How to Test Cranial Nerves

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There are 12 pairs of cranial nerves that extend from the brain to parts of the head, face and trunk. They are identified by Roman numerals by their position and have names related to their function. Testing cranial nerves with simple tasks can determine which, if any, are injured or deficient.

Things You'll Need

  • Items with specific odors, such as mint, cloves or soap
  • Eye chart
  • Flashlight or penlight
  • Pin
  • Wisp of cotton
  • Sugar
  • Item with sour taste, such as lemon juice
  • Salt
  • Aspirin, quinine or something that tastes bitter
  • Tuning fork
  • Tongue depressor
  • CN I Olfactory: This nerve controls the sense of smell. Place a strong smelling item under each nostril individually and ask the person to identify it.

  • CN II Optic: This nerve controls vision. Display an eye chart to the test subject, and hold items to the side of their head to test their peripheral vision.

  • CN III Oculomotor: This controls eye movement upward, downward and inward, as well as narrowing and dilation of the pupils in response to light. Have the test subject follow a moving target, such as the tester's finger. Then shine a light in each pupil to test reaction to light.

  • CN IV Trochlear: This controls the movement of the eye downward and inward. Have the test subject follow a moving target with their eye.

  • CN V Trigeminal: Controls facial sensation and chewing. Gently test areas of the face using the pin and the wisp of cotton. Subject should clench their teeth and then open their jaw against resistance.

  • CN VI Abducens: This controls the abductor muscles of the eye, which move the eye outward. Have the person look to the side.

  • CN VII Facial: This nerve controls the muscles of facial expression, plus taste on the front two-thirds of the tongue. Test the muscles by having the subject open and close their mouth, open their eyes and squeeze their eyes shut. Use the sweet, salty, sour and bitter items to test taste.

  • CN VIII Vestibulocochlear: This nerve controls hearing and balance. Test hearing with a tuning fork and have the test subject walk a straight line.

  • CN IX Glossopharyngeal/CN X Vagus: These nerves control swallowing, gag reflex and speech and so are tested the same way. (The vagus nerve also controls internal organs such as the heart and digestive tract.) Have the test subject swallow and say "ah." The tester can touch the back of the person's throat with a tongue depressor to check the gag reflex.

  • CN XI Accessory: This nerve innervates the sternocleidomastoid and trapezius muscles, which control neck turning and shoulder shrugging. The test subject should turn their head and lift their shoulders against resistance.

  • CN XII Hypoglossal: This nerve controls tongue movement. The test subject should stick out their tongue.

Tips & Warnings

  • If any result is unusual or painful, consult a physician.

References

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