Term: Purkinje neuron

Definition: According to Ramon y Cajal (1911), their cell bodies are between 35 and 65 micrometers in man. In the rat the cell bodies are 21 micrometers in diameter and 25 micrometers long on the average. There are 3.5 X 105 [Purkinje cells] in the rat (Armstrong & Schild, 1970). The cell bodies are arranged in a sheet one cell thick at the interface between the molecular and granular layers without any obvious pattern or clustering. In the rat Armstrong and Schild obtained a mean density of 1200 Purkinje cells per mm2 of Purkinje cell sheet by one methosd of counting, and by other method of counting a mean density of 1080 cell per mm 2. In Nissl preparations the cell body is characterized by its large, pale nucleus, an intensely basophilic nucleus, and scattered, rather small, polygonal Nissl bodies. The nucleolus of the Purkinje cell is an impressive, approximately spherical body usually lying near the center of the nucleus, but occasionally near the nuclear envelope. The dendritic tree of the Purkinje cell arises from one to four trunks that issue out of the apical pole of the cell body. The trunks extend directly outward or at an angle toward the surface of the folium, depending upon the location of the cell in the folium. The most remarkable characteristic of the Purkinje cell dendritic tree is its three-dimensional form. It is spread out in a vertical plane at right angles to the longitudinal axis of the folium, and is therefore displayed best in parasagittal sections. In this plane the tree extends to 300 to 400 micrometers, while in the longitudinal axis of the folium it is only 15 to 20 micrometers wide (see Fig. 10). The second remarkable characteristic of the Purkinje cell dendritic tree is its rich complement of thorns (Figs 7 and 23). The axon of the Purkinje cell arises from a barely perceptible projection on the basal pole of the soma. As Ramon y Cajal (1911) remarked, there is no clear line of demarcation between the cell body and the axon, as small granules of Nissl substance enter into the first part of the latter.