The Autonomic Nervous System PDF

The Autonomic Nervous System Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 Fxns of the Autonomic Nervous System (ANS) Functionally maintains homeostasis • regula...

The Autonomic Nervous System Images from Human Anatomy 6th ed., © 2009, by Martini, Timmins and Talitsch, denoted by “Ma”. Images from Human Anatomy, 2nd ed., © 2008 by McKinley & O’Loughlin, denoted by “Mc”. 1 Fxns of the Autonomic Nervous System (ANS) Functionally maintains homeostasis • regulates body temperature via control of sweat glands and vascular smooth muscle • regulates the activity of body systems: – cardiovascular – respiratory – digestive – excretory – reproductive systems • monitors and adjusts body fluids, fine-tuning concentrations of – electrolytes – nutrients – dissolved gases 2 The ANS differs from the Somatic NS Anatomically: • in the somatic NS, neurons in the CNS synapse directly onto effectors: Brain stem or spinal cord (CNS) Somatic motor neuron Skeletal muscle Peripheral nerve • in the ANS, the CNS controls effectors via a two neuron chain: Brain stem or spinal cord (CNS) Preganglionic neuron Autonomic ganglion Postganglionic neuron Peripheral nerve Smooth or cardiac muscle or glands • The somatic NS and the ANS may share a given peripheral nerve • there are two subdivisions of the ANS, the sympathetic nervous system (SyNS) and the parasympathetic nervous system (PsyNS) 3 The SyNS & PsyNS Differ Functionally • the PSyNS predominates during resting conditions: “rest & digest” • the SyNS predominates during exertion or emergencies: “fight or flight” • within a given system, the two divisions usually oppose each other – e.g. SyNS  HR, PSyNS  HR – e.g. PSyNS  digestion, SyNS  digestion • occasionally they work independently – SyNS alone controls most vascular smooth muscle and all smooth muscle in the limbs & body wall (BVs, erector pili muscle, glands) 4 The SyNS & PSyNS Differ Anatomically The two divisions differ in the locations of their: A Preganglionic neuron Autonomic ganglion Postganglionic neuron B Peripheral nerve Smooth or cardiac muscle or glands A. preganglionic neuronal cell bodies in the CNS • SyNS (“thoracolumbar division”): spinal cord, T1-L2 levels • PSyNS (“craniosacral division”): brainstem cranial nerve nuclei & spinal cord, S2-S4 levels B. postganglionic neuronal cell bodies in the PNS • sympathetic ganglia located near the spinal cord in either the paired sympathetic chain ganglia or unpaired preaortic ganglia • parasympathetic ganglia located in or near effector organs 5 Organization of the Spinal Grey Matter • deep, forms a continuous column extending the length of the cord Gray matter White matter Ventral root • at all levels, grey matter forms a butterfly in XS, divided into: Spinal nerve Dorsal root ganglion Dorsal root – dorsal horns: sensory, receives input via spinal nerves and dorsal roots – ventral horns: somatic motor, conducts output via ventral roots, spinal Ns Ma14.2 • at certain levels, (T1-L2 & S2-S4) intermediolateral cell column (IML), contains autonomic preganglionic motor neurons, conducts output via ventral roots, ensuing nerves 8 The Sympathetic Division targets: A. smooth muscle of limbs & body wall B. viscera of head & thorax C. viscera of abdomen & pelvis preganglionic neurons (for ALL targets) • cell bodies located in lateral gray horns, T1-L2; • axons travel via ventral roots, spinal nerves, synapse onto: postganglionic neurons • cell bodies located in sympathetic ganglia near the vertebral column, either: – in bilaterally paired sympathetic chain ganglia (targets A&B) or – in unpaired prevertebral (preaortic) ganglia (targets C) • postganglionic axons innervate the target organ 9 Somatic Innervation of the Body Wall & Limbs • somatic motor neurons innervate skeletal muscle – cell bodies in the ventral grey horn of the spinal cord • sensory Ns monitor skin, joints, skeletal muscle – cell bodies in dorsal root ganglia (DRG), axons convey info to dorsal grey horn of spinal cord • their axons form peripheral nerves A. Dorsal horn B. Lateral horn H E G I C. Ventral horn D F A D. Dorsal root B E. DRG C F. Ventral root G. Spinal nerve H. Dorsal ramus XS through spinal cord between T1 and L2 I. Ventral ramus 10 A. Sympathetic Innervation of the Body Wall & Limbs • the body wall & limbs are innervated by postganglionic sympathetic neurons located in the paravertebral or sympathetic chain ganglia • target organs are smooth muscle of erector pili, BVs, glands in ALL dermatomes of body Rami communicantes Paravertebral ganglion XS through spinal cord between T1 and L2 11 Preganglionic sympathetic fibres can ascend or descend within the sympathetic chain before synapsing. In this way, sympathetics are distributed to dermatomes* ABOVE T1 and BELOW L2 *dermatome: the area of skin innervated by a specific spinal segment and nerve 12 Summary: The Sympathetic Nervous System PONS Dermatomes C2–C3 NV C2–C3 Cervical Superior sympathetic Middle ganglia Inferior C2 C3 Gray rami to spinal nerves T2 C6 L1 L2 C8 Postganglionic fibers to spinal Ns (innervating BVs, sweat glands, erector pili muscles, adipose tissue) C7 T1 L3 L4 L5 Sympathetic chain ganglia C3 C4 C5 T2 3 T1 T T4 T2 T T3 T5 T4 T67 T5 T8 T6 T9 T7 T10 T8 T11 T9 T L12 T10 L21 T11 L4L3 T12 L5 S2 C4 C5 T2 C6 C7 T1 SS 4 3 L1 S5 S1L5 C8 L2S2 L3 S1 Ma17.4 Preganglionic Ns Ganglionic Ns Coccygeal ganglia (Co1) fused together (ganglion impar) L4 ANTERIOR POSTERIOR 13 B. Sympathetic Innervation of Thoracic Viscera & Face Thoracic viscera & targets in the face are innervated by postganglionic sympathetic Ns located in the paravertebral or sympathetic chain ganglia. For targets in the thorax: Axons of postganglionic Ns form splanchnic Ns (cardiac, pulmonary, esophageal splanchnic Ns) which contribute to autonomic plexuses (cardiac, pulmonary, esophageal plexuses) that innervate targets in the thorax. For targets in the face: Axons of postganglionic Ns form autonomic plexuses, which “hitch a ride” with arteries to reach their targets. Named for artery, eg. carotid plexus. 