Oh Oh Oh to Touch and Feel Very Good Velvet, Such Heaven

Names the twelve cranial nerves (CN I–XII) in rostral-to-caudal order to guide a systematic cranial nerve exam and localize deficits.

Oh — Olfactory (CN I)

Sensory — smell

CN I consists of bipolar receptor neurons in the olfactory epithelium whose axons cross the cribriform plate to the olfactory bulb. Test with a familiar non-irritating scent (coffee, vanilla), one nostril at a time. Anosmia/hyposmia follows head trauma, URI, COVID-19, or neurodegenerative disease.

Physiology. Olfactory receptors are chemoreceptors; the filaments pass through the thin cribriform plate, making them uniquely vulnerable to shearing. It is the only sense that reaches cortex without relaying through the thalamus.

Safety. Never test with ammonia or alcohol — irritants stimulate trigeminal (CN V) pain fibers, not CN I, and give a false 'present' smell.

Oh — Optic (CN II)

Sensory — vision

CN II is a CNS tract (meninges/CSF-wrapped), not a true peripheral nerve. Test acuity (Snellen), fields (confrontation), fundoscopy, and the afferent pupillary reflex. Lesions along the pathway produce localizing field defects (e.g., bitemporal hemianopia from chiasmal compression).

Physiology. Retinal ganglion cell axons form the optic nerve, partially decussate at the chiasm (nasal fibers cross), and project via optic tracts to the LGN and visual cortex.

Safety. New visual field loss or sudden visual loss is a neurological emergency and a fall/driving risk.

Oh — Oculomotor (CN III)

Motor (+ parasympathetic) — most eye movement, lid elevation, pupil constriction

CN III supplies all extraocular muscles except superior oblique (IV) and lateral rectus (VI), plus the levator palpebrae. Its parasympathetic fibers constrict the pupil. A lesion causes a 'down and out' eye, ptosis, and a dilated pupil. Compression (aneurysm/herniation) hits the pupil first; ischemia (diabetic) often spares it.

Physiology. Pupillary light reflex: light -> CN II (afferent) -> midbrain -> CN III (efferent) -> sphincter pupillae constricts. Parasympathetic fibers run on the nerve's surface, so external compression dilates the pupil first.

Safety. A fixed, dilated pupil with decreasing LOC = uncal herniation — notify immediately and obtain emergent imaging.

To — Trochlear (CN IV)

Motor — superior oblique (eye down-and-in)

CN IV is the only nerve exiting the dorsal brainstem, the only one with fully crossing fibers, and the most commonly injured in head trauma. A palsy causes vertical diplopia worst on downgaze (reading/stairs) and a compensatory head tilt away from the affected side.

Physiology. The superior oblique tendon passes through a pulley (trochlea); its main job is depression when the eye is adducted.

Safety. New vertical diplopia is a fall hazard, especially on stairs.

Touch — Trigeminal (CN V)

Both — facial sensation (V1/V2/V3) + muscles of mastication

CN V is the largest cranial nerve and main sensory nerve of the face, cornea, and anterior two-thirds of tongue (general sensation). Motor root supplies the muscles of mastication. Test light touch/pain in all three divisions, jaw clench, and corneal reflex (afferent). Trigeminal neuralgia causes paroxysmal electric-shock facial pain.

Physiology. V1 = forehead/upper eyelid/cornea, V2 = cheek/upper lip/upper teeth, V3 = jaw/lower lip/lower teeth + motor.

Safety. Absent corneal reflex leaves the eye unprotected — use lubrication and an eye shield to prevent corneal ulceration.

And — Abducens (CN VI)

Motor — lateral rectus (eye abduction)

CN VI has the longest subarachnoid course and is the most common isolated cranial nerve palsy (trauma, raised ICP, microvascular). A palsy causes failure of abduction and horizontal diplopia. New CN VI palsy with headache can be a 'false localizing' sign of raised intracranial pressure.

Physiology. The lateral rectus is the only muscle that abducts its eye, so its loss causes medial drift and horizontal diplopia.

Safety. Horizontal diplopia impairs depth perception — restrict driving and protect against falls.

Feel — Facial (CN VII)

Both — facial expression + taste (anterior 2/3 tongue) + lacrimation/salivation

CN VII supplies the muscles of facial expression, taste to the anterior two-thirds of the tongue (chorda tympani), and parasympathetic output to lacrimal and submandibular/sublingual glands. Peripheral lesion (Bell's palsy) drops the entire ipsilateral face including forehead; central lesion (stroke) spares the forehead (bilateral cortical input).

Physiology. Upper face receives bilateral cortical innervation, so only a peripheral CN VII lesion affects the forehead.

Safety. Inability to close the eye risks corneal drying and ulceration — institute lubrication/taping and exclude stroke before labeling Bell's palsy.

