Cranial Nerve I — Olfactory Nerve

• Function: Sense of smell.

• Examination: Test each nostril separately with familiar, non-irritating odors (e.g., coffee, vanilla).

• Clinical relevance: Anosmia (loss of smell) may indicate trauma, frontal lobe tumors, Parkinson’s disease, or COVID-19.

• Tip: Avoid irritants like ammonia that stimulate trigeminal nerve instead.

Cranial Nerve II — Optic Nerve

• Function: Vision.

• Examination:

  • Visual acuity (Snellen chart).

  • Visual fields by confrontation.

  • Fundoscopy to assess optic disc.

  • Pupillary light reflex (afferent limb).

• Clinical relevance: Visual field defects (e.g., bitemporal hemianopia from pituitary tumors), optic neuritis, papilledema.

• Tip: Compare both eyes carefully and document any asymmetry.

Cranial Nerve III — Oculomotor Nerve

• Function: Eyelid elevation, most extraocular muscles, pupillary constriction (parasympathetic).

• Examination:

  • Assess eyelid for ptosis.

  • Test extraocular movements (up, down, medial).

  • Check pupillary size and light response (efferent limb).

• Clinical relevance: Third nerve palsy causes ptosis, “down and out” eye position, and pupil dilation if parasympathetics involved.

• Tip: Pupil involvement in third nerve palsy suggests aneurysm; absence suggests microvascular ischemia.

Cranial Nerve IV — Trochlear Nerve

• Function: Innervates superior oblique muscle (eye movement downwards and inwards).

• Examination: Test downward and inward eye movement.

• Clinical relevance: Trochlear palsy causes vertical diplopia, worsened by looking down (e.g., when reading or descending stairs).

• Tip: Ask patient about head tilt to compensate for diplopia.

Cranial Nerve V — Trigeminal Nerve

• Function:

  • Sensory: Face (ophthalmic, maxillary, mandibular branches).

  • Motor: Muscles of mastication.

• Examination:

  • Test facial sensation with light touch and pinprick over all three divisions.

  • Assess corneal reflex (afferent limb).

  • Test jaw movements and muscle bulk.

• Clinical relevance: Trigeminal neuralgia causes severe facial pain; weakness may suggest brainstem lesions or nerve injury.

• Tip: Be gentle with corneal reflex test; avoid causing discomfort.

Cranial Nerve VI — Abducens Nerve

• Function: Lateral rectus muscle (eye abduction).

• Examination: Ask patient to look laterally.

• Clinical relevance: Sixth nerve palsy leads to inability to abduct the eye, causing horizontal diplopia.

• Tip: Sixth nerve palsy can result from increased intracranial pressure or microvascular ischemia.

Cranial Nerve VII — Facial Nerve

• Function:

  • Motor: Facial expression muscles.

  • Sensory: Taste from anterior 2/3 of tongue.

  • Parasympathetic: Lacrimal and salivary glands.

• Examination:

  • Ask patient to raise eyebrows, close eyes tightly, smile, puff cheeks.

  • Test taste (if needed).

• Clinical relevance:

  • Bell’s palsy: peripheral facial nerve palsy affecting all muscles of one side.

  • Central lesion spares forehead due to bilateral cortical innervation.

• Tip: Differentiate between central and peripheral facial palsy.

Cranial Nerve VIII — Vestibulocochlear Nerve

• Function: Hearing and balance.

• Examination:

  • Hearing tests: Whisper test, Rinne and Weber tests.

  • Vestibular function: Assess balance, nystagmus.

• Clinical relevance: Vestibular neuritis, acoustic neuroma, Meniere’s disease.

• Tip: Compare hearing between ears carefully; note any asymmetry.

Cranial Nerve IX — Glossopharyngeal Nerve

• Function:

  • Sensory: Posterior 1/3 tongue taste and sensation.

  • Motor: Stylopharyngeus muscle (swallowing).

  • Parasympathetic: Parotid gland.

• Examination: Assess gag reflex (afferent limb) and swallowing.

• Clinical relevance: Rare isolated lesions; often tested with CN X.

• Tip: Test gag reflex gently; note asymmetric elevation of the palate.

Cranial Nerve X — Vagus Nerve

• Function:

  • Motor: Palate, pharynx, larynx muscles.

  • Parasympathetic: Heart, lungs, gut.

• Examination:

  • Observe uvula and soft palate elevation when patient says “ah.”

  • Check for hoarseness, swallowing difficulty.

  • Assess gag reflex (efferent limb).

• Clinical relevance: Vagus nerve palsy causes hoarseness, dysphagia, uvula deviation away from lesion.

• Tip: Look for vocal cord paralysis in laryngoscopy if indicated.

Cranial Nerve XI — Accessory Nerve

• Function: Motor to sternocleidomastoid and trapezius muscles.

• Examination:

  • Ask patient to shrug shoulders against resistance (trapezius).

  • Turn head against resistance (sternocleidomastoid).

• Clinical relevance: Weakness causes difficulty turning head away from affected side and shoulder droop.

• Tip: Palpate muscles for wasting or fasciculations.

Cranial Nerve XII — Hypoglossal Nerve

• Function: Motor to tongue muscles.

• Examination:

  • Ask patient to stick out tongue; note deviation.

  • Assess tongue strength and fasciculations.

• Clinical relevance: Lesion causes tongue deviation toward side of weakness and atrophy.

• Tip: Differentiate from jaw deviation (CN V).

General Examination Tips for Cranial Nerves:

• Perform tests in a quiet, well-lit environment.

• Always compare both sides for symmetry.

• Take note of any compensatory head or eye movements.

• Integrate history findings with physical exam for better localization.

• Consider systemic or neurological disease context when interpreting abnormalities.