Trigeminal nerve: The chief nerve of sensation for the face, which is also the motor nerve that controls the muscles used for chewing. Problems with the sensory part of the trigeminal nerve result in pain or loss of sensation in the face. Problems with the motor root of the trigeminal nerve result in deviation of the jaw toward the affected side and trouble chewing. The trigeminal nerve is the fifth cranial nerve.
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Last Editorial Review: 3/19/2012