432
UNIT THREE
b. The cord provides a two-way communication
system between the brain and structures outside
the nervous system.
(1) Ascending tracts carry sensory impulses to the
brain; descending tracts carry motor impulses
to muscles and glands.
(2) Many of the F
bers in the ascending and
descending tracts cross over in the spinal cord
or brain.
11.5
BRAIN (PAGE 397)
The brain is the largest and most complex part of the
nervous system. It contains nerve centers associated with
sensations. The brain issues motor commands and carries
on higher mental functions.
1. Brain development
a. Brain structure refl
ects the way it forms.
b. The brain develops from a neural tube with three
cavities—the forebrain, midbrain, and hindbrain.
c. The cavities persist as ventricles, and the walls
give rise to structural and functional regions.
2. Structure of the cerebrum
a. The cerebrum consists of two cerebral hemispheres
connected by the corpus callosum.
b. Its surface is marked by ridges and grooves; sulci
divide each hemisphere into lobes.
c. The cerebral cortex is a thin layer of gray matter
near the surface.
d. White matter consists of myelinated nerve F
bers
that connect neurons and communicate with other
body parts.
3. ±unctions of the cerebrum
a. The cerebrum provides higher brain functions,
such as thought, reasoning, interpretation of
sensory impulses, control of voluntary muscles,
and memory storage.
b. The cerebral cortex has sensory, association, and
motor areas.
c. Areas that interpret sensory impulses from the skin
are in the parietal lobes near the central sulcus;
other specialized sensory areas are in the temporal
and occipital lobes.
d. Association areas analyze and interpret sensory
impulses and provide memory, reasoning,
verbalizing, judgment, and emotions.
e. The primary motor regions lie in the frontal lobes
near the central sulcus. Other areas of the frontal
lobes control special motor functions.
f. One cerebral hemisphere usually dominates for
certain intellectual functions.
g. Short-term memory is probably bioelectrical. Long-
term memory is thought to be encoded in patterns
of synaptic connections.
4. Basal nuclei
a. Basal nuclei are masses of gray matter deep within
the cerebral hemispheres.
b. The neurons of the basal nuclei interact with other
brain areas to facilitate voluntary movement.
CHAPTER SUMMARY
11.1
INTRODUCTION (PAGE 384)
The central nervous sytem (CNS) consists of the brain and
spinal cord.
1. The brain oversees sensation and perception,
movement, and thinking.
2. The brainstem connects the brain and spinal cord,
allowing communication between the two.
3. The spinal cord provides communication between the
CNS and the peripheral nervous sytem (PNS).
11.2
MENINGES (PAGE 384)
Bone and protective membranes called meninges
surround the brain and spinal cord.
1. The meninges consist of a dura mater, arachnoid
mater, and pia mater.
2. Cerebrospinal fl
uid occupies the space between the
arachnoid and pia maters.
11.3
VENTRICLES AND CEREBROSPINAL
FLUID (PAGE 385)
Ventricles, F
lled with cerebrospinal fl
uid (CS±), are
connected cavities in the cerebral hemispheres and
brainstem.
1. Choroid plexuses in the walls of the ventricles secrete
CS±.
2. Ependymal cells of the choroid plexus regulate the
composition of CS±.
3. CS± circulates through the ventricles and is
reabsorbed into the blood of the dural sinuses.
4. CS± helps maintain a stable ion concentration in the
CNS and provides a pathway to the blood for waste.
11.4
SPINAL CORD (PAGE 387)
The spinal cord is a nerve column that extends from the
brain into the vertebral canal. It terminates at the level
between the F
rst and second lumbar vertebrae.
1. Structure of the spinal cord
a. The spinal cord is composed of thirty-one
segments, each of which gives rise to a pair of
spinal nerves.
b. It is characterized by a cervical enlargement, a
lumbar enlargement, and two deep longitudinal
grooves that divide it into right and left halves.
c. White matter surrounds a central core of gray
matter.
d. The white matter is composed of bundles of
myelinated nerve F
bers.
2. ±unctions of the spinal cord
a. The spinal cord is the center for spinal refl exes.
(1) Refl
exes are automatic, subconscious
responses to changes.
(2) They help maintain homeostasis.
(3) The knee-jerk refl
ex employs only two
neurons. Other refl
exes involve more neurons.
(4) Withdrawal refl
exes are protective actions.
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