The cranial nerves are 12 sets of nerves that arise from the brain and not the spinal cord.The cranial nerves serve multiple functions mostly in the area of the face.  They are responsible for smell, sight, taste, sensation of the face, muscle movement of the face, and hearing.

Cranial nerve 1 - Olfactory

The olfactory nerve is responsible for the sense of smell.

How is it tested? Place a smelly object (a lemon or a dirty sock) under the nose with the eyes closed.  The patient should be able to recognize that a smell is present.  The patient's ability to determine the source of the smell (a dirty sock) is less important.

Cranial nerve 2 - Optic

The optic nerve is responsible for the sense of sight.  Lesions of this nerve can cause full or partial blindness.

How is it tested? Using a wall eye chart, determine the visual acuity (how sharp images appear far away).  Also, having the patient look directly forward, check the ability to see things at an angle (peripheral vision). With an opthalmoscope (the doctor's eye-looking device), look within the eye at the optic disk.  Does the disk have sharp borders or are they raised and blurry (from papilloedema).

Cranial nerve 3 - Oculomotor

The oculomotor nerve is responsible for movement of the eyelids, dilation of the pupil, and coordinated movement of the eyes.

How is it tested? Is one of the eyelids drooping?  Do the eyeballs move in all four directions (up, down, left, and right) together?  Are the pupils the same size?  Do both pupils shrink when light is shined at the eye?

Cranial nerve 4 - Trochlear

The trochlear nerve is responsible for rotation of the eyeballs.

How is it tested? Do the eyeballs move in all four directions (up, down, left, and right) together?

Cranial nerve 5 - Trigeminal

The trigeminal nerve is responsible for sensation of the face and movement of the chewing muscles.

How is it tested? With the eyes closed, can the patient feel light touch on both sides of the face?   Does the patient have difficulty chewing?

Cranial nerve 6 - Abducens

The abducens nerve is responsible for movement of the eyes to the side.

How is it tested? Do the eyeballs move in all four directions (up, down, left, and right) together?

Cranial nerve 7 - Facial

The facial nerve is responsible for the muscles of the fac.

How is it tested?  Does the face appear symmetric when the patient smiles or frowns? Can the patient whistle or "pucker" the lips?

Cranial nerve 8 - Vestibulocochlear

The vestibulocochlear nerve is responsible for the sense of hearing and balance.

How is it tested? Can the patient hear with both ears?  Does the patient have normal balance? Can the patient stand on one foot?

Cranial nerve 9 - Glossopharyngeal

The glossopharyngeal nerve is responsible for the sense of taste and movement of the tongue.

How is it tested? Can the patient taste the difference between sour, sweet, and bitter?  When the patient opens her mouth and says "Ahhhh..." does the roof of the mouth move up symmetrically?  Does the tongue lean to one side?  Is there difficulty swallowing or eating?

Cranial nerve 10 - Vagus

The vagus nerve is responsible for movement of the laryngx and affects voice.

How is it tested? Is there unexplained hoarseness of the voice?  Is there difficulty swallowing or eating?

Cranial nerve 11 - Accessory

The accessory nerve is responsible for movement of the shoulder and some neck muscles.

How is it tested? Can the patient "shrug" the shoulders?  Do both shoulders rise equally?

Cranial nerve 12 - Hypoglossal

The hypoglossal nerve is responsible for movement of the tongue.

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