(3) The 12 pairs of cranial nerves connect at the sides of the brainstem.
b. Cerebellum. The cerebellum is a 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. A peduncle is a stem-like 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 space separating the two cerebral hemispheres is called the
longitudinal fissure. The shallow grooves in the surface of the cerebrum are called sulci
(sulcus, singular). The ridges outlined by the sulci are known as gyri (gyrus, singular).
(2) The cerebral cortex is the gray outer layer of each hemisphere. The
occurrence of sulci and gyri helps to increase the amount of this layer. Deeper within
the cerebral hemispheres, the tissue is white. The "gray matter" represents cell bodies
of the neurons. The "white matter" represents the axons.
(3) The areas of the cortex are associated with groups of related functions.
(a) For example, centers of speech and hearing are located along the
lateral sulcus, at the side of each hemisphere.
(b) Vision is centered at the rear in the area known as the occipital lobe.
(c) Sensory and motor functions are located along the central sulcus,
which separates the frontal and parietal lobes of each hemisphere. The motor areas
are located along the front side of the central sulcus, in the frontal lobe. The sensory
areas are located along the rear side of the central sulcus, in the parietal lobe.