C om parison o f th e SNS and ANS • Figure 7.1 4
a.
Somatic nervous system (SNS)
• Voluntarily contracts skeletal muscle
• One motor neuron has
cell body inside CNS
and axon synapses
directly on skeletal
muscle fiber
(cell)
• Neurons use
acetylcholine
(ACh) as the
neurotransmitter
• Effect is always
excitatory ^ contraction
Spinal cord
Somatic
motor neuron
(myelinated)
ACh
Effector: skeletal muscle
NE
Adrenal cortex
Adrenal medulla
ACh
Adrenal medulla
b. Autonomic nervous system (ANS) -
Sympathetic division
• Involuntarily controls
cardiac muscle,
smooth muscle,
and glands
• One motor
neuron inside
CNS (preganglionic
cell) usually synapses
on a second neuron
(postganglionic cell) outside
CNS, which synapses directly on effector
• Neurons use ACh as preganglionic
neurotransmitter and
epinephrine or
norepinephrine (NE)
as postganglionic
neurotransmitter
• Effect can be
excitatory
(contraction,
increased secretions) or
inhibitory (relaxation,
decreased secretions)
Autonomic
motor neurons
ACh
Spinal cord
Spinal cord
Sympathetic
preganglionic
neuron
(myelinated)
v } —
-
-----------
■ '
Sympathetic
Autonomic
ganglion
postganglionic
neuron
(unmyelinated)
Effectors: glands, cardiac
muscle (in the heart), and
smooth muscle (mainly in
the walls of blood vessels)
Chromaffin cell
Epinephrine
and NE
Sympathetic
preganglionic
neuron
(myelinated)
Distributed in the
blood throughout
the body
c.
Autonomic nervous
system (ANS) -
Parasympathetic
division
• Involuntarily
controls cardiac
muscle, smooth
muscle, and glands
• One motor neuron inside
CNS (preganglionic cell)
synapses on a second neuron
(postganglionic cell) outside CNS
which synapses directly on
effector
• Neurons use ACh as
preganglionic and postganglionic
neurotransmitter
Spinal cord
Parasympathetic
preganglionic
neuron
(myelinated)
ACh
ACh
Parasympathetic
postganglionic
neuron
(unmyelinated)
Effectors: glands, cardiac
muscle (in the heart), and
smooth muscle (mainly in
the organs of the gastro-
intestinal and respiratory
tracts)
The Autonomic Nervous System Controls the Activities of Smooth Muscle, Cardiac Muscle, and Glands
209
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