior Tubercles of 4th to 6th cervical vertebrae o Levator Scapulae o Splenius Capitis o Accessory Nerve Provides motor to sternocleidomastoid and trapezius o Phrenic Nerve The phrenic nerve is made up nerves from C3 – C5 The cervical and brachial plexuses emerge between scalenus anterior and posterior muscles o Cervical Plexus made up of C1 to C5 o C5 to C8, T1
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2021MSC – Head and Neck Anatomy 10. General Nervous System -
Notes here will skip most of the general stuff which should be remembered from APS. Nervous system is designed for rapid communication and illiciting rapid responses and changes.
Nervous System
Central Nervous System
Brain
Peripheral Nervous System
Somatic Nervous System (single fibres)
Spinal Cord
Sensory Fibres
Sensory Fibres
Motor Fibres
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Visceral Nervous System (Autonomic)
Special Senses
Sympathetic Nervous System
Parasympathetic Nervous System
Dual fibres with ganglion close to CNS
Dual fibre with ganglion close to end organ
CNS occupies a central midline position in the body
Sensory Nerve Endings -
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Exteroceptors o Pain, Temperature, Touch and Pressure Proprioceptors o Provide data for reflex adjustments and awareness for movement and positioning. Reflexes occur at the spinal level via interneurons Awareness occurs at the brain Interoceptors o Arise in the viscera.
Ganglia -
Ganglia are aggregations of nerve cell bodies found on some peripheral nerves Present in the dorsal roots of spinal nerves and sensory roots of V, VII, VIII, IX and X and in parasympathetic secretomotor fibres
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To understand: o Function and role of myelin sheathes Pain fibres are unmyelinated o Glial Cells Give structure and form to nervous system Cancer causing at times.
10.1. CNS -
The cerebrum forms the largest component of the brain. It features gyro (folds) and sulci (gaps/valleys) A large longitudinal fissure divides the right and left cerebral hemispheres. Corpus Callosum connects the two hemispheres. Gray Matter = Cell Bodies White = myelinated wiring and axons Tracts are bundles of axons that travel together. o In the cerebrum, grey matter on the outside, white matter on the inside. Specific areas of the cerebrum perform specific functions as demonstrated in the image below. o It isn’t necessary to know which part of the brain does what, but it is important to be aware of this.
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2021MSC – Head and Neck Anatomy 10.1.1. The Spinal Cord
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Roughly half a metre long in the adult. Runs down the vertebral foramen of the vertebral column. It is highly protected by the vertebrae and their ligaments as well as the Meninges and the CSF cushion running down the Central Canal in the Arachnoid Mater. It runs down to Conus Medullaris around L1 and L2 The spinal cord forms the link between the CNS and the rest of the body via the PNS o It also provides reflex arcs for rapid control via interneurons The core is grey matter whilst the outside is white matter, the inverse of the cerebrum. o The white matter is made up of bundles of myelinated nerve fibres called Spinal Tracts which provide communication between the brain and spinal cord. Ascending Tracts carry information to the brain Descending Tracts carry information from the brain Direction reflects the direction of the nerve impulse. It is responsible for the innervation of the body excluding the head and visceral structures which are innervated by the cranial nerves. Substantia Gelatinosa
Central Canal
Figure 13 General Structure and Function of a Spinal Nerve. Sensory fibres are blue and motor fibres are red
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Afferent (sensory) fibres enter the spinal cord via the dorsal roots of the spinal nerve o They pass through the Dorsal Root Ganglion In the body, PNS sensory bodies cannot enter the CNS (except for one area to be discussed later) Therefore the sensory bodies must be stored somewhere and in this case, it’s in the dorsal root ganglion. Efferent (motor) fibres leave the spinal cord via the ventral roots. The Central Canal runs longitudinally down the middle of the spinal cord and is the canal in which CSF flows within the arachnoid mater Page | 72
2021MSC – Head and Neck Anatomy o
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Immediately around the central canal are the Dorsal and Ventral Grey Commissures which form the connection between the left and right halves of the spinal cords. The segmented nature of the spinal cord is made clear by the existence of the 31 pairs of spinal nerves. There is however, little evidence for segmentation in its internal structure and as such we must focus on the white matter. Tracts are groups of axons that serve similar function that are grouped and travel together. o Tracts are named based on their origin and destination. o There are two main types of tracts Ones which communicate with the brain and brainstem Ascending and Descending Inter-segmental Tracts o Tracts also allow for some redundancy in that they can provide compensatory routes if there is damage. The dorsal horn and the intermediate zone immediately surrounding the grey matter consists mainly of tract cells. o As well as internuncial neurons which: Receive afferent signals from the sensory fibres and; Send them to the motor cells (for reflex loops) or; Onto tract cells for communication to other spinal levels. A structure called Substantia Gelatinosa is found at the junction between the dorsal horn grey matter and dorsolateral tract and is represents a concentration of pain fibres within that area. o It plays a major role in perception of pain. o It is at this area where Peripheral Sensory Fibres terminate to connect with other neurons that either: Ascend to the brain/brainstem Ascend and descend to different spinal nerve levels Interneurons to initiate a reflex arc.
Dorsolateral Tract
Substantia Gelatinosa
Intersegmental Tracts
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2021MSC – Head and Neck Anatomy Path of Sensory Fibres -
Enter the spinal nerve from the dorsal root via the dorsolateral sulcus into the dorsolateral tract o From here it can either ascend, descend or terminate at that spinal level.
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2021MSC – Head and Neck Anatomy 11. Autonomic/Visceral Nervous System -
The Visceral Nervous System is associated with the regulation of homeostasis via negative feedback mechanisms It is made up of both CNS and PNS components o The PNS component is concerned with Innervation of viscera, glands, smooth muscles and blood vessels
11.1. Afferent Pathways -
The afferent component of the VNS is not divided into Sympathetic and Parasympathetic Cell bodies of afferent neurons are located in either the Dorsal Root Gangla of Spinal Nerves or the Cranial Nerve Ganglia Like sensory somatic neurons, they do not synapse during their course from the sensory source to the CNS.
11.2. Efferent Pathways -
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Divided into Sympathetic and Parasympathetic Unlike somatic motor pathways, two visceral neurons are required in the visceral motor pathway. o Preganglionic o Postganglionic o Therefore there is a ganglion will be found along the nerve to accommodate the cell bodies of the postganglionic neuron. Visceral Motor Neurons are arranged very specifically o They lie in the visceral motor parts of various cranial nerve nuclei o Lateral Grey Columns of the Spinal Cord Their preganglionic neurons are usually myelinated and travel with the cranial or spinal nerves to reach their visceral ganglia o Short in sympathetic, long in parasympathetic Sympathetic is short as it only has to reach the sympathetic trunk which runs alongside the vertebral column The postganglionic neurons are usually unmyelinated and travel to their effector organ. o Long in sympathetic, short in parasympathetic o The bodies of the postganglionic neurons form the sympathetic trunk It should be noted that the ratio of preganglionic to postganglionic neurons is not 1:1. o There are many more postganglionic which creates a wide diffusion and distribution of innervation. Induces widespread response
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2021MSC – Head and Neck Anatomy 11.3. The Sympathetic System -
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Preganglionic Neuron cell bodies found in the grey matter of the spinal cord from T1 to L2 o Termed thoracolumbar Therefore there is sympathetic outflow from only T1 to L2 o No outflow from any other cranial or spinal nerves. Despite this, they still need to be widely distributed to the body. o Therefore the postganglionic fibres must be able to travel to more superior or inferior spinal nerves by spreading themselves out along the sympathetic chain/trunk The Sympathetic Trunk is a chain of connected ganglia running alongside the vertebral column. o It is made up of the cell bodies of the Postganglionic Sympathetic Motor Cells. .
