Basic Structure of the Cerebellar Cortex – In striking contrast to the cortex of the cerebral hemispheres, the cerebellar cortex has a uniform structure in all portions of the cerebellum. Molecular layer. B. Purkinje cell layer. C. Granular layer, which rests on white matter. A. Purkinje cells, forming the layer named after them. B. Granule cells, forming the granular layer. C. Outer stellate cells, and – d.
Basket cells, lying in the molecular layer. E. Golgi cells, present in the granular layer. F. Brush cells present in the granular layer. The processes of those neurons have a definite orientation in relation to cerebellar folia. The main relationships are illustrated in Figs 12.1 and 12.2. The neurons in the molecular layer are supported by large neuroglial cells. Purkinje cells – The Purkinje cell layer is unusual in that it contains only one layer of neurons. The cell bodies of those neurons are large and flask shaped. The cells are evenly spaced. A dendrite arises from the neck of the flask and pass upwards into the molecular layer.
Here it divides to form an elaborate dendritic tree. The branches of this tree all lie in one plane. This plane is transverse to the long axis of the folium. As a consequence of this arrangement the dendritic trees of Purkinje’s neighboring cells lie in planes give or take parallel to each other. The axon of every Purkinje cell passes downwards throughout the granular layer to enter the white matter. As described later these axons constitute the only efferents of the cerebellar cortex. They end, predominantly, by synapsing with neurons in cerebellar nuclei. They’re inhibitory to these neurons. Granule cells – These are very small, numerous, spherical neurons that occupy the greater part of the granular layer.
The spaces not occupied by them are called cerebellar islands. These islands are occupied by special synaptic structures called glomeruli. Each granule cell gives off 3 to five short dendrites. These end in claw like endings which enter the glomeruli where they tune with the terminals of mossy fibres. The axon of every granule cell enters the molecular layer. Here it divides into two subdivisions each of which is at right angles to the parent axon. These axonal branches of granular cells are called parallel fibres. The granule cells being extremely numerous, the parallel fibres are also abundantand almost fill the molecular layer.