Autonomic Nervous System.docx

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Western University
Anatomy and Cell Biology
Anatomy and Cell Biology 3319
Kem Rogers

Autonomic Nervous System Overview • System of motor neurons that innervate smooth muscle, cardiac muscle & glands of the body • Regulates visceral functions as heart rate, blood pressure, digestion & urination • General visceral motor division of PNS – distinct from general somatic motor division (skeletal muscle) • Considers both general visceral motor functions and general visceral senses • Enteric nervous system o Innervates smooth muscle & glands – specifically those in digestive tract o Functions completely independently of the CNS • Autonomic neurons to digestive tract can influence enteric neurons by stimulating or inhibiting activity • ANS influence acts as “volume control” rather than as an “on/off” switch Comparison of Autonomic & Somatic Motor Systems • Each somatic motor neuron runs from CNS all the way to muscle being innervated & each motor unit consists of a single neuron plus skeletal muscle cells that it innervates • Typical somatic motor axons are thick, heavily myelinated fibres that conduct nerve impulses rapidly • Motor unit inANS includes a chain of two motor neurons • First of these is called preganglionic neuron, whose cell body lies within CNS • Its axon, preganglionic axon (preganglionic fibre), synapses with 2 motor neuron, postganglionic neuron in a peripheral autonomic ganglion • Postganglionic axon (postganglionic fibres) then extends to visceral organs • Functionally – preganglionic neuron signals postganglionic neuron which stimulates muscles or glands • Preganglionic axons are thin, lightly myelinated fibres • Postganglionic axons are thinner, & unmyelinated • Impulses are conducted throughANS more slowly than the somatic motor system • Autonomic ganglia are motor ganglia containing cell bodies of motor neurons • Unlike dorsal root ganglia – not sensory ganglia Division ofANS • Both divisions have chains of two motor neurons that mostly innervate the same visceral organs but cause opposite effects • One divisions stimulates and the other inhibits the action Sympathetic Division • Mobilizes the body during extreme situations such as fear, exercise or rage • Becomes active when extra metabolic effect is needed • Responsible for “fight-or-flight” response • Pounding heart, dilated (widened) pupils & cold, sweaty skin are signs of division • Help us to respond to dangerous situations • Increased heart rate deliver more blood & oxygen to skeletal muscles used for fighting or running • Widened pupils let in more light for clearer vision • Cold skin indicates blood is being diverted from skin to more vital organs • Small air tubes (bronchioles) dilate – increasing uptake of2O – consumption increases O2 • Liver releases more sugar in the blood to provide for body’s energy needs • Body’s motor are revved up for vigorous activity • Temporarily nonessential functions – such as digestion & motility of urinary tract are inhibited • Innervates smooth muscle in walls of blood vessels • Input to blood vessels servicing skeletal muscle rises, causing the smooth muscle of walls to contract • Vessels dilate, bringing more blood to active muscles • At the same time, increased sympathetic input to smooth muscle in other blood vessels stimulates contraction: vasoconstriction • Narrowing of vessel diameter forces heart to work harder to pump blood around vascular circuit • Sympathetic activity causes blood pressure to rise during excitement & stress Parasympathetic Division • Enables body to unwind & relax & works to conserve body energy • Controls routine maintenance functions • Most active when body is at rest • Division is concerned with conserving body energy & directing vital housekeeping activities (digestion & eliminating feces & urine) • “Rest & digest” • Heart rate & respiratory rates are low-normal levels • Gastrointestinal tract is digesting food • Pupils are constricted as eyes focus for close vision Autonomic nerves, plexuses & ganglia • All autonomic plexuses contain both parasympathetic & sympathetic axons • Ganglia are almost exclusively sympathetic Epipen • Makes heart contract faster • Bronchodilation • Norepinephrine • Effects of Parasympathetic & Sympathetic Divisions on Various Organs Parasympathetic Division Cranial Outflow • Preganglionic axons run in Oculomotor (III), Facial (VII), Glossopharyngeal (IX), & Vagus (X) nerves • Cell bodies of these preganglionic neurons are located in motor cranial nerve nuclei in gray matter of brain stem Oculomotor Nerve (III) • Innervate smooth muscles in eye that cause pupil to constrict & lens of eye to bulge – actions that allow focusing on close objects in field of vision • Two-neuron pathway • Preganglionic axons originate from cell bodies in accessory Oculomotor nucleus in midbrain • Postganglionic cell bodies lie in ciliary ganglion, in posterior part of the orbit just lateral to optic nerve Facial Nerve (VII) • Stimulate the secretion of many glands in the head o Lacrimal (tear) gland above the eye o Mucus-secreting glands in the nasal cavity o Two salivary glands inferior to the mouth (submandibular & sublingual) • Pathway leading to lacrimal & nasal glands o Preganglionic neurons originate in lacrimal nucleus in pons o Synapse with postganglionic neurons in perygopalatine ganglion – just posterior to maxilla • Pathway leading to submandibular & sublingual glands o Preganglionic neurons originate in superior salivatory nucleus in the pons o Synapse with postganglionic neurons in submandibular ganglion – deep to mandibular angle Glossopharyngeal Nerve (IX) • Stimulate secretion of large salivary parotid gland - lies anterior to ear • Preganglionic neurons originate in inferior salivatory nucleus in medulla • Synapse with postganglionic neurons in otic ganglion • 3 cranial nerves considered (III, VII, IX) supply parasympathetic innervation of the head • Only preganglionic axons run within these three nerves • Axons synapse in ganglia – located along the bath of the trigeminal nerve (V) • Postganglionic axons travel via trigeminal to their final destination • Routing by way of trigeminal nerve occurs because the trigeminal has widest distribution within the face Vagus Nerve (X) • Innervate the visceral organs of the thorax & most of abdomen • Does not include innervation of pelvic organs • Vagal innervation of digestive tube ends halfway along the large intestine • Contains nearly 90% of preganglionic parasympathetic fibres in the body • Bring typical rest & digest activities in visceral muscle & glands o Stimulation of digestion (secretion of glands & increased motility of smooth muscle of tract) o Reduced heart rate o Constriction of bronchi in lungs • Preganglionic cell bodies are mostly in dorsal motor nucleus of vagus in medulla • Preganglionic axons run the entire length of nerve • Most postganglionic neurons are confined within walls of organs being innervated & cell bodies form intramural ganglia • As vagus descends through neck & trunk – sends branches through many autonomic nerve plexuses to organs being innervated • Sends branches o Through cardiac plexus to heart o Through pulmonary plexus to lungs o Through esophageal plexus to esophagus & stomach wall o Through celiac plexus & superior mesenteric plexus to other abdominal organs • Fibres from both divisions of ANS, parasympathetic & sympathetic travel to thoracic & abdominal organs through plexuses Sacral Outflow • Sacral part of parasympathetic outflow emerges from segments2S 4S of spinal cord • Continuing where vagus ends – innervates organs in pelvis o Distal half of large intestine o Bladder o Reproductive organs – uterus & erectile tissues of external genitalia • Parasympathetic effects on these organs include stimulation of defecation, voiding of urine & erection • Preganglionic cell bodies of sacral parasympathetics lie in visceral motor region of spinal gray matter • Axons of preganglionic neurons run in ventral roots to ventral rami – from which they branch to form pelvic splanchnic nerves • Nerves then run through autonomic plexus in pelvic floor – inferior hypogastric plexus – to reach pelvic organs • Some preganglionic axons synapse in ganglia in this plexus – but most synapse in intramural ganglia in organs • Plexus also contains fibres from both divisions of thisANS • Specific effects of parasympathetic innervation on various organs are presented in comparison with effects of sympathetic innervation Sympathetic Division Basic Organization • Exits from thoracic & superior lumbar part of spinal cor1 (T t2 L ) • Preganglionic cell bodies lie in visceral motor region of spinal gray matter – form lateral gray horn • More complex than parasympathetic – innervates more organs & has more ganglia o Supplies all visceral organs in internal body cavities & visceral structures in superficial regions  Sweat glands  Hair-raising arrector pili muscles of skin  Smooth musculature in walls of all arteries & veins o Parasympathetic division does not innervate sweat glands, arrector pili or (with minor exceptions) blood vessels o Sympathetic ganglia fall into two classes: sympathetic trunk ganglia & collateral ganglia • 2 Pathways o Bilaterally paired sympathetic chain (paravertebral) ganglia o Unpaired Prevertebral ganglia (preaortic or collateral) Sympathetic Trunk Ganglia • Also called chain ganglia & paravertebral ganglia (motor ganglia) • Contain the cell bodies of postganglionic sympathetic neurons • Bilateral –longitudinal trunks on left & right side – from neck to pelvis – lateral to vertebral1b5dies C -S • Linked by short nerves into long sympathetic trunks (sympathetic chains) that resemble strings of beads • Ganglia are joined to ventral rami of nearby spinal nerves by white & gray rami communicantes • White rami communicantes lie lateral to gray rami communicantes • Approx. 1 sympathetic trunk ganglion for each spinal nerve but: o # of sympathetic trunk ganglia & spinal nerves: not identical o Some ganglia fuse during development o Most fusion in neck - 8 spinal nerves but only 3 sympathetic trunk ganglia – cervical ganglia  Superior  Middle  Inferior • Inferior cervical ganglion usually fuses with 1 thoracic ganglion to form stellate ganglion in superior thorax • 22-24 sympathetic trunk ganglia per side
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