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Cranial nerves at a glance
Exit foramen, main functions, the lesion sign to know, and how to test each nerve at the bedside.
| Nerve | Leaves the skull via | Main functions | Lesion sign | Bedside test |
|---|---|---|---|---|
| I Olfactory | Cribriform plate | Smell | Anosmia | Familiar scent, each nostril |
| II Optic | Optic canal | Vision; afferent limb of the pupillary light reflex | Field defects; relative afferent pupillary defect | Acuity, fields, pupils, fundoscopy |
| III Oculomotor | Superior orbital fissure | Superior, inferior and medial recti, inferior oblique, levator; pupil constriction | Eye "down and out", ptosis, dilated pupil | H-pattern eye movements; pupils |
| IV Trochlear | Superior orbital fissure | Superior oblique | Vertical diplopia worse looking down; head tilt away from the lesion | Look down and in |
| V Trigeminal | V1 superior orbital fissure · V2 foramen rotundum · V3 foramen ovale | Facial sensation; muscles of mastication | Facial numbness; jaw deviates toward the lesion; lost corneal reflex (afferent) | Sensation in V1–V3; clench teeth; corneal reflex |
| VI Abducens | Superior orbital fissure | Lateral rectus | Eye turned in; horizontal diplopia | Abduction |
| VII Facial | Internal acoustic meatus → stylomastoid foramen | Facial expression; taste (anterior ⅔ of tongue); lacrimal and submandibular/sublingual glands | Bell palsy (whole half-face) vs stroke (forehead spared) | Raise eyebrows, close eyes tightly, smile |
| VIII Vestibulocochlear | Internal acoustic meatus | Hearing; balance | Sensorineural hearing loss; vertigo | Whisper test, Weber and Rinne, Dix–Hallpike |
| IX Glossopharyngeal | Jugular foramen | Taste and sensation of the posterior ⅓ of the tongue and pharynx; stylopharyngeus; parotid gland | Lost gag reflex (afferent) | Gag reflex |
| X Vagus | Jugular foramen | Palate, pharynx, larynx; thoracic and abdominal parasympathetics | Uvula deviates away from the lesion; hoarseness | Say "ah"; gag reflex; voice |
| XI Accessory | Jugular foramen | Sternocleidomastoid and trapezius | Shoulder droop; weak head turning | Shrug; turn the head against resistance |
| XII Hypoglossal | Hypoglossal canal | Tongue muscles (except palatoglossus) | Tongue deviates toward the lesion | Protrude the tongue |
Nerves in the lateral wall of the cavernous sinus: III, IV, V1, V2. Running through it: CN VI and the internal carotid artery — see dural venous sinuses.