Anatomy 5.8 ANS_Javier

Anatomy 5.8

January 17, 2012 Dr. Javier

ANS OUTLINE I. Functional components of peripheral nerves II. Overview of ANS III. Spinal Cord, Roots & Nerves IV. Sympathetic Nervous System V. Parasympathetic Nervous System VI. ANS Control by the Brain VII. Visceral Afferents

Objectives:  To describe the general organization of the Autonomic Nervous System, its functions and principle divisions  To describe the origin and general distribution of each of the principle divisions  To differentiate the principle divisions by anatomic features, the involved neurotransmitters and their systemic effects  To describe the higher control of ANS  To briefly touch the Visceral Afferent Pathways

I. FUNCTIONAL COMPONENTS OF PERIPHERAL NERVES  Motor system (general visceral efferent, GVE) which provides for the innervations of the smooth muscle, cardiac muscle and glandular tissue of the body.  GVE fibers are found in: 1. Body wall structure – Blood vessels of skeletal muscles and skin, arrector pili muscles and glands of the skin 2. Internal organs – Blood vessels and glands of these organs  Nervous impulses are conveyed along two-neuron chains from CNS to target structure o Preganglionic neurons  Located in the brainstem or the spinal cord  Their axons constitute preganglionic fibers o Postganglionic neurons  Located in autonomic ganglia (outside CNS)  Their axons constitute post ganglionic fibers Functional Components  Each nerve can be differentiated according to: 1. Afferent vs Efferent 2. Somatic vs Visceral 3. General vs Special 4. Somatic vs Autonomic

B. SOMATIC VS. VISCERAL Attribute

Somatic System

Visceral System

Embryological origin of tissue

Derived from the body wall Related to somatic (parietal) mesoderm o dermatome (skin) o myotome (muscles)

Derived from splanchnic (visceral) mesoderm, endoderm

Examples of adult tissues

Dermis of the skin, skeletal muscles, connective tissues

Perception

Conscious, voluntary

Glands, cardiac muscle, smooth muscle of GIT and blood vessels Unconscious, involuntary

C. GENERAL VS. SPECIAL Sensory/Motor + Somatic/Visceral Sensory (afferent) Motor (efferent)

Somatic Somatic sensory General Somatic Afferent (GSA) Somatic motor General Somatic Efferent (GSE)

Visceral Visceral sensory General Visceral Afferent (GVA) Visceral motor General Visceral Efferent (GVE)

Somatic nerves – Somatic Nervous System Visceral nerves – Autonomic Nervous System D. SOMATIC VS. AUTONOMIC  Somatic nervous system o Only one neuron from the ventral horn cells to effector organ (Skeletal ms) Release of ACh

A. AFFERENT VERSUS EFFERENT  Afferent o Stimulus from the periphery towards the CNS o Example: Pseudounipolar neurons conducting impulses from sensory origin to CNS

 Autonomic nervous system o Preganglionic and postganglionic neuron synapse at the ganglion o Postganglionic neuron has the nerve cell bodies in the ganglion o “Location” of neuron is in the nerve cell body of the neuron o Preganglionic fiber is myelinated but the postganglionic fiber is unmyelinated o Innervated organs: Smooth muscle, cardiac muscle, glands (myoepithelial cells)

 Efferent o From CNS (ex. multipolar neurons, muscles and glands o Located at the ventral horn o Motor nerve fibers

Group 6 | Bautista A., Bautista B., Bautista C., Bautista V., Bello C., Bello H., Bernardo, Biag E.

