Nervous System—
Autonomic Nervous System and Cranial Nerves
Lecture 10
Today we’re going to continue and wind up our general look at the
nervous system by examining the anatomy and the physiology of the
autonomic nervous system and then of all the cranial nerves.
T
he autonomic nervous system is the set of nerves that is functioning all
the time, whether you’re awake, asleep; sometimes even when you’re
in coma. Within the autonomic nervous system , the parasympathetic
nervous system promotes rest and recovery, and the sympathetic nervous
system promotes “ ght and ight.” The two main pathways for the autonomic
nervous system are the general visceral motor (efferent) neurons and the
general visceral sensory (afferent) neurons.
The entire system is involuntary. Some degree of cerebral control is possible
during times of extreme fear and anxiety. Modern biofeedback methods have
achieved some control in trained individuals.
Here are some differences between the autonomic and somatic
nervous systems:
Somatic nervous system
Motor activity is always excitatory—muscles at rest are signaled to
perform speci c tasks.
Sensory input is conscious.
There is only one neuron between the CNS and a given effector
organ, making for a very, very long cell in some cases.
53
, Autonomic nervous system
Motor activity is either excitatory or inhibitory.
Sensory input is generally unconscious, although extremes of
sensation may be consciously perceived.
There are two neurons between the CNS and an effector organ, with
a synapse in the paraspinal ganglion.
Lecture 10: Nervous System—Autonomic Nervous System and Cranial Nerves
Divisions of the autonomic nervous system
The parasympathetic system promotes rest, recovery, and relaxation. It
is generally an inhibitory pathway. It is mediated by acetylcholine at the
end organ. It has a craniosacral origin in the CNS, and there is very little
divergence (1:3) at the ganglia.
The sympathetic system promotes “fright, ght, and ight.” It is generally an
excitatory pathway. It is mediated by norepinephrine at the effector organ. It
has a thoracolumbar origin in the CNS. There is extreme divergence (1:20)
at the ganglia. The sympathetic system also stimulates adrenal glands, which
excite effector organs in the entire body.
The sympathetic and parasympathetic nervous systems
The sympathetic system prepares the body for fright, ght, and ight, which
has the following effects:
The pupils dilate.
The heart rate and force of contraction increase.
Blood glucose levels rise.
Respiratory effort increases in rate and depth.
Blood is shunted away from nonessential organs.
54
Autonomic Nervous System and Cranial Nerves
Lecture 10
Today we’re going to continue and wind up our general look at the
nervous system by examining the anatomy and the physiology of the
autonomic nervous system and then of all the cranial nerves.
T
he autonomic nervous system is the set of nerves that is functioning all
the time, whether you’re awake, asleep; sometimes even when you’re
in coma. Within the autonomic nervous system , the parasympathetic
nervous system promotes rest and recovery, and the sympathetic nervous
system promotes “ ght and ight.” The two main pathways for the autonomic
nervous system are the general visceral motor (efferent) neurons and the
general visceral sensory (afferent) neurons.
The entire system is involuntary. Some degree of cerebral control is possible
during times of extreme fear and anxiety. Modern biofeedback methods have
achieved some control in trained individuals.
Here are some differences between the autonomic and somatic
nervous systems:
Somatic nervous system
Motor activity is always excitatory—muscles at rest are signaled to
perform speci c tasks.
Sensory input is conscious.
There is only one neuron between the CNS and a given effector
organ, making for a very, very long cell in some cases.
53
, Autonomic nervous system
Motor activity is either excitatory or inhibitory.
Sensory input is generally unconscious, although extremes of
sensation may be consciously perceived.
There are two neurons between the CNS and an effector organ, with
a synapse in the paraspinal ganglion.
Lecture 10: Nervous System—Autonomic Nervous System and Cranial Nerves
Divisions of the autonomic nervous system
The parasympathetic system promotes rest, recovery, and relaxation. It
is generally an inhibitory pathway. It is mediated by acetylcholine at the
end organ. It has a craniosacral origin in the CNS, and there is very little
divergence (1:3) at the ganglia.
The sympathetic system promotes “fright, ght, and ight.” It is generally an
excitatory pathway. It is mediated by norepinephrine at the effector organ. It
has a thoracolumbar origin in the CNS. There is extreme divergence (1:20)
at the ganglia. The sympathetic system also stimulates adrenal glands, which
excite effector organs in the entire body.
The sympathetic and parasympathetic nervous systems
The sympathetic system prepares the body for fright, ght, and ight, which
has the following effects:
The pupils dilate.
The heart rate and force of contraction increase.
Blood glucose levels rise.
Respiratory effort increases in rate and depth.
Blood is shunted away from nonessential organs.
54
