Human Anatomy Part 2 - K. A. Diubenko, A. K. Kolomiitsev, Yu. B. Chaikovsky 2008

Special Part
Nervous system, systema nervosum - Special Part
Brain - Embryogenesis of the brain - Cerebellum

The Cerebellum, or little Brain, is the largest unpaired Structure belonging to the Hindbrain, metencephalon (Fig. 139 A, B). It is located in the posterior cranial fossa beneath the occipital lobes of the cerebral hemispheres, posterior to the Medulla Oblongata and the Pons. The cerebellum has a superior and an inferior surface, as well as superior and inferior borders. The superior surface of the cerebellum faces the occipital lobes of the cerebral hemispheres, separated from them by the cerebellar tentorium. Inferiorly, the cerebellum reaches the foramen magnum. The cerebellum participates in forming the roof of the Fourth ventricle. The weight of an adult human cerebellum is 136-139 g, its transverse dimension is 10-12 cm, and its longitudinal dimension is 6 cm.

The cerebellum has reciprocal connections with the medulla oblongata, the pons, and the Midbrain (red Nucleus and reticular formation), as well as with areas of the motor cortex of the cerebrum. The cerebellum performs several important Functions, including:

- regulating Muscle tone;

- automatically regulating the function of the motor apparatus;

- maintaining body posture and balance;

- participating in the programming of purposeful movements;

- regulating autonomic functions (L. A. Orbeli).

The cerebellum consists of a central part, the cerebellar vermis, and two lateral parts, the cerebellar hemispheres, hemispherii cerebelli (Fig. 139 A, B). The vermis coordinates movements during walking and standing, while the cerebellar hemispheres contain mechanisms for precise coordination of movements, primarily for executing upper limb movements. The vermis is subordinate to the cerebellar cortex, which in turn functions under the Influence of the Cerebral Cortex. The vermis is separated from the hemispheres by two longitudinal grooves, which are clearly visible on the Inferior surface of the cerebellum. The surface of the cerebellar hemispheres and vermis is divided by cerebellar fissures, fissurae cerebelli, into folia, folia cerebelli, which form lobules, lobuli cerebelli (Fig. 139 A, B).

The deepest fissure is the horizontal fissure, fissura horizontalis, which lies on the boundary between the superior and inferior surfaces of the cerebellum. Each lobule of the vermis corresponds to specific lobules of the cerebellar hemispheres (see Table).

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Fig. 139. A, B. Cerebellum (external structure). A - superior view. B - anterior view.

Anatomical relationships between the lobules of the vermis and the cerebellar hemispheres.

140. Cerebellum in sagittal section (arbor vitae, "tree of life")

Internal Structure of the cerebellum

Sections of the cerebellum show that it consists of gray and White matter. The majority of the Gray matter is located superficially, forming the cerebellar cortex, which is 1 to 2.5 mm thick and has a surface area of 85,000 mm². The cerebellar cortex consists of three layers (Fig. 141):

- the outer molecular layer, stratum moleculare;

- the middle Purkinje Cell (ganglionic) layer, stratum purkinjense*;

- the inner granular layer, stratum granulosum.

Fig. 141. Cytoarchitectonics of the cerebellar cortex - Morphology and topography of Purkinje Cells (light Microscopy, hematoxylin-picrofuchsin staining, 250x (after T. A. Malysheva))

1 - molecular layer of the cerebellar cortex, stratum moleculare; 2 - dendritic branching of Purkinje cells; 3 - Blood vessel (capillary); 4 - cell body (perikaryon) of Purkinje cells; 5 - Purkinje layer, stratum purkinjense; 6 - granular layer of the cerebellar cortex, stratum granulosum

The smaller portion of the gray matter is represented by the paired cerebellar nuclei, which are embedded deep within the white matter, known as the medullary body, corpus medullare. The cerebellar nuclei are collections of gray matter of various shapes (Fig. 142). They include the following:

- dentate nucleus, nucleus dentatus;

Fig. 142. Schematic diagram of the cerebellar nuclei

1 - superior cerebellar peduncles, pedunculus cerebellaris anterioris; 2 - hilum of the dentate nucleus, hilum nuclei dentati; 3 - emboliform nucleus, nucleus emboliformis; 4 - medullary body of the cerebellum, corpus medullare cerebelli; 5 - fastigial nucleus, nucleus fastigii; 6 - globose nucleus, nucleus globous; 7 - cerebellar vermis, vermis cerebellaris; 8 - cerebellar cortex, cortex cerebelli

Fig. 142 A. Main Pathways of the cerebellum (schematic diagram) after E. Villiger, with additions

Of the three pairs of human cerebellar peduncles, the middle cerebellar peduncles are the most highly developed. Their prominent development and larger size compared to the other peduncles underscore their key Structural and functional significance. The middle cerebellar peduncles also contribute to The formation of the cerebellopontine angle.

The superior cerebellar peduncles, pedunculi cerebellares superiores, consist mainly of fibers of efferent systems. They connect the cerebellum with the midbrain, Diencephalon, and brainstem structures. They carry:

- anterior spinocerebellar tract (Gowers);

- cerebellotegmental tract.

Cerebellar lesions lead to various disorders of motor activity and muscle tone, as well as autonomic dysfunction. The main motor system disorders are characterized by features such as ataxia, tremor, and movement asynergy. Cerebellar ataxia manifests with the following symptoms: atonia, astasia, and asthenia (Luciani's triad).