Connecting the CNS to all parts of the body are individual organs known as nerves.
A nerve is a collection of neuron processes together and outside of the CNS.
Peripheral nerves are nerves which pass from the CNS to the periphery of the body.
Together, they are referred to as the peripheral nervous system (PNS).
Page 2 Peripheral Nerves
These nerves are bilateral and segmental.
Bilateral nerves are peripheral nerves that occur in pairs.
In each pair, there is one nerve to the right and one to the left.
Segmental nerves are pairs of peripheral nerves that occur in intervals, corresponding to the segments of the human embryo.
Page 3 Cranial Nerves
Peripheral nerves connected to the brainstem are called cranial nerves.
They are numbered from I through XII and also have individual names.
Page 4 Spinal Nerves
Peripheral nerves connected to the spinal cord are called spinal nerves.
They are identified by a letter representing the region of the vertebral column and a
number representing the sequence in the region:
(1) Cervical: C-1 through C-8.
(2) Thoracic: T-1 through T-12.
(3) Lumbar: L-1 through L-5.
(4) Sacral: S-1 through S-5.
Thus, there are 31 pairs of spinal nerves.