c. Cerebrospinal Fluid. The cerebrospinal fluid (CSF) is a liquid that is thought
to serve as a cushion and circulatory vehicle within the central nervous system.
5-11. THE HUMAN BRAIN
The human brain has three major subdivisions: brainstem, cerebellum, and the
cerebrum. The central nervous system is first formed as a simple tube like 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 the cerebrum, as well as the spinal cord. As development continues, the brain is
located within the cranium in the cranial cavity. See Figure 5-5 for illustrations of the
Figure 5-5. Human brain: A side view, B bottom view.