Neurons may be identified according to shape, diameter of their processes, or function.
a. According to Shape. A pole is the point where a neuron process meets the cell body. To determine the type according to shape, count the number of poles.
(1) Multipolar neurons. Multipolar neurons have more than two poles (one axon and two or more dendrites).
(2) Bipolar neurons. Bipolar neurons have two poles (one axon and one dendrite).
(3) Unipolar neurons. Unipolar neurons have a single process which branches into a T-shape. One arm is an axon; the other is a dendrite.
b. According to Diameter (Thickness) of Processes. Neurons may be rated according to the thickness of myelin surrounding the axon. In order of decreasing thickness, they are rated A (thickest), B, and C (thinnest). The thickness affects the rate at which impulses are transmitted. The thickest are fastest. The thinnest are slowest.
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