3
The Autonomic Nervous System Controls
the Activities of Smooth Muscle, Cardiac
Muscle, and Glands 208
• The autonomic nervous system (ANS), as shown, regulates
involuntary functions that are vital to life. It consists of the
sympathetic division and the parasympathetic division.
Autonomic nervous system—sympathetic division • Figure 7.14
NE
Spinal cord
Autonomic
motor neurons
A
ACh \
Sympathetic
l
• ••••
Sympathetic
preganglionic
-
postganglionic
neuron
Autonomic
ganglion
neuron
Effectors: glands, cardiac
muscle (in the heart), and
smooth muscle (mainly in
the walls of blood vessels)
Adrenal cortex
Adrenal medulla
ACh
Adrenal medulla
Spinal cord
Chromaffin cell
Sympathetic
preganglionic
neuron
Epinephrine
and NE
' t r
Blood vessel
• The motor nerves of the autonomic nervous system usually
consist of a preganglionic neuron that releases acetylcholine
and a postganglionic neuron that releases the neurotrans-
mitters epinephrine or norepinephrine (sympathetic) or
acetylcholine (parasympathetic) to the effector cells
(cardiac muscle, smooth muscle, or glands).
• Because of the use of different neurotransmitters, the
sympathetic and parasympathetic divisions have opposite
effects. The sympathetic division produces “fight-or-flight”
responses in target organs, while the parasympathetic divi-
sion produces “rest-and-digest” responses.
Summary 221
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