CHAPTER 7
Nervous Tissue
117
The higher levels of the CNS include large groups of
nuclei
including the
thalamus
and the
basal nuclei
as well as sensory
and motor nuclei in the brainstem associated with cranial
nerves. The
cerebellum
is a large, specialized structure com-
posed of nuclei and cortex, and the
cerebral cortex
envelops the
surface of the cerebral hemispheres (Figs. 7-10 and 7-11).
MENINGES
are brain hemisphere and spinal cord coverings
with three layers of connective tissue membranes that protect the
nervous system, provide mechanical stability,
provide a
support
framework for arteries and veins, and enclose a space that is
± lled with cerebrospinal fl
uid (CSF), a fl
uid that is essential to the
survival and normal function of the CNS. The meninges include
the
dura mater
, the
arachnoid
, and the
pia mater
(Fig. 7-12).
GLIAL CELLS
are nonneural cells that provide a variety
of
support functions for the neurons that relate to nutrition,
regulation of the extracellular environment including the blood-
brain barrier, immune system, myelin insulation for many
axons, and a host of other support functions (Fig. 7-13).
Autonomic Nervous System
The
autonomic nervous system
(
ANS
) is composed of three
divisions:
sympathetic
,
parasympathetic
, and
enteric
. The
sym-
pathetic
and
parasympathetic
divisions
function under direct
CNS control; the
enteric division
functions somewhat more
independently. The ANS, together with the
endocrine system
and under the general control of certain systems within the
CNS, maintains the
homeostasis
of the internal environment
of the body. That is, the autonomic and endocrine systems
ensure that the levels of nutrients, electrolytes, oxygen, carbon
dioxide, temperature, pH, osmolarity, and many other related
variables are maintained within optimal physiological limits
(Fig. 7-14).
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