Cranial Nerves — INBDE Review
All 12 cranial nerves — function, foramina, lesions, and dental relevance. Quick-reference table, mnemonics, clinical pearls, and 11 board-style practice MCQs with full explanations.
Concept summary & clinical relevance.
Quick-reference structure first, then nerve-by-nerve detail. Mnemonics in amber, clinical pearls in blue.
The 12 cranial nerves carry sensory and motor information directly between the brain and the head, neck, and viscera. For the INBDE — and for safe local anesthesia, oral surgery, and clinical localization — you need to know each nerve's function, the foramen it travels through, and what lesions look like. Start with the reference table, then drill into individual nerves below.
| Nerve | Type | Primary function | Key foramen | Classic lesion finding |
|---|---|---|---|---|
| I — Olfactory | S | Smell | Cribriform plate (ethmoid) | Anosmia |
| II — Optic | S | Vision | Optic canal | Monocular blindness; chiasm = bitemporal hemianopia |
| III — Oculomotor | M | Most eye muscles, eyelid, pupil constriction | Superior orbital fissure | “Down and out” eye, ptosis, dilated pupil |
| IV — Trochlear | M | Superior oblique (down + in) | Superior orbital fissure | Head tilt; trouble walking downstairs |
| V — Trigeminal | B | Facial sensation; muscles of mastication (V3) | V1: SOF · V2: foramen rotundum · V3: foramen ovale | Loss of facial sensation; weak chewing |
| VI — Abducens | M | Lateral rectus (eye abduction) | Superior orbital fissure | Inability to abduct eye (cross-eyed) |
| VII — Facial | B | Facial expression; taste anterior 2/3 tongue; lacrimal/salivary glands | Internal acoustic meatus → stylomastoid foramen | Bell's palsy; hyperacusis |
| VIII — Vestibulocochlear | S | Hearing + balance | Internal acoustic meatus | Vertigo, tinnitus, sensorineural hearing loss |
| IX — Glossopharyngeal | B | Taste posterior 1/3 tongue; swallowing; parotid | Jugular foramen | Loss of gag; impaired swallowing |
| X — Vagus | B | Larynx, pharynx, parasympathetic to viscera | Jugular foramen | Hoarseness; uvula deviates away from lesion |
| XI — Accessory | M | Trapezius + sternocleidomastoid | Jugular foramen | Weak shoulder shrug, weak head turn |
| XII — Hypoglossal | M | Tongue muscles | Hypoglossal canal | Tongue deviates toward lesion |
CN I — Olfactory (Smell)
- Pure sensory → smell.
- Travels through the cribriform plate of the ethmoid bone.
- Damage = anosmia (loss of smell).
CN II — Optic (Vision)
- Pure sensory → vision.
- Fibers cross at the optic chiasm.
- Chiasm lesion = bitemporal hemianopia (tunnel vision).
CN III — Oculomotor (Eye Mover)
- Motor → most eye muscles + lifts eyelid (levator palpebrae).
- Parasympathetic → constricts pupil.
- Damage → eye stuck “down and out,” ptosis, dilated pupil (mydriasis).
CN IV — Trochlear (Pulley)
- Motor → superior oblique (moves eye down and in).
- Only cranial nerve to exit the dorsal brainstem.
- Damage → head tilt, trouble going downstairs.
CN V — Trigeminal (Face Sensation & Chewing)
- V1 (ophthalmic): forehead, cornea, upper nose.
- V2 (maxillary): cheeks, upper lip, upper teeth.
- V3 (mandibular): lower jaw, lower teeth, muscles of mastication.
- Dentist’s favorite nerve — target for local anesthesia.
- Afferent limb of the corneal reflex.
CN VI — Abducens (Abducts Eye)
- Motor → lateral rectus (eye moves outward).
- Damage → eye stuck medially (cross-eyed appearance).
CN VII — Facial (Expression, Taste, Stapedius)
- Motor → muscles of facial expression.
- Sensory → taste from anterior 2/3 of tongue (chorda tympani).
- Parasympathetic → lacrimal and salivary glands (except parotid).
- Stapedius muscle dampens loud sound.
- Damage → Bell’s palsy or hyperacusis.
CN VIII — Vestibulocochlear (Balance & Hearing)
- Sensory → hearing (cochlea) + balance (vestibule).
- Damage → vertigo, tinnitus, hearing loss.
CN IX — Glossopharyngeal (Tongue & Throat)
- Sensory → taste posterior 1/3 of tongue.
- Motor → swallowing.
- Parasympathetic → parotid gland.
- Afferent limb of the gag reflex.
CN X — Vagus (the Wandering Nerve)
- Mixed nerve to throat, chest, and gut.
- Motor → swallowing and voice (larynx).
- Parasympathetic → slows heart, aids digestion.
- Lesion → hoarse voice + uvula deviates away from the lesion.
CN XI — Accessory (Shoulders & Head Turn)
- Motor → trapezius (shrug) + sternocleidomastoid (head turn).
- Lesion → weak shoulder shrug + weak head turn.
CN XII — Hypoglossal (Tongue)
- Motor → all intrinsic and most extrinsic tongue muscles.
- Lesion → tongue deviates toward the side of the lesion.
11 board-style MCQs.
Active recall is the highest-yield study method for the INBDE. Pick an answer, check it, and read why every distractor is wrong — that's where the learning compounds.
The MCQs above are Core Recall — testing what you've memorized. The book adds a full Clinical Integration set: board-style patient scenarios where you apply this anatomy to real clinical reasoning. That's the section the INBDE actually weights heaviest.
- Question 1EasyCN I passes through which skull structure?
- Question 2EasyLoss of smell is called:
- Question 3ModerateDamage to the optic chiasm most classically produces:
- Question 4EasyWhich cranial nerve constricts the pupil?
- Question 5ModerateDamage to CN III results in which finding?
- Question 6HardThe only cranial nerve to exit the dorsal brainstem is:
- Question 7EasyThe superior oblique muscle is innervated by:
- Question 8ModerateDifficulty walking downstairs suggests a lesion of:
- Question 9EasyWhich branch supplies the lower teeth?
- Question 10EasyThe main motor function of CN V is:
- Question 11ModerateA lesion of CN VI produces:
900 INBDE-style MCQs with full explanations across 18 chapters — Core Recall plus board-style Clinical Integration scenarios — alongside Learning Summaries, Integration Bridges, and Review Boxes. Built by Dr. Isaac Sun for dental students who want to think like a clinician, not just memorize.
Founder, KYT Dental Services · Author, KYT INBDE series. These MCQs and Learning Summaries are part of a structural-thinking framework Dr. Sun uses with patients in the chair.