Figure 14 The path of the Sympathetic Fibres
1. The myelinated pre-ganglionic fibre originates from the cell body in the lateral grey horn. 2. It exits via the ventral root and into the Ventral Ramus 3. From the ventral ramus, a branch called the White Ramus Communicans branches out to connect with the Sympathetic Trunk a. The preganglionic fibre runs through this branch to synapse with its Post-Ganglionic Neuron 4. At this point, the unmyelinated Post-Ganglionic Neuron can either: a. Return to the same-level ventral ramus via the Gray Ramus Communicans or; b. Ascend or descend to a different level and enter the ventral ramus at that level through a different gray ramus communicans.
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2021MSC – Head and Neck Anatomy -
It is interesting to note that sympathetic fibres often travel with arteries o They are the only known nerves that do this. o It is so that we can still retain control over the arterial walls even if the spinal nerve is damaged.
11.3.1. Sympathetic Nervous System – Cranial Part
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This is the only part of the SNS that we need to be familiar with as dentists. In the neck/cervical region the ganglia of the eight preganglionic fibres are consolidated into just 3. o Superior Cervical Ganglion Represents the fused ganglia of C1 – C4 o Middle Cervical Ganglion Fused ganglia of C5 – C6 o Stellate Ganglion Fusion of C7 – T1
11.3.1.1. The Internal Carotid Nerve
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Recall that sympathetic fibres run in the walls of arteries. It is regarded as an ascending continuation of the sympathetic trunk.
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At the superior end of the sympathetic trunk, the Internal Carotid Nerve leaves the Superior Cervical Ganglion and travels with the Internal Carotid Artery. o It accompanies the artery into the cranial cavity where it forms a plexus in the arterial wall. o It mainly carries vasoconstrictor fibres It branches off to communicate with: o II, III, IV, V, VI o Pterygopalatine Ganglion The branch to connect with this ganglion is the Deep Petrosal Nerve It joins with the Greater Petrosal Nerve to form the Nerve of the Pterygoid Canal which then exits the Pterygoid Fossa Ciliary Ganglion
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2021MSC – Head and Neck Anatomy 11.4. Parasympathetic System -
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The Preganglionic Fibres are confined to the cranial and sacral regions. o Hence referred to sometimes as the Craniosacral System They are present in: o III, VII, IX and X o S2 – S4 In the cranial part of the PS system, there are four parasympathetic motor ganglia o Ciliary Ganglion In the orbit o Pterygopalatine Ganglion For lacrimal and salivary glands o Otic Ganglion Deep to V3, innervates the parotid gland o Submandibular Ganglion Found on the Submandibular gland. Controls the Submandibular and Sublingual Glands
11.4.1. The Facial Nerve
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The parasympathetic fibres from here originate in the Superior Salivatory Nucleus in the midbrain. o They emerge from the midbrain within the sensory root of VII (nervus intermedius) This may seem counterintuitive since PS in this case is a motor fibre, but REMEMBER! Both Sensory and PS require a ganglion somewhere. o They continue with the Facial Nerve just before it exits the stylomastoid foramen o At this point, they leave the main trunk as part of the Chorda Tympani. o Chorda Tympani leaves the skill via the Anterior Canaliculus for the Chorda Tympani at the medial end of the petrotympanic fissure. It then joins onto the Lingual Nerve from the posterior branch of V3 o From the lingual nerve, they pass to the Submandibular Ganglion where they synapse with their Secretomotor Postganglionic Fibres for the Submandibular and Sublingual glands.
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2021MSC – Head and Neck Anatomy 11.4.2. Glossopharyngeal Nerve (IX)
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The efferent fibres of this nerve pass to the Parotid Gland.
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Unlike VII, the fibres originate at the Inferior Salivary nucleus They run with the main trunk of IX and then as part of the tympanic branch o This branch passes up through the Tympanic Canaliculus in the roof of the Jugular Fossa The fibres then cross the Tympanic Plexus and enter the Lesser Petrosal Nerve o The nerve exits the cranium via Foramen Ovale to reach the Otic Ganglion At the Otic Ganglion, they synapse with their Postganglionic Secretomotor Fibres which then run in the Auriculotemporal Nerve to reach the parotid gland.
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2021MSC – Head and Neck Anatomy 12. VII, IX, XII and the Cervical Plexus 12.1. The Facial Nerve (VII) -
Main focus for this section. o Clinically it is important as it can be accidentally anaesthetised when attempted an Inferior Dental Block There exists an anatomical anomaly where hitting VII is nearly certain to happen every time.
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The nerve is predominantly motor in function with its sensory component only providing general sensation to the external ear and taste to the tongue. The Motor Component is responsible for the motor supply of the Muscles of Facial Expression and any other muscle derived from the Second Branchial Arch. It also contains a Parasympathetic Secretomotor component that travels with both the Facial and Lingual nerves to supply the sublingual, Submandibular and lacrimal glands. o Therefore there will be a ganglion somewhere (recall from above)
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12.1.1. Course of the Facial Nerve
1. It arises from the Pons as two separate roots, Motor and Sensory (nervus intermedius) o The larger Motor Root carries the motor fibres to all muscles of Facial Expression, the posterior belly of the Digastric muscle, stapedius and stylohyoid muscle. o The sensory root carries general sensory fibres, taste fibres and parasympathetic secretomotor fibres. 2. The two roots run together with the C-shaped Vestibulocochlear nerve (VIII) with nervus intermedius sandwiched between the motor root and groove on VIII’s trunk. 3. Together, the enter the Internal Acoustic Meatus o At this point, these two nerves separate in their course. VIII moves off to the middle ear The two roots of VII join to form a single trunk in the Facial Canal 4. Initially, the trunk of VII runs anteriorly and laterally. When it gets close to the cavity of the middle ear, it turns sharply posteriorly and inferiorly and heads down to the stylomastoid foramen o At the bend, the nerve trunk swells up to form the Geniculate Ganglion where the cell bodies of somatic sensory fibres are stored. Also termed the External Genu. 5. At the Geniculate Ganglion, an important branch called the Greater Petrosal Nerve 6. Before exiting the Stylomastoid Foramen, it gives off another important branch called the Chorda Tympani. a. The nerve is vulnerable to potential damage from operations on the middle ear at this point. 7. The main trunk of VII then exits the Stylomastoid Foramen and travels into the Parotid Gland Page | 80
2021MSC – Head and Neck Anatomy
Main trunk of VII exits via Stylomastoid Foramen Trigeminal Ganglion Chorda Tympani
Greater Petrosal Nerve
Motor Root of VII
Geniculate Ganglion Nervus Intermedius
Vestibulocochlear Nerve Figure 15 Track the Facial Nerve's Course Using This Image
12.1.1.1. The Greater Petrosal Nerve