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Table 1. Differences between sympathetic and parasympathetic Location of preganglionic cell Sympathetic Parasympathetic bodies Neurotransmitters  Preganglionic  Preganglionic (potential for neurons – release neurons —release pharmacologic Ach and are Ach and are (+) modulation excitatory (+) responses)  Postganglionic  Postganglionic *excitation or inhibition neurons – NE and neurons – Ach and is a receptorare excitatory* (+) or are (+)/(-); dependent and inhibitory* (-); Ach at muscarinic receptor- mediated eccrine sweat receptors response glands; nicotinic α and β receptors Branching of axons

Target tissues

II. OVERVIEW OF THE ANS

 Preganglionic neurons –More ganglia from the same axon  Postganglionic neurons – Branched (greater distribution/ diffused; prolonged effect)

 Preganglionic neurons – 1 axon

 Organs of head, neck, trunk and external genitalia

 Organs of head, neck, trunk and external genitalia

 Adrenal medulla

 Never reaches limbs or body wall except for external genitalia

 Sweat glands in skin

 Postganglionic neurons – Branched but not as extensive as in sympathetic n (more localized effect)

 Arrector muscles of hair  ALL vascular smooth muscle

Functional differences

 Distributed to essentially all tissues because of vascular smooth muscle  “Fight or flight”  Catabolic (expend energy)

 “Feed and breed”, “rest and digest”  Maintain homeostasis

 Similarities between Sympathetic and Parasympathetic o Both are efferent (motor) systems: “Visceromotor” o Both involve regulation of the internal environment generally outside of our conscious control: Autonomous o Both involve 2 neurons that synapse in a peripheral ganglion o Innervate glands, smooth muscles, cardiac muscles  Differences between Sympathetic and Parasympathetic o Neurotransmitters and their receptors: basis for pharmacological modification (medication or anesthetics) o Dual innervations of many organs- having a break and an accelerator provides more control o Predominance of one over the other

Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez

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 Dual innervation of organs o having a “break and an accelerator” provides more control o Interplay of opposing/antagonistic effects  Exemption to the dual innervations rule: o Sweat glands and blood vessel smooth muscle are only innervated by sympathetic o Rely strictly on up- down control  Higher frequency of stimulation, increased smooth muscle contraction or increased sweat secretion  Exemption to the antagonism rule: o Sympathetic and parasympathetic work cooperatively to achieve male sexual function. o Parasympathetic is responsible for erection while sympathetic is responsible for ejaculation. o There’s a similar ANS cooperation in the female sexual response. III. SPINAL CORD, ROOTS AND NERVES

 Somatic Pathways o Interneuron between GSA and GSE o Mixed spinal nerves  Sympathetic pathway o Nerve cell bodies at intermedial gray column/ lateral horn IV. SYMPATHETIC NERVOUS SYSTEM  Fight or flight  Afferent fibers will come from the ventral root and then exit the intervertebral canal and join the dorsal root to form the spinal nerve  Ventrally located branches (rami communicantes; sing. Communicans) join sympathetic chain ganglion  Group of SCG ->becomes sympathetic trunk (both sides of the vertebral column) -> becomes paravertebral ganglia  Ganglion impar (fuses at midline) A. PREGANGLIONIC CELL BODIES  Exit spinal cord via ventral root -> spinal nerve -> white ramus communicans -> synapse at ganglion within sympathetic trunk -> axon of the ganglion of the post-ganglionic fiber leave the sympathetic trunk -> spinal nerve via gray ramus communicans  Thoracolumbar area

Figure 1. Arrangement of spinal cord, spinal nerve and sympathetic chain ganglion.

 Efferent fibers branch out to ventral root, exit IV canal , join with dorsal root to form the spinal nerve  2 ventral branches of rami communicantes  merge to form the sympathetic chain ganglion  ventral root + dorsal root= spinal nerve → rami communicantes → sympathetic chain ganglion  Spinal Nerve & Sympathetic Trunk o Ganglia (pairs)  3 cervical  11-12 thoracic  2-4 lumbar  4 sacral  1 coccygeal (Located at midline, anterior to the vertebral body of the coccyx; a.k.a. ganglion impar) o 14 pairs white rami communicantes (T1-L2) o 31 pairs gray rami communicantes Note:  Ventral root + dorsal root= Spinal nerve  White matter - More lateral  Gray matter - Medial  For each spinal nerve, there is a gray ramus  Preganglion - Myelinated - White  Postganglion - Unmyelinated - Gray

