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Chapter 11
Autonomic Nervous
System (ANS)
Copyright 2010, John Wiley & Sons, Inc.
Introduction to the ANS
Somatic nervous system (SNS) + ANS 
peripheral nervous system (PNS)
ANS
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Not under conscious control
Is regulated by hypothalamus, brainstem
The ANS supplies nerves to viscera
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Smooth muscle (stomach, blood vessels)
Cardiac muscle (heart)
Glands (sweat and digestive glands)
Copyright 2010, John Wiley & Sons, Inc.
Comparison: SNS vs ANS
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SNS
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Controls skeletal muscle
Conscious, voluntary
control
Motor pathway: one neuron
from CNS to effector
Does include sensory
neurons (from skin, skeletal
muscles, and special sense
organs)
All release the
neurotransmitter ACh
ANS
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Controls viscera: smooth
and cardiac muscle, and
glands
Unconscious, involuntary
Motor pathway: series of
two neurons from CNS to
effector
Does include sensory
neurons (monitors viscera)
Two divisions: sympathetic,
parasympathetic
Release either ACh or NE
Copyright 2010, John Wiley & Sons, Inc.
Somatic Nervous System
Copyright 2010, John Wiley & Sons, Inc.
ANS Motor Pathways

Autonomic motor pathway includes two motor
neurons
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Preganglionic neuron from CNS to neuron in
autonomic ganglion
Postganglionic neuron from cell body in ganglion
to effector
Copyright 2010, John Wiley & Sons, Inc.
ANS Motor Pathways
Copyright 2010, John Wiley & Sons, Inc.
Divisions of the ANS
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Sympathetic (S) division +
parasympathetic (P) division
Most viscera supplied with nerves of both S
and P divisions: dual innervation
S and P have opposite (antagonistic) effects
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Heart rate: S stimulates, P inhibits
Digestive organs: S inhibit, P stimulate
S: “flight or flight” P: “rest and digest”
Some viscera receive only S (not P) nerves:
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Sweat glands, many blood vessels, hair muscles
Copyright 2010, John Wiley & Sons, Inc.
Sympathetic (S) Division

Sympathetic preganglionic neurons

Have cell bodies located in lateral gray of spinal
cord segments T1-T12 + L1-L2
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So S division is called “thoracolumbar”
Axons pass through ventral roots of spinal nerves
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May branch many times
May ascend or descend to many levels of S trunk
ganglia (from cervical to sacral)
Can synapse with 20 or more postganglionic neuron
cell bodies
Results: widespread S effects (viscera respond “in
sympathy with one another”)
Copyright 2010, John Wiley & Sons, Inc.
Sympathetic (S) Division

