The cerebellar hemispheres are divided by transverse fissures into lobules. The surfaces of lobules are marked by folds (folia or lamina) running parallel to the fissure and runs transversely to the longitudinal axis of brain.
In cross section of folds, it is seen that they give off secondary and tertiary lamina the whole producing the appearance known as arbor vitae. The surface of secondary cerebellum is composed of gray matter – the cortex that encloses white matter.
Cortex
- Has an outer molecular layer (plexiform layer) with few cells and few medullated nerve fibres, an inner granular or nuclear layer. Between these two layers a single row of large flask shaped cells called the Purkinje cells are present. These cells give off several antler like main dendrites which enter molecular layer and form a remarkably rich arborization extending to the surface.
- The dendritic arborization is fan-shaped and extends at right angles to the laminae. The axon is given off from the end of the cell opposite to the dendrites and acquiring a medullary sheath passes through the granular layer to the white matter.
- Purkinje cells are almost the only ones whose axons reach the white matter. Axons of the Purkinje cells give off collaterals, which enter molecular layer and appear to terminate there in “end buttons” upon the bodies of adjacent Purkinje cells. Cell bodies of Purkinje cells contain concentric chromophylic bodies.
- The cells in the molecular layer are either superficial stellate cells with irregular branching dendrites and short axon or deep stellate (basket) cells.
- Axon of the latter extend at right angles to the laminae for a distance of several Purkinje cells giving off to each Purkinje cell one or more collaterals which pass towards the granular layer and envelop with their terminal arborizations of the body and proximal non medullated portion of the axons of Purkinje cell. Collateral’s of other basket cell axons may terminate around the same Purkinje Cell, thus forming the basket.
- The granular layer in ordinary preparations presents the appearance of closely packed nuclei with clear spaces here and there and a few larger cell. Most of these nuclei belong to granule cells. Their short dendrites 3 to 6 in number terminate in compact arborizations in the granular layer. Their nonmedullated axons ascent into molecular layer to end in varicosities.
- These are the parallel fibres of molecular layer and they run at right angles to and through the dendritic expansions of Purkinje cells and their cross sections together with terminal dendritic arborizations of Purkinje cells give the molecular layer its punctate appearance.
- In the cortex there are also the termination of afferent fibres, mossy fibres and climbing fibres.
- Mossy fibres are the coarsest of the white matter while in the white matter they bifurcate, branches going to different laminae. These main branches give off secondary branches which enter the granular layer and arborize there. The climbing fibres pass from the white matter to the cells of Purknije cells. The medullated fibres of cerebellum pass through the white matter into the granular layer, separating groups of granular cells.
- The above details are best demonstrated by the Golgi method.
