Cerebellum

The cerebellum is the portion of the brain whose function is the coordination of movement and the maintenance of the body’s posture, tone, and balance. It is also involved in the regulation of autonomic, sensory, adaptive, tropic, and conditioned reflexive activities. Like the basal ganglia, it belongs to the motor system. It occupies the posterior cranial fossa, lying below the occipital lobe of the cerebrum and behind the brainstem (on dorsal aspect). The cerebellum is connected with the brainstem through the three cerebellar peduncles; the superior, middle, and inferior. The superior cerebellar penduncle contains most of the fibers that convey impulses out of the cerebellum (in other words, efferent fibers).

The cerebellum has two hemispheres which are connected by a median section called the vermis. The bodies of nerve cells form its gray surface layer, which is called the cerebellar cortex. Paired nuclei of the gray matter are distributed in the cerebellum’s white matter, which consists of myelinated nerve fibers. The aforementioned three pairs of cerebellar peduncles link up the cerebellum the corpora quadrigemina, the pons, and the medulla oblongata. The cortex of the cerebellum consists of three layers made up of five types of cells, of which four are inhibitory. The surface (molecular) layer covers the Purkinje (gangliar) layer, which, in turn, covers the granular (deep) layer. Neural impulses reach the cortex mainly along the mossy fibers and, to some extent, along the climbing fibers. The axons of the Purkinje cells originating in the ganglionic layer are the only exit from the cortex, and they end at the cerebellar nuclei.

The surface of the cerebellum is extensively folded, forming numerous narrow sheets which are predominantly oriented in a transverse manner. These sheets, or folia, are separated by deep fissures and sulci. The deepest fissures divide the cerebellum into lobes. The middle part of the cerebellum is called the vermis, which is also present in the anterior part of this organ. A small bulbous part on each cerebellar hemisphere is connected medially with a thin stalk to the vermis. This part is called the flocculus and lies close to the middle cerebellar peduncle, just posterior to the VII and VIII cranial nerve. The white substance of the cerebellum forms a tree-like structure called the arbor vitae.

Blood Supply

The cerebellum is supplied by three blood vessels: the superior cerebellar, anterior inferior cerebellar, and the posterior inferior cerebellar artery. All three blood vessels arise from the basilar artery, which is formed by the union of the vertebral arteries.

Bioelectric Activity

The bioelectric activity of the cerebellum is characterized by rapid and slow potentials. The slow rhythms are associated with the cerebral cortex; the rapid rhythms are an internal property of the cerebellum. Bioelectric potentials arise in certain regions of the cerebellar cortex in response to the stimulation of various regions of the cerebrum; the proprioreceptors of the muscles, the tendons and ligaments; and the receptors of the viscera, skin, eyes, and ears. All of these phenomena are indications of the complex and varied functions of the cerebellum, which may be regarded as a universal regulator of the body’s somatic and autonomic functions.

Above, superior aspect of the cerebellum (seen from above)

The cerebellum seen from the left side of brain.