Term: pyramidal cell

Definition: Pyramidal cells are similar to vertical fusiform cells in most respects. They have a vertically elongated cell body, about 15 micrometers in transverse diameter, in the deeper half of the zone of vertical cells. The dendritic field is narrow and cylindrical, 100 to 250 micrometer in diameter, and extends from the upper margin of the zone of horizontal cells to the lower margin of the zone of vertical cells, about 500 micrometers. Rather than having superficial and deep fields, the pyramidal cell has the deep field reduced to a circumsomatic field, or a diminuitive basal field, and the superficial field is relatively elongated to accord with the deeper cell body. Pyramidal cells are usually multipolar, with one or two thick apical dendrites, which branch several times on the way to the surface, particularly in the upper portion of the zone of horizontal cells, and several smaller dendrites which form a small field about the cell body. It is of interest that smooth pyramidal cells tend to have two primary dendrites, like smooth vertical fusiform cells. The axon takes its origin from the soma or a low order dendrite and runs down into the deep zones. It is smooth and thin, about like that of the vertical fusiform cells.