The trigeminal nerve is one of 12 pairs of nerves that are attached to the brain and it is the largest nerve supplying various parts of head and face.
It has three branches which carry sensations from head and face to the brain. The upper branch covers scalp, forehead, and vertex of head, middle branch covers the cheek, upper jaw and upper lip, upper teeth and gums, and side of the nose. The lower branch covers lower jaw, lower lip, and lower teeth and gums.
One or more branches can be affected at the same time. The site of pain depends upon which branch is affected. Very rarely both sides of the face are affected.