Purkinje cells

Morphology and Location

The cerebellar cortex has a strictly ordered three-layered structure. Purkinje cells are located in the ganglionic layer, between the outer molecular layer and the inner granular layer.

• Cell bodies: the largest in the cerebellar cortex, specific pear-shaped; located in a single row within the Purkinje cell layer.
• Dendrites: form an extensive dendritic tree, densely branching, extending outwardly, weaving into the molecular layer and stretching perpendicularly to the longitudinal axis of the cerebellar folium.
• Axons: descend through the granular layer into the white matter of the cerebellum.

Afferent Connections (Inputs)

Purkinje cells are the final stage of a complex polysynaptic pathway in the cerebellar cortex. Several types of fibers terminate on their dendrites and cell bodies:

• Climbing (climbing-like) fibers: originate from the inferior olive. They ascend into the molecular layer, where they directly wrap around and form multiple synapses with the dendrites of Purkinje cells; they exert an excitatory effect, with aspartate as the neurotransmitter.
• Parallel fibers: represent the axons of granule cells, which receive signals from mossy fibers. They form excitatory synapses on the dendrites of Purkinje cells, with glutamate as the neurotransmitter. Approximately 200,000 parallel fibers converge on a single Purkinje cell.
• Inhibitory interneurons: basket cells, stellate cells, and Golgi cells are classified as inhibitory interneurons. These inhibitory interneuronal cells inhibit Purkinje cells, with GABA as the neurotransmitter. The processes of basket cells wrap around the bodies of Purkinje cells, forming a characteristic "basket".

Quantitative ratio: excitatory neurons numerically dominate in the cerebellar cortex. There are approximately 1,600 granule cells, 5 stellate cells, and 0.3 Golgi cells per 1 Purkinje cell.

Efferent Function and Mechanism of Action

Purkinje cell axons are the sole type of outgoing efferent fibers from the cerebellar cortex.

• Direction: most axons project to the deep cerebellar nuclei. Exception: efferent fibers from the vestibulocerebellar cortex do not synapse in the deep nuclei, but project directly to nervous system structures outside the cerebellum.
• Integration mechanism: two streams of signals are compared within the deep cerebellar nuclei. Primary information arrives directly from the collaterals of afferent pathways, while modulated information arrives from the cerebellar cortex as inhibitory signals from Purkinje cells. By releasing GABA, Purkinje cells inhibit the neurons of the cerebellar nuclei.
• Recurrent inhibition: Purkinje cells serve as an example of neurons involved in recurrent inhibition. In this process, a copy of the impulse travels via an axon collateral to an intercalated inhibitory neuron, which becomes activated and exerts a suppressive effect on the same nerve cell.

Clinical Significance and Age-Related Changes

Since the primary signal transmission to Purkinje cells is mediated by glutamate, in cerebellar lesions the administration of drugs — glutamate antagonists — predictably exacerbates its dysfunction.

In ontogeny: in middle and old age, there is a reduction in the total number of neurons. Purkinje cells in the cerebellum, along with giant pyramidal neurons—Betz cells—die most intensely. The mechanism of their cell death is apoptosis, triggered by the accumulation of irreparable cell damage: impaired blood flow, toxins, stress, and lipofuscin accumulation.

Do Not Confuse: Purkinje Cells in the Heart

The term "Purkinje fibers/cells" is also used to describe the cardiac conduction system. It contains three types of atypical cardiomyocytes: P cells, transitional cells, and Purkinje fibers.

Class and exam questions

What else to study on this topic

• Deep cerebellar nuclei
• Granule cells and parallel fibers
• Climbing and mossy fibers
• Conduction system of the heart

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.