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Chapter 9 The Autonomic Nervous System Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-1 Chapter 9 Outline Introduction ANS Neurons Divisions of ANS ANS Neurotransmitters ANS Innervation of Organs Higher Control of ANS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-2 Introduction 9-3 Overview Autonomic nervous system (ANS) manages our physiology By regulating organs and organ systems, and their smooth muscles and glands Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-4 ANS Control of Smooth Muscle Smooth muscle maintains a resting tone in absence of nerve stimulation Smooth becomes more sensitive when ANS input is cut (=denervation hypersensitivity) Many types of smooth are spontaneously active and contract rhythmically without ANS input ANS input simply increases or decreases intrinsic activity Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-5 ANS Neurons 9-6 Autonomic Neurons ANS has 2 neurons in its efferent pathway 1st neuron (=preganglionic neuron) has cell body in brain or spinal cord Synapses with 2nd neuron (=postganglionic neuron) in an autonomic ganglion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-7 Autonomic Neurons Postganglionic axon extends from autonomic ganglion to target tissue Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-8 Divisions of the ANS 9-9 Divisions of the ANS ANS has sympathetic and parasympathetic divisions Which usually have antagonistic effects These coordinate physiology with what’s going on in person's life Sympathetic mediates "fight, flight, and stress" reactions Parasympathetic mediates "rest and digest" reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-10 Sympathetic Division Is also called thoracolumbar division because its preganglionics exit spinal cord from T1 to L2 Most then synapse on postganglionics in the paravertebral ganglia Which form chain of interconnected ganglia paralleling spinal cord Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-11 Sympathetic Division continued Is characterized by divergence and convergence which cause Symp to mostly act as a unit (=mass activation) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-12 Sympathetic Division continued Divergence: preganglionics branch to synapse with a number of postganglionic neurons Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-13 Sympathetic Division continued Convergence: postganglionics receive synaptic input from a large number of preganglionics Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-14 Sympathetic Division continued Some postganglionics do not synapse in paravertebral ganglion but go to outlying collateral ganglion Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-15 Sympathoadrenal System The adrenal medulla, located in adrenal gland on top of kidney, appears to be a modified collateral ganglion Its secretory cells appear to be modified postganglionics That release 85% epinephrine (Epi) and 15% norepinephrine (Norepi) into blood in response to preganglionic stimulation Adrenal is stimulated during mass activation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-16 Sympathoadrenal System continued Epi is made by methylating Norepi Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-17 Parasympathetic Division Is also called the craniosacral division because its long preganglionics originate in midbrain, medulla, pons, and S2 - S4 These synapse on postganglionics in terminal ganglia located next to or within a target organ Postganglionics have short axons that innervate target Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-18 Parasympathetic Division continued The long vagus nerve carries most Parasymp fibers Innervates heart, lungs, esophagus, stomach, pancreas, liver, small intestine, and upper half of the large intestine Preganglionic fibers from S2-4 innervate lower half of large intestine, rectum, urinary and reproductive systems Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-19 ANS Overview Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-21 ANS Neurotransmitters 9-22 ANS Neurotransmitters Both Symp and Parasymp preganglionics release ACh Parasymp postganglionics also release ACh Called cholinergic synapses Most Symp postganglionics release Norepi (noradenaline) Called adrenergic synapses A small number release ACh Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-23 ANS Neurotransmitters continued Postganglionics have unusual synapses called varicosities Which release NTs along a length of axon = synapses en passant Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-24 Adrenergic Stimulation Causes both excitation and inhibition depending on tissue Because of different subtypes of receptors for same NT 2 major subtypes are and adrenergic receptors Each has own subtypes: 1, 2 and 1, 2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-25 Adrenergic Stimulation continued Many useful drugs have been developed to affect ANS receptors Drugs that promote actions of a NT are agonists Drugs that inhibit actions of a NT are antagonists Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-26 Cholinergic Stimulation ACh is used at all motor neuron synapses on skeletal muscle, all preganglionics, and Parasymp postganglionics Cholinergic receptors have 2 subtypes: Nicotinic which is stimulated by nicotine; blocked by curare And muscarinic which is stimulated by muscarine (from poisonous mushrooms); blocked by atropine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-29 Other ANS NTs Some postganglionics do not use Norepi or ACh Called nonadrenergic, noncholinergic fibers Appear to use ATP, VIP, or NO as NTs NO produces smooth muscle relaxation in many tissues Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-30 ANS Innervation of Organs 9-31 Organs With Dual Innervation Most visceral organs receive dual innervation (supplied by both Symp and Parasymp) The 2 branches are usually antagonistic, e.g. in controlling heart rate But can be complementary (cause similar effects), e.g. in controlling salivation Or cooperative (produce different effects that work together to cause desired effect) such as with micturition Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-32 Organs Without Dual Innervation Regulation is achieved by increasing or decreasing firing rate E.g. adrenal medulla, arrector pili muscle, sweat glands, and most blood vessels receive only sympathetic innervation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-33 Higher Control of ANS 9-34 Control of the ANS by Higher Brain Centers The medulla oblongata most directly controls activity of ANS It has centers for control of cardiovascular, pulmonary, urinary, reproductive, and digestive systems Hypothalamus has centers for control of body temperature, hunger, and thirst; and can regulate medulla Limbic system is responsible for visceral responses that reflect emotional states Cerebral cortex and cerebellum also influence ANS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-35