Cerebellum

The cerebellum (cerebellum, small brain) is located posteriorly (dorsally) from the bridge and from the upper (dorsal) part of the medulla oblongata. It lies in the posterior cranial fossa. Above the cerebellum hang the occipital lobes of the cerebral hemispheres, which are separated from the cerebellum by the transverse slit of the large brain (fissura transversa cerebralis).

The cerebellum distinguishes the upper and lower surfaces, the border between which is the posterior edge of the cerebellum, where a deep horizontal slit (fissura horizontalis) passes. It begins at the point of entry into the cerebellum of its middle legs. The upper and lower surfaces of the cerebellum are convex. On the lower surface there is a wide depression - the lobe of the cerebellum (vallecula cerebelli). This dilation is the dorsal surface of the medulla oblongata. The cerebellum distinguishes two hemispheres (hiispheria cerebelli) and an unpaired middle part - a cerebellar worm (vermis cerebelli, phylogenetically the old part). The upper and lower surfaces of the hemispheres and worm are cut by a multitude of transverse parallel slits of the cerebellum (fissura cerebelli), between which are the long and narrow leaves of the cerebellum (folia cerebelli). Groups of convolutions, separated by deeper furrows, form lobules of the cerebellum (lobuli cerebelli). Furrows of the cerebellum go, without interruption, through the hemisphere and through the worm. Each wedge of the worm corresponds to two (right and left) segments of the hemispheres. A more isolated and phylogenetically old lobule of each of the hemispheres is a scrap (flocculus). It is attached to the ventral surface of the middle cerebellar pedicle. Using a long pedicle flocculi, the scrap is connected to the cerebellum worm, with its nodulus. With the adjacent parts of the brain the cerebellum is connected by three pairs of legs. The lower cerebellar pedunculi (pedunculi cerebellares cauddles, s. Inferiores, rope bodies) are directed downward and connect the cerebellum with the medulla oblongata. The middle cerebellar legs (pedilnculi cerebellares medii) are the thickest, they go anteriorly and pass into the bridge. The upper cerebellar pedunculi (peduncuii cerebellares rostrales, S. Siiperiores) connect the cerebellum to the middle brain. In the cerebellar peduncles fibers of the conducting pathways pass between the cerebellum and other parts of the brain and the spinal cord.

The hemispheres of the cerebellum and the worm consist of a corpus medullare located inside the body, a white matter and a thin plate of gray matter covering the white matter around the periphery, the cortex of the cerebellum (cortex segue-belli).

There are three cell layers in the cerebellar cortex. The most superficially located molecular layer, under it is a layer of pear-shaped neurons (ganglionic layer), and even deeper - a granular layer.

The molecular layer is formed mainly by basilar and star-shaped neurons. The basket-shaped neurons are located in the lower part of the molecular layer. These cells have sizes from 10 to 20 microns, irregular shape and long processes. Dendrites of basket neurons branch mainly across the tortuosity of the cerebellum. Axons of basilar neurons also run across the gyri above the pear-shaped neurons. From the axons, the collaterals go down to the bodies of pear-shaped neurons, braid them, forming baskut-like figures. The basket-shaped neurons with their impulses inhibit the functions of the pear-shaped cells. Stellate cells have various lengths of dendrites and an axon forming synapses on dendrites of pear-shaped cells.

The granular layer is formed by numerous small neurons-cells-grains. The processes of the cell-grains form numerous synapses (synaptic tangles) on other cells of this layer, as well as by the endings of fibers ("moss-like") ending in the cerebellum and transmitting exciting impulses.

The pear-shaped neuron layer is formed by large cells (Purkinje cells) arranged in a single row. Axons of pear-shaped cells emerge from the cerebellar cortex and terminate on the cells of its nuclei.

The afferent nerve impulses that enter the cerebellum exert an exciting effect on pear-shaped neurons. These impulses are transmitted along the fibers of the spinal-cerebellar and pre-vertebral-cerebellar pathways. Nerve fibers pass through the granular layer to pear-shaped cells, along their dendrites ("climbing" fibers) and end with synapses on the bodies of pear-shaped neurons. The afferent impulses from the vestibular (statovestibular) receptors of the inner ear, from the proprioceptors of skeletal muscles that come to the cerebellum are analyzed and compared with impulses coming from the cortex of the cerebral hemispheres. In the thickness of the leaves of the cerebellum, the white substance looks like thin white strips (laminae, laminae albae).

In the white substance of the cerebellum there are paired nuclei of the cerebellum (nuclei cerebelli). The most significant of these is the dentate nucleus (nucleus dentatus). On the horizontal section of the cerebellum, this nucleus is in the form of a thin, curved gray strip, which is convex laterally and backward with its convex part. In the medial direction, the gray band is not closed, this place is called the gate of the jagged nucleus (hilum nuclei dentati). Inside the dentate nucleus, in the white substance of the hemisphere of the cerebellum, there is a nucleus iboliformis and a nucleus globosus. Here, in the white substance of the worm, is the most medial nucleus - the nucleus of the tent (nucleus fastigii).

The white substance of the worm, bordered by the bark and divided along the periphery by numerous deep and small grooves, has a bizarre pattern on the sagittal section resembling a branch of a tree, hence its name is the tree of life (arbor vitae cerebelli).

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