DESCRIPTION and FUNCTION: The trigeminal nerve is the largest cranial nerve! The "tri" in trigeminal stands for THREE main branches or divisions: ophthalmic division (V1), maxillary division (V2) and mandibular division (V3). As major general sensory nerves of the face, this nerve transmits afferent impulses from touch, temperature, and pain receptors. Even though the mandibular division is the only one to contain motor fibers that innervate the massication (chewing) muscles, the trigeminal nerve is considered a mixed nerve. Interesting note: dentists desensitize upper and lower jaws by injecting a local anesthetic into the alveolar branches of maxiallary and mandibular divisions, respectively, so the surrounding tissues become numb!
ORIGIN and COURSE: The three divisions stem from the pons and run to the face. V1 is the superior branch which innervates the upper third portion of the face, V2 supplies the middle portion and V3 runs to the lower part of the face but also to the temporal region. See Figures 5A and 5B
CLINICAL TESTING: V1 is tested using the corneal refelx test: touching the cornea, anterior portion of eye, with wisp of cotton should elicit blinking. V2 sensory fibers are tested with a safety pin, hot and cold objects to the skin region innervated. V3 motor branch is assessed by asking the subject to clench his/her teeth, open mouth against resistance and move jaw side to side.
HOMEOSTATIC IMBALANCE: Trigeminal neuralgia, or tic douloureux (tik doo"loo-roo'), caused by inflammation of the trigeminal nerve, is widely considered to produce the most excruciating pain known. The stabbing pain may last for a few seconds to a minute, but it can occur up to a hundred times a day! Analgesics may be partially effective and in severe cases, surgery is performed to remove a compressing vessel or even destroy the nerve.