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They develop in the cerebellar primordium that covers the fourth ventricle and below a fissure-like region called the isthmus of the developing brain. Purkinje cells migrate toward the outer surface of the cerebellar cortex and form the Purkinje cell layer. Purkinje cells are born during the earliest stages of cerebellar neurogenesis.
The Purkinje fibers are further specialized to rapidly conduct impulses (having numerous fast voltage-gated sodium channels and mitochondria, and fewer myofibrils, than the surrounding muscle tissue). Purkinje fibers take up stain differently from the surrounding muscle cells because of having relatively fewer myofibrils than other cardiac cells.
Each climbing fiber will form synapses with 1-10 Purkinje cells. Early in development, Purkinje cells are innervated by multiple climbing fibers, but as the cerebellum matures, these inputs gradually become eliminated resulting in a single climbing fiber input per Purkinje cell.
The middle layer contains only one type of cell body—that of the large Purkinje cell. Purkinje cells are the primary integrative neurons of the cerebellar cortex and provide its sole output. Purkinje cell dendrites are large arbors with hundreds of spiny branches reaching up into the molecular layer (Fig. 6).
Sensory information relayed from the pons through the mossy fibers to the granule cells is then sent along the parallel fibers to the Purkinje cells for processing. Extensive branching in white matter and synapses to granular cells ensures that input from a single mossy fiber axon will influence processing in a very large number of Purkinje cells.
The only excitatory neurons present in the cerebellar cortex are granule cells. [10] Plasticity of the synapse between a parallel fiber and a Purkinje cell is believed to be important for motor learning. [11] The function of cerebellar circuits is entirely dependent on processes carried out by the granular layer.
A parallel fiber runs for an average of 3 mm in each direction from the split, for a total length of about 6 mm (about 1/10 of the total width of the cortical layer). [1] As they run along, the parallel fibers pass through the dendritic trees of Purkinje cells , contacting one of every 3–5 that they pass, making a total of 80–100 synaptic ...
The main synapse made by these cells is a synapse onto the mossy fibre–granule cell excitatory synapse in a glomerulus. The glomerulus is made up of the mossy fibre terminal, granule cell dendrites, and the Golgi terminal, and is enclosed by a glial coat. [3] The Golgi cell acts by altering the mossy fibre - granule cell synapse.