The German scientist Jan Evangelista Purkinje discovered large, branching cells in the cortex of the cerebellum in 1837. The so-called Purkinje neurons have been fervently studied since that time by scientists hoping to obtain a better understanding of the cerebellum. Featured below is a low magnification montage (also at low resolution) of a rat cerebellum thin section. The Purkinje neurons are labeled red and the glia are labeled green.

Purkinje Neurons and Glia of Rat Cerebellum Specimen: Double fluorescent labeled thin section Technique: Two-Photon Microscopy

Purkinje neurons are some of the largest and most complex cells in the mammalian brain, possessing diameters almost as large as a human hair. Each of the cells exhibits an abundance of very active dendrites and is capable of receiving input from over 200,000 other cells. Yet, Purkinje neurons are the lone source of output from the cerebellum’s cortex. Their primary function is believed to be inhibitory, selectively suppressing and limiting excitatory impulses from other cells and crafting them into a coherent message that the rest of the brain can understand.

Various types of brain cells and fibers are involved with sending information to the Purkinje neurons, but the act is believed to be primarily achieved by mossy fibers and climbing fibers. Mossy fibers ascend from the brain stem and spinal cord dividing into numerous parallel rays to meet Purkinje cells. Almost a million of the parallel fibers may meet a single neuron. Climbing fibers, however, contact Purkinje cells on a one-on-one basis, although they also extend from the brain stem. Wrapping itself around the neuron and dendrites, a single climbing fiber can powerfully react with a Purkinje cell, resulting in the electrical firing known as a complex spike.