<P> The deep nuclei of the cerebellum are clusters of gray matter lying within the white matter at the core of the cerebellum . They are, with the minor exception of the nearby vestibular nuclei, the sole sources of output from the cerebellum . These nuclei receive collateral projections from mossy fibers and climbing fibers as well as inhibitory input from the Purkinje cells of the cerebellar cortex . The four nuclei (dentate, globose, emboliform, and fastigial) each communicate with different parts of the brain and cerebellar cortex . (The globose and the emboliform nuclei are also referred to as combined in the interposed nucleus). The fastigial and interposed nuclei belong to the spinocerebellum . The dentate nucleus, which in mammals is much larger than the others, is formed as a thin, convoluted layer of gray matter, and communicates exclusively with the lateral parts of the cerebellar cortex . The flocculonodular lobe is the only part of the cerebellar cortex that does not project to the deep nuclei--its output goes to the vestibular nuclei instead . </P> <P> The majority of neurons in the deep nuclei have large cell bodies and spherical dendritic trees with a radius of about 400 μm, and use glutamate as their neurotransmitter . These cells project to a variety of targets outside the cerebellum . Intermixed with them are a lesser number of small cells, which use GABA as a neurotransmitter and project exclusively to the inferior olivary nucleus, the source of climbing fibers . Thus, the nucleo - olivary projection provides an inhibitory feedback to match the excitatory projection of climbing fibers to the nuclei . There is evidence that each small cluster of nuclear cells projects to the same cluster of olivary cells that send climbing fibers to it; there is strong and matching topography in both directions . </P> <P> When a Purkinje cell axon enters one of the deep nuclei, it branches to make contact with both large and small nuclear cells, but the total number of cells contacted is only about 35 (in cats). Conversely, a single deep nuclear cell receives input from approximately 860 Purkinje cells (again in cats). </P> <P> From the viewpoint of gross anatomy, the cerebellar cortex appears to be a homogeneous sheet of tissue, and, from the viewpoint of microanatomy, all parts of this sheet appear to have the same internal structure . There are, however, a number of respects in which the structure of the cerebellum is compartmentalized . There are large compartments that are generally known as zones; these can be divided into smaller compartments known as microzones . </P>

Effects of age on tissues and regions of the cerebrum and cerebellum