Parallel fiber

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Parallel fiber
Microcircuitry of the cerebellum. Excitatory synapses are denoted by (+) and inhibitory synapses by (-).
MF: Mossy fiber.
DCN: Deep cerebellar nuclei.
IO: Inferior olive.
CF: Climbing fiber.
GC: Granule cell.
PF: Parallel fiber.
PC: Purkinje cell.
GgC: Golgi cell.
SC: Stellate cell.
BC: Basket cell.
Dorlands/Elsevier f_05/12361338

Parallel fibers arise from granule cells in the cerebellar cortex. They form synapses onto the dendrites of Purkinje cells (the output neurons of the cerebellum).

Granule cells are very small and very numerous. They are thought to make up as many as 90% of the neurons in the brain.