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Peripheral nervous system

The peripheral nervous system or PNS, is part of the nervous system, and consists of the nerves and neurons that reside or extend outside the central nervous system--to serve the limbs and organs, for example. The peripheral nervous system is further divided into the somatomotoric nervous system and the autonomic nervous system.

Nerves

  • Cranial nerves originate from the brainstem, and mainly control the functions of the anatomic structures of the head.
  • Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the body. In humans, there are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. The naming convention for spinal nerves is to name it after the vertebra immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertabra and 8 cervical spinal nerves.
    • The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that subserve the neck and back of head.
    • The last 4 cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1,combine to form the brachial plexus, a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the arm and upper back. Although the brachial plexus may appear tangled, it is highly organized and predictable, with little variation between people. See brachial plexus injuries[?].



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