The peripheral nervous system

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Spinal Cord

Hospital Corpsman Revised Edition

The autonomic nervous system

PERIPHERAL NERVOUS SYSTEM
The peripheral nervous system (PNS) consists of the nerves that branch out from the CNS and connect it to the other parts of the body. The PNS includes 12 pairs of cranial nerves and 31 pairs of spinal nerves. Cranial and spinal nerves carry both voluntary and involuntary impulses.

Cranial Nerves
The 12 pairs of cranial nerves are sensory, motor, or mixed (sensory and motor). Table 1-3 shows the 12 cranial nerves and parts of the body they service.

Spinal Nerves
There are 31 pairs of spinal nerves that originate from the spinal cord. Although spinal nerves are not named individually, they are grouped according to the level from which they arise, and each nerve is numbered in sequence. Thus, there are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves, and 1 pair of coccygeal nerves. See figure 1-46.

Spinal nerves (mixed) send fibers to sensory surfaces and muscles of the trunk and extremities. Nerve fibers are also sent to involuntary smooth muscles and glands of the gastrointestinal tract, urogenital system, and cardiovascular system.

Figure 1-45.-Cross section of the spinal cord and reflex arc-arrows and numbers show impulse pathway.