Cranial nerves are a set of 12 nerve pairs that connect from the brain to areas of the face, neck, shoulders and some internal organs. The nerves run through holes in the skull. Each set of nerves are paired for service on each side of the body. Cranial nerves serve several functions in the nervous system. Some are responsible for delivering messages from sense organs, while others help control muscles or regulate internal organs. Damage may occur to one or more of the cranial nerves. Specific testing for each nerve signifies if a problem exists.
Olfactory Nerve
The first cranial nerve is the olfactory nerve. It is responsible for the sense of smell. To test for normal function of the olfactory nerve, each nostril sniffs specific smells, such as coffee or soap, according to the Merck Manual.
Optic Nerve
The optic nerve is the second cranial nerve. This nerve detects light and allows vision from the eye. Testing the optic nerve includes reading an eye chart, testing for peripheral vision and checking the eye's ability to see light by shining a bright light in it.
Oculomotor Nerve
The third cranial nerve, the oculomotor nerve, controls the upward, downward and inward movements of the eye. It also controls the movement of the pupil and opens the eyelids. Testing of the oculomotor nerve consists of directing the direction to move the eye, shining a light into the eye to watch the movement of the pupil and checking for a drooping eyelid.
Trochlear Nerve
The trochlear nerve is the fourth cranial nerve. This nerve controls the downward and inward movement of the eye. Checking the motor movement of the eye also determines proper functioning of the nerve.
Trigeminal Nerve
The fifth cranial nerve is the trigeminal nerve. The trigeminal nerve senses feeling on the face and is responsible for chewing movement. Testing this nerve includes touching different areas of the face with something soft and something sharp, like a pin, to check for sensation. Testing the muscles responsible for chewing includes clenching teeth together and attempting to open the mouth with resistance placed on the jaw.
Abducens Nerve
The abducens nerve controls the outward movement of the eye and is the sixth cranial nerve. Looking to the side without moving the head checks this nerve.
Facial Nerve
The facial nerve, the seventh cranial nerve, controls facial expressions, is responsible for the production of saliva and tears and senses taste on the front of the tongue. Testing the function of the facial nerve includes checking the ability to move areas of the face, including the mouth. The tongue is tested to see if it is able to perceive sour, salty, bitter and sweet tastes.
Vestibulocochlear Nerve
The vestibulocochlear nerve, also called the auditory nerve, allows for hearing and balance. This eighth nerve is tested by performing a hearing test and by attempting to walk a straight line while keeping balance.
Glossopharyngeal Nerve
The ninth cranial nerve, the glossopharyngeal nerve, controls swallowing, the gag reflex and speaking. Testing this nerve includes attempting to swallow, speak and invoking the gag by touching the back of the throat.
Vagus Nerve
The vagus nerve, the tenth cranial nerve, controls speaking, swallowing and gagging. This nerve also controls the muscles of internal organs, including the heart and lungs. Testing the function of this nerve is the same as for testing the glossopharyngeal nerve.
Accessory Nerve
The accessory nerve controls the muscle movements for turning the neck and shrugging the shoulders. Testing this eleventh cranial nerve includes turning the head and shrugging the shoulders.
Hypoglossal Nerve
The twelfth and final cranial nerve is the hypoglossal nerve. This nerve controls the movement of the tongue. Sticking out the tongue tests this nerve.