Very — Vestibulocochlear (CN VIII)

Sensory — hearing (cochlear) + balance (vestibular)

CN VIII has cochlear (hearing) and vestibular (balance) divisions. Test hearing with the whisper test and Rinne/Weber tuning forks (distinguishing conductive vs. sensorineural loss) and balance with Romberg/gait. A vestibular schwannoma typically presents with unilateral hearing loss and tinnitus.

Physiology. Sound vibrates the ossicles and cochlear fluid, bending hair cells that fire the cochlear nerve; semicircular canals and otoliths drive the vestibulo-ocular reflex.

Safety. Vertigo and imbalance cause falls — keep bed low, assist ambulation, and avoid sudden position changes.

Good — Glossopharyngeal (CN IX)

Both — posterior 1/3 tongue taste/sensation, stylopharyngeus, parotid, carotid body/sinus

CN IX provides sensory/taste to the posterior third of the tongue and pharynx, motor to the stylopharyngeus, parasympathetic to the parotid, and sensory from the carotid body/sinus. It is the afferent limb of the gag reflex (CN X is efferent). Tested with CN X via gag, swallow, and 'ah'.

Physiology. Touching the pharynx triggers CN IX afferents, and CN X efferents contract the pharynx — the gag reflex.

Safety. A weak or absent gag can mean an unprotected airway — keep NPO until a swallow screen is done.

Velvet — Vagus (CN X)

Both — pharynx/larynx (voice, swallow) + parasympathetic to heart/lungs/GI

CN X supplies motor to the pharynx/larynx (recurrent laryngeal nerve) and parasympathetic outflow to the heart, lungs, and GI tract to the splenic flexure. Test with 'ah' (uvula), gag (efferent), voice, and swallow. A unilateral lesion makes the uvula deviate away from the weak side, with hoarseness and dysphagia.

Physiology. Parasympathetic fibers slow heart rate, constrict bronchi, and stimulate GI motility ('rest and digest').

Safety. Vagus-mediated dysphagia risks silent aspiration — keep NPO until a formal swallow evaluation, and watch for a weak/wet voice after drinking.

Such — Spinal Accessory (CN XI)

Motor — sternocleidomastoid + trapezius

CN XI arises from the cervical cord (C1–C5), enters through the foramen magnum, and exits via the jugular foramen to supply the sternocleidomastoid and trapezius. Test by shrugging shoulders and turning the head against resistance. Commonly injured in neck surgery/trauma, causing ipsilateral shoulder drop and weak contralateral head turn.

Physiology. SCM turns the head to the opposite side; trapezius elevates and retracts the scapula.

Safety. Trapezius weakness destabilizes the shoulder — support the arm and avoid overstretching.

Heaven — Hypoglossal (CN XII)

Motor — tongue movement

CN XII supplies the intrinsic and most extrinsic tongue muscles (except palatoglossus, CN X). In a lower motor neuron lesion the tongue deviates toward the lesion on protrusion, with atrophy/fasciculations; an upper motor neuron lesion deviates contralaterally without atrophy.

Physiology. Each genioglossus protrudes its half of the tongue; a weak side lets the intact side push the tongue across midline toward the lesion.

Safety. Tongue weakness impairs swallowing and airway protection — assess for dysphagia and aspiration risk.

Memory aids

• Oh = Olfactory (CN I)
• Oh = Optic (CN II)
• Oh = Oculomotor (CN III)
• To = Trochlear (CN IV)
• Touch = Trigeminal (CN V)
• And = Abducens (CN VI)
• Feel = Facial (CN VII)
• Very = Vestibulocochlear (CN VIII)
• Good = Glossopharyngeal (CN IX)
• Velvet = Vagus (CN X)
• Such = Spinal Accessory (CN XI)
• Heaven = Hypoglossal (CN XII)

Quick review

• Oh = Olfactory (CN I) — Sensory — smell
• Oh = Optic (CN II) — Sensory — vision
• Oh = Oculomotor (CN III) — Motor (+ parasympathetic) — most eye movement, lid elevation, pupil constriction
• To = Trochlear (CN IV) — Motor — superior oblique (eye down-and-in)
• Touch = Trigeminal (CN V) — Both — facial sensation (V1/V2/V3) + muscles of mastication
• And = Abducens (CN VI) — Motor — lateral rectus (eye abduction)
• Feel = Facial (CN VII) — Both — facial expression + taste (anterior 2/3 tongue) + lacrimation/salivation
• Very = Vestibulocochlear (CN VIII) — Sensory — hearing (cochlear) + balance (vestibular)
• Good = Glossopharyngeal (CN IX) — Both — posterior 1/3 tongue taste/sensation, stylopharyngeus, parotid, carotid body/sinus
• Velvet = Vagus (CN X) — Both — pharynx/larynx (voice, swallow) + parasympathetic to heart/lungs/GI
• Such = Spinal Accessory (CN XI) — Motor — sternocleidomastoid + trapezius
• Heaven = Hypoglossal (CN XII) — Motor — tongue movement