Figure 113

Schematic diagram showing arrangement of motor and sensory neurons. The cell body of a motor neuron is located in the ventral (anterior) horn of the gray matter of the spinal cord. Its axon, surrounded by myelin, leaves the spinal cord via a ventral (anterior) root and becomes part of a spinal nerve that carries it to its destination on striated (skeletal) muscle fibers. The sensory neuron originates in the skin within a receptor (here, a Pacinian corpuscle) and continues as a component of a spinal nerve, entering the spinal cord via the dorsal muscle

(posterior) root. Note the location of its cell body in the dorsal root ganglion (sensory ganglion). A segment of the spinal nerve is enlarged to show the relationship of the nerve fibers to the surrounding connective tissue (endoneurium, perineurium, and epineurium). In addition, segments of the sensory and motor neurons have been enlarged to show the relationship of the axons to the Schwann cells and myelin. (Autonomic nerve fibers are not shown in the diagram.)

True bipolar neurons are limited to the retina of the eye and the ganglia of the vestibulocochlear nerve (cranial nerve VIII) of the ear

Neurons associated with the receptors for the special senses (taste, smell, hearing, sight, and equilibrium) often do not fit the above generalizations. For example, the amacrine cells of the retina have no axons, and the olfactory receptors resemble neurons of primitive neural systems, in that they retain a surface location and remain a slowly renewing cell population.

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