By Elizabeth A. Murray, Mount St. Joseph University
The cranial nerves control most functions in the head and neck. There are 12 pairs of cranial nerves that supply most structures in the head and neck. Let’s learn more about their functions.
The 12 Cranial Nerves
The cranial nerves are designated with Roman numerals I through XII as they come off the brain from anterior to posterior. However, it must be noted that not all cranial nerves control muscles.
Cranial nerve I is the olfactory nerve; II is the optic nerve; cranial nerve III is the oculomotor; IV is the trochlear nerve; cranial nerve V is the trigeminal; VI is the abducens nerve; VII is the facial nerve; VIII is the auditory nerve, also known as the vestibulocochlear; cranial nerve IX is the glossopharyngeal; X is the vagus nerve; XI is the spinal accessory, sometimes just called the accessory nerve; and cranial nerve XII is the hypoglossal.
In the Eye Muscles
There are a surprising number of small muscles throughout the head and neck. For example, there’s a set of six muscles in each eye orbit—the socket containing the eyeball—which move the eye in complex patterns important to our sight. These are muscles of great precision, but obviously of little strength, since their only job is to accurately coordinate movements between the two eyes for optimal vision.
Some of those muscles have an entire cranial nerve dedicated to them. In fact, of the 12 pairs of cranial nerves, two of the tiniest ones are solely devoted to controlling a single eye muscle each—cranial nerve IV, the trochlear nerve, and cranial nerve VI, the abducens nerve.
Another cranial nerve, number III, the oculomotor nerve, controls the other four muscles that steer the eyeballs, as well as the muscle that opens the upper eyelid.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Nerves in the Mouth
There are also numerous tiny muscles within the soft palate—that’s the fleshy portion of the posterior roof of the mouth—and many other muscles within the walls of the throat. Together, these aid in the voluntary phase of swallowing and in opening the eustachian tube to help equalize pressure in the middle ear, like when we are subject to altitude changes in a plane or a car going up a mountainside.
There are also many small muscles associated with the larynx, commonly called the voice box. These aid with breath holding and sound production. The vagus nerve, cranial nerve X, supplies most of these small muscles.
Neck Muscles
In the neck are a group of suprahyoid muscles that connect the hyoid bone to bones of the skull, and a group of infrahyoid muscles that connect the hyoid bone to the sternum, larynx, or pectoral girdle. The suprahyoid muscles elevate the hyoid bone and larynx during swallowing, and the infrahyoid muscles depress the hyoid bone and larynx.
Most of the suprahyoid muscles are supplied by cranial nerves, but the infrahyoid muscles are more inferior in the neck and are supplied by nerves of the cervical plexus—a group of ventral rami off spinal nerves C1 to C4.
For the Muscles on the Tongue
Also important to swallowing and speech, the tongue is essentially a group of muscles covered by mucous membrane, peppered with taste buds on its superior surface. The intrinsic muscles of the tongue give shape to the surface of the tongue, and extrinsic tongue muscles move the tongue in and out and left and right.
Some muscles of the tongue originate on bones of the skull, like the mandible or temporal bone; others take origin off the hyoid bone. Most muscles of the tongue are controlled by cranial nerve XII, the hypoglossal nerve, as glosso means “tongue”.
In the Ears
The two tiniest muscles in the body are inside the middle ear cavity—the tensor tympani and stapedius—and are attached to two of the small ossicle bones in the middle ear. These muscles aid hearing, as when the tensor tympani muscle contracts to protect us from many loud sounds.
The middle ear is a tiny chamber—an air-filled space that would hold just a few drops of fluid—but despite their close proximity, these two tiny muscles are each supplied by a different cranial nerve.
For the Face
There are several main groups of facial muscles to consider that are associated with the forehead and eyes, there’s a group around the mouth, and some odds and ends between. And as a group all muscles of facial expression are supplied by cranial nerve VII, the facial nerve.
But the trigeminal nerve—cranial nerve V—provides sensations from the face. The name trigeminal implies its three main branches, and each one supplies sensations from a portion of the face. Its ophthalmic branch supplies skin of the forehead and down the nose, mainly by the supraorbital nerve; the maxillary branch supplies skin of the cheeks by the infraorbital nerve, as well as being sensory to the upper teeth; and its mandibular branch supplies skin of the chin and lower face, mainly by the mental nerve, and is also sensory to the lower teeth.
So, facial skin is covered by a different cranial nerves than our facial muscles.
Common Questions about Cranial Nerves
There are 12 pairs of cranial nerves found in the human body that supply most structures in the head and neck.
Cranial nerve I is the olfactory nerve; II is the optic nerve; cranial nerve III is the oculomotor; IV is the trochlear nerve; cranial nerve V is the trigeminal; VI is the abducens nerve; VII is the facial nerve; VIII is the auditory nerve, also known as the vestibulocochlear; cranial nerve IX is the glossopharyngeal; X is the vagus nerve; XI is the spinal accessory, sometimes just called the accessory nerve; and cranial nerve XII is the hypoglossal.
Most muscles of the tongue are controlled by cranial nerve XII, the hypoglossal nerve, as glosso means “tongue”.
