Short answer
Cranial nerves I (olfactory), II (optic) and VIII (vestibulocochlear).
The 12 Cranial Nerves and How to Test Them
| Nerve | Main function | How to test |
|---|---|---|
| I — Olfactory | Smell | Identify a familiar scent in each nostril |
| II — Optic | Vision | Snellen acuity, visual fields, pupillary light reflex |
| III — Oculomotor | Most eye movements, pupil constriction, eyelid elevation | H-pattern eye movements, pupils |
| IV — Trochlear | Superior oblique (look down and in) | H-pattern eye movements |
| V — Trigeminal | Facial sensation, chewing | Light touch on V1–V3, clench jaw, corneal reflex |
| VI — Abducens | Lateral rectus (look outward) | H-pattern eye movements |
| VII — Facial | Facial expression, taste (front 2/3 of tongue) | Raise eyebrows, close eyes tightly, smile, puff cheeks |
| VIII — Vestibulocochlear | Hearing and balance | Whisper test, Weber and Rinne tests |
| IX — Glossopharyngeal | Swallowing, taste (back 1/3), gag sensation | Gag reflex, say “ah” |
| X — Vagus | Palate, pharynx, larynx, organs | Uvula and palate rise, voice, swallowing |
| XI — Accessory | Trapezius and SCM | Shoulder shrug and head turn against resistance |
| XII — Hypoglossal | Tongue movement | Stick out the tongue and move it side to side |
USA Cranial Nerve Exam: Quick Facts
- Number of nerves
- 12 pairs
- Sensory only
- I, II, VIII
- Eye movement
- III, IV, VI
- Gag reflex
- IX (sensory) and X (motor)
- Tongue deviates
- Toward a CN XII lesion
- Uvula deviates
- Away from a CN X lesion
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