Purkinje cell

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Drawing of pigeon Purkinje cells (A) by Santiago Ramon y Cajal

Transverse section of a cerebellar folium.

Purkinje cells are a class of GABAergic neuron located in the cerebellar cortex. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně.

Anatomy

These cells are some of the largest neurons in the brain, with an intricately elaborate dendritic arbor, characterized by a large number of dendritic spines. Purkinje cells are found within the Purkinje layer in the cerebellum. Purkinje cells are aligned like dominos stacked one in front of the other. Their large dendritic arbors form nearly two dimensional layers through which parallel fibers from the deeper-layer granule cells pass. These parallel fibers make relatively weaker excitatory (glutamatergic) synapses to spines in the Purkinje cell dendrite, whereas climbing fibers originating from the inferior olivary nucleus in the medulla provide very powerful excitatory input to the proximal dendrites and cell soma. Parallel fibers pass orthogonally through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers forming a synapse with a single Purkinje cell. Alternatively, each Purkinje cell only receives a synapse from a single climbing fiber. Both basket and stellate cells (found in the cerebellar molecular layer) provide inhibitory (GABAergic) input to the Purkinje cell, with basket cells synapsing on the Purkinje cell body and stellate cells onto the dendrites.

Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all motor coordination in the cerebellar cortex.

Electrophysiological activity

Purkinje cells show two distinct forms of electrophysiological activity.

Simple spikes occur when mossy fibers activate granule cell parallel fibers via amplitude-invariant, "all or nothing" action potential propagation. Simple spikes occur spontaneously at rates of 50 - 150/s.

Complex spikes are large, amplitude variant (gradient), plateau-potentials caused by climbing fiber activation, and involve the generation of calcium-mediated action potentials in the dendrites. During complex spike activity simple spikes are suppressed or washed-out by the powerful complex spike input.

Purkinje cells show spontaneous electrophysiological activity in the form of bursts, which may be important for cerebellar function. Climbing fiber activation of the Purkinje cell can shift its activity from a quiet state to a spontaneously bursting state, and vice-versa, serving as a type of switch.

Purkinje cells also release endocannabinoids that modulate both excitatory and inhibitory synapses.

Medical conditions related to Purkinje cells

In some domestic animals, a condition where the Purkinje cells begin to atrophy shortly after birth, called Cerebellar Abiotrophy, can lead to symptoms including ataxia, intention tremors, hyperreactivity, lack of menace reflex, stiff or high-stepping gait, apparent lack of awareness of where the feet are (sometimes standing or walking with a foot knuckled over), and a general inability to determine space and distance. A similar condition known as cerebellar hypoplasia occurs when Purkinje cells either fail to develop in utero or die off in utero prior to birth.

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