The Facial Nerve and Its Function
The facial nerve is the 7th cranial nerve. It originates from the brain stem and traverses through the skull until it exits just behind the ear. After it exits the skull, the facial nerve divides into five main branches and further divides to innervate all of the facial muscles on one side of the face. Our facial muscles work intricately together to create a myriad of facial expressions including smiling, laughing, puckering to kiss or whistle, snarling, pouting, frowning, looking surprised, sad, angry or simply closing the eyes. When the facial nerve is injured, the result is a partial or full loss of movement on one side of the face.
The facial nerve also innervates glands that produce tears to lubricate the eyes and produces mucus to line the nasal passages and mouth. Thus, insult to the facial nerve can result in less tears in the affected eye, dry mouth on one side and less nasal secretions on one side.
Another function of the facial nerve is to supply a tiny muscle called the stapedius which stabilizes a tiny bone in the ear. It helps to regulate the loudness of the sounds that we hear. So when the facial nerve is injured, one may become highly sensitive to sounds. This is called hyperacusis.
As the facial nerve also supplies taste sensation to the anterior 2/3 of the tongue, injury to the facial nerve can result in altered sensation on one side of the tongue. Some patients report a “metallic” taste. All other sensations of the face are supplied by the trigeminal nerve (5th cranial nerve) and is not associated with injury to the facial nerve.
From a physical therapist perspective, it is imperative to evaluate all expressions of the face, the physical state of each of the many facial muscles, eye care in terms of dryness and eyelid opening or closure, functional difficulties in eating, drinking, dental/oral hygiene, speech and articulation as well as understanding the social, psychological and emotional difficulties that can result from facial palsy and asymmetrical facial expressions.
Facial Paralysis Conditions
Bell’s Palsy is the most commonly known cause of facial paralysis. However, the facial nerve may become partially or fully injured from many other conditions including:
- Bell’s Palsy
- Ramsay Hunt Syndrome
- Lyme Disease
- Congenital facial palsies
- Tumors – acoustic neuromas, facial nerve tumors, parotid tumors
- Trauma – skull fractures, facial lacerations, surgical procedures to the face, brain or skull area.
Depending on how severely the facial nerve is injured will determine how soon and how much recovery will occur.