Cranial Nerves
There are a total of 12 pairs of cranial nerves. These are bundles of nerve fibres that leave the CNS above the spinal cord. Except for the vagus nerve or parasympathetic nerve, which extends into the abdominal cavity, the cranial nerves supply the head and neck region. Since the cranial nerves carry very long and cumbersome names, they were numbered consecutively with Roman numerals for simplicity's sake.
A further differentiation depends on the function of the cranial nerves. The nerve pairs I and II and VIII are sensory cranial nerves. They thus pass on sensations from the various sensory organs to the brain.
The nerve pairs III / IV / VI / XI and XII work arbitrarily motorically.
Nerves which work arbitrarily motorically, sensory and parasympathetically are called mixed cranial nerves. They include the cranial nerves V / VII / IX and X.