Preganglionic cell bodies in intermediolateral cell column (Lamina VII)  Spinal cord level: T1- L2/L3  Somatotrophic organization Clinical significance:  Dysfunction due to cord injury - Spinal nerve impingement Referred pain

Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez

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SUMMARY: SNS

Figure 1: Sympathetic Pathways B. POSTGANGLIONIC CELL BODIES  For coccygeal to cervical 1. Paravertebral ganglia  Located just beside the vertebrae  United by preganglionic into sympathetic trunk  Preganglionic neurons are thoracolumbar but postganglionic neurons span from the cervical area down to coccyx  Some preganglionic fibers ascend or descend in trunk o Synapse at same level o Ascend to synapse at higher ganglion o Descend to synapse at lower ganglion

 Thoracolumbar preganglionic cell bodies (intermediolateral gray)  Short preganglionic fiber releasing ACh  Ganglia with nicotinic receptors at sympathetic trunk, prevertebral ganglia, adrenal medulla  Long postganglionic fiber releasing NE (+ Epi at adrenal medulla; Ach in sweat glands)  Diffuse and prolonged effect on target organs with α/β receptors  Lansang Notes: st  Inferior cervical ganglion + 1 thoracic ganglion = stellate ganglion  Thoracic splanchnic nerves (greater, lesser, and least; T5 –T12) o Carry preganglionic fibers (T5-T12) through sympathetic trunk to postganglionic prevertebral ganglia  preganglionic fibers o T5-T9: greater splanchnic nerve o T10-T11: lesser splanchnic nerve o T12: least  postganglionic fiber – reach abdominal viscera  lumbar splanchnic nerves  carry preganglionic fiber from upper lumbar spinal cord (L1-L2)  reach lower abdomen and pelvis  distribution of sympathetic outflow  T1 to T5 – head and neck  T1 to T2 – eye  T2 to T6 – heart and lungs  T6 to L2 – abdominal viscera  L1 to L2 – urinary, genital  Superior cervical ganglion (postganglionic fiber) – form carotid plexus which innervates head V. PARASYMPATHETIC NERVOUS SYSTEM A. CRANIAL OUTFLOW

2. Prevertebral (preaortic) ganglia  Located anterior to abdominal aorta in plexuses surrounding its major branches  Example: Celiac ganglion, superior and inferior mesenteric ganglia  Preganglionic fibers reach prevertebral ganglia via abdominopelvicsplanchnic nerves

 CN III, VII, IX, X  Four ganglia in head  Vagus nerve (CN X) - major preganglionic parasympathetic supply to thorax and abdomen  synapse in ganglia within wall of target organs (e.g. enteric plexus)

3. Adrenal Medulla  Certain splanchnic nerves synapse on hormone-producing cells of the adrenal medulla (modified postganglionic neurons)  Cells of the adrenal medulla are derived from the neural crest  Norepinephrine and epinephrine are released to the blood stream to reach their target organs

B. SACRAL FLOW  S2-S4 via pelvic splanchnic  Hindgut/pelvic viscera distal to the left colonic (colic) flexure, and external genitalia  As with SNS, have preganglionic bodies located in gray areas of spinal cord (analogous to lateral horn/IMLC)

C. Sympathetic System: Preganglionic Pathways 1. Synapse at same level 2. Synapse above or below spinal level within sympathetic chain 3. Exit through splanchnic nerves to synapse to collateral ganglion or to adrenal medulla

Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez

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    

bronchial smooth muscle pulmonary blood vessels and glands stomach and intestines until left colic (splenic) flexure gallbladder and biliary ducts kidneys

SUMMARY: PNS  Craniosacral preganglionic cell bodies (cranial nerve nuclei and sacral gray matter)  Long preganglionic fiber releasing Ach  Ganglia with nicotinic receptors near or in walls of target organs  Short postganglionic fibers releasing Ach  In contrast to SNS, has localized and short-lived effect on the target organ VI. ANS CONTROL BY THE BRAIN     C. PARASYMPATHETIC CRANIAL OUTFLOW  CN III Oculomotor o o o o o

