Class 12: Cranial Nerves

Cranial Nerve 1

Olfactory

Cranial Nerve 2

Optic

Cranial Nerve 3

Oculomotor

Cranial Nerve 4

Trochlear

Cranial Nerve 5

Trigeminal

Cranial Nerve 6

Abducens

Cranial Nerve 7

Facial

Cranial Nerve 8

Acoustic (vestibulocochlear)

Cranial Nerve 9

Glossopharyngeal

Cranial Nerve 10

Vagus

Cranial Nerve 11

Spinal accessory

Cranial Nerve 12

Hypoglossal

Which nerves are sensory?

Cranial nerves 1, 2, and 8

Olfactory, optic, and acoustic

Which nerves are motor?

Cranial nerves 4, 6, 11, and 12

Trochlear, abducens, spinal, and hypoglossal

Which nerves are mixed (carries a combination)?

Cranial nerves 3, 5, 7, 9, and 10

Oculomotor, trigeminal, facial, glossopharyngeal, and vagus

Cranial Nerve 1 Objective data

Only tested when:

• Patient reports change in sense of smell

• Head injury

• Suspected brain lesion

Hold one nostril closed and assess sense of smell

• Hold familiar aromatic substance eg. vanilla, under nostril

• Patient should identify substance

Cranial nerve 2 objective data

• Tested by testing visual acuity (snellen chart) and visual fields by confrontation

• Use ophthalmoscope to check the ocular fundus for colour, size, and shape of optic disc

• Round, bright optic disc, yellow/peach/orangish fundus

Cranial nerves 3,4,6 objective data

• Check width of palpebral fissures bilaterally

  • Abnormal: Ptosis

• Check pupils (PERRLA)

  • Abnormal: Unilateral dilation or nonreactivity

• Check cardinal positions of gaze

  • Abnormal: Strabismus or Limited Movement or Nystagmus

Cranial nerve 5 motor function

• Motor function

  • Palpate temporal and masseter muscles

  • Patient asked to clench teeth

  • Push down on chin to assess strength

• Abnormal findings:

  • Decreased strength, asymmetry of jaw movement, pain with clenching

Cranial nerve 5 sensory function

Sensory function

-Patient closes eyes

-Touch a cotton ball to forehead, cheeks, and chin

-Ask patient to say “now” when they feel it

-Compare bilaterally

Cranial nerve 5 Corneal reflex

-Only done if patient has abnormal facial sensation or facial movement

-Patient looks forward (take out contact lenses)

-Cotton ball brought in from the side and touched lightly off the cornea

-Assess for bilateral blinking

-Abnormal: decreased or unequal sensation

Cranial nerve 7 motor function

•Facial nerve

•Motor assessment:

–Ask patient to smile, frown, close eyes tightly (against examiner trying to open them), lift eyebrows, show teeth, and puff cheeks

–Press puffed cheeks in and note if air escapes equally

•Abnormal: Unable to do movements, air leaks different bilaterally

Cranial nerve 7 sensory function

•Not tested routinely. Test when there is concern about facial nerve injury

•Assess taste of sweet, salty, and sour by applying each solution to a cotton tipped applicator and then to the tongue

•Ask patient to identify the taste

Cranial nerve 8 objective data

•Acoustic (vestibulocochlear nerve)

•Tested using the whispered voice test

–Stand 2 feet behind patient

–Cover one ear and whisper in open ear

–3 random letters or numbers

–Ok is correctly identify 3 out of 6 letters or numbers

Cranial nerve 9 and 10 objective data

• Sensory function of cranial nerve 10 is usually not checked because it relates to taste in the posterior one-third of the tounge and is too difficult to test

• Motor function:

  • Depress tongue with tongue blade and note pharyngeal movement when patient says “ahhhh” or yawns. Uvula should should rise and tonsillar pillars move medially

  • Check gag reflex by touching posterior pharyngeal wall with tongue blade

  • Take note of quality of voice

  • Abnormal: deviated uvula, absence of movement, lack of gag reflex, hoarseness

Cranial nerve 11 objective data

•Spinal accessory nerve

•Examine sternomastoid and trapezius muscle for equal size and strength

•Ask patient to turn head against resistance and to shrug shoulders against resistance

•Abnormal: atrophy of muscle, weakness or paralysis of muscle

Cranial nerve 12 objective data

•Hypoglossal nerve

•Inspect the tongue for any wasting or tremors

•Ask patient to stick out tongue and note if it is midline

•Ask patient to say words like “light”, “tight”, and “dynamite” and listen for annunciation of the letters “l”, “t”, “d”, and “n”

•Abnormal: deviation of tongue, atrophy of tongue, quick movements of tongue (fasciculations)