Cranial nerves are peripheral nerves associated with the brain and, thus, provide sensory, motor, and autonomic innervation to the head and parts of the body.
They share many similarities with peripheral nerves that emerge from the spinal cord. Most cranial nerves exit the central nervous system (CNS) at the level of the brainstem (Fig. 14-1). Two cranial nerves (i.e., the olfactory [I] and optic [II]) enter the CNS at the level of the forebrain. Only one cranial nerve, the accessory nerve (cranial nerve [CN] XI), does not emerge from the brain. Instead, it emerges from the spinal cord.