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11-6. TYPES OF NEURONS

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.

c. According to Function.

(1) Sensory neurons. In sensory neurons, impulses are transmitted from receptor organs (for pain, vision, hearing, etc.) to the central nervous system (CNS).

(2) Motor neurons. In motor neurons, impulses are transmitted from the CNS to muscles and glands (effector organs).

(3) Interneurons. Interneurons transmit information from one neuron to another. An interneuron "connects" two other neurons.

(4) Others. There are other, more specialized types, for example, in the CNS.

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