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After it branches off, it runs forward and medially in a small canal. It emerges from the facial canal via a tiny hole in the cranial surface of the Petrous Temporal Bone called the Hiatus for the Greater Petrosal Nerve. It then continues to run anteriorly in a groove in the middle cranial fossa. It runs underneath the Trigeminal Ganglion and over the roof of Foramen Lacerum towards the Pterygoid Canal which lies in the anterior wall of Foramen Lacerum o Before entering the canal, it joins with the Deep Petrosal Nerve (recall from Sympathetic System) to form the Nerve of the Pterygoid Canal o It travels through this canal to reach the Pterygopalatine Fossa where the Pterygopalatine Ganglion sits Here, the preganglionic fibres synapse with the postganglionic secretomotor fibres for the lacrimal and minor salivary glands of the palate and upper lip o The postganglionic fibres follow the branches of V to reach their destinations. o Secretomotor fibres for the Nasal Cavity travel in the Sphenopalatine nerve. Taste fibres do not synapse and pass straight to the palate via the Greater and Lesser Palatine Nerves of V2
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2021MSC – Head and Neck Anatomy
Deep Petrosal Nerve Greater Petrosal Nerve
Nerve of the Pterygoid Canal
Superior Salivary Nucleus
Pterygopalatine Ganglion in the Pterygopalatine Fossa
Facial Nerve Geniculate Ganglion Superior Cervical Ganglion
Figure 16 Lateral View of the Facial Nerve's Course
12.1.1.2. Chorda Tympani
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Branches off before the main trunk of the Facial Nerve passes through the stylomastoid foramen. This nerve provides parasympathetic secretomotor fibres to the Submandibular, sublingual and minor glands of the floor of the mouth as well as taste fibres to the anterior 2/3 of the tongue. To reach the glands, it ‘hitches a ride’ with the Lingual Nerve of V3 o Recall that Parasympathetic fibres can piggyback off other nerves. o Chorda tympani reaches the Lingual nerve by travelling through the Canaliculus of Chorda Tympani and exiting via the Petrotympanic Fissure (of the temporal bone) Petrotympanic Fissure
Geniculate Ganglion Facial Nerve Main Trunk
Otic Ganglion (will be visited later)
Chorda Tympani
Lesser Petrosal Nerve Lingual Nerve
Greater Petrosal Nerve
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2021MSC – Head and Neck Anatomy 12.1.2. The Facial Nerve’s Main Trunk (continued)
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So we’ve discussed the two major nerves that branch off the main trunk to perform sensory and secretomotor functions. Now to come back to the main trunk. As stated before: o The main trunk exits the cranium via the Stylomastoid Foramen in the temporal bone. o It then travels to and resides in the Parotid Gland. Before the parotid gland, it gives off motor branches to the: o Posterior Belly of the Digastric Muscle o Stylohyoid Muscles Furthermore, it gives off its Five Major Branches that spread to cover the face. (you may remember the trick of covering your face with your hand) The five major branches are: o Temporal o Zygomatic o Buccal o Mandibular o Cervical Just need to know that cervical branch supplies the platysma. You only need to know the five branches and that they are distributed to the Muscles of Facial Expression. o Don’t need to know which branch goes to which muscle.
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2021MSC – Head and Neck Anatomy 12.1.3. Clinical Considerations: Paralysis
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Recall at the beginning of this section that there exists an anomaly where it is almost certain that the facial nerve will be anaesthetised. In some cases, the deep lobe of a patient’s parotid gland can extend around the back of the mandible and be in close proximity to the area that the Inferior Dental Block is applied. o Recall that the Facial Nerve sits in the parotid gland so if you inject into it, the fluid we flow through the gland and anaesthetise the nerve. o You will only get paralysis on the affected side. It is important to note that only motor functions will be blocked. Sensory functions will still be present. o This is because you are only anaesthetising the Main trunk of the Facial Nerve which is predominantly motor in function.
12.1.3.1. Other lesions of the Facial Nerve
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The effects of a lesion on the Facial Nerve’s function can vary depending on where the lesion is located. Therefore we can relate the symptoms to where the lesion is present. o Obviously, damage to the originating roots or the trunk prior to the geniculate ganglion will result in full paralysis of the Facial Nerve
Lesion Location
Symptoms
Chorda Tympani
Reduced saliva production Inability to taste (anterior 2/3)
Greater Petrosal Nerve
No taste sensation in the palate and upper lip No salivation from the palate and upper lip Inability to lacrimate
Facial Nerve’s Main Trunk Branches
Paralysis to muscles of facial expression depending on the side and branch/es that the lesion affects.
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2021MSC – Head and Neck Anatomy 12.2. The Glossopharyngeal Nerve (IX) -
It originates from the upper part of the Medulla Oblongata below the Pons. It contains motor, sensory and secretomotor fibres. o Motor to Stylopharyngeus o Sensory to the Pharynx, Tonsils and Posterior 1/3 of the Tongue o Secretomotor to the Parotid Gland
12.2.1. Course of IX
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It exits the cranium via the Jugular Foramen alongside X and XI and becomes wrapped in a layer of Dura Mater as it approaches the opening of the foramen. As it passes through the canal, it features two swellings called the Superior and Inferior Ganglia. o They are both sensory ganglia with the superior ganglia often being referred to as a detached part of the larger inferior one. They both contain sensory cell bodies. Parotid Gland
Trigeminal Nerve
Otic Ganglion Lesser Petrosal Nerve Tympanic Plexus
Facial Nerve Tympanic Branch
Superior and Inferior Ganglia of the Glossopharyngeal Nerve
12.2.1.1. The Tympanic Branch(Contains Parasympathetic Secretomotor)
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Just after IX leaves the Jugular Foramen, it gives off a small branch called the Tympanic Branch It passes through the Tympanic Canaliculus, a small foramen between the jugular and carotid canals The Tympanic Branch travels up to the middle ear via this canaliculus and it joins with a branch of VII to form the Tympanic Plexus in the wall of the middle ear. The most important branch to originate from this plexus is the Lesser Petrosal Nerve which contains Parasympathetic Secretomotor fibres from IX, originating in the Inferior Salivary Nucleus It runs in a small canal to appear in the Middle Cranial Fossa alongside the Greater Petrosal Nerve
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2021MSC – Head and Neck Anatomy -
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From here, it passes through Foramen Ovale or in some cases, if it is present, Canaliculus Innominatus which lies medially to foramen Spinosum when present. After passing through the foramen, it runs inferiorly to the Otic Ganglion. o The Otic Ganglion is one of four parasympathetic ganglia situated in the Infratemporal Fossa. o It is where the preganglionic fibres of IX synapse with their postganglionic fibres. o V DOES NOT TRAVEL THROUGH OR SYNAPSE IN THE OTIC GANGLION. IT LIES DEEP TO V3 The Postganglionic fibres hitch a ride with the Auriculotemporal Nerve, a branch of V3 in order to reach and supply the Parotid Gland.
