1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 The Autonomic Nervous System 9-1

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Outline  Introduction  ANS Neurons  Divisions of ANS  ANS Neurotransmitters  ANS Innervation of Organs  Higher Control of ANS 9-2

3. Introduction 9-3

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Overview  Autonomic nervous system (ANS) manages our physiology  By regulating organs & organ systems, & their smooth muscles & glands 9-4

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ANS Control of Smooth Muscle  Smooth muscle maintains 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 & contract rhythmically without ANS input  ANS input simply increases or decreases intrinsic activity 9-5

6. ANS Neurons 9-6

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Fig 9.1 9-7

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Autonomic Neurons  Postganglionic axon extends from autonomic ganglion to target tissue Fig 9.1 9-8

9. Divisions of the ANS 9-9

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Divisions of the ANS  ANS has sympathetic & parasympathetic divisions  Usually have antagonistic effects  These coordinate physiology with what’s going on in person's life  Sympathetic mediates "fight, flight, & stress" reactions  Parasympathetic mediates "rest & digest" reactions 9-10

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Fig 9.2 9-11

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic Division continued  Is characterized by divergence & convergence which cause Symp to mostly act as a unit (mass activation) 9-12

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic Division continued  Divergence: preganglionics branch to synapse with number of postganglionic neurons Fig 9.3 9-13

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic Division continued  Convergence: postganglionics receive synaptic input from large number of preganglionics Fig 9.3 9-14

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathetic Division continued  Some postganglionics do not synapse in paravertebral ganglion but go to outlying collateral ganglion Fig 9.4 9-15

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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) & 15% norepinephrine (Norepi) into blood in response to preganglionic stimulation  Stimulated during mass activation 9-16

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Sympathoadrenal System continued  Epi is made by methylating Norepi Fig 9.8 9-17

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parasympathetic Division  Is also called craniosacral division because long preganglionics originate in midbrain, medulla, pons, & S2 - S4  Synapse on postganglionic in terminal ganglia located next to or within target organ  Postganglionic has short axon that innervates target 9-18

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parasympathetic Division continued  The long vagus nerve carries most Parasymp fibers  Innervates heart, lungs, esophagus, stomach, pancreas, liver, small intestine, & upper half of the large intestine  Preganglionic fibers from S2-4 innervate lower half of large intestine, rectum, urinary & reproductive systems 9-19

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ANS Overview Fig 9.6 9-20

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-21

22. ANS Neurotransmitters 9-22

23. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ANS Neurotransmitters  Both Symp & 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 Fig 9.7 9-23

24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ANS Neurotransmitters continued  Postganglionics have unusual synapses called varicosities  Which release NTs along a length of axon  = synapses en passant Fig 9.9 9-24

25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adrenergic Stimulation  Causes both excitation & inhibition depending on tissue  Because of different subtypes of receptors for same NT  2 major subtypes are  &  adrenergic receptors  Each has own subtypes:  1,  2 &  1,  2 9-25

26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 Fig 9.10 9-26

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cholinergic Stimulation  ACh is used at all motor neuron synapses on skeletal muscle, all preganglionics, & Parasymp postganglionics  Cholinergic receptors have 2 subtypes:  Nicotinic which is stimulated by nicotine; blocked by curare  & muscarinic which is stimulated by muscarine (from poisonous mushrooms); blocked by atropine 9-27

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig 9.11 9-28

29. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9-29

30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 9-30

31. ANS Innervation of Organs 9-31

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organs With Dual Innervation  Most visceral organs receive dual innervation (supplied by both Symp & Parasymp)  While 2 branches are usually antagonistic, such as their effects on heart rate  Can be complementary (cause similar effects) such as with salivation  Or cooperative (produce different effects that work together to cause desired effect) such as with micturition 9-32

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Organs Without Dual Innervation  Regulation achieved by increasing or decreasing firing rate  Adrenal medulla, arrector pili muscle, sweat glands, & most blood vessels receive only sympathetic innervation 9-33

34. Higher Control of ANS 9-34

35. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Control of the ANS by Higher Brain Centers  Medulla most directly controls activity of ANS  It has centers for control of cardiovascular, pulmonary, urinary, reproductive, & digestive systems  Hypothalamus has centers for control of body temperature, hunger, & thirst; & can regulate medulla  Limbic system is responsible for visceral responses that reflect emotional states  Cerebral cortex & cerebellum also influence ANS 9-35