(1) The peripheral nervous system (PNS) is that portion of the nervous system generally concerned with commands for skeletal muscles and other muscles made up of striated muscle tissue, as well as sensory information from the periphery of the body. The sensory information is carried to the CNS where it is processed. The PNS carries commands from the CNS to musculature.
(2) A nerve is a collection of neuron processes, together and outside the CNS. (A fiber tract is a collection of neuron processes, together and inside the CNS.)
b. General Characteristics of the Peripheral Nerves. The PNS is made up of a large number of individual nerves. These nerves are arranged in pairs. Each pair includes one nerve on the left side of the brainstem or spinal cord and one nerve on the right side. The nerve pairs are in a series, each pair resembling the preceding, from top to bottom.
c. Categories of PNS Nerves. PNS nerves include cranial nerves and spinal nerves.
(1) Cranial nerves. The 12 pairs of nerves attached to the right and left sides of the brainstem are called cranial nerves. Each cranial nerve is identified by a Roman numeral in order from I to XII and an individual name. For example, the Vth ("fifth") cranial nerve is known as the trigeminal nerve (N.).
TRI = three
GEMINI = alike
TRIGEMINAL = having three similar major branches
(2) Spinal nerves. Attached to the sides of the spinal cord are 31 pairs of spinal nerves. The spinal nerves are named by:
(a) The region of the spinal cord with which the nerve is associated.
(b) An Arabic numeral within the region. For example, T-5 is the fifth spinal nerve in the thoracic region.
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