The facial nerve is the seventh of 12 pairs of cranial nerves. Cranial nerves run from the back of the brain and control everything from voluntary facial expressions to involuntary actions related to the senses. The facial nerve begins at the base of the brain, in the brain stem, and travels a long, twisted path through the facial bones, with five major branches that control the facial features and facial expressions. Damage or inflammation to this nerve at any point along this path can result in partial paralysis, which is usually temporary, but may be permanent in some circumstances.
There are two facial nerves, one on the left side of the face and one on the right. Each divides into five branches as it travels across the face, from back to front. These branches, from top to bottom, are called the temporal branch, the zygomatic branch, the buccal branch, the marginal mandibular branch, and the cervical branch. Together, they control the muscles responsible for facial movements such as smiling, blinking, and wrinkling of the forehead. They also carry sensory input to the brain from the eyes, nose, ears, tongue, and skin.
Because these nerves travel a fairly long distance and branch out, there are several areas where damage may result in impaired function, or paralysis, of part or all of the face. Any type of tumor on the face or side of the head may compress the nerve, resulting in paralysis of the side of the face where the tumor is located. A stroke, which is a blood clot in the brain, may disrupt its function, also resulting in paralysis. In fact, one-sided facial paralysis is often the first and most notable symptom of a stroke. Physical trauma, such as a motor vehicle accident or sports injury, may also cause swelling of the face and paralysis of part or all of the nerve.
Facial nerve paralysis can also be caused by disease processes that cause irritation or inflammation along the nerve pathways. Lyme's disease can cause facial paralysis if it spreads to the nervous system. Bell's palsy is another cause of facial paralysis; recent research suggests that it may be caused by the herpes simplex virus, which is the virus that causes cold sores. Many cases of Bell's palsy resolve on their own, with no noticeable loss of nerve function. Ramsey Hunt syndrome is another condition that can cause facial paralysis; it is linked to the herpes zoster, or shingles, virus.
When a patient experiences partial or full paralysis of the face, there are several procedures a doctor may use to treat the condition. A CT or MRI scan will often be done to check for stroke, tumor, or other areas of the nerve that may be inflamed. Nerve conduction studies help to determine which portion of the nerve is damaged. Treatment for facial paralysis depends on its cause; sometimes, it is treated conservatively with steroids or anti-inflammatory medications. In cases where a tumor or other blockage is causing the paralysis, surgery may be necessary to restore function.