Term: vertical fusiform cell

Definition: Vertical fusiform cells have narrow, cylindrical, vertically oriented dendritic fields and generally an elongated cell body, fusiform in its vertical axis. Both the cell body and the dendritic field vary in their dimensions depending upon the particular type of vertical fusiform cell. There are three types of vertical fusiform cells. All have dendritic fields 100 to 200 micrometers wide, with the more superficial cells having narrower fields. The cell bodies of vertical fusiform cells may be bipolar, with ascending and descending trunks or they may be multipolar. The most common configuration is of two ascending dendritic trunks and two descending dendritic trunks. The bipolar vertical fusiform cells are usually smooth cells and the multipolar vertical fusiform cells are usually spiny. The smooth vertical fusiform cells have thinner dendrites that branch less frequently, thus are less voluminous. The dendrites which arise from the superficial surface of the vertical fusiform cell soma are the principal source of the superficial field, and those which arise from the deep surface are the principal source of the deep field, but frequently branches from one of the primary dendrites will contribute to the other field. Usually the deep dendrites turn superficially. In the extreme case the entire deep field will turn to extend superficially. The axon of vertical fusiform cells commonly arises from one of the low order dendrites. It runs deep toward the ganglion zone of the superior colliculus. A few cells have local distributions which may extend throughout the depth of the superficial zones. The axon is similar to other intrinsic axons but thicker than those of the marginal or horizontal cells.