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Introduction to the ANS Somatic nervous system (SNS) + ANS
peripheral nervous system (PNS) ANS
Not under conscious control Is regulated by hypothalamus, brainstem
The ANS supplies nerves to viscera Smooth muscle (stomach, blood vessels) Cardiac muscle (heart) Glands (sweat and digestive glands)
Copyright 2010, John Wiley & Sons, Inc.
Comparison: SNS vs ANS SNS
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 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.
ANS Motor Pathways Autonomic motor pathway includes two motor
neurons Preganglionic neuron from CNS to neuron in
autonomic ganglion Postganglionic neuron from cell body in ganglion
to effector
Copyright 2010, John Wiley & Sons, Inc.
Divisions of the ANS 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
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:
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
So S division is called “thoracolumbar” Axons pass through ventral roots of spinal nerves
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
S postganglionic neurons cell bodies located 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)
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 Axons pass from ganglia to viscera in S nerves
Copyright 2010, John Wiley & Sons, Inc.
Parasympathetic (P) Division P preganglionic neurons
Cell bodies located in brainstem + in spinal cord segments S2-S4 Therefore P division is called “craniosacral”
Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4 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 P postganglionic neurons
Cell bodies lie in terminal ganglia 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.
ANS Neurotransmitters: Comparison Acetylcholine (ACh) ACh more common;
released by: 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
Norepinephrine (NE) NE less common;
released by: 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 Fight-or-flight activities
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 Rest-and-digest activities
SLUDD Salivation Lacrimation Urination Digestion Defecation
Decrease heart rate, airway diameter, pupil diameter
Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 11
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