14 Summary: The Sympathetic Nervous System Eye PONS Salivary glands Cervical Superior sympathetic Middle ganglia Inferior Gray rami to spinal nerves Heart Cardiac and pulmonary plexuses Lung Postganglionic fibers to spinal Ns (innervating BVs, sweat glands, erector pili muscles, adipose tissue) Sympathetic chain ganglia Ma17.4 Preganglionic Ns Ganglionic Ns 15 C. Sympathetic Innervation of Abdominopelvic Viscera Abdominopelvic viscera are innervated by postganglionic sympathetic neurons located in the prevertebral ganglia, eg. the celiac, superior mesenteric and inferior mesenteric ganglia. Axons of postganglionic neurons contribute to autonomic plexuses, which “hitch a ride” with arteries to reach their target organs. The plexuses are named by the BV, ie. celiac, superior and inferior mesenteric plexuses. 16 The Adrenal Medulla • is a modified sympathetic ganglion • is innervated by preganglionic sympathetic neurons of the lateral gray horns • postganglionic “neurons” of the adrenal medulla release epinephrine & norepinephrine which is picked up by blood vessels for systemic distribution • consequences? 17 Summary: The Sympathetic Nervous System Eye PONS Salivary glands Cervical Superior sympathetic Middle ganglia Inferior Gray rami to spinal nerves Heart Celiac ganglion Cardiac and pulmonary plexuses Lung Superior mesenteric ganglion Liver and gallbladder Stomach Spleen Pancreas Large intestine Small intestine Inferior mesenteric ganglion Postganglionic fibers to spinal Ns (innervating BVs, sweat glands, erector pili muscles, adipose tissue) Adrenal medulla Kidney Sympathetic chain ganglia Ma17.4 Preganglionic Ns Ganglionic Ns Coccygeal ganglia (Co1) fused together (ganglion impar) Urinary bladder Ovary Uterus Testicle 18 Mc18.7 19 The Parasympathetic Division preganglionic neuronal cell bodies located either in: 1. brainstem cranial nerve nuclei; axons travel via cranial nerves (III, VII, IX, and X (the vagus nerve)), OR 2. IML cell column, S2-S4 • preganglionic fibres synapse onto postganglionic PS neurons within: S2 – S4 parasympathetic ganglia • located in or near the effector organ (intramural or terminal ganglia) • short postganglionic fibres innervate the cells of the effector organ CN III, VII & IX innervate viscera of the face CN X (the vagus nerve) innervates viscera of the thorax & most of abdomen pelvic splanchnic nerves innervate the viscera of the distal abdomen & pelvis note: no parasympathetic innervation of smooth muscle targets in limbs or body wall, nor most vascular smooth muscle elsewhere 20 Lacrimal gland Eye PONS Salivary glands N X (Vagus) Heart Lungs Liver and gallbladder Autonomic plexuses Stomach Spleen Pancreas Pelvic splanchnic nerves Large intestine Small intestine Rectum Spinal cord Kidney Urinary bladder Ma17.8 Preganglionic neurons Ganglionic neurons Uterus Ovary Penis Testicle 21 • visceral organs have dual innervation Autonomic Plexuses • two divisions generally antagonistic Trachea Left vagus nerve Right vagus nerve Aortic arch Thoracic Spinal nerves Esophagus Splanchnic nerves Diaphragm Celiac trunk Superior mesenteric artery Inferior mesenteric artery • overlap of SyNS & PSyNS Autonomic Plexuses in autonomic plexuses: and Ganglia Cardiac plexus Pulmonary plexus Thoracic sympathetic chain ganglia Esophageal plexus Celiac plexus and ganglion Superior mesenteric ganglion Inferior mesenteric plexus and ganglion Hypogastric plexus Pelvic sympathetic chain – cardiac plexus – pulmonary plexus – esophageal plexus – celiac plexus – superior mesenteric plexus – inferior mesenteric plexus – hypogastric plexus – pelvic plexus Ma17.9 22 Autonomic Afferents: Homeostatic Input • afferents from an organ retrace the path taken by the efferents to the organ  if you know the motor output pathway, you know the sensory input pathway! • afferents carrying homeostatic sensory information (eg. BP from baroreceptors, blood gas from chemoreceptors) generally travel with parasympathetic efferents • other than the distal digestive tract and pelvis, this is via the vagus nerve! 23 Autonomic Afferents: Visceral Pain • viscera are insensitive to cutting, burning, freezing • visceral pain is caused by ischemia, distension, inflammation, blood etc. • visceral pain usually travels with the sympathetic efferents eg., the Sy efferents to the heart originate from spinal cord levels T1 – T5  pain afferents from the heart travel with sympathetic efferents back to spinal cord levels T1 – T5 Sensory neuron from body wall Both project to the same dorsal horn cell • in the spinal cord, overlap with afferents from the T1 – T5 dermatomes gives rise to the referral of cardiac pain to these dermatomes, ie. chest, armpit, medial arm • this is the anatomical basis of “referred pain” Sensory neuron from viscus 24