12.2.1.2. Back to the Main Trunk of IX
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The main branch continues to run inferiorly giving off the following branches: o Pharyngeal o Tonsillar o Lingual Run deep to the hyoglossus muscles of the tongue Supply general sensation and taste to Posterior 1/3 of the tongue. o Carotid (terminal branch)
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2021MSC – Head and Neck Anatomy 12.3. The Vagus Nerve (X) -
Contains both somatic and visceral sensory and motor nerves and has a wider distribution than any other cranial nerve. o The sensory and motor roots do not exists separately but it does have a sensory ganglia like IX. o Contains Visceral Sensory Nerves
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It’s sensory fibres are distributed to the larynx and epiglottis. Visceral components distributed to the autonomic muscles of the heart, bronchi and most of the GIT along with some taste fibres o It helps control the Heart Rate, innervates the organs of respiration and has sensors to help control blood pressure. o It helps us control digestion and movement of food through most of the GIT up to the middle colon. Motor innvervation to the muscles of the Larynx and is important in speech. o Works closely with V, VII, IX and XII in speech. Distribution of fibres to the thorax and abdomen doesn’t need to be known.
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It leaves the cranium via the Jugular Foramen alongside IX and XI and similarly to IX, has two ganglia. o Superior Ganglion lies in the Jugular Foramen o Inferior Ganglion found just after the nerve exits the canal. o Both ganglia contain somatic sensory cell bodies.
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2021MSC – Head and Neck Anatomy 12.4. The Hypoglossal Nerve (XII) -
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It arises from the medulla as a series of filaments, which pass behind the vertebral arteries to form a common nerve trunk. The nerve trunk exits the cranial cavity through the Hypoglossal Canal anterior to the condyle. o Remember it provides motor innervation to the tongue and must therefore run anteriorly to reach it. It descends in the carotid sheath and turns forward to hook around the origin of the Occipital Artery (branch of maxillary artery) It passes deep to the stylohyoid and enters the floor of the mouth between the mylohyoid and hyoglossus muscles. It communicates with the Lingual Nerve before penetrating the tongue below the Sublingual Gland. It supplies the intrinsic and all extrinsic muscles of the tongue except palatoglossus which is supplied by XI (accessory nerve) If there is damage to one of the Hypoglossal nerves (since there is one on each side), the tongue will deviate towards the damaged side when stuck out.
12.5. The Cervical Plexus
Figure 17 The sources of sensory innervation for the head and neck
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The branches of the Cervical Plexus emerge from the posterior border of the sternocleidomastoid and therefore at the anterior border of the posterior triangle It is comprised of the ventral rami of C1 – C4 Each of the nerves that make up the cervical plexus receive at least one Gray Ramus Communicans from the Sympathetic Trunk. All the nerves of the cervical plexus receive it from the Superior Cervical Ganglion It supplies branches to the muscles of the neck, parts of the skin of the head, neck and chest.
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2021MSC – Head and Neck Anatomy -
For ease of study, branches of the cervical plexus are divided into which are subdivided further: o Superficial Branches Ascending Lesser Occipital Greater Auricular Transverse Cervical Descending Medial Supraclavicular Intermediate Supraclavicular Lateral Supraclavicular o Deep Branches Medial Communicating Branches with X and XII Muscular Branches o Including Phrenic Nerve o Inferior Root of Ansa Cervicalis Lateral Communicating Branches with XI Muscular Branches
Figure 18 General Schema of the Cervical Plexus. The Cervical Plexus formed by the Ventral Rami of the first four cervical nerves.
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2021MSC – Head and Neck Anatomy 12.5.1. Superficial Ascending Branches
Lesser Occipital Nerve -
Contributed to by the ventral ramus of C2 It loops around the Accessory Nerve (XI) and ascends along the posterior border of the sternocleidomastoid. It passes upwards on the lateral side of the head behind the ear where it supplies the skin in this region.
Great Auricular Nerve -
Contributed to by the ventral rami of C2 and C3 Curves around the posterior border to the Sternocleidomastoid Muscle and ascends along the Sternocleidomastoid beneath the platysma It runs up to the parotid gland where it gives off an anterior and posterior branch o Anterior Branch innervates the skin of the face over the parotid gland o Posterior Branch innverates the skin over the mastoid process and the posterior portion of the auricle of the ear.
Transverse Cervical (Cutaneous) Nerve -
Curves around the posterior border of the Sternocleidomastoid to run obliquely forwards, deep to the External Jugular to reach the anterior border. It then penetrates the deep cervical fascia and divides into ascending and descending branches deep to the platysma muscle o Ascending Branch passes upwards to form a plexus with the Cervical Branch of VII. Some passes through the platysma to supply the skin of the upper and anterior parts of the neck. Also sometimes form an accessory nerve supply to the lower anterior teeth o Descending Branch pierces the platysma to supply the front and sides of the neck down to the sternum.
12.5.2. Superficial Descending Branches
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Medial Supraclavicular o Supply the skin down to the second rib and medially to the midline Intermediate Supraclavicular o Supply skin overlying the pectoralis major and deltoid muscles Lateral Supraclavicular o Supply skin over the upper and posterior parts of the shoulder.
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2021MSC – Head and Neck Anatomy
Greater Auricular Nerve Accessory Nerve Transverse Cutaneous Nerve of the Neck Supraclavicular Nerves
Figure 19 Superficial Branches of the Cervical Plexus
12.5.3. Deep Branches
Ansa Cervicalis -
Derived from C1 to C3 o Is the motor component of the Cervical Plexus Innervates the Omohyoid, Sternohyoid and Sternothyroid
Phrenic Nerve -
Only source of motor innervation to the diaphragm Arises from C3 - C5 o “Three, four and five keep the diaphragm alive!”
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2021MSC – Head and Neck Anatomy 13. The Trigeminal Nerve (V1 and V2) 13.1. V in general -
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Clinically, it is the most important cranial nerve to a dentist. It provides sensory innervation to the front of the head and face as well as the oral cavity and paradental structures o This is why dental blocks will usually target a branch of the trigeminal nerve. It provides motor innervation to the muscles of mastication, the anterior belly of the digastric muscle and the mylohyoid muscle. It is comprised of Three Major Divisions being: o Opthalmic (V1) o Maxillary (V2) o Mandibular (V3) This is the big one and therefore gets its own section. It is also a bitch.
13.1.1. Cutaneous Distribution
Figure 20 LEARN HOW TO DRAW THIS DIAGRAM
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The three peripheral divisions of V supply common sensation (i.e. touch, temperature, pressure, pain) to the sin of the face and scalp. V1 supplies the skin in the anterior portion of the scalp, forehead, upper eyelid and the front of the nose down to the tip. V2 supplies the skin at the sides of the nose, lower eyelid and upper parts of the cheek and lip. V3 supplies the chin, lower lip, skin in front of the ear and on the side of the head up to where V1 supplies it. Note from the image above that the angle of the mandible is not innervated by the Trigeminal Nerve but by the Cervical Plexus along with the back of the head and neck
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2021MSC – Head and Neck Anatomy 13.1.2. Central Connections
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The unipolar somatic sensory cells in the Trigeminal nerve cannot have their cell bodies and are instead, found in the Trigeminal Ganglion o They then terminate in the spinal nucleus/nucleus of the spinal tract and chief sensory nucleus Nuclei for General Sensation in brainstem Proprioceptive Fibres involved in the Proprioceptive Reflexes controlling the jaw and because of the speed in which they need to act, they are the only Peripheral Sensory Neurons where the cell bodies are located in the CNS. o They lie in the Mesencephalic Nucleus. Motor cells of the Trigeminal Nerve originate in the Trigeminal Motor Nucleus
Trigeminal: Mesencephalic Nucleus Trigeminal Motor Nucleus
Trigeminal: Chief Sensory Nucleus
Spinal Nucleus/Nucleus of the Spinal Tract
Figure 21 The Brainstem. This image will be revisited in the last topic.
