The facial nerve resembles a telephone cable and contains 7,000 individual nerve fibers. Each fiber carries electrical impulses to a specific facial muscle. Information passing along the fibers of this nerve allows us to laugh, cry, smile, or frown, hence the name, “the nerve of facial expression.”
When half or more of these individual nerve fibers are interrupted, facial weakness occurs. If these nerve fibers are irritated, then movements of the facial muscles appear as spasms or twitching. The facial nerve not only carries nerve impulses to the muscles of the face, but also to the tear glands, to the saliva glands, and to the muscle of the stirrup bone in the middle ear (the stapes). It also transmits taste from the front of the tongue.
Since the function of the facial nerve is so complex, many symptoms may occur when the fibers of the facial nerve are disrupted. A disorder of the facial nerve may result in twitching, weakness, or paralysis of the face, dryness of the eye or the mouth, or disturbance of taste.
The facial nerve passes through the base of the skull in transit from the brain to the muscles that control facial expressions. After leaving the brain, the facial nerve enters the temporal bone through the internal auditory canal, a small bony tube, in very close association with the hearing and balance nerves. Along its inch-and-a-half course through a small canal within the temporal bone, the facial nerve winds around the three middle ear bones, in back of the eardrum, and then through the mastoid (the bony area behind the part of the ear that is visible).
After the facial nerve leaves the mastoid, it passes through the salivary or parotid gland and divides into many branches. The facial nerve has four components with several distinct functions: facial expression, taste sensation, skin sensation, and saliva and tear production.
Infections, injuries, or tumors can cause facial nerve disorders, but the most common cause of facial weakness is Bell’s palsy. This disorder, which often comes on suddenly and reaches its peak within 48 hours, is probably due to the body’s response to a virus. When there is a virus, the facial nerve within the ear (temporal bone) swells, and this pressure on the nerve in the bony canal damages it.
The paralysis is likely to affect only one side of the face, but in rare cases it affects both sides of the face at once. Bell’s palsy may last from two to three weeks or longer. An early sign of improvement, such as getting a sense of taste back, is often a good indication that there will be a complete recovery.
Since otolaryngologists—head and neck surgeons have special training and experience in managing facial nerve disorders, they are the most qualified physicians to perform an in-depth evaluation of abnormal movement or paralysis of the face. An evaluation will include an examination of the head, neck, and ears, as well as a series of tests.
Some of the most commonly used tests are:
The results of diagnostic testing will determine treatment. The goal of the treatment is to eliminate the source of the nerve damage. Patients with less nerve damage have better chances of recovery. Medications are often used as part of the treatment:
What treatments are recommended for permanent facial paralysis?
Patients with a permanent facial paralysis may be rehabilitated through a variety of procedures including:
How does the facial nerve affect the health of the eye?
Remember, when the facial nerve is paralyzed, considerable attention must be given to maintaining a healthy eye through a constant flow of tears. Tears are spread out over the eye by blinking. Since blinking is diminished or eliminated when facial nerve paralysis is present, special care must be given to prevent drying, erosion, and ulcer formation on the cornea which may result in possible loss of the eye.
What are the common signs or symptoms?
Tips to help recovery
Reprinted with permission of the American Academy of Otolaryngology-Head and Neck Surgery Foundation, copyright © 2008. All rights reserved.