Human Anatomy - Kotsan I. Ya. 2009

Brain
Cerebellum

The Cerebellum is located dorsally to the Pons and the upper dorsal part of the Medulla Oblongata. It plays a primary role in maintaining body balance and coordinating movements. All vertebrates have a cerebellum, The Development of which depends on The Nature of the animal's locomotion. The cerebellum reaches its greatest development in humans in connection with bipedalism and the adaptation of the hand for labor. It is situated in the posterior cranial fossa. Superiorly, the occipital lobes of the cerebral hemispheres hang over the cerebellum, separated from it by the transverse cerebral fissure (fissura transversa cerebralis).

Anatomically, the cerebellum consists of two hemispheres (hemispheriae cerebelli) and an unpaired median part, the vermis (vermis cerebelli). Phylogenetically, a distinction is made between the archicerebellum (archaeocerebellum), represented by the flocculus and nodulus; the paleocerebellum (palaeocerebellum), which includes the vermis; and the neocerebellum (neocerebellum), which comprises the cerebellar hemispheres (hemispheriaе cerebelli) and three pairs of cerebellar peduncles (pedunculi cerebellares).

The cerebellum has superior and inferior surfaces, the boundary between which is the posterior margin of the cerebellum, where the deep horizontal fissure (fissura horisontalis) runs. Both the superior and inferior surfaces are convex. On the inferior surface, There is a wide depression—the cerebellar vallecula (vallecula cerebelli)—which is adjacent to the dorsal surface of the medulla oblongata.

The superior and inferior surfaces of the hemispheres and the vermis are intersected by numerous parallel transverse fissures (sulci) (fissuraе cerebelli), between which lie long, narrow cerebellar folia (folia cerebelli). Groups of folia, separated by deeper sulci, form the cerebellar lobules (lobuli cerebelli). Because the cerebellar sulci run continuously across both the hemispheres and the vermis, each lobule of the vermis corresponds to two lobules (right and left) of the hemispheres. A more isolated lobule of the hemispheres is the flocculus, which lies adjacent to the ventral surface of the middle cerebellar peduncle. By means of its peduncle (pedunculus floccularis), the flocculus connects to the cerebellar vermis, specifically to its nodule (nodulus). The cerebellum is connected to neighboring PARTS OF THE Brain by three pairs of peduncles. The inferior cerebellar peduncles (pedunculi cerebellares inferiores) extend downward and connect the cerebellum to the medulla oblongata. The middle cerebellar peduncles (pedunculi cerebellares medii) are the thickest, running anteriorly to merge with the pons. The superior cerebellar peduncles (pedunculi cerebellares superiores) connect the cerebellum to the Midbrain. The cerebellar peduncles contain tract fibers that link the cerebellum with other parts of the brain and the Spinal Cord.

The cerebellum is composed of white and Gray matter.

The White matter, or medullary body (corpus medullare), lies within the core of the cerebellum and extends as white stripes into each lobule. The WHITE MATTER OF the vermis is bordered by the cortex and divided peripherally by numerous deep and shallow sulci. On a sagittal section, it forms an intricate pattern resembling the frond of a fern. This sectional view through the cerebellar vermis is known as the "tree of life" of the cerebellum (arbor vitae cerebelli).

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Fig. 248. Cerebellar nuclei, diagram (after M. G. Prives)

1 — fastigial Nucleus; 2 — globose nucleus; 3 — emboliform nucleus; 4 — dentate nucleus

The gray matter forms the cerebellar cortex (cortex cerebellaris), as well as isolated paired cellular clusters located within the white matter—the cerebellar nuclei: the dentate nucleus (nucleus dentatus), emboliform nucleus (nucleus emboliformis), globose nucleus (nucleus globosus), and fastigial nucleus (nucleus fastigii) (Fig. 248). The cerebellar cortex consists of three layers: an outer molecular layer, a middle Purkinje Cell (ganglionic) layer, and an inner granular layer. The molecular and granular layers primarily contain small Neurons. Large Purkinje Cells, measuring up to 40 µm, are arranged in a single row in the middle layer and serve as the sole efferent neurons of the cerebellar cortex. Their axons, originating from the Base of the cell bodies, form the initial segment of the efferent pathways. They project to the cerebellar nuclei, while their dendrites arborize in the superficial molecular layer. The other neurons of the cerebellar cortex are interneurons (association neurons) that transmit nerve impulses to the Purkinje cells.

Thus, all nerve impulses entering the cerebellar cortex ultimately reach the Purkinje cells.