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2021MSC – Head and Neck Anatomy 13.2. V1: The Ophthalmic Division -
Purely sensory
13.2.1. Course
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It originates from the Trigeminal Ganglion and passes forward along the lateral wall of the Cavernous Sinus alongside III, IV and VI. o Link this to symptoms of cavernous sinus thrombosis It enters the orbit by passing through the Superior Orbital Fissure (which separates the great and lesser wings of the Sphenoid bone). At this point, it divides into Three Branches: o Lacrimal o Frontal o Nasociliary
Supratrochlear Nerve
Frontal Nerve
Supraorbital Nerve
Lacrimal Nerve
Nasociliary Nerve Maxillary Division Ophthalmic Division
Mandibular Division Trigeminal Ganglion
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2021MSC – Head and Neck Anatomy 13.2.2. Frontal Nerve
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Runs across the top of the orbit. As it approaches the face, it divides into two major branches o Supraorbital Nerve Emerges onto the face through the Supraorbital Foramen Runs up onto the forehead to supply the forehead and scalp. o Supratrochlear Nerves Runs medially and emerges from the orbit at the medial edge. Runs up to supply: Medial Portion of the Upper eyelid, skin of the forehead and scalp towards the medial aspect and the skin above the root of the nose.
13.2.3. Lacrimal Nerve
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Supplies the conjunctiva, the skin of the lateral upper eyelid and the lacrimal gland with common sensation V2 supplies the secretomotor for the lacrimal gland.
13.2.3. Nasociliary Nerve
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Supplies the medial structures of the orbit. o Lining membranes of the Sphenoidal and Ethmoidal sinuses o Tissues of the roof of the nose o Skin over the front of the nose down to the tip.
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2021MSC – Head and Neck Anatomy 13.3. The Maxillary Division (V2) -
Also purely sensory
13.3.1. Course
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Emerges as the intermediate branch of the Trigeminal Ganglion Runs forward in the middle cranial fossa along the lateral wall of the Cavernous Sinus Exits the cranium via Foramen Rotundum o Before it passes through the foramen, it gives off a small branch to supply the dura mater of the middle cranial fossa called the Middle Meningeal Nerve
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After exiting through Foramen Rotundum, it emerges into the Pterygopalatine Fossa superior to the Pterygopalatine Ganglion. At this point it gives off a number of branches. o Two branches travel into the ganglion o The main trunk continues anteriorly to run through the Inferior Orbital Fissure and runs along the floor of the orbit in the Infraorbital Groove and becomes the Infraorbital Nerve. It then travels through the Infraorbital Canal before emerging on the facial surface of the maxilla through the Infraorbital foramen. As it moves anteriorly it also gives off several branches. The Infraorbital Groove forms the roof of the Infraorbital Canal Infraorbital Nerve gives off the Anterior Superior Dental Nerve as it passes through the canal. o Anterior Superior Dental Nerve runs through Canaliculus Sinosus Once on the maxilla, the Infraorbital Nerve gives off branches to the upper lip, lower eyelid and sides of the nose.
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13.3.2. The Branches
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The branches include: o Those in the pterygopalatine Fossa Posterior Superior Dental Palatine Sphenopalatine Pharyngeal Zygomatic o Infraorbital Anterior and Middle Superior Dental Palatine and Sphenopalatine come from the Pterygopalatine Ganglion whilst Zygomatic receives fibres from it without going through it.
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2021MSC – Head and Neck Anatomy 13.3.2.1. Posterior Superior Dental Nerves
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Contribute to the nerve supply of the upper teeth. o Targeted in a Superior Dental Block They run downwards on the back of the maxilla and pass into the bone through a series of foramina around the maxillary tuberosity. They run into the body of the maxilla and reach the lining of the Maxillary Sinus to supply sensory nerve endings. From here, the fibres are then distributed even further to form the Molar Part of the nerve plexus that supplies the upper teeth called the Superior Dental Nerve Plexus They also supply small endings to the Buccal gingivae of the molars and superior portion of the cheek in this area. Because the Molars and Maxillary Sinus share the same nervous supply, pain from the Maxillary Sinus can be referred to the upper teeth.
13.3.2.2. The Palatine Nerves
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Provides somatic sensory nervous supply to the palate and parasympathetic secretomotor fibres to the minor salivary glands in the palatal mucosa. o The somatic fibres come from the branches of V2 that extend into the Pterygopalatine Ganglion They emerge from the ganglion WITHOUT HAVING SYNAPSED. o Some postganglionic PS secretomotor fibres from the ganglion hitch a ride and run with the somatic fibres to be distributed to the minor salivary glands. Also contain some taste fibres. The branch travels from the Ganglion inferiorly, branching into Greater and Lesser Palatine Nerves. o Lesser Palatine Nerves emerge through the Lesser Palatine Foramina in the palatine bones Provide taste, secretomotor and somatosensory fibres to the tissues of the Soft Palate o Greater palatine nerves pass through the Greater Palatine Foramen and run forwards in the palate up to the canine where they meet and anastamose with fibres from the Sphenopalatine Nerve Recall that the palate has separate innervations at different points These two also need to be targeted in a Superior Dental Block
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2021MSC – Head and Neck Anatomy 13.3.2.3. Sphenopalatine Nerve
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From the Pterygopaatine Ganglion, it passes medially through the Sphenopalatine Foramen which lies in the deepest part of the Fossa. After passing through the foramen, it gives off some small lateral branches which are distributed over the lateral wall of the nasal cavity. The Long Sphenopalatine or Nasopalatine Nerve then crosses the roof of the nasal cavity and descends on the nasal septum to supply the mucous membrane It then continues through the Incisive Canal to communicate with the Greater Palatine Nerves o Small terminal branches help to supply the palatine supporting structures of the central and lateral incisors.
13.3.2.4. The Pharyngeal Nerves
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Supply the mucous membrane of the upper nasopharynx They reach this by running posteriorly through the Pharyngeal Canal
13.3.2.5. The Zygomatic Nerve
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Runs into the orbit through the inferior orbital fissure alongside the Infraorbital Nerve Instead of running across the floor like the infraorbital nerve, it runs along the lateral wall of the zygomatic bone Whilst not running through the Pterygopalatine Ganglion, it does receive parasympathetic secretomotor fibres from it. Eventually, it divides into two branches: o Zygomaticotemporal Nerve o Zygomaticofacial Nerve Both branches run into the zygomatic bone and via two small foramina which are named according to the branch it carries. The parasympathetic secretomotor fibres from the Ganglion don’t actually travel with the zygomatic nerve all the way. o A branch from the Zygomaticotemporal Nerve called the Lacrimal Branch joins onto the Lacrimal Nerve from V1 and travels with it to reach the lacrimal glands.
13.3.2.6. The Infraorbital Nerve
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Discussed in detail before. Most important branches it gives off whilst still in the orbit are the middle superior and anterior superior dental nerves which contribute to the superior dental plexus.
