Editing Cerebellum (section)

====Deep nuclei====
{{Main|Deep cerebellar nuclei}}
[[File:Gray707.png|thumb|right|upright=1.25|Sagittal cross-section of human cerebellum, showing the dentate nucleus, as well as the pons and inferior olivary nucleus]]
The [[deep cerebellar nuclei|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 [[nucleus (neuroanatomy)|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 nucleus|dentate]], [[Globose nucleus|globose]], [[Emboliform nucleus|emboliform]], and [[Fastigial nucleus|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 flocculus of 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.<ref name=SOB/>

The majority of neurons in the deep nuclei have large cell bodies and spherical dendritic trees with a radius of about 400&nbsp;μm, and use [[glutamic acid|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 [[Gamma-Aminobutyric acid|GABA]] as a neurotransmitter and project exclusively to the [[inferior olivary nucleus]], the source of [[climbing fiber]]s. Thus, the nucleo-olivary projection provides an inhibitory [[Feedback#Biology|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.<ref name=SOB/>

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).<ref name=SOB/>