Download Human Anatomy & Physiology I

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
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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.
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.
End of Chapter 11

Copyright 2010 John Wiley & Sons, Inc.
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Copyright 2010, John Wiley & Sons, Inc.