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2021MSC – Head and Neck Anatomy 13.3.3. Branches of the Maxillary Nerve from a Lateral View and Associated Structures
Lacrimal Nerve (from V1)
Lacrimal Branch Zygomatic Nerve
Foramen Rotundum
Maxillary Sinus Trigeminal Ganglion
Pterygopalatine Ganglion Anterior Superior Dental Nerve Maxillary Nerve (V2) Greater and Lesser Palatine Nerves Posterior Superior Dental Nerve
Infraorbital Nerve entering the Infraorbital Canal
Middle Superior Dental Nerve
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2021MSC – Head and Neck Anatomy 13.4. Nerve Supply of the Upper Teeth -
When looking at the nervous supply of the upper teeth, it is important to take note of several things; namely: o Nerve supply for the upper teeth (especially the molars) are closely related to the nerve supply of the maxillary sinus. o The Superior Dental Plexus is made up of twiglets from the Posterior Superior, Anterior Superior and – when it’s present – Middle Superior Dental Nerves NOTE THAT THE PRESENCE OF THE MIDDLE SUPERIOR DENTAL NERVES DO NOT MEAN THE AREA IS MORE SENSITIVE.
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When the Middle Superior Dental Nerve is present: o Posterior Superior supplies the Molars and a twig to the Second Premolar o Middle Superior supplies MB root of 6, Premolars and may jointly supply the Canines. o Anterior Superior supply the anterior teeth and some of 4 o So: P and M jointly supply 5 and 6 M and A jointly supply 3 and 4 If it is present: o Posterior Superior supplies the molars and 5 o Anterior Superior does Anterior teeth and 4 and some of 5
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If anaesthesia is required for a restoration, only the nerve to the teeth need to be hit. Anaesthesia for extractions need to get the nerve supply of the palatal tissues as well.
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2021MSC – Head and Neck Anatomy 14. The Mandibular Division of the Trigeminal Nerve (V3) -
Recall from the section above the areas that are supplied with Sensory Innervation from V3
14.1. Course -
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V3 is the only branch of the Trigeminal Nerve that contains both Sensory and Motor. o The Sensory component of the nerve passes into the ganglion and then to the brainstem alongside the sensory fibres from the other divisions. o The Motor fibres leave from the pons as a separate motor root which joins the main trunk of the nerve just after the main trunk leaves the cranium. The Mandibular Nerve then exits the cranium through Foramen Ovale The trunk of the nerve then gives off its first branch called the Recurrent Meningeal Nerve o Known to cause many headaches o It is a small branch containing sensory fibres that re-enters the cranium alongside the Middle Meningeal Artery through Foramen Spinosum to supply the dura mater with sensation. The main trunk then gives off several small muscular branches containing motor fibres to the tensor palate and tensor tympani muscles as well as the Medial Pterygoid Muscle. o Tensor Tympani is a muscle that adjusts the tympanic membrane to change the sensitivity of hearing. Pain from lower jaw can be reffered to the ear via this nerve. It also receives some communicating branches from the Otic Ganglion without actually passing through it. o These communicating branches allow parasympathetic fibres to run with the nerve. After the main trunk runs past the Otic Ganglion, it divides into Posterior and Anterior Divisions.
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2021MSC – Head and Neck Anatomy 14.2. Branches of the Posterior Division -
Auriculotemporal Nerve (Sensory and Parasympathetic) Inferior Dental Nerve (Sensory) Lingual Nerve (Sensory and Parasympathetic) Nerve to Mylohyoid Muscle and Anterior Belly of Digastric Muscle (Sensory and Motor)
14.2.1. Auriculotemporal Nerve
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IMPORTANT as it provides sensory innervation to the TMJ and carries parasympathetic secretomotor fibres from the Otic Ganglion to the Parotid Gland It is BAD PRACTICE to anaesthetise it.
It branches from the main trunk of the Mandibular Nerve shortly after the motor root joins on. It runs posteriorly toward the Middle Meningeal Artery, at which point it splits into two branches which pass around the artery in a circle before joining back up to form a single branch. It continues to run posteriorly, running between the medial aspect of the neck of the mandibular condyle and sphenomandibular ligament It then curves around the TMJ which it supplies with sensory fibres and runs into the Parotid Gland. It gives off sensory and parasympathetic fibres to the gland. It then runs superiorly and terminates with the Superior Temporal Branches which supply common sensation to the skin and underlying structures in the posterior temple area and side of the scalp.
14.2.2. Inferior Dental Nerve (VERY IMPORTANT)
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I repeat. VERY IMPORTANT. It provides the sensory supply to the pulps of the lower teeth and does so by entering the body of the mandible. o It also supplies the PDL fibres, the mandible itself as well as the labial gingivae and Buccal gingivae as far back as the second premolar.
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It does this by entering the Mandibular Foramen found on the medial surface of the Ramus of the mandible and then runs in the Mandibular Canal Initially it travels as a single trunk but soon gives off smaller branches which form a plexus in the body of the mandible. The nerve then splits into two branches o The first branch is called the Incisive Plexus and continues forward in the body of the mandible to supply: Labial Gingivae and the pulps of the anterior teeth The second branch is called the Mental Nerve and exits the mandible via the Mental Foramen.
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2021MSC – Head and Neck Anatomy
The position of this foramen can vary but it is generally between the roots of 4 and 5 .
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BEWARE the position of the Mental Nerve when designing a periodontal flap. o NEVER make an incision near the premolars. You are better off making the flap larger and exposing the nerve. The Mental Nerve supplies common sensation to the lower lip and the front of the chin.
14.2.3. Nerve to the Mylohyoid
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This nerve supplies motor function to the Mylohyoid and Anterior Belly of the Digastric Muscle o It was recently found however that it has a sensory component as well. It branches off from the Inferior Dental Nerve just before it passes into the Mandibular Foramen. o At times, it can branch off quite high up from the inferior dental nerve to the point that it can avoid being bathed in anaesthetic when attempting an inferior dental block. Therefore some patients, despite being successfully anaesthetised still showed sensitivity due to this nerve.
14.2.4. The Lingual Nerve
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Carries parasympathetic fibres after Chorda Tympani from VII joins onto it. Branches from the Posterior Division anteriorly to the Inferior Dental Nerve and runs parallel with it for some time without entering the body of the mandible. Instead, it curves above the mylohyoid muscle passing between the body of the mandible and the duct of the Submandibular gland. It rises again medially to terminate in the anterior part of the tongue.
It is the major sensory nerve of the Anterior 2/3 of the tongue for common sensation and taste. The parasympathetic fibres acquired from Chorda Tympani are distributed to the Submandibular, sublingual and minor salivary glands. o The preganglionic fibres synapse in the Submandibular ganglion which is located inferiorly to the lingual nerve, close to the gland where the postganglionic fibres exit and travel. It also supplies common sensation to the floor of the mouth, lingual gingival tissues and sometimes an accessory nerve supply to the lower anteriors must therefore be anaesthetised during an extraction of a lower tooth along with the inferior dental nerve.
