Merck Manual

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Testing Cranial Nerves

Testing Cranial Nerves

Cranial Nerve Number

Name

Function

Test

1st

Olfactory

Smell

The ability to smell is tested by asking the person to identify items with very specific odors (such as soap, coffee, and cloves) placed under the nose. Each nostril is tested separately.

2nd

Optic

Vision

The ability to see is tested by asking the person to read an eye chart. Peripheral (side) vision is tested by asking the person to look straight ahead while the doctor gradually moves a finger toward the person's center of vision from above, below, left, and right. The person is then asked to say when the finger is first seen.

Detection of light

The ability to detect light is tested by shining a bright light (as from a flashlight) into each pupil in a darkened room.

3rd

Oculomotor

Eye movement upward, downward, and inward

The ability to move each eye up, down, and inward is tested by asking the person to follow a target moved by the examiner.

Narrowing (constriction) or widening (dilation) of the pupil in response to changes in light

The pupils’ response to light is checked by shining a bright light (as from a flashlight) into each pupil in a darkened room.

Raising the eyelids

The upper eyelid is checked for drooping (ptosis).

4th

Trochlear

Eye movement downward and inward

The ability to move each eye down and inward is tested by asking the person to follow a target moved by the examiner.

5th

Trigeminal

Facial sensation

Sensation in areas of the face is tested using a pin and a wisp of cotton.

The blink reflex is tested by touching the cornea of the eye with a cotton wisp.

Chewing

Strength and movement of muscles that control the jaw are tested by asking the person to clench the teeth and open the jaw against resistance.

6th

Abducens

Eye movement outward

The ability to move each eye outward beyond the midline is tested by asking the person to look to the side.

7th

Facial

The ability to move muscles in the face (for example, in facial expressions), taste in the front two thirds of the tongue, production of saliva and tears, and control of a muscle involved in hearing

The ability to move the face is tested by asking the person to smile, to open the mouth and show the teeth, and to close the eyes tightly.

Taste is tested using substances that are sweet (sugar), sour (lemon juice), salty (salt), and bitter (aspirin, quinine, or aloes).

8th

Auditory (vestibulocochlear)

Hearing

Hearing is tested with a tuning fork or with headphones that play tones of different frequencies (pitches) and loudness (audiometry).

Balance

Balance is tested by asking the person to walk a straight line.

9th

Glossopharyngeal

Swallowing, the gag reflex, and speech

Because both the 9th and 10th cranial nerves control swallowing and the gag reflex, they are tested together.

The person is asked to swallow. The person is asked to say “ah-h-h” to check movement of the palate (roof of the mouth) and uvula (the small, soft projection that hangs down at the back of throat).

The back of the throat may be touched with a tongue blade, which evokes the gag reflex in most people.

The person is asked to speak to determine whether the voice sounds nasal (another test of palate movement).

10th

Vagus

Swallowing, the gag reflex, and speech

Control of muscle in some internal organs and the heart rate

This function is not tested as part of the cranial nerve examination.

11th

Accessory

Neck turning and shoulder shrugging

The person is asked to turn the head and to shrug the shoulders against resistance provided by the examiner.

12th

Hypoglossal

Tongue movement

The person is asked to stick out the tongue, which is observed for deviation to one side or the other.