a. The Brainstem. The term brainstem refers to that part of the brain that would
remain after the removal of the cerebrum and the cerebellum. The brainstem is the
basal portion (portion of the base) of the brain. The brainstem can be divided as
(1) The brainstem is continuous with the spinal cord. Together, the
brainstem and the spinal cord are sometimes known as the neuraxis.
(2) The brainstem provides major relays and controls for passing
information up or down the neuraxis.
The 12 pairs of cranial nerves connect at the sides of the brainstem.
b. Cerebellum. The cerebellum is the spherical mass of nervous tissue
attached to and covering the hindbrainstem. It has a narrow central part called the
vermis and right and left cerebellar hemispheres.
(1) Peduncles. The peduncles is a stemlike connecting part. The
cerebellum is connected to the brainstem with three pairs of peduncles.
(2) General shape and construction. A cross section of the cerebellum
reveals that the outer cortex is composed of gray matter (cell bodies of neurons), with
many folds and sulci (shallow grooves). More centrally located is the white matter
(myelinated processes of neurons).
(3) Function. The cerebellum is the primary coordinator/integrator of motor
actions of the body.
c. Cerebrum. The cerebrum consists of two very much-enlarged hemispheres
connected to each other by a special structure called the corpus callosum. Each
cerebral hemisphere is connected to the brainstem by a cerebral peduncle. The surface
of each cerebral hemisphere is subdivided into areas known as lobes. Each lobe is
named according to the cranial bone under which it lies: frontal, parietal, occipital, and
(1) The cerebral cortex is the gray outer layer of each hemisphere. Deeper
within the cerebral hemispheres the tissue is white. The "gray matter" represents cell
bodies of neurons. The "white matter" represents the axons.