Figure 111

Diagram of a motor neuron. The perikaryon, dendrites, and initial part of the axon are within the CNS. The axon leaves the CNS and, while in the PNS, is part of a nerve (not shown) as it courses to its effectors (striated muscle). In the CNS, the myelin for the axon Is produced by, and is part of, an oligodendrocyte; in the PNS, the myelin is produced by, and is part of, a Schwann cell. (Adapted from Jun-queira LC, Carneiro J, Kelley RO. Basic Histology. 9th ed. Norwalk, CT: Appleton & Lange, 1998.)

cialized terminal (synapse), that makes contact with another neuron or an effector cell (e.g., a muscle cell or glandular epithelial cell). A neuron usually has many dendrites, shorter processes that transmit impulses from the periphery (i.e., other neurons) toward the cell body.

Neurons are classified on the basis of the number of processes extending from the cell body (Fig. 11.2):

• Multipolar neurons have one axon and two or more dendrites.

• Bipolar neurons have one axon and one dendrite.

• Unipolar (actually pseudounipolar) neurons have one process, the axon, which divides close to the cell body into two long processes. The vast majority of unipolar neurons are located in the dorsal root ganglia and cranial nerve ganglia.

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