TREATMENT OF FACIAL PARALYSIS
What is a Smile?
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, in dryness of the eye or the mouth, or in disturbance of taste.
The anatomy of the facial nerve is very complex. The facial nerve passes through the base of the skull in transit from the brain to the muscles of facial expression. After leaving the brain, the facial nerve enters the bone of the ear (temporal bone) through a small bony tube (the internal auditory canal) 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 gland in the face (parotid gland) and divides into many branches, which supply the various facial muscles. The facial nerve gives off many branches as it courses through the temporal bone: to the tear gland, to the stapes muscle, to the tongue (for taste sensation), and to the saliva glands.
1 American Academy of Otolaryngology-Head & Neck Surgery
The facial nerve exits the skull behind the ear at stylomastoid foramen and enters the core of a salivary gland in front of the ear (parotid gland). The Facial nerve divides into an upper and lower division within the parotid gland. It further divides into 5 main branches including the frontal, zygomatic, buccal, marginal mandibular and platysmal. There is extensive arborization of the facial nerve branches and significant variations exist in different individuals. Major types and percentages of a facial nerve branching and anastomosis exists. In 13%, major divisions (temporal and facial) are independent; in 11%, anastomosis occur between rami of the temporal division; in 22%, connections occur between adjacent rami from the major divisions; in 21%, anastomosis representing a composite of those in the11% and 22% categories occur; in 12%, proximal anastomosis occur within the temporal component, as well as distal interconnection between the latter and the cervical component; in 9%, two anastomotic rami connect the buccal division of the cervical to the zygomatic part of the temporal; in 5%, a transverse ramus, from the trunk of the nerve, contributes to the buccal ramus formed by anastomosis between the two major divisions; in 7% richly plexiform communications occur, especially within the temporal portion of the nerve. Variations of the facial nerve include branches that pass through clefts in superficial veins or the formation nerve loops through which pass superficial veins. Redrawn from McCormack, L.J., Cauldwell, E. W. and Anson. The surgical anatomy of the facial nerve with special reference to the parotid gland. Surg. Glynecol. Obstet. 80:620-630, 1945, and from Dargent, M. and P.E. Duroux. Donnees anatomiques concernant la morphologie et certains rapports du facial intra-parotidien. La Presse medicale No. 37, pp. 523-524,1946.
