4-2. Mossy Fibers

Mossy fibers are the most numerous afferent fibers that reach the cerebellar cortex through the white matter and terminate in the cerebellum’s granular layer, forming a mosslike structure (Figure 14). Some mossy fibers originate as sensory peripheral nerves, but most mossy fibers arise from neurons located within the spinal cord and brainstem. They also arise from unipolar brush cells in the granular layer (see below) and from cerebellar nuclei (Chapter 6, “Pre- and Post-Cerebellar Cortex Neurons”). Mossy fibers terminate within a glomerulus, which forms a characteristic rosette structure. Within a glomerulus, granule cell dendrites receive a-amino-3-hydroxy-5-methyl-4-isoxazolone propionic acid (AMPA)-mediated excitatory synapses from a mossy fiber terminal. Granule cells receive also inhibitory synapses supplied by a Golgi cell axon terminal. Descending dendrites of mostly deep Golgi cells also receive excitatory synapses directly from a mossy fiber terminal.