Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Lecture Outline

Chapter 9 Outline  Autonomic Control of Involuntary Effectors  Divisions of ANS  Fuctions of the ANS 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 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 9-5

ANS Neurons 9-6

Autonomic Neurons  ANS has 2 neurons in its efferent pathway  1 st neuron (=preganglionic neuron) has cell body in brain or spinal cord  Synapses with 2 nd neuron (=postganglionic neuron) in an autonomic ganglion 9-7

Autonomic Neurons  Postganglionic axon extends from autonomic ganglion to target tissue  Target tissues are smooth muscle, cardiac muscle, and glands 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 9-10

Sympathetic Division  Is also called thoracolumbar division because its preganglionic neurons exit spinal cord from T1 to L2  Most then synapse on postganglionic neurons in the paravertebral ganglia  Which form chain of interconnected ganglia paralleling spinal cord called sympathetic ganglionic chain 9-11

Sympathetic Division continued  Is characterized by divergence through white rami communicantes and convergence through gray rami communicantes which cause Symp to mostly act as a unit (=mass activation) 9-12

Sympathetic Division continued  Divergence: preganglionics branch to synapse with a number of postganglionic neurons 9-13

Sympathetic Division continued  Convergence: postganglionics receive synaptic input from a large number of preganglionics 9-14

Sympathetic Division continued  Some postganglionics do not synapse in paravertebral ganglion but go to outlying collateral ganglion 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 postganglionic neurons  That release 85% epinephrine (Epi) and 15% norepinephrine (Norepi) into blood in response to preganglionic stimulation  Adrenal is stimulated during mass activation 9-16

Sympathoadrenal System continued  Epi is made by methylating Norepi 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 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 9-19

ANS Overview 9-20

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 9-23

ANS Neurotransmitters continued  Postganglionics have unusual synapses called varicosities  Which release NTs along a length of axon  = synapses en passant 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, 

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 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 9-27

9-28 Comparison of nicotinic and muscarinic ACh receptors

9-29

Other ANS Neurotransmitters  Some postganglionics do not use Norepi or ACh  Called nonadrenergic, noncholinergic fibers  Appear to use ATP, VIP (vasoactive intestinal peptide), or NO (nitiric oxide) as neurotransmitters  NO produces smooth muscle relaxation in many tissues 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 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 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 9-35