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2021MSC – Head and Neck Anatomy 14.3. Branches of the Anterior Division -
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Masseteric Nerve (M) o Masseter Muscle Anterior and Posterior Deep Temporal Nerves (M) o Temporalis Muscle Medial Pterygoid Nerve (M) o Medial Pterygoid Muscle Lateral Pterygoid Nerve (M) o Lateral Pterygoid Muscle Buccal Nerve (S)
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You only need to know the names and destinations of the nerves to the muscles of mastication
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14.3.1. The Buccal Nerve (aka Long Buccal Nerve)
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Provides common sensation to most of the cheek and the Buccal gingivae of the lower posterior teeth. o Therefore, it also needs to be anaesthetised if a lower posterior tooth is to be extracted.
14.4. A Nice Visual Summary of the Branches
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2021MSC – Head and Neck Anatomy 15. Brainstem and Nuclei -
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The brainstem represents the union between the brain and the spinal cord. It is made up of three main parts: o Midbrain o Pons o Medulla Oblongata It transmits all sensory and motor pathways and information between the brain and the spinal cord. Also in the brainstem, we find the central connections of the Cranial Nerves and their associated nuclei.
Midbrain Pons Cerebellum Medulla Oblongata
15.1. The Reticular Formation -
Scattered deeply through the brain stem are loosely organised groups of tissue, collectively known as the Reticular Formation.
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It has the important task of controlling our level of awareness or consciousness to certain things o It directs you to changes in your environment like loud noises It also has a role in respiratory and cardiac functions
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2021MSC – Head and Neck Anatomy 15.2. The Midbrain -
Forms the most superior part of the brainstem. It also contains a channel that connects the Third and Fourth Ventricles, the two most inferior of four cavities that contain Cerebrospinal Fluid, by the Cerebral Aqueduct, which is continuous with the central canals of the spinal cord. o All part of circulation of CSF
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The part of the midbrain posterior to the Cerebral Aqueduct is called the Tectum and on its surface are four small elevations called the Colliculi, which are arranged in pairs. o Inferior and Superior Colliculi
Third Ventricle Superior Colliculi Inferior Colliculi
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These structures are important in reflex activity. o The Superior Colliculi are associated with Vision o The Inferior Colliculi are associated with Hearing and Balance
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2021MSC – Head and Neck Anatomy -
The part of the midbrain anterior to the Cerebral Aqueduct is formed by the Cerebral Peduncles which enter the cerebral hemispheres
Colliculi of the Tectum Cerebral Peduncles Pons
Cerebellum Cerebral Aqueduct
Fourth Ventricle
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The Cerebral peduncles are tracts of white matter entering and exiting the brain. They are a destination of ascending and descending fibres.
15.3. The Pons -
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It is the part of the brainstem located between the midbrain and the medulla. It lies anteriorly to the connections of the cerebellum and much of its structure is made up of fibres passing the midline and connecting the two cerebral hemispheres o i.e. It provides communication between the left and right halves of the cerebellum. The pons is joined to the cerebellum via the Cerebellar peduncles o In diagrams, these peduncles are usually only visible if the cerebellum has been removed and appear as ovoid masses.
Dorsally, the pons contains sensory and motor tracts as well as the nuclei of Cranial Nerves V, VI and VII Ventrally, it contains fibres that connect the two hemispheres of the cerebellum. Cranial Nerves V – VIII all leave the brain stem from the pons. Many of the cranial nuclei associated with V are found here too. It was also found that within the pons, the motor nuclei tend to be more medially situated than the sensory nuclei. Furthermore, nuclei that have similar or related functions tended to be grouped fairly closely to each other.
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2021MSC – Head and Neck Anatomy 15.4. The Medulla Oblongata -
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Forms the most inferior part of the brain stem. It serves as a direct continuation of the spinal cord as it passes through foramen magnum o There is point at which the spinal cord ends and medulla oblongata begins is very arbitrary. Conventionally, foramen magnum acts as the dividing point but does not reflect anatomical change. o It runs up to and ends at the pons. On the anteriolateral surfaces of the medulla, there are swellings call the Olives Anteriomedially, two more swellings occur called the Pyramids o They are separated at the midline by the Anteromedian Fissure.
Middle Cerebellar Peduncle Pons Olives
Pyramids Anteriomedian Fissure
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Pyramidal Decussation
Recall that: o In the spinal cord, white matter is on the outside and grey matter on the inside o In the cerebrum, it is the other way around. It is in this area that the swapping around occurs. Furthermore, recall that the right half of the brain supplies the left side of the body and viceversa. o For the motor part (the ventral grey horns) of the spinal cord, this crossing over or decussation also occurs in this area. o Note in the diagram above that the anteriomedian fissure momentarily stops and starts up again. The space in between is where the decussation occurs and it is called the Pyramidal Decussation The nuclei of Cranial Nerve IX – XII are found in the medulla with VIII being partially in the pons and partially in the medulla. o Cranial nerve IX – XII all exit close to the olives. Page | 108
2021MSC – Head and Neck Anatomy 15.5. The Trigeminal Nerve (V) -
The cell bodies of most of its somatic sensory neurons are stored in the Trigeminal Ganglion The central fibres from these cell bodies form the majority of the Sensory root of V which enters the side of the pons.
At this point, let’s recall a couple things about spinal nerves. -
Sensory fibres terminate in the dorsal horn. o Specifically, fibres for pain and temperature terminate in the Substantia Gelatinosa Furthermore, remember that sensory fibres do not have to terminate at their spinal levels and can ascend or descend a certain amount via the Dorsolateral Fasciculus/Tract before reaching the dorsal horn at another level.
Now link this to the fact that the brainstem is the continuation of the spinal cord into the cranium. -
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Therefore we can assume that there will be similar structures found within the brainstem, and there are. We find three sensory nuclei which simulate the dorsal gray horn o Mesencephalic Nucleus o Chief Sensory Nucleus o Nucleus of the Spinal Tract In particular, this structure simulates and is continuous with the Substantia Gelatinosa Histologically speaking, there aren’t any visible differences between these two! We also find a tract that simulates the Dorsolateral Fasciculus o Called the Tract of the Spinal Nucleus
Mesencephalic Nucleus Chief Sensory Nucleus
Nucleus of the Spinal Tract
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2021MSC – Head and Neck Anatomy 15.5.1. Mesencephalic Nucleus
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Exclusively trigeminal nuclei. It deals with proprioception and is involved in the reflex control of mastication The reflex for control of mastication is the fastest in the body and the need for this speed is obvious. o To achieve this, an exception is made in that this is the only nucleus in the CNS where PNS sensory Cell Bodies are found. They are also located very close to the motor nucleus of V such that interneurons aren’t needed for the reflex arc.
Fibres from proprioceptive organs in the: o TMJ, PDL fibres, muscle spindles in the muscles of mastication and sutures of the maxilla terminate here.
15.5.2. Chief Sensory Nucleus
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Mainly serves the function of discriminative touch Holds nuclei for common sensation o i.e. The cell bodies of general sensory cells that relay to higher centres are located here. Fibres from the TMJ also relay to here to allow for conscious information about the joint position.
15.5.3. Nucleus of the Spinal Tract
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It is partly responsible for perception of simple touch and pressure It also relays degrees of pain and temperature It also holds the nuclei for V, VII, IX and X. Because pain and temperature fibres of all these nerves terminate in the same portion of the nucleus of the spinal tract, there is potential of referral of pain to areas served by other nerves. o E.g. Pain in a lower 8 could be felt as an earache. This communication between nuclei is so active that no nuclei operate on their own.
