Cranial nerves are nerves that emerge directly from the the brainstem and supply the face and neck, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves (although an additional anterior pair of nerves, numbered 0, also exists). The first three pairs (including nerve 0) emerge from the cerebrum; the remaining ten pairs emerge from the brainstem. The cranial nerves are part of the peripheral nervous system (PNS), with the exception of cranial nerve II (the optic nerve), which is not a true peripheral nerve but a tract of the diencephalon leading to the retina; both the optic nerve and the retina are hence part of the central nervous system (CNS).
The axons of the remaining twelve nerves extend beyond the brain and are therefore considered part of the PNS.
The ganglia of the cranial nerves originate in the CNS.
They are the following:
the olfactory nerves (I),
the optic nerves (II),
the oculomotor nerves (III),
the trochlear nerves (IV),
the trigeminal nerves (V),
the abducens nerves (VI),
the facial nerves (VII),
the vestibulocochlear nerves (VIII),
the glossopharyngeal nerves (IX),
the vagus nerves (X),
the accessory nerves (XI), and the hypoglossal nerves (XII).
see Cranial nerve palsy.