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Nervous tissue consists of two principal types of cells: nerve cells (neurons) and supporting cells.
The neuron or nerve cell is the functional unit of the nervous system. All neurons have a cell body and processes, the axon and dendrites.
The cell body of a neuron contains the nucleus and those organelles that maintain the nerve cell.
Most neurons have only one axon, usually the longest process extending from the cell; some axons may be more than 1 meter long. A neuron usually has many dendrites, processes that are shorter and usually thicker that an axon.
Neurons are classified on the basis of the number of processes extending from the cell body. Thus:
1. Multipolar neurons have only one axon and two or more dendrites
2. Bipolar neurons have one axon and one dendrite
3. Unipolar (actually pseudounipolar) neurons have one process the axon that divides close to the cell body into two long processes.
Figure 31. Diagram of a motor neuron
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