15.5.4. The Tract of the Spinal Nucleus
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It is in many ways, the equivalent of the Dorsolateral Fasciculus in the spinal cord. It is continuous with this structure and within, there is blending of fibres from the spinal cord and brainstem. o This is CLINICALLY SIGNIFICANT as it means that pain originating in the spinal cord can be referred up and interpreted as pain from e.g. the TMJ and vice versa.
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2021MSC – Head and Neck Anatomy 15.5.5. The Motor Part
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The Motor Fibres for V from the CNS originate in their brain centres, descend and terminate in the Trigeminal Motor Nucleus which lies medially to the chief sensory nucleus. At this point, they synapse with their Peripheral Fibres whose cells bodies make up this nucleus. These axons form the bulk of the motor root of V which joins onto the sensory trunk of V3 Most of these fibres will originate from the opposite side of the brain to what they innervate but not all of them meaning that there is a certain amount of insurance if there is a central lesion. o Ratio is about 85% cross-over, 15% stay on the same side.
15.6. The Facial Nerve (VII) -
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The nuclei of importance for the Facial Nerve include: o Facial Motor Nucleus In the pons medially to the nucleus of the spinal tract and inferior to the Chief Sensory Nucleus o Superior Salivatory Nucleus For Parasympathetic Secretomotor Fibres to the salivary glands o Nucleus of the Spinal Tract General Sensory of VII The motor fibres pass towards the Abducens Nerve Nucleus which they curve around en route to the Internal Acoustic Meatus
Facial Nerve
Facial Nucleus Abducens Nerve -
The sharp turn made by the facial nerve as it goes around the Abducens Nerve is called the Internal Genu
15.7. Glossopharyngeal Nerve -
Originates in the Inferior Salivatory Nucleus
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2021MSC – Head and Neck Anatomy 16. Clinical Case Studies 16.1. Cavernous Sinus Thrombosis Definition: -
It is the formation of a blood clot within the cavernous sinuses; a pair of venous cavities at the base of the brain bordered by the temporal and sphenoid bones. o Each cavity sits either side of the Sella Turcica and are connected by the Intercavernous Sinuses
Cause: -
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These clots result from the spreading of infections from the nose, sinuses, ears and/or teeth. The infections can spread very easily since the flow of venous blood in the brain isn’t unidirectional due to the lack of valves. Furthermore, the venous system of the brain is highly anastamotic forming a complex network of vessels. o In this case, the Cavernous Sinuses communicate with: Superior Ophthalmic Vein Pterygoid Plexus Each other via Intercavernous Sinuses Spread of infection results in the veins initiating the inflammatory response which results in blood stasis. o The clot forms and the build of up fluid pressure can then alter the direction of veinous blood flow until the clot ends up in the Cavernous Sinus
Relevance to Dentistry -
Whilst dental infections only account for around 10% of occurrences, it is still necessary to keep it in mind. Dental-related occurrences are due to spread of streptococcus and staphylococcus aureus from tooth infections with the most common origin being the canines, both maxillary and mandibular The upper and lower teeth are drained by the Superior and Inferior Alveolar Veins. o These two veins then drain into the facial vein which then anastamoses with the Superior Ophthalmic vein.
Symptoms -
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General symptoms include: o Loss of, or blurred vision o Sensitivity to light o Headaches
o o o
High Fever Swelling of the optic region Paralysis of certain cranial nerves which pass through the cavernous sinus. (III, IV, V and VI) Remember that certain cranial nerves run along the lateral wall of the cavernous sinus and can be compressed by the clot or swelling. Page | 112
2021MSC – Head and Neck Anatomy Treatment -
Patients are treated with high-dose antibiotics given intravenously. Corticosteroids can also be used to reduce the swelling. No response to medication will result in surgery to drain the fluid.
16.2. Designing a Periodontal Flap
16.3. Bell’s Palsy Definition: -
It is a TEMPORARY facial paralysis resulting from damage or trauma to the Facial Nerves (VII). If the lesion is peripheral, it will only affect one side of the face. Central lesions will result in partial paralysis on both sides but to different degrees depending on which motor nucleus is affected. When talking about Bell’s Palsy, we are only looking at paralysis of the MOTOR FUNCTIONS of the Facial Nerve, not the sensory.
Causes: -
It occurs when the Facial Nerve is swollen, inflamed or compressed.
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For the moment, Bell’s Palsy is idiopathic in that no one knows for certain what causes it. Most scientists believe that a viral infections such as meningitis or herpes simplex causes the nerve to swell and become inflamed, generating pressure within the Facial Canal and restricting the blood and oxygen supply to the nerve cells.
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In some milder cases, there is damage only to the myelin sheathes of the nerve.
Symptoms -
Paralysis of the muscles of facial expression. The severity of the paralysis may vary. Drooping of the eyelid and corner of the mouth, drooling, dryness of the eye or mouth, restriction of taste and excessive lacrimation in one eye.
Treatment/Management -
Remember that the severity of Bell’s Palsy will vary between individuals. Most cases are mild and will not require treatment and usually subside eventually on their own. Acyclovir is used to treat herpes and can be used to stop progression. Steroids such as Prednison can be used to reduce the inflammation and swelling. Analgesics like aspirin may help relieve any pain
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2021MSC – Head and Neck Anatomy -
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Eye protection is also important as Bell’s Palsy can inhibit the eye’s ability to close and will therefore be exposed to irritation and drying out. Eye patches are used and lubricating eye drops also help. For some, physical therapy to stimulate the facial nerve may help.
For Dentists -
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The point of this is that when performing an Inferior Dental block, if we inject into the parotid gland we anaesthetise the Facial Nerve resulting in Bell’s Palsy-LIKE symptoms but not Bell’s Palsy. We can also help diagnose it.
16.4. Ludwig’s Angina Definition -
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Ludwig’s Angina is a severe, potentially life-threatening cellulitis or connective tissue infection of the floor of the mouth/Submandibular space. o It is seen as an extra-oral swelling of the lower jaw and upper neck. It occurs bilaterally o Because the retropharyngeal space in which it occurs spans the whole floor of the mouth allowing for this spread.
Causes -
Dental infections account for approx. 80% of cases of Ludwig’s Angina. Most of the time, it is an infection of the roots of the Lower Molars such as a tooth abcess. Infections of the gums around partially erupted molars (usually lower 8) can also cause it.
Signs and Symptoms -
Bilateral swelling of the lower jaw and upper neck. Difficulty breathing and swallowing due to constriction of the neck. If serious, it can spread to the mediastinum and cause pericarditis Fever Faster, weaker heart rate. Constriction of voice box will change the voice.
Treatment/Management -
Penicillin is usually used to fight the infection given intravenously. A referral to a max-fax surgeon may be necessary to incise and drain the fluid If airways are constricted enough, a tracheostomy may be necessary to allow airflow. Dental treatment to remove infection.
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2021MSC – Head and Neck Anatomy 16.5. Principles for Injecting Local Anaesthesia 1. Palpate the location to inject before you pick up the needle as once the needle is in your working hand, you other hand cannot be in the patient’s mouth. a. Use the mirror to retract instead. 2. When inserting the needle, insert until you hit bone and retract a little before injecting a. Don’t inject into the bone as the Periosteum is very sensitive 3. Before injecting, pull the plunger a little to suck up some fluid to make sure you aren’t injecting into a vessel.
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