There are two ways that nerves exit the central nervous system and become part of the peripheral nervous system--through openings in the vertebrae of the spine or through openings in the skull, or cranium. Twelve cranial nerves conduct signals to and from the brain. All of them pass through various canals, or openings, in the skull.
Cranial Nerve 1
Cranial nerve 1, the olfactory nerve, is a sensory nerve that provides the sense of smell. It passes from the brain and into the nasal cavities through the cribiform plate, a part of the ethmoid bone that is perforated with numerous openings called foramen. The cribiform plate is in the skull at the top of the nasal sinuses.
Cranial Nerve 2
Cranial nerve 2, the optic nerve, is a sensory nerve that enables sight. The optic nerve passes through the back of the eye socket through an opening called the optic foramen.
Cranial Nerves 3, 4, 5 and 6
These nerves all pass through the superior orbital fissure, a foramen in the sphenoid bone at the rear of the eye socket.
Cranial nerve 3, the oculomotor nerve, is a motor nerve that controls muscles around the eye, as well as the ability of the pupil to respond to light changes. Cranial nerve 4, the trochlear nerve, controls one of the muscles that allow the eye to move. Cranial nerve 5, the trigeminal nerve, has three branches, one of which, the ophthalmic nerve, passes through the superior orbital foramen. The ophthalmic branch of the trigeminal nerve is a sensory nerve that serves the area around the eye, forehead and scalp. Cranial nerve 6, the abducent nerve, is a motor nerve that allows the eye to move laterally.
Cranial Nerve 5, Maxillary Branch
The maxillary branch of the trigeminal nerve, a sensory branch that supplies the upper lip, sinuses and palate, passes through the foramen rotundum, an opening in the middle of the skull.
Cranial Nerve 5, Mandibular Branch
The mandibular branch of the trigeminal nerve is both a sensory and motor nerve, supplying the muscles that allow chewing, and sensation to parts of the jaw, mouth and tongue. It exits the central nervous system through the foramen ovale, an opening in the base of the skull.
Cranial Nerve 7
Cranial nerve 7, the facial nerve, has both sensory and motor functions. It allows the sensation of taste, as well as sensing feeling around the ear. It supplies the face muscles, as well as the glands in the mouth and mucus membranes. The facial nerve exits the brain and passes through the internal auditory canal, also called the internal acoustic meatus, then travels through facial canal in the middle ear and finally passes through the stylomastoid foramen, an opening at the base of the skull.
Cranial Nerves 9, 10 and 11
These nerves pass through an opening called the jugular foramen, which is at the base of the skull and bounded by two bones, the temporal bone and the occipital bone. Cranial nerve 9, the glossopharyngeal nerve, detects taste, as well as sensation to the middle ear, auditory tube and other parts of the head. It also supplies motor signals to a muscle called the stylopharyngeal muscle. Cranial nerve 10, the vagus nerve, supplies sensory, motor and taste functions, and serves the larynx, pharynx and abdominal and chest organs. Cranial nerve 11, the accessory nerve, is a motor nerve that supplies two muscles, the sternocleidomastoid and the trapezius.
Cranial Nerve 12
Cranial nerve 12, the hypoglossal nerve, is a motor nerve that supplies most of the tongue muscles. It exits through the hypoglossal canal, a small opening at the base of the skull, located in the occipital bone.