Sympathetic postganglionic neurons
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S postganglionic neurons cell bodies located
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In S “trunk ganglia” (2 long chains lateral to vertebrae)
From cervical to sacral regions  widespread S effects
 Many axons from these cell bodies pass back into
spinal nerves to reach viscera in skin (sweat glands,
hair muscles, blood vessels)
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In S “prevertebral ganglia” anterior to 3 large
abdominal arteries
Named celiac, superior and inferior mesenteric ganglia
 Supply abdominal viscera: stomach, intestine, kidneys,
liver, spleen
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
Axons pass from ganglia to viscera in S nerves
Copyright 2010, John Wiley & Sons, Inc.
Sympathetic (S)
Division
Copyright 2010, John Wiley & Sons, Inc.
Parasympathetic (P) Division
P preganglionic neurons
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Cell bodies located in brainstem + in spinal cord
segments S2-S4
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Therefore P division is called “craniosacral”
Axons in cranial nerves III, VII, IX and X and in
pelvic nerves from S2-S4
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Vagus nerves (cranial nerves X) carry 80% of all P
nerve impulses.
Vagus nerves carry both motor and sensory neurons
to/from viscera within the thorax and most of the
abdominal cavity.
P preganglionic axons do not branch or pass though
S trunk ganglia but pass directly almost to viscera
Copyright 2010, John Wiley & Sons, Inc.
Parasympathetic (P) Division
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P postganglionic neurons
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Cell bodies lie in terminal ganglia
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Located within or near the innervated organ
So P nerves cause precise, localized (not
widespread) effects
Because of anatomical arrangement, S nerves supply
all viscera but P nerves do not reach some viscera.
These include sweat glands, arrector pili muscles of
hairs in skin, kidneys, spleen, adrenal medullae, and
the walls of most blood vessels.
Axons pass from ganglia to viscera in P nerves
Copyright 2010, John Wiley & Sons, Inc.
Parasympathetic (P) Division
Copyright 2010, John Wiley & Sons, Inc.
ANS Neurotransmitters: Comparison
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Acetylcholine (ACh)
ACh more common;
released by:
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All S and P preganglionic
axons
All P postganglionic
axons
Some S postganglionic
axons (to sweat glands)
ACh destroyed by
enzyme ACh-ase so
short-lived response
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Norepinephrine (NE)
NE less common;
released by:
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Almost all S
postganglionic axons
NE has longer lasting
effects enhanced by
epinephrine + NE from
adrenal medullae
Copyright 2010, John Wiley & Sons, Inc.
Sympathetic Effects
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“Fight-or-flight” activities
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Increase heart rate and contraction, and blood
pressure (BP)
Dilate pupils
Dilate airways
Dilate vessels to skeletal muscles, heart, liver and
adipose tissue
Constrict blood vessels to nonessential organs:
skin, GI tract, kidneys
Mobilize nutrients for energy: glucose and fats
Copyright 2010, John Wiley & Sons, Inc.
Activities of the sympathetic division of the ANS
(Generally: "Fight-or-flight responses")
Organ/Tissue
Activity
Effect
Eye
Heart
Blood
Lungs
increased
increased
increased
increased
decreased
contracted
increased
Skin
Pancreas
Pupil dilation
Heart rate & force
Pressure
Airway dilation
Blood vessel diameter;
urine production
Blood vessel diameter
Sphincter
Blood vessel diameter
Blood vessel diameter
Breakdown of TGs and FAs
Blood vessel diameter
Release of bile acids
sweat gland activity
Glucagon secretion
Pancreas
Insulin/Digestive enzyme secretion
decreased
Pituitary gland (post.)
ADH hormone secretion
increased
Urinary bladder
Muscle wall & diameter of sphincter
relaxation & decrease
Skin
Smooth muscles of hair follicles
contract ("goose bumps")
Uterus
Smooth muscles of uterine wall
contract (pregnant)
relax (non-pregnant)
Sex organs
Muscles for ejaculation of semen (man)
contract
Mouth
Salivary gland secretion
decreased
Kidney
GI tract
Skeletal muscle
Adipose tissue
Liver
decreased
increased
increased
increased
increased
Parasympathetic Effects
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Rest-and-digest activities
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SLUDD
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Salivation
Lacrimation
Urination
Digestion
Defecation
Decrease heart rate, airway diameter, pupil
diameter
Copyright 2010, John Wiley & Sons, Inc.
Activities of the parasympathetic division of the ANS
(Generally: "SLUDD responses")
Organ/Tissue
Activity
Effect
Eye
Radial muscle/Pupil dilation
n.e.
Heart
Heart rate & force
decreased
Blood
Pressure
decreased
Lungs
Airway narrowing (bronchoconstriction)
increased
Kidney
Blood vessel diameter;
urine production
n.e.
GI tract
Blood vessel diameter, motility
Sphincter
increased
relaxed
Skeletal muscle
Blood vessel diameter
n.e.
Adipose tissue
Blood vessel diameter
TG, FA build-up
n.e.
Liver
Blood vessel diameter
Storage of bile
decreased
increased
Skin
sweat gland activity
n.e.
Pancreas
Secretion of digestive enzymes & insulin
increased
Pituitary gland (post.)
ADH hormone secretion
n.e.
Urinary bladder
Muscle wall & diameter of sphincter
contraction & increase
Skin
Smooth muscles of hair follicles
n.e.
Uterus
Smooth muscles of uterine wall
minimal effect
Sex organs
Erection of penis and clitoris
increased
Mouth
Salivary gland secretion
increased
ANS & Human Health
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Understand the important aspect of mind-body
harmony and control means,
such as music, yoga, tai-chi,
forms of meditation (e.g.
prayers), hiking, gardening
to sustain human health
These activities are able to
stimulate/activate the
parasympathetic division of
the ANS to restore PNS
homeostasis and feelings of relaxation and
“happiness”
Copyright 2010, John Wiley & Sons, Inc.
Pathology – Disease & disorders
connected with ANS
Horner's syndrome
Loss of sympathetic stimulation of muscles of one side
of the face due to inherited mutation, an injury or a disease that affects
the sympathetic outflow through the cervical ganglion.
Symptoms include drooping of the upper eyelid, constricted pupil and
loss of sweating.
Autonomic dysreflexia
Exaggerated sympathetic ANS response which occurs in 85% of
individuals with spinal cord injury above the T6 level.
Mass stimulation of sympathetic nerves below the level of injury
due to ascending sensory nerve impulses from the lower body.
Symptoms include: pounding head ache, severe high blood pressure,
pale cold skin below injury level; warm, flushed sweating skin above
injury level;
Can lead to stroke, seizures and heart attacks if untreated!
Copyright 2010, John Wiley & Sons, Inc.
Raynaud's syndrome (RS)
Human skin microcirculation disorder caused
by hyperactivation of the sympathetic system causing extreme vasoconstriction of peripheral blood vessel & episodic skin ischemia.
Disorder is manifested by pallor, cyanosis
and erythema of the fingers in response to
different forms of stress, e.g. cold or emotional.
Exact pathophysiology of RS is currently not
known, but it has been hypothetized that it
may be caused by an autonomic alteration
in the sympathetic innervation of the blood
vessels of the skin.
RS can progress into a systemic autoimmune
disease mainly due to progressive systemic
sclerosis (= hardening) of the blood vessels.
Copyright 2010, John Wiley & Sons, Inc.
Parasympathicomimetics (Part-1)
Generally drugs which elicit the same effects as the post-synaptic nerves of
the parasympathetic division of the ANS.
Have acetyl choline-like effects on the effectors; many are used for
treatment of high blood pressure.
Prominent examples are:
1. Acetyl choline
- very short-lived within the body therefore not very useful for therapy or
treatment
2. Carbachol
- stimulates smooth muscles of intestines
and bladder;
Copyright 2010, John Wiley & Sons, Inc.
Parasympathicomimetics (Part 2)
3. Muscarin
- molecule of the poisonous mushroom Amanita muscaria;
- leads to very strong Vagus nerve
stimulation with typical intoxication
syndromes, which include:
- increased salivation, excessive sweat
production, diarrhea, vomiting,
cardiovascular collapse
4. Pilocarpin
- toxic component of the South American
plant Pilocarpus jaborandi; toxic effects
on the human include:
- excessive sweat production, strong bronchial mucus secretion,
increased motility of GI tract; vomiting,
- often used in low doses to treat Glaucoma;
Copyright 2010, John Wiley & Sons, Inc.