The Autonomic Nervous System

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

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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

• Neurotransmitters
• 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

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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 Ni
cotone 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

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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

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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. Youll 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

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Autonomic Nervous System Review
24
Autonomic Nervous System Online Review

• Neuroscience For Kids
• http//faculty.washington.edu/chudler/neurok.html
• 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.

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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

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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
35
Autonomic Nervous System Actions
36
Autonomic Nervous System Actions
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
Raynauds Disease

• causes sudden severe vasoconstriction in the
  fingers, toes and, occasionally, the ears and
  nose
• during a Raynauds 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 Raynauds 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

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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

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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

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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)

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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 14.4.1
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Drugs that Influence the ANS
59
Drugs that Influence the ANS
60
Drugs Which Influence the ANS
Table 14.4.2
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End Additional Materialon Chapter 14