The neurons, derivatives of the epithelium of the embryonic neural tube, greatly vary in appearance. In the cerebral cortex, most neurons are pyramidalshaped, whereas those in the spinal ganglia are round. The largest pyramidal cells in the motor cortex (Betz cells) measure up to 100 microns, whereas the granular cells of the cerebellar cortex measure only 5 microns. A neuron consists of (a) the cell body, or soma; (b) the dendrites, and (c) the axon (nerve fiber) (Fig. 2.1).

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