a. Major Subdivisions of the CNS. The major subdivisions of the CNS are
the brain and the spinal cord.
b. Coverings of the CNS. The coverings of the CNS are skeletal and fibrous.
c. Cerebrospinal Fluid (CSF). The CSF is a liquid thought to serve as a
cushion and circulatory vehicle within the CNS.
11-9. THE HUMAN BRAIN
The human brain has three major subdivisions: brainstem, cerebellum, and
cerebrum. The CNS is first formed as a simple tubelike structure in the embryo. The
concentration of nervous tissues at one end of the human embryo to produce the brain
and head is referred to as cephalization. When the embryo is about four weeks old, it is
possible to identify the early forms of the brainstem, cerebellum, and cerebrum, as well
as the spinal cord. As development continues, the brain is located within the cranium
(para 4-13c(1)) in the cranial cavity. See figures 11-5A and 11-5B for illustrations of the
Figure 11-5A. Human brain (side view).