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Chapter 9

Chapter 9. The Autonomic Nervous System. 9-1. Chapter 9 Outline Introduction ANS Neurons Divisions of ANS ANS Neurotransmitters ANS Innervation of Organs Higher Control of ANS. 9-2. Introduction. 9-3. Overview. Autonomic nervous system (ANS) manages our physiology

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Chapter 9

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  1. Chapter 9 The Autonomic Nervous System 9-1

  2. 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. Overview • Autonomic nervous system (ANS) manages our physiology • By regulating organs & organ systems, & their smooth muscles & glands 9-4

  5. 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. 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 Fig 9.1 9-7

  8. Autonomic Neurons • Postganglionic axon extends from autonomic ganglion to target tissue Fig 9.1 9-8

  9. Divisions of the ANS 9-9

  10. 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. 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. Sympathetic Division continued • Is characterized by divergence & convergence which cause Symp to mostly act as a unit (mass activation) 9-12

  13. Sympathetic Division continued • Divergence: preganglionics branch to synapse with number of postganglionic neurons Fig 9.3 9-13

  14. Sympathetic Division continued • Convergence: postganglionics receive synaptic input from large number of preganglionics Fig 9.3 9-14

  15. Sympathetic Division continued • Some postganglionics do not synapse in paravertebral ganglion but go to outlying collateral ganglion Fig 9.4 9-15

  16. 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. Sympathoadrenal System continued • Epi is made by methylating Norepi Fig 9.8 9-17

  18. 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. 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. ANS Overview Fig 9.6 9-20

  21. 9-21

  22. ANS Neurotransmitters 9-22

  23. ANS Neurotransmitters Fig 9.7 • 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 9-23

  24. ANS Neurotransmitters continued Fig 9.9 • Postganglionics have unusual synapses called varicosities • Which release NTs along a length of axon • = synapses en passant 9-24

  25. 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. Adrenergic Stimulation continued Fig 9.10 • 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

  27. 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. Fig 9.11 9-28

  29. 9-29

  30. 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. 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. 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. 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

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