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P-type calcium channels were named after Purkinje cells, where they were initially encountered (Llinas et al. 1989), which are crucial in cerebellar function. Activation of the Purkinje cell by climbing fibers can shift its activity from a quiet state to a spontaneously active state and vice versa, serving as a kind of toggle switch. [25]
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 connections with Purkinje cell dendritic spines. [1] Granule cells use glutamate as their neurotransmitter, and therefore exert excitatory effects on their targets.
Purkinje cells receive more synaptic inputs than any other type of cell in the brain—estimates of the number of spines on a single human Purkinje cell run as high as 200,000. [11] The large, spherical cell bodies of Purkinje cells are packed into a narrow layer (one cell thick) of the cerebellar cortex, called the Purkinje layer.
Each Purkinje cell receives excitatory input from 100,000 to 200,000 parallel fibers. Parallel fibers are said to be responsible for the simple (all or nothing, amplitude invariant) spiking of the Purkinje cell. Purkinje cells also receive input from the inferior olivary nucleus via climbing fibers. A good mnemonic for this interaction is the ...
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. These fibers provide very powerful, excitatory input to the cerebellum which results in the generation of complex spike excitatory ...
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. Therefore, the function of granule cells determines the cerebellar function as a whole. [12]
This period is an important developmental stage of the cerebellum. The expansion of the EGL precursor cells creates a large population of neurons that outnumber Purkinje cells 250:1 in the adult cerebellar cortex. [6] The granule neurons in EGL express genes that play a specific and crucial role in cell proliferation.
One exception is that fibers from the flocculonodular lobe synapse directly on vestibular nuclei without first passing through the deep cerebellar nuclei. The vestibular nuclei in the brainstem are analogous structures to the deep nuclei, since they receive both mossy fiber and Purkinje cell inputs. [2]