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The central nervous system is weIl protected against externaI
forces as it lies inside the skull and the vertebral canal. In
addition to this bony protection, the central nervous system is
wrapped in three membranes of connective tissue, with fluid-filled
spaces between the membranes. It is, in fact, loosely suspended in a
fluid-filled container. Since the specific weight of nervous tissue
is only slightly higher than that of water, the brain and spinal
cord almost float. This further serves to reduce the impact of
externa! forces on the brain and spinal cord.
The central nervous system can be subdivided anatomically into
different parts (Figs. 3.1. and 3.2). The spinal cord lies
in the vertebral canal, whereas the brain is located in the cranial
cavity. The brain is further subdivided into the brain stem,
which constitutes the upward continuation of the spinal. cord,
the cerebellum (little brain"), and the cerebrum
or cerebral hemispheres. The cerebellum and cerebrum
largely cover the brain stem and constitute the major part of the
brain in higher mammals and particularly in humans.
In this charter we will give an overview of the main features of
the anatomy of the central nervous system, with brief rnention of
the functional significance of the various parts. Structure and
function of rnany of these parts will be treated in more depth in
the later chapters dealing with functional systems. It will then be
assumed, however, that the reader is familiar with the names and the
locations of the major cell groups of
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