Nucleus: Edinger-Westphal preganglionic fibers: oculomotor nerve ganglion: ciliary ganglion postganglionic fibers: short ciliary nn target organs:  ciliary muscle - relaxes zonal fibers, making lens more convex  sphincter papillae - constricts pupils (myosis)

 CN VII Facial o 2 sets of nuclei, ganglia, and target organ(s) o Tears:  nucleus: lacrimal/lacrimatory  preganglionic fibers: nervus intermedius  greater petrosal n.  nerve of pterygoid canal  ganglion: pterygopalatine  postganglionic fibers: maxillary n.  zygomaticotemporal n.  lacrimal n.  target organ:  lacrimal gland  mucosa of nasal cavity, paranasal sinuses, palate, pharynx

The hypothalamus is the boss! Anterior, Medial regions-control Parasympathetic Nervous System Posterior, Lateral Regions-control Sympathetic Nervous System These fibers exert direct control via nuclei in the reticular formations o Ex: There are respiratory and cardiovascular centers in the Medulla Oblongata

 The Brain controls the ANS by: 1) Subconscious cerebral input via the limbic lobe connections influences hypothalamic function  Mediates our “fight or flight” response to emotional situations  The relationship between the hypothalamus and the periaqueductal gray matter and amygdale allow us to respond to fear 2)Other controls come from the cerebral cortex, reticular formation and the spinal cord

 CN IX Glossopharyngeal o nucleus: inferior salivatory o preganglionic fibers: tympanic branch of CN IX  lesser petrosal n. o ganglion: otic ganglion o postganglionic fibers: auriculotemporal nerve o target organ: parotid gland VII. VISCERAL AFFERENTS  CN X Vagus o o o o o

nucleus: dorsal motor nucleus of CN X preganglionic fibers: vagal nerve trunks and branches ganglia: on plexuses near or within walls of target organ postganglionic fibers: short direct fibers target organ:  cardiac muscle

 Visceral Sensory Nerves (GVA) o Run with sympathetic and parasympathetic nerves o Cell bodies in dorsal root ganglion (pseudo-unipolar) o Nerve ending in viscera  Somatic Sensation o Conscious, sharp, well-localized o Touch, pain, temperature, pressure, proprioception

Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez

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 Visceral Sensation o Often unconscious. If conscious: it is dull, poorly localized o Distension, cramping, blood gas, blood pressure, irritants  Visceral pain is carried almost exclusively by the sensory component of the SNS  Visceral pressure and movement sensation is carried almost exclusively by the sensory component of the PNS

B. VISCERAL AFFERENTS AND REFERRED PAIN

S

A. VISCERAL REFLEX ARC

C. REFERRED PAIN  Pain originating in a visceral structure perceived as being from an area of skin innervated by the same segmental level as the visceral afferent  Results from convergence of somatic and visceral afferents on the same segmental level of the spinal cord o Ex: Pain originating in the chest can also radiate down the left side of the arm  “cross talk” in the dorsal horn

somatic afferent

convergence & “cross-talk” “cross-talk”

Rectal or Defecation Reflex 1) Sensory stretch receptors in rectum sense distension 2) Stimulus sent to spinal cord segments S2-S4 3) Integrate with pre-ganglionic cell bodies 4) Efferent signal travels to pelvic splanchnic nerves 5) Contraction of muscles  defecation Micturition Reflex 1) Distension in the bladder 2) Stimulus sent to spinal cord segments S2-S4 3) Integrate with pre-ganglionic cell bodies 4) Efferent signal travels to pelvic splanchnic nerves 5) Contraction of Detrusor muscle  micturition

Group 2 | Agustin B, Al-Qaseer, Alegre, Almario, Almazan, Almodiente, Altabano, Alvarez

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