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Lesson 5. The Peripheral Nervous System

2-5. THE PERIPHERAL NERVOUS SYSTEM

a. Connecting the CNS to all parts of the body are nerves. A nerve is a collection of neuron processes, grouped together, and located outside of the CNS. (Neuron processes, grouped together, and inside the CNS are the fiber tracts of the spinal cord.) Nerves outside the CNS are referred to as peripheral nerves, or the PNS. These nerves connect the CNS to the periphery of the body.

b. The PNS is made up of a large number of nerves arranged in pairs. Each pair includes one nerve for the left side of the body and one nerve for the right side.

(1) Peripheral nerves connected to the brainstem are called cranial nerves. They are numbered from I through XII and have individual names.

(2) Peripheral nerves connected to the spine are called spinal nerves. They are identified by a letter, representing the corresponding region of the vertebral column, and a number representing the sequence within the region. For example, L-5 is the fifth spinal nerve in the lumbar region.

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