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Chapter 14 The Autonomic Nervous System

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1 Chapter 14 The Autonomic Nervous System
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.

2 Autonomic Nervous System Overview
automatic, involuntary primarily involved in maintaining homeostasis of the internal environment visceral efferent neurons innervate visceral effectors: smooth muscle, cardiac muscle, exocrine glands and endocrine glands

3 The ANS Is Clinically Significant!
If you plan to succeed in a Health-Related Career, you will need to understand the Autonomic Nervous System very well!

4 Two Functional Divisions
Parasympathetic and Sympathetic Divisions Structurally, each division consists of nerves, nerve plexuses, and autonomic ganglia Each motor command is carried over a two-cell circuit Most effector organs and tissues receive impulses from both ANS divisions, a dual or parallel innervation The two divisions often serve as antagonists to each other in adjusting and maintaining internal homeostasis Parasympathetic system dominates in sleep and other relaxed or resting states Sympathetic dominates during skeletal muscle activities and various emergency situations (fright, panic, rage, aggression) There is a constant interplay between the two divisions

5 Comparison of Somatic to Autonomic
somatic: one motor neuron to skeletal muscle effectors autonomic: two motor neurons to visceral effectors

6 Autonomic Visceral Reflex Arc

7 Two Types of Autonomic Neurons
Preganglionic neurons cell bodies in the CNS (brain or spinal cord) transmit Action Potentials from the CNS Postganglionic neurons cell bodies in autonomic ganglia in the periphery transmit APs to effectors

8 Two Cell Motor Pathways in the ANS
preganglionic neurons in the sympathetic division, the cell body is located in the lateral gray horns (thoraco-lumbar) of the spinal cord in the parasympathetic division, the cell body is located in various nuclei of brain stem or in the lateral gray horns (cranio-sacral) postganglionic neurons the postganglionic fiber sends impulses to a target organ the effects at the target organ are due to type of neurotransmitter and specific cell surface receptors on the effector cells

9 Dual Innervation The Sympathetic and Parasympathetic Divisions of the ANS innervate many of the same organs Different effects are due to specific molecular differences in the neurotransmitters and in the receptor types on the effectors

10 ANS Dual Innervation The Parasympathetic Division exerts short-lived, highly localized control. The Sympathetic Division exerts long-lasting, diffuse effects. Due to differences in target responsiveness to neurotransmitters

11 Parasympathetic Ganglia
parasympathetic terminal ganglia = intramural ganglia ganglia are located very close to or in the wall of the visceral organs each preganglionic neuron synapses with a only few postganglionic neurons parasympathetic preganglionic fibers are long parasympathetic postganglionic fibers are short

12 Sympathetic Ganglia sympathetic trunk = vertebral chain ganglia (paravertebral ganglia) a vertical row on either side of the vertebral column these ganglia are interconnected thoracic and lumbar origin each preganglionic neuron synapses with many postganglionic neurons other sympathetic ganglia are located in the walls of major abdominal arteries short preganglionic fibers long postganglionic fibers

13 ANS Neurotransmitters & Receptors
Preganglionic - Acetylcholine Postganglionic Parasympathetic - acetylcholine Sympathetic – norepinephrine & in a few locations acetylcholine Receptors Parasympathetic nicotinic - excitatory muscarinic - excitatory or inhibitory Sympathetic alpha - excitatory beta - excitatory or inhibitory

14 ANS Neurotransmitters
Acetylcholine (ACh) and norepinephrine (NE) are the two major neurotransmitters of the ANS Cholinergic fibers = ACh-releasing fibers ACh is released by all preganglionic axons and all parasympathetic postganglionic axons Adrenergic fibers = NE-releasing fibers Most sympathetic postganglionic axons Neurotransmitter effects can be excitatory or inhibitory depending upon the receptor type

15 Neurotransmitters and Receptors of the Autonomic Nervous System
Receptor Class Agonist Antagonist Nicotinic Nicotone Curare Muscarinic Muscarine Atropine

16 Nicotinic Receptors Nicotinic receptors are found on:
Motor end plates (skeletal muscle) All postganglionic neurons of both sympathetic and parasympathetic divisions The hormone-producing cells of the adrenal medulla The effect of ACh binding to nicotinic receptors is always excitatory

17 Muscarinic Receptors Muscarinic receptors occur on all effector cells stimulated by parasympathetic cholinergic fibers and by those few effectors stimulated by sympathetic cholinergic fibers The effect of ACh binding at muscarinic receptors: Can be either inhibitory or excitatory Depends on the receptor type of the target organ

18 Adrenergic Receptors The two fundamental types of adrenergic receptors are alpha and beta Each type has subclasses: (1, 2, 1, 2 , 3) Effects of NE binding to:  receptors is generally excitatory to effectors  receptors is generally inhibitory to effectors A clinically important exception – NE binding to  receptors in the heart is excitatory

19 ANS Neurotransmitters & Receptors
See Table 14.3 “Cholinergic and Adrenergic Receptors” (p. 543) for all the details Cholinergic receptors = nicotinic and muscarinic Adrenergic receptors = alpha1,2 and beta1,2,3 These details about receptor subtypes will be very important in later courses, such as Pharmacology (in Nursing)

20 ANS Neurotransmitter Performance
Cholinergic fibers/neurons tend to cause relatively short-lived effects due to the rapid hydrolysis of acetylcholine by cholinesterase in the synapse Adrenergic fibers/neurons tend to cause relatively longer-lived effects due to the slower degradation of norepinephrine by catechol-o-methyltransferase (COMT) and monoamine oxidase (MAO) in the synapse or in body fluids Adrenergic receptors also respond to the closely-related hormone, epinephrine = adrenalin, secreted by the adrenal medulla

21 Drugs Related to ANS Neurotransmitters
Drugs which mimic the action of ACh and NE at their receptors are termed cholinergic and adrenergic agonists respectively Drugs which block or inhibit the action of ACh and NE at their receptors are termed cholinergic and adrenergic antagonists (or “blockers”) respectively Drugs which enhance the action of ACh and NE at their synapses by delaying enzymatic degradation are termed anticholinesterases monoamine oxidase inhibitors (MAO-inhibitors)

22 Drugs Related to ANS Neurotransmitters
Table 14-3, p. 537, list examples of a number of autonomic drugs classes and some specific examples. Take a look. You’ll probably recognize some. Many are available in over-the-counter preparations. There are many more. Some of the drug classes will be on the exam But no specific drugs will be on the exam

23 Autonomic Nervous System Review

24 Autonomic Nervous System Online Review
Neuroscience For Kids This web site has many good reviews and illustrations.

25 Autonomic Nervous System Controls
Different regions of the CNS have responsibility for different functions. The cerebral cortex, limbic system, hypothalamus, and the brain stem cooperate to initiate autonomic motor commands.

26 Autonomic Nervous System Controls
Most control is unconscious and originates from the hypothalamus But strong conscious emotional states can trigger autonomic, usually sympathetic, responses

27 Autonomic Nervous System Actions
See Table 14.4 (pg. 538) for complete details for the responses of each effector organ Parasympathetic S(alivation) L(acrimation) U(rination) D(efecation) metabolic “business as usual” “rest and digest” – “feed and breed” – basic survival functions Sympathetic fight or flight = emergency “survival” situations any increase in skeletal muscular activity for these activities - increase heart rate, blood flow, breathing decrease non-survival activities - food digestion, etc.

28 Parasympathetic Tone Parasympathetic tone:
Slows the heart Directs normal activities of the digestive and urinary systems The sympathetic division can override these effects during times of stress or muscular exertion Drugs that block parasympathetic stimuli increase heart rate and interfere with fecal and urinary retention

29 Cooperative Effects ANS cooperation is involved in the complex control of the cardiovascular system ANS cooperation is also seen in control of the external genitalia during sexual activities Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and clitoris Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in the female reproductive tract

30 Sympathetic Stimulation
Sympathetic stimulation is long-lasting because norepinephrine (NE): NE is inactivated more slowly by MAO and COMT NE is an indirectly acting neurotransmitter, triggering a second-messenger system NE and epinephrine are released into the blood by the adrenal medulla in certain situations and remain there until inactivated by liver enzymes

31 Solitary Sympathetic Stimulation
Regulates some effectors not innervated by the parasympathetic division Therefore, acting more as an on-off switch These include the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels

32 Solitary Sympathetic Stimulation
The sympathetic division controls: Thermoregulatory responses to heat Cutaneous vasodilation and sweating Release of renin from the kidneys Increased blood pressure from a complex regulatory response Metabolic effects (in a complex coordination with the endocrine system) increases the metabolic rate of body cells elevates blood glucose levels for use by nervous tissue shifts cellular metabolism to fats for other tissues stimulates the reticular activating system (RAS) of the brain, increasing mental alertness These actions serve to support the body during strenuous physical activities and emergencies but may contribute to undesirable side effects in cases of long term stress such as illnesses

33 Sympathetic Tone The sympathetic division controls blood pressure, keeping the blood vessels in a continual state of partial constriction (vasomotor tone) Blood pressure rises or falls with sympathetic activity Blood is also diverted to or away from different organ systems depending on the level of muscular activity or the presence of emergency or stressful states Alpha-blocker drugs inhibit vasomotor tone and are used to treat hypertension

34 Autonomic Nervous System Actions
Structure Sympathetic Stimulation Parasympathetic Stimulation iris of the eye pupil dilation pupil constriction salivary glands reduce salivation increase salivation oral/nasal mucosa reduce mucus production increase mucus production heart increase rate and force of contraction decrease rate and force of contraction lung relax bronchial smooth muscle constrict bronchial smooth muscle

35 Autonomic Nervous System Actions
Structure Sympathetic Stimulation Parasympathetic Stimulation stomach reduce peristalsis; decrease gastric secretions increase peristalsis; increase gastric secretions small intestine reduce peristalsis; decrease intestinal secretions increase peristalsis; increase intestinal secretions large intestine liver increase conversion of glycogen to glucose; release glucose into bloodstream n/a

36 Autonomic Nervous System Actions
Structure Sympathetic Stimulation Parasympathetic Stimulation kidney decrease urinary output increase urinary output urinary bladder wall relaxed; sphincter closed wall contracted; sphincter relaxed adrenal medulla secrete epinephrine and norepinephrine n/a sweat glands increase sweat secretion blood vessels increase supply to skeletal muscles; decrease supply to most viscera decrease supply to skeletal muscles; increase supply to most viscera

37 Developmental Aspects of the ANS
During youth, ANS impairments are usually due to injury In old age, ANS efficiency decreases, resulting in constipation, dry eyes, and orthostatic hypotension Orthostatic hypotension is a form of low blood pressure that occurs when sympathetic vasoconstriction centers respond slowly to positional changes

38 Raynaud’s Disease causes sudden severe vasoconstriction in the fingers, toes and, occasionally, the ears and nose during a Raynaud’s attack, or episode, several skin color changes (pallor, cyanosis, rubor) may occur, which are often accompanied by paresthsias, a throbbing or burning sensation, cold, or numbness ischemia can be so extreme as to cause gangrene The exact cause of Raynaud’s Disease remains unknown.

39 Referred Pain Visceral afferents run in the same nerves with somatic afferents Pain in the viscera is transferred or interpreted as if it came from somatic areas Heart attack afferents in T1 - T5 pain in the chest, arm, neck or face

40 Risk Factors For Hypertension
age heredity race gender weight diet lifestyle/activity level stress: overstimulates sympathetic division? alcohol tobacco

41 End Chapter 14 Some additional information is presented in slides beyond this end point for the lecture. While you will not be tested on this additional material in 2010, you will see it again in some professional courses!

42 Structure of the Autonomic Nervous System
Preganglionic neuron somata in the thoracic and lumbar spinal cord segments. Preganglionic neurons synapse onto postganglionic neurons in the sympathetic chain ganglia. The postganglionic neurons extend a long distance (usually) to the target organs. Preganglionic neuron somata in the brain and sacral spinal cord. Preganglionic neurons synapse onto postganglionic neuron ganglia near or in the target organs. The postganglionic neurons do not extend a long distance to the target organs.

43 Parasympathetic and Sympathetic Divisions
Structurally, each division consists of nerves, nerve plexuses, and autonomic ganglia Each motor command is carried in a two-cell circuit Most effector organs and tissues receive impulses from both divisions, a dual or parallel innervation The two divisions often serve as antagonists to each other in adjusting and maintaining internal homeostasis Parasympathetic system dominates in sleep and relaxation Sympathetic dominates during vigorous activity/strong emotion

44 sympathetic parasympathetic
preganglionic fiber short, myelinated, cholinergic long, myelinated, cholinergic postganglionic fiber long, unmyelinated, usually adrenergic short, unmyelinated, cholinergic ganglia sympathetic chain (= paravertebral), collateral (= prevertebral), adrenal medullae terminal (on or in effector) (= intramural) dominant? fight or flight, “E” situations rest and relaxation, “SLUD”

45 Parasympathetic Pathways
Cranial Outflow vial cranial nerves III, VII, IX, and X Cranial nerves III, VII, & IX innervate structures in head Cranial Nerve X (Vagus) innervates ventral body cavity; carries 90% of parasympathetic fibers Sacral Outflow Innervates distal half of large intestine, urinary bladder, ureters, & genitalia

46 Sympathetic Ganglia sympathetic trunk ( = sympathetic chain or paravertebral) ganglia lateral to vertebrae collateral (=prevertebral) ganglia are located near the major abdominal arteries adrenal medullae function as sympathetic ganglia, but neurotransmitters released into blood

47 Sympathetic Paths

48 Sympathetic Paths All preganglionic fibers exit spinal cord via ventral root of spinal nerve, travel into ventral ramus, and into sympathetic chain ganglion via white ramus communicans Then, 1 of 4 (sometimes overlapping) possibilities: synapse with postganglionic neurons at that level of sympathetic chain travel up and/or down sympathetic chain to synapse with postganglionic neurons at other level(s) Pass through sympathetic chain to prevertebral ganglion (via splanchnic nerves) and synapse with postganglionic neurons there (pass through prevertebral ganglion to adrenal medullae)

49 Unique Roles of the Sympathetic Division
Regulates many functions not subject to parasympathetic influence These include the activity of the adrenal medulla, sweat glands, arrector pili muscles, kidneys, and most blood vessels The sympathetic division controls: Thermoregulatory responses to heat Release of renin from the kidneys Metabolic effects: increased metabolic rate, increased blood glucose, fat breakdown (lipolysis)

50 Interactions of ANS Divisions
Antagonistic: most common, organs stimulated by one division inhibited by the other Sympathetic and Parasympathetic Tone Sympathetic tone controls most blood vessels (even at rest) Parasympathetic tone controls the normal activity of the heart, digestive, and urinary systems Cooperative Effects Important in normal sexual function

51 Thermoregulatory Responses to Heat
Applying heat to the skin causes reflex dilation of blood vessels Systemic body temperature elevation results in widespread dilation of blood vessels This dilation brings warm blood to the surface and activates sweat glands to cool the body When temperature falls, blood vessels constrict and blood is retained in deeper vital organs

52 Release of Renin from the Kidneys
Sympathetic impulses activate the kidneys to release renin Renin is an enzyme that promotes increased blood pressure

53 Metabolic Effects The sympathetic division promotes metabolic effects that are not reversed by the parasympathetic division Increases the metabolic rate of body cells Raises blood glucose levels Mobilizes fat as a food source Stimulates the reticular activating system (RAS) of the brain, increasing mental alertness

54 Localized Versus Diffuse Effects
The parasympathetic division exerts short-lived, highly localized control The sympathetic division exerts long-lasting, diffuse effects because NE: Is inactivated more slowly than Ach Acts indirectly, using a second-messenger system And epinephrine are released into the blood and remain there until destroyed by the liver

55 Localized Versus Diffuse Effects
The parasympathetic division exerts localized control because preganglionic fiber travels directly to specific targets and synapses with fewer ganglionic neurons acetylcholine is rapidly degraded The sympathetic division exerts diffuse effects because preganglionic fibers branch and synapse with many ganglionic neurons stimulation of adrenal medullae causes secretion of epinephrine into blood slower inactivation of norepinephrine and epinephrine

56 Effects of Drugs (see Table 14.4, p. 545)
Atropine – blocks parasympathetic effects Neostigmine – inhibits acetylcholinesterase and is used to treat myasthenia gravis Tricyclic antidepressants – prolong the activity of NE on postsynaptic membranes Over-the-counter drugs for colds, allergies, and nasal congestion – stimulate -adrenergic receptors Beta-blockers – attach mainly to 1 receptors and reduce heart rate and prevent arrhythmias

57 Drugs Which Influence the ANS
Table

58 Drugs that Influence the ANS

59 Drugs that Influence the ANS

60 Drugs Which Influence the ANS
Table

61 End Additional Material on Chapter 14


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