Cranial Nerve Assessment Reference

Function: Smell

Bedside test: Ask patient to identify familiar scents (coffee, mint) with each nostril. Rarely tested acutely unless frontal lobe injury suspected.

Loss of smell (anosmia) may indicate frontal lobe injury or cribriform plate fracture.

Function: Vision

Bedside test: Visual acuity (near card, count fingers). Visual field by confrontation — test each quadrant of each eye.

Homonymous hemianopia = contralateral occipital lobe or optic tract lesion. Bitemporal hemianopia = chiasm compression.

Function: Eyelid elevation, most eye movements, pupil constriction

Bedside test: Pupil size and reactivity to light. Extraocular movements (H-pattern). Ptosis (eyelid droop).

CN III compression = fixed and dilated pupil + ptosis + 'down and out' eye. Classic herniation sign.

Function: Superior oblique muscle — downward gaze (looking toward nose)

Bedside test: Ask patient to look down and inward. Diplopia on downward gaze suggests CN IV palsy.

CN IV palsy causes vertical diplopia; often from trauma or vascular lesions.

Function: Facial sensation (V1 forehead, V2 cheek, V3 jaw); mastication muscles

Bedside test: Light touch in all three distributions bilaterally. Corneal reflex (afferent limb). Jaw clench strength.

V1–V3 sensory loss patterns help localize nerve vs. central lesions.

Function: Lateral rectus muscle — lateral gaze

Bedside test: Ability to abduct eye laterally. Diplopia on lateral gaze suggests CN VI palsy.

CN VI has the longest intracranial course — a false localizing sign with elevated ICP (stretched by downward brainstem displacement).

Function: Facial expression muscles; taste anterior 2/3 tongue; salivary and lacrimal glands

Bedside test: Raise eyebrows (forehead wrinkle), close eyes tight, show teeth, puff cheeks.

UMN lesion (cortex/tract): spares forehead (bilateral cortical representation). LMN lesion (nerve/nucleus): involves full face including forehead — Bell's palsy.

Function: Hearing (cochlear) and balance/vestibular input

Bedside test: Finger rub or whisper test for hearing bilaterally. Bedside watch-tick test. Weber/Rinne if available.

Sensorineural vs. conductive hearing loss distinguished by Weber/Rinne. Nystagmus may indicate vestibular component.

Function: Taste posterior 1/3 tongue; gag reflex (afferent); swallowing

Bedside test: Gag reflex (CN IX afferent, CN X efferent). Assess swallowing.

Assessed together with CN X. Absent gag in a conscious patient warrants dysphagia evaluation.

Function: Palate elevation, gag reflex (efferent), voice, swallowing, parasympathetic to organs

Bedside test: Soft palate rises midline with phonation ('Aah'). Voice quality (hoarse/nasal). Gag (efferent limb).

Unilateral vagal palsy: palate deviates away from the lesion side ('curtain sign').

Function: Sternocleidomastoid (head turn) and trapezius (shoulder shrug)

Bedside test: Shoulder shrug against resistance. Head rotation to each side against resistance.

Weakness of shoulder shrug or head turn can follow neck surgery or jugular foramen lesions.

Function: Tongue movement

Bedside test: Tongue protrusion midline. Lateral tongue movement. Tongue strength against cheek pressure.

Tongue deviates toward the side of the lesion (LMN). Fasciculations suggest LMN involvement.