Medicine: Physical examination of the cranial nerves

describe CN I exam

1. ask patient if they have had any decrease in ability to smell

2. ask patient to close eyes and pinch 1 nostril shut and put a familiar scent (coffee, cinnamon, etc.) underneath nose and ask to identify

3. repeat for opposite nostril with different scent

positive test for CN I exam

inability to identify scent

what is CN I?

olfactory nerve

what is CN II?

optic nerve

sensory for vision receives sensory stimuli to the _______

retina

there are several different exams that can be done to test CN II. what are they?

• pupillary constriction

• Snellen Eye Chart

• visual field test for peripheral vision

describe CN II exam for pupillary constriction

1. shine a light in patient’s eye while blocking other eye and observe for pupil constriction on same side

2. repeat same pupil for accommodation reflex (pupil constriction on opposite side)

what’s a positive CN II exam for pupillary constriction?

loss of pupil constriction bilaterally

describe CN II exam using Snellen Eye Chart

1. patient stand 20 ft from eye chart and read smallest line they can read easily

2. progress down chart until they reach a line where at least 2 errors are made

3. compare number on that line with the 20 ft where they stand

   1. 20/30 = stood 20 fee but could only read a line that a normal eye can read from 30 ft

describe CN II exam for visual field (peripheral vision)

use hand to see where patient can begin seeing in all fields

what is CN III? what does it innervate?

occulomotor

rest of intrinsice muscles that move eyeball in directions (excluding superior oblique and lateral rectus)

what is CN IV? what does it innervate?

trochlear

superior oblique muscle (move eyeball infero-medially)

what is CN VI? what does it innervate?

abducens

lateral rectus m. (moves eyeball laterally)

which CNs are responsible for motor to eyeball movement?

CN III, IV, VI

describe CN III, IV, and VI exam

ask patient to watch tip of finger with eyes only while u trace an H-pattern in the air

what is a positive exam for CN III, IV, or VI?

inability to move eyeball in respective directions (ipsilateral lesion)

what is CN V? what does it innervate?

trigeminal n.

sensory to face
motor to muscles of mastication

describe sensory CN V exam. positive result?

ask patient to close eyes and distinguish between sharp and soft touch on maxilla and mandible

positive = inability to distinguish or feel

• right/left side of forehead → opthalmic branch

• right/left side of cheek area → maxillary branch

• right/left side of jaw → mandibular branch

describe motor CN V exam. positive result?

put fingers on bilateral temporalis muscles and ask patient to bite down. put fingers on bilateral masseter muscles and ask patient to move jaw side to side.

positive = unequal tension bilaterally in muscles

sensory limb of CN V has how many major branches?

3 (each covers 1/3 of face)

• opthalmic

• maxillary

• mandibular

The Ophthalmic branch of CN 5 also receives sensory input from the surface of the eye. To assess this component:

• Pull out a wisp of cotton.

• While the patient is looking straight ahead, gently brush the wisp against the lateral aspect of the sclera (outer white area of the eye ball).

• This should cause the patient to blink. Blinking also requires that CN 7 function normally, as it controls eye lid closure.

what is CN VII? what does it innervate?

facial n.

sensory to cornea + taste
motor to muscles of facial expression

describe sensory CN VII exam. what’s a positive result?

ask patient to open eye, touch cornea w cotton wisp for corneal reflex

• positive = not blinking in response (patients who wear contacts may have lost this reflex)

• too much overlap of CNs to use taste as assessment technique

describe motor CN VII exam. what’s a positive result?

• ask patient to frown, smile → both corners should rise to same height and equal amounts of teeth visible

• puff out cheeks (both sides should puff equally, no air leakage from mouth)

• wrinkle eyebrows and close eyes tightly

  • VII = close lids

  • III = open lids

• positive = inability/asymmetrical facial expression

what is CN VIII? what does it innervate?

vestibulocochlear n.

sensory for hearing
motor for balance

describe exams for CN VIII.

• hearing → whisper something while occluding opposite ear

• Weber and Rinne test (conductive vs snsorineural hearing loss)

t/f: Any suspected loss should prompt formal audiologic testing to confirm findings and help differentiate conductive hearing loss from sensorineural hearing loss.

true

describe the Weber test.

CN VIII lateralization

1. wrap tuning fork strongly on palm and press butt of instrument on top of head in midline and ask where they hear the sound

   1. should be heard in center/equally in both ears

   2. conductive hearing loss = vibration louder on side with hearing loss

2. no vibration heard at all, attempt again and press butt harder on head

describe the Rinne test.

compares air conduction to bone conduction

1. wrap tuning fork firmly on palm and place butt on mastoid eminence firmly

2. ask patient to say “now” when they can no longer hear the vibration

3. when patient says “now”, remove butt from mastoid process and place U of tuning fork near the ear without touching it

The vestibular division of CN VIII detects changes in the position of the head relative to gravity: our sense of _________

balance and equilibrium

Vestibular function can be evaluated by testing for _______-

nystagmus. ... If patients have acute vertigo during the examination, nystagmus is usually apparent during inspection.

what is CN IX? what does it innervate?

glossopharyngeal n.

motor to muscles of pharynx and larynx
sensory to taste

the motor portion of gag reflex is due to CN ___. describe the exam.

CN IX

touch back of patient’s throat w tongue depressor (not gagging is positive)

what is CN X? what does it innervate?

vagus n.

sensory to taste
motor to soft palate and vocal cords (observe for hoarseness of voice)

describe CN X exam.

1. observe for hoarseness of voice

2. shine light in mouth and ask patient to say Ahhhh

3. check to see if uvula is deviated to one side

4. uvula will deviate away from side of CN X lesion

which nerves are responsible for raising the soft palate of the mouth and the gag reflex, a protective mechanism which prevents food or liquid from traveling into the lungs. As both CNs contribute to these functions, they are tested together.

CN IX and X

testing elevation of the soft palate is used for CN IX and X. describe the steps.

1. ask patient to open mouth and say AHhhh (soft palate will rise upward)

2. look for uvula (use tongue depressor if necessary)

3. uvula should rise up straight and in the midline

left CN IX dysfunction will result in what clinical presentation?

uvula pulled over towards right (often in post-stroke patients but other processes can cause deviation as well like peritonsilar abscess)

describe steps for testing gag reflex

1. ask patient to widely open mouth

2. identify posterior pharynx (use tongue depressor if necessary)

3. take tongue depressor or cotton tipped applicator and gently brush it against posterior pharynx or uvula and observe for gag

   1. small percent of normal population has minimal or non-existent gag reflex

what is CN XI? what does it innervate?

accessory spinal n.

trapezius m. (permit shrugging of shoulders) and SCM m. (turn head laterally)

describe CN XI exam. positive result?

place hands on top of either shoulder and cheek and ask patient to shrug and turn head into hand (repeat on other side) while u provide resistance

positive = weakness/absence of movement on affected side

what is CN XII? what does it innervate?

hypoglossal n.

motor to tongue muscles (each CN XII innervates ½ of tongue)

describe CN XII exam.

1. ask patient to stick tongue straight out of mouth

2. look for deviation to one side/weakness and direct them to push tip of tongue into either cheek while u provide counter pressure from outside

   1. tongue will deviate toward side of CN XII lesion

if the right CN XII is dysfunctional, the tongue will deviate to the right/left.

right

because the normally functioning left half will dominate as it no longer has opposition from the right. Similarly, the tongue would have limited or absent ability to resist against pressure applied from outside the left cheek