b. Major Subdivisions. The fully formed CNS can be considered in two major
subdivisions: the brain and the spinal cord.
THE HUMAN BRAIN
The human brain (Figures 12-3 and 12-4) has three major subdivisions:
brainstem, cerebellum, and cerebrum.
a. The Brainstem. The brainstem is the core of the brain. We consider it in
three parts--the hindbrainstem, the midbrainstem, and the forebrainstem. In general,
the brainstem is made up of many nuclei and fiber tracts. It is a primary coordinating
center of the human nervous system.
b. The Cerebellum. Over the hindbrainstem is the cerebellum. The
cerebellum is connected to both the midbrainstem and the hindbrainstem. The
cerebellum is the primary coordinating center for muscle actions. Here, patterns of
movements are properly integrated. Thus, information is sent to the appropriate
muscles in the appropriate sequences. Also, the cerebellum is very much involved in
Figure 12-3. Human brain; sideview.