Definition of Cranial nerve, fifth

Cranial nerve, fifth: The fifth cranial nerve is the trigeminal nerve.

The trigeminal nerve is quite complex. It functions both as the chief nerve of sensation for the face and the motor nerve controlling the muscles of mastication (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 cranial nerves, the trigeminal nerve included, emerge from or enter the skull (the cranium), as opposed to the spinal nerves which emerge from the vertebral column. There are twelve cranial nerves.

The term "trigeminal" comes from the Latin "trigeminus" meaning "threefold," referring to the three divisions (ophthalmic, maxillary and mandibular) of this nerve.