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Chapter 14
The Autonomic Nervous System
J.F. Thompson, Ph.D. & J.R. Schiller, Ph.D. & G. Pitts, Ph.D.
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
The ANS Is Clinically Significant!
If you plan to succeed in a HealthRelated Career, you will need to
understand the Autonomic Nervous
System very well!
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
Comparison of Somatic to Autonomic
 somatic: one motor neuron to skeletal muscle effectors
 autonomic: two motor neurons to visceral effectors
Autonomic Visceral Reflex Arc
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
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
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
ANS Dual Innervation
The Parasympathetic
Division exerts shortlived, highly localized
control.
The Sympathetic Division
exerts long-lasting,
diffuse effects.
Due to differences in
target responsiveness to
neurotransmitters
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
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
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
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
Neurotransmitters and Receptors of
the Autonomic Nervous System
Receptor Class
Nicotinic
Muscarinic
Agonist
Nicotone
Muscarine
Antagonist
Curare
Atropine
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
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
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
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)
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-omethyltransferase (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
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)
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
Autonomic Nervous System Review
Autonomic Nervous System Online Review

Neuroscience For Kids
http://faculty.washington.edu/chudler/neurok.html
This web site has many good reviews and illustrations.
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.
Autonomic Nervous System Controls
Most control is
unconscious and
originates from the
hypothalamus
But strong conscious
emotional states can
trigger autonomic,
usually sympathetic,
responses
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.
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
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
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
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
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
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
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 rate and
force of contraction
increase mucus
production
decrease rate and
force of contraction
relax bronchial
smooth muscle
constrict bronchial
smooth muscle
heart
lung
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
reduce peristalsis;
decrease intestinal
secretions
increase peristalsis;
increase intestinal
secretions
liver
increase conversion of
glycogen to glucose;
release glucose into
bloodstream
n/a
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
n/a
blood vessels
increase supply to skeletal
decrease supply to skeletal
muscles; decrease supply to muscles; increase supply to
most viscera
most viscera
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
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.
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
Risk Factors For Hypertension
age
heredity
 race
 gender
 weight
diet
lifestyle/activity level
stress: overstimulates
sympathetic division?
alcohol
tobacco
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!
Structure of the Autonomic
Nervous System
Preganglionic neuron somata in
the thoracic and lumbar spinal
cord segments.
Preganglionic neuron somata in
the brain and sacral spinal cord.
Preganglionic neurons synapse
onto postganglionic neurons in
the sympathetic chain ganglia.
Preganglionic neurons synapse
onto postganglionic neuron
ganglia near or in the target
organs.
The postganglionic neurons
extend a long distance (usually) to
the target organs.
The postganglionic neurons do
not extend a long distance to the
target organs.
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
sympathetic
parasympathetic
preganglionic
fiber
short, myelinated,
cholinergic
long, myelinated,
cholinergic
postganglionic
fiber
long,
unmyelinated,
usually adrenergic
sympathetic chain
(= paravertebral),
collateral
(= prevertebral),
adrenal medullae
fight or flight,
“E” situations
short,
unmyelinated,
cholinergic
ganglia
dominant?
terminal (on or in
effector)
(= intramural)
rest and relaxation,
“SLUD”
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
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
Sympathetic Paths
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:
1. synapse with postganglionic neurons at that level of
sympathetic chain
2. travel up and/or down sympathetic chain to synapse with
postganglionic neurons at other level(s)
3. Pass through sympathetic chain to prevertebral ganglion
(via splanchnic nerves) and synapse with postganglionic
neurons there
4. (pass through prevertebral ganglion to adrenal medullae)
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)
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
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
Release of Renin from the Kidneys
Sympathetic impulses activate the kidneys to
release renin
Renin is an enzyme that promotes increased
blood pressure
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
Localized Versus Diffuse Effects
 The parasympathetic division exerts shortlived, highly localized control
 The sympathetic division exerts long-lasting,
diffuse effects because NE:
1. Is inactivated more slowly than Ach
2. Acts indirectly, using a second-messenger system
3. And epinephrine are released into the blood and
remain there until destroyed by the liver
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
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
Drugs Which Influence the ANS
Table 14.4.1
Drugs that Influence the ANS
Drugs that Influence the ANS
Drugs Which Influence the ANS
Table 14.4.2
End Additional Material
on Chapter 14