Autonomic Nervous System Lecture Notes PDF

Autonomic Nervous System BB - Chap 14, MTT – Chap 17 I. Introduction A. function 1. regulates activity of glands, smooth & cardiac muscle 2. motor (output) system, requires sensory input 3. involuntary (autonomic (Gk) = self governing) 4. m...

Autonomic Nervous System BB - Chap 14, MTT – Chap 17 I. Introduction A. function 1. regulates activity of glands, smooth & cardiac muscle 2. motor (output) system, requires sensory input 3. involuntary (autonomic (Gk) = self governing) 4. maintains homeostasis a. blood pressure b. fluid volume c. temperature d. etc. 5. coordinates responses to external stimuli II. Comparison of Somatic & Autonomic Systems A. somatic motor system 1. sensation consciously perceived 2. effector - skeletal muscle 3. effector is excited 4. single motor axon 5. no ganglia 6. neurotransmitter = acetylcholine 7. distinct neuromuscular junction w. NT receptors on motor endplate 8. denervation leads to flaccid paralysis and atrophy B. autonomic system 1. visceral sensation usually unconscious 2. effector - glands, smooth muscle, cardiac muscle 3. effector may be excited or inhibited 4. two motor neurons in ANS pathway 5. paravertebral, peripheral or terminal ganglia 6. neurotransmitter = acetylcholine or norepinephrine 7. smooth muscle membrane has scattered NT receptors 8. denervation principally effects control of autonomic function  9. three divisions a. sympathetic - stress, emergency behavior b. parasympathetic - vegetative, restful functions c. enteric - neuron network (plexus) within gastrointestinal system C. somatic vs autonomic reflexes 1. same general components (e.g. afferent & efferent routes) 2. autonomic has two neuron efferent pathway III. Anatomy of Autonomic Motor Pathways A. overview 1. preganglionic neuron a. first autonomic motor neuron b. cell body in CNS c. myelinated axon exits CNS 2. postganglionic neuron a. 2nd autonomic motor neuron b. cell body & dendrites w/i autonomic ganglion c. axon (unmyelinated) terminates at visceral effector 3. autonomic ganglia a. clusters of cell bodies outside CNS b. types: (1) paravertebral (sympathetic chain) (a) chain of ganglia parallels spinal cord (b) 22 pair of ganglia (2) peripheral (prevertebral, collateral) (a) isolated clusters of cell bodies (b) e.g. superior and inferior mesenteric, celiac (3) terminal (a) ganglia located on surface of effector tissue (b) found in parasympathetic branch of ANS B. sympathetic division 1. preganglionic neurons originate in thoracic & first two lumbar segments 2. sometimes referred to as thoracolumbar division 3. preganglionic cell bodies in lateral horns 4. axon exits via anterior (ventral) root w. somatic motor neurons 5. paravertebral chain (sympathetic chain) a. paired chain of ganglia which lie anterior & lateral to spinal cord b. preganglionic neuron either: (1) synapse in paravertebral chain at level of anterior root (2) traverse up or down sympathethic chain before synapsing (3) pass through chain to synapse with post-ganglionic neuron in peripheral ganglion 6. peripheral sympathetic ganglia positioned near visceral organs 7. each preganglionic axon may synapse w. as many as 200 post- ganglionic neurons 8. postganglionic axon longer than PSN division 9. preganglionic axons also supply adrenal medulla C. parasympathetic division 1. cell bodies originate in brain stem nuclei or lateral horn of sacral spinal cord 2. also termed craniosacral division 3. cranial preganglionics distribute with four cranial nerves a. oculomotor - III b. facial - VII c. glossopharyngeal - IX d. vagus - X 4. sacral preganglionics originate from: a. S2 b. S3 c. S4 5. preganglionic fibers synapse with terminal ganglia 6. often lie within walls of peripheral organs 7. post-ganglionic fibers are short 8. vagus carries 80% of all PSN fibers IV. Physiological Effects of Autonomic Nervous System A. Introduction 1. In organs stimulated during physical activity, SNS is excitatory, PNS is inhibitory. a. SNS increases heart rate b. PNS decreases heart rate 2. In organs where activity increases during rest, PNS is excitatory, SNS is inhibitory. a. PNS stimulates intestinal peristalsis b. SNS inhibits intestinal peristalsis 3. SNS mediates "fight or flight responses", PNS - vegetative a. responses usu. antagonistic i. SNS → ↑ heart rate ↓ ←PSN ii. SNS → ↑ pupil dilation ↓ ←PSN b. complementary (?) effects i. PNS → ↑ watery saliva ii. SNS → ↓ salivary gland perfusion →thick, viscous saliva 4. ANS synapses specialized for function a. many have varicosities along axon within their target organs b. increases # of target sites for neurotransmitters c. wider distribution of autonomic output B. autonomic neurotransmitters 1. cholinergic neurons a. release acetylcholine (ACh) b. inactivated by acetylcholine esterase c. preganglionic neurotransmitter of both divisions & neuromuscular junctions i. nicotinic receptor ii. agonists – nicotine, antagonists - curare, α-bungarotoxin iii. ligand gated (ionotropic) cationic channel iv. leads to postganglionic cell depolarization d. all postganglionic parasympathetic neurons i. muscarinic receptor ii. agonists – muscarine, antagonists - scopolamine, atropine iii. G protein-coupled receptor (metabotropic) iv. can be inhibitory or stimulatory v. slow, variable and prolonged response 2. adrenergic neurons a. secrete norepinephrine b. deactivated by monoamine oxidase c. primary SNS postganglionic neurotransmitter i. G protein coupled receptor ii. two major classes α & β, several subtypes (1) α - activated by norepinephrine (epinephrine less effective) (a) α1 - smooth muscle (blood vessels, sphincter control) (b) α2 - presynaptic, inhibition of insulin, induction of glucagon (2) β - activated by epinephrine (norepinephrine less effective) (a) β1 - heart, increase cardiac output (b) β2 - bronchiole dilation, skeletal muscle vasodilation d. few SNS postganglionic cholinergic endings i. sweat glands ii. muscarinic V. Parasympathetic and Sympathetic Responses A. sympathetic system 1. Cannon's original fight or flight proposal (1915) a. in response to fear, fright, exercise, all types of stress: i. increase in heart rate, contractility (increase in cardiac output) ii. bronchodilation, increase ventilation rate iii. sweating, piloerection iv. glucose liberation v. vasoconstriction of splanchnic beds, skin vi. vasodilation of skeletal muscle vii. adrenal medullary secretion viii. pupil dilation B. parasympathetic system 1. conserves and restores body energy 2. dominate control of GI motility and secretion 3. acronym – “SLUD” a. salivation b. lacrimation c. urination d. defecation