09 TRIGEMINAL CN V
# 10 TRIGEMINAL CN V
The trigeminal is the largest cranial nerve and the main sensory supply to the face. Its name — tri-geminal, "three twins" — reflects its three divisions: ophthalmic (V1), maxillary (V2) and mandibular (V3). For MRCS Part A you must know which division does what, where each exits the skull, and how to localise a lesion from the pattern of sensory or motor loss.
What the trigeminal does
👩⚕️ Sensory ➡ general sensation from the face, scalp to the vertex, cornea, dura of the anterior and middle cranial fossae, nasal and oral cavities, paranasal sinuses, teeth and the anterior 2/3 of the tongue. Taste from that same anterior 2/3 is not trigeminal — it is chorda tympani (CN VII), hitch-hiking on the lingual nerve.
👩⚕️ Motor ➡ via V3 only. Four muscles of mastication (masseter, temporalis, medial and lateral pterygoid) plus four "extras": mylohyoid, anterior belly of digastric, tensor tympani and tensor veli palatini.
👩⚕️ Parasympathetic ➡ trigeminal is only a post-ganglionic carrier. Fibres come from III, VII and IX; trigeminal branches deliver them:
- III → ciliary g. → short ciliary (V1) → sphincter pupillae, ciliary muscle
- VII → pterygopalatine g. → zygomatic (V2) → lacrimal (V1) → lacrimal gland
- VII → chorda tympani → submandibular g. → lingual (V3) → submandibular + sublingual glands
- IX → otic g. → auriculotemporal (V3) → parotid gland
👩⚕️ Memorise these four verbatim — they reappear constantly in MRCS.
Course in one paragraph
All three divisions arise from the trigeminal (Gasserian) ganglion in Meckel's cave, a dural pouch on the petrous temporal bone. V1 enters the cavernous sinus and exits via the superior orbital fissure; V2 exits via the foramen rotundum; V3 via the foramen ovale. Mnemonic: Standing Room Only — SOF, Rotundum, Ovale.
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Divisions
Ophthalmic division, CN V1
V1 is purely sensory, exits via the superior orbital fissure, and splits into three branches: lacrimal, frontal and nasociliary (L-F-N, lateral to medial).
- Lacrimal n. — 👩⚕️ S ➡ lacrimal gland, lateral upper eyelid, conjunctiva. Delivers parasympathetics from VII.
- Frontal n.
- Supraorbital n. — 👩⚕️ S ➡ forehead, scalp to vertex, upper eyelid, frontal sinus.
- Supratrochlear n. — 👩⚕️ S ➡ medial forehead, medial upper eyelid, root of nose.
- Nasociliary n.
- Long ciliary n. — 👩⚕️ S ➡ cornea — afferent of corneal reflex. Sympathetics to dilator pupillae.
- Short ciliary n. — 👩⚕️ S ➡ eyeball. Parasympathetics from III to sphincter pupillae and ciliary muscle.
- Infratrochlear n. — 👩⚕️ S ➡ medial eyelid, medial canthus, lacrimal sac, root of nose.
- Anterior ethmoidal n. — 👩⚕️ S ➡ anterior ethmoid cells, nasal cavity; ends as external + internal nasal nn.
- External nasal n. — 👩⚕️ S ➡ tip and ala of nose — Hutchinson's sign territory.
- Posterior ethmoidal n. — 👩⚕️ S ➡ posterior ethmoid cells, sphenoid sinus.
Maxillary division, CN V2
V2 is purely sensory, exits via the foramen rotundum into the pterygopalatine fossa, and ends as the infraorbital nerve.
- Meningeal n. — 👩⚕️ S ➡ dura of middle cranial fossa.
- Zygomatic n.
- Zygomatico-facial n. — 👩⚕️ S ➡ skin over cheek prominence.
- Zygomatico-temporal n. — 👩⚕️ S ➡ temple. Conveys parasympathetics to lacrimal gland.
- Infraorbital n. (terminal — exits infraorbital foramen)
- Anterior superior alveolar n. — 👩⚕️ S ➡ upper incisors, canines, anterior maxillary sinus.
- Middle superior alveolar n. — 👩⚕️ S ➡ upper premolars, part of maxillary sinus.
- Inferior palpebral n. — 👩⚕️ S ➡ lower eyelid.
- Lateral nasal n. — 👩⚕️ S ➡ lateral nose.
- Superior labial n. — 👩⚕️ S ➡ upper lip.
- Posterior superior alveolar n. — 👩⚕️ S ➡ upper molars, maxillary sinus, upper gingiva.
- Pterygopalatine branches (via pterygopalatine ganglion)
- Greater palatine n. — 👩⚕️ S ➡ hard palate, palatal gingiva.
- Lesser palatine n. — 👩⚕️ S ➡ soft palate, uvula, tonsillar region.
- Nasopalatine n. — 👩⚕️ S ➡ nasal septum, anterior hard palate.
- Pharyngeal n. — 👩⚕️ S ➡ nasopharynx, auditory tube region.
Mandibular division, CN V3
V3 is the only mixed division — sensory + motor. Exits via the foramen ovale and splits into anterior (mostly motor) and posterior (mostly sensory) divisions.
From the main trunk:
- Meningeal n. (nervus spinosus) — Re-enters via foramen spinosum with the middle meningeal artery. 👩⚕️ S ➡ middle fossa dura.
- N. to medial pterygoid — 👩⚕️ M ➡ medial pterygoid, tensor veli palatini, tensor tympani.
Anterior division (mostly motor):
- Deep temporal nn. — 👩⚕️ M ➡ temporalis.
- N. to masseter — 👩⚕️ M ➡ masseter.
- N. to lateral pterygoid — 👩⚕️ M ➡ lateral pterygoid — the only mastication muscle that opens the jaw.
- Buccal n. — 👩⚕️ S ➡ buccal gingiva, cheek mucosa. Sensory — don't confuse with motor buccal branch of VII.
Posterior division (mostly sensory):
- Auriculotemporal n. — 👩⚕️ S ➡ temple, auricle, EAM, TMJ. Carries parasympathetics from IX to parotid.
- Lingual n. — 👩⚕️ S ➡ general sensation anterior 2/3 tongue, floor of mouth, lingual gingiva. Carries chorda tympani fibres.
- Inferior alveolar n. — 👩⚕️ S ➡ lower teeth via mandibular canal — blocked in dental anaesthesia.
- N. to mylohyoid — 👩⚕️ M ➡ mylohyoid + anterior belly digastric. Branches before the IAN enters the canal.
- Mental n. — 👩⚕️ S ➡ lower lip, chin, labial gingiva. Exits mental foramen.
- Incisive n. — 👩⚕️ S ➡ anterior mandibular teeth.
High-yield clinical patterns
👩⚕️ Nasal tip + cornea numb = nasociliary (V1). Both supplied by nasociliary (long ciliary to cornea, external nasal to tip). Vesicles on the nasal tip in shingles — Hutchinson's sign — predict ocular involvement in herpes zoster ophthalmicus.
👩⚕️ Cheek + upper teeth numb after midface trauma = infraorbital (V2). Classic in zygomatic and orbital floor ("blow-out") fractures.
👩⚕️ Anterolateral tongue numb, taste intact = lingual (V3). Chorda tympani joins lingual proximal to the surgical field. Classic after lower third molar or submandibular duct surgery.
👩⚕️ Gustatory sweating post-parotidectomy = