Cranial Nerve Function- A&P Review

1. Cranial Nerve Function- A&P Review • 12 pairs of cranial nerves originate from brain & brainstem • Have sensory, motor or mixed functions. • Enter and exit the brain rather than spinal cord • Essentially reflects brainstem activity

2. Cranial Nerve I- Olfactory Nerve • Not routinely tested. • Test with: • Report of loss of smell • Head trauma • Abnormal mental status • Suspected intracranial lesion • Sensory function • With eyes closed occlude nares and present aromatic substance Able to correctly identify aromatic substance

3. Cranial Nerve II- Optic Nerve • Sensory Function • Visual acuity • Snellen: 20/20 OS, 20/20 OD, 20/20 OU • Visual fields by confrontation • Peripheral fields intact by confrontation • Assess optic disc • Color & shape • Optic disc creamy yellow, round, with distinct margins

4. Cranial Nerve III, IV, VI • CN III- Oculomotor • Motor Function • Medial, superior, inferior rectus muscles & inferior oblique muscles • Levator palpebrae muscles (elevate eyelids) • Palpebral fissures symmetrical, no ptosis • Parasympathetic • Muscles of iris & ciliary body • PERRLA • CN IV- Trochlear • Motor Function • Superior oblique • CN VI- Abducens • Motor Function • Lateral rectus • EOMS intact without nystagmus

5. Cranial Nerve V- Trigeminal • Motor Function • Palpate temporal & masseter muscles as patient clenches teeth • Try to separate jaw by pushing down on chin Jaw strength equal bilaterally • Sensory Function • Test light sensation with cotton ball over • Forehead (ophthalmic) • Cheeks (maxillary) • Chin (mandibular) Sensation intact and equal bilaterally

6. Cranial Nerve VII- Facial • Motor Function • Smile, frown, close eyes tightly(against attempt to open, lift eyes, show teeth & puff cheeks Facial muscles intact & symmetrical • Sensory Function • Not tested routinely • Test only if suspect facial nerve injury • Taste on anterior 2/3rds of tongue • Apply cotton applicator to tongue with solution of sugar, salt, or lemon juice Able to correctly identify sweet, salty & sour

7. Corneal Reflex • Only perform if patient with abnormal facial sensation or movement • Remove contact lenses • Lightly touch cornea with wisp of cotton from side • Tests the sensory afferent in CN V & motor efferent CN VII Corneal Reflex Intact

8. Cranial Nerve VIII- Acoustic • AKA • Vestibulocochlear Nerve • Sensory Function • Assess hearing acuity: • Ability to hear normal conversation • Whispered voice test Whispered words heard bilaterally • Weber tuning fork test Tone heard midline without lateralization • Rinne tuning fork test AC >BC

9. Cranial Nerve IX and X • CN IX- Glossopharyngeal • CN X- Vagus • Motor Function • Swallow • Swallowing intact • Depress with tongue blade & note pharyngeal movement as patient says “ahhh” • Uvula rises midlines with phonation • Touch posterior pharyngeal wall to illicit gag reflex • Gag reflex intact • Note sound of voice • Sensory Function • Taste on posterior 1/3 of tongue • Not routinely tested

10. Cranial Nerve XI- Spinal Accessory • Motor Function • Rotate head against resistance • Shrug shoulders against resistance Shoulder shrug and head movement intact and equal bilaterally

11. Cranial Nerve XII-Hypoglossal • Motor Function • Have patient protrude tongue • No wasting or tremors • Tongue midline • Tongue protrudes midline without tremors • Say “light, tight, dynamite” • Note if clear and distinct • “Light, tight, dynamite” clear and distinct