Nerves are found throughout the human body, and some of the most important nerves originate in the brain. Twelve cranial nerves exist in humans. Each nerve serves a sensory, motor, or dual function. The following make up the 12 cranial nerves: oculomotor, trochlear, abducens, accessory, hypoglossal, olfactory, optic, vestibulocochlear, facial, trigeminal, glossopharyngeal, and vagus.
Three of the aforementioned 12 cranial nerves operate primarily to receive stimuli from the outside environment, and are thus associated with the senses. The first such sensory nerve is the optic nerve, which transmits visual impulses to the brain that will ultimately help a person see. This cranial nerve is located in the optic canal. The nerve responsible for smell transmission — the olfactory nerve — is found in an area around the nasal cavity. These two nerves are the only two of the 12 cranial nerves that emerge from the cerebrum portion of the brain. Cranial nerves in the ear canals called vestibulocochlear nerves serve a dual function, as they carry sound impulses related to balance and hearing.
Of the 12 pairs of cranial nerves, five are motor nerves that help the brain direct the body’s movements. Eye motions are assisted by the oculomotor nerves, the trochlear nerves, and the abducens nerves, all of which are located in the orbital fissure of the skull. The latter originates in the pons of the brain, with the former two originating in the midbrain. The accessory and hypoglossal nerves send impulses from the brain that control upper body muscles and the tongue, respectively. These final motor nerves originate around the spine and the brain’s medulla.
The remaining four cranial nerves have both sensory and motor capacities. The trigeminal nerve derives from the pons, as does the facial nerve. Trigeminal nerves transmit facial impulses to the brain and send impulses to the mouth that help instigate chewing. Conversely, facial nerves send impulses from the brain that control facial movements and transmit impulses from the mouth to the brain. The medulla-located glossopharyngeal nerve helps the brain control muscles related to saliva production, swallowing, and the heart’s reflex, and it also carries impulses to the brain from the pharynx and mouth relating to taste. Finally, the medulla’s vagus nerve controls throat muscles and provides sensory information regarding temperature, pressure and taste.
Memorizing 12 distinct items can prove difficult. Therefore, many scholars have created a mnemonic for cranial nerves to help retain the information. One popular memory retention device involves composing a sentence in which each word contains the beginning letter or letters of each nerve. Some examples include “On Old Olympus's Towering Tops, A Fine-Vested German Viewed Some Hops” and “Old Opie Occasionally Tries Trigonometry and Feels Very Gloomy, Vague, and Hypoactive.”
