cranial nerve
any of the 12 pairs of nerves that arise directly from the brain and are distributed mainly to structures in the head and neck. Some of the cranial nerves are sensory, some are motor, and some are mixed (i.e., both sensory and motor). Cranial nerves are designated by Roman numerals, as follows: I, olfactory nerve; II, optic nerve; III, oculomotor nerve; IV, trochlear nerve; V, trigeminal nerve; VI, abducens nerve; VII, facial nerve; VIII, vestibulocochlear nerve; IX, glossopharyngeal nerve; X, vagus nerve; XI, accessory nerve; and XII, hypoglossal nerve.