Page 336 - Atlas of Histology with Functional Correlations

fenestrated capillaries that penetrate the interior of brain ventricles. Blood that is

selectively filtered through the cells of the choroids plexus forms the CSF, a
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−
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clear, colorless fluid with Na , K , and Cl ions that are needed for neuronal
functions. The CSF circulates through the ventricles and around the outer
surfaces of the brain and spinal cord in the subarachnoid space and in the central
canal of the spinal cord.

CSF is important for homeostasis and brain metabolism. It brings nutrients to
nourish brain cells, removes metabolites that enter the CSF from the brain cells,
and provides an optimal chemical environment for neuronal functions and

impulse conduction. After circulation, CSF is reabsorbed from the arachnoid
space via the arachnoid villi into venous blood, mainly at the superior sagittal
sinus—a major vein that drains the brain. Arachnoid villi are small, thin-walled

arachnoid extensions that penetrate the dura mater and project into the venous
sinuses located between the periosteal and meningeal layers of dura mater.

MORPHOLOGY OF A TYPICAL NEURON

The nervous system contains complex intercommunicating networks of nerve
cells that receive and conduct impulses along their neural pathways or axons to
the CNS for analysis, integration, interpretation, and response. The appropriate

response to a stimulus from the neurons of the CNS is the activation of muscle
(skeletal, smooth, or cardiac) functions or glandular secretions (endocrine or
exocrine).

The structural and functional cells of the nervous tissue are the neurons

(Fig. 9.2). Although neurons vary in size and shape, they share common features.
Each neuron consists of soma or cell body, numerous dendrites, and a single
axon. The cell body contains the nucleus, nucleolus, numerous different
organelles, and the surrounding cytoplasm or perikaryon. Projecting from the

cell body are numerous cytoplasmic extensions called dendrites that form a
dendritic tree.

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