Granule cells are the smallest cells found in the brain and are
an extremely small type of neuron. Granule cells are found
within the granular layer of the cerebellum (which is also known
as layer II and IV layer), the inner most layer of cerebellar
cortex with the middle layer being the Purkinje cell layer and
the outermost being the Molecular layer), the dentate gyrus of
the hippocampus, the superficial layer of the dorsal cochlear
nucleus, and in the olfactory bulb. Cerebellar granule cells
account for nearly half of the neurons in the central nervous
system. Granule cells receive excitatory input from mossy fibers
originating from pontine nuclei. Cerebellar granule cells send
parallel fibers up through the Purkinje layer into the molecular
layer where they branch out and spread through Purkinje cell
dendritic arbors. These parallel fibers form thousands of
excitatory Granule-cell-Purkinje-cell synapses onto the
intermediate and distal dendrites of Purkinje cells using
glutamate as a neurotransmitter. Laye