Cell Types

Abstract

Pyramidal cells include a variety of morphological types that have the following features in common: A single, dominant apical dendrite, larger in diameter than the other dendrites, which usually extends vertically from the cell body toward the pial surface, and several basal dendrites, which radiate more or less horizontally from the base of the cell body (Figure 2.1). All the dendrites of pyramidal cells bear spines that tend to occur with greatest frequency in the middle regions of the dendrite (Globus and Scheibel, 1967). For a review of the possible role of spines in synaptic transmission and plasticity, see Coss and Perkel (1985) and Rall and Segev (1987). The axon of a pyramidal cell originates typically from the base of the cell body, or less frequently from the proximal portion of a basal dendrite, and projects into the white matter, giving off collateral branches on the way. Pyramidal cells with axons that do not enter the white matter have been observed in the cat, monkey, and human; in these instances the output of the pyramidal cell is presumed to be entirely local or to adjacent cortical areas (see Feldman, 1984; p. 161; Katz, 1987).

Cortical neurons are classified into two broad morphological categories: pyramidal, and stellate or nonpyramidal (e.g., Peters and Jones, 1984).