Nervous System II
b. Although most cranial nerves are mixed, some are
pure sensory, and others are primarily motor.
c. The names of cranial nerves indicate their primary
functions or the general distributions of their F bers.
d. Some cranial nerve F
bers are somatic, and others
4. Spinal nerves
a. Thirty-one pairs of spinal nerves originate from the
spinal cord. All but the F
rst pair are mixed nerves.
b. These mixed nerves provide a two-way
communication system between the spinal cord
and the upper limbs, lower limbs, neck, and trunk.
c. Spinal nerves are grouped according to the levels
from which they arise, and they are numbered
d. Each nerve emerges by a dorsal and a ventral root.
(1) A dorsal root contains sensory F
bers and has a
dorsal root ganglion.
(2) A ventral root contains motor F
e. Just beyond its foramen, each spinal nerve divides
into several branches.
f. Most spinal nerves combine to form plexuses that
direct nerve F
bers to a particular body part.
AUTONOMIC NERVOUS SYSTEM
The autonomic nervous system functions without
conscious effort. It regulates visceral activities that
1. General characteristics
a. Autonomic functions are reﬂ
exes controlled from
centers in the hypothalamus, brainstem, and spinal
b. Autonomic nerve F
bers are associated with ganglia
where impulses are integrated before distribution
c. The integrative function of the ganglia provides a
degree of independence from the CNS.
d. The autonomic nervous system consists of the
visceral efferent F bers associated with these ganglia.
e. The autonomic nervous system is subdivided into
two divisions—sympathetic and parasympathetic.
f. The sympathetic division prepares the body for
stressful and emergency conditions.
g. The parasympathetic division is most active under
2. Autonomic nerve F
The autonomic F
bers are efferent, or motor.
3. Sympathetic division
a. Sympathetic F bers leave the spinal cord and
synapse in ganglia.
b. Preganglionic F bers pass through white rami to
reach paravertebral ganglia.
c. Paravertebral ganglia and interconnecting F
comprise the sympathetic trunks.
d. Preganglionic F
bers synapse with paravertebral or
e. Postganglionic F bers usually pass through gray rami
to reach spinal nerves before passing to effectors.
f. A special set of sympathetic preganglionic F
passes through ganglia and extends to the adrenal
a. The diencephalon includes the thalamus and
b. The thalamus selects incoming sensory impulses
and relays them to the cerebral cortex.
c. The hypothalamus is important in maintaining
d. The limbic system produces emotional feelings and
a. The brainstem extends from the base of the brain
to the spinal cord.
b. The brainstem consists of the midbrain, pons, and
c. The midbrain contains reﬂ
ex centers associated
with eye and head movements.
d. The pons transmits impulses between the
cerebrum and other parts of the nervous system
and contains centers that help regulate rate and
depth of breathing.
e. The medulla oblongata transmits all ascending and
descending impulses and contains several vital and
f. The reticular formation F
lters incoming sensory
impulses, arousing the cerebral cortex into
wakefulness in response to meaningful impulses.
g. Normal sleep results from decreasing activity of
the reticular formation, and paradoxical sleep
occurs when activating impulses are received by
some parts of the brain, but not by others.
a. The cerebellum consists of two hemispheres
connected by the vermis.
b. A thin cortex of gray matter surrounds the white
matter of the cerebellum.
c. The cerebellum functions primarily as a reﬂ ex
center, coordinating skeletal muscle movements
and maintaining equilibrium.
PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system consists of cranial and
spinal nerves that branch out from the brain and spinal
cord to all body parts. It can be subdivided into somatic
and autonomic portions.
1. Structure of peripheral nerves
a. A nerve consists of a bundle of nerve F
surrounded by connective tissues.
b. The connective tissues form an outer epineurium,
a perineurium enclosing bundles of nerve F
and an endoneurium surrounding each F
2. Nerve and nerve F
a. Nerves are cordlike bundles of nerve F
can be classiF
ed as sensory nerves, motor nerves,
or mixed nerves, depending on which type of
bers they contain.
b. Nerve F bers in the CNS are subdivided into groups
with general and special functions.
3. Cranial nerves
a. Twelve pairs of cranial nerves connect the brain to
parts in the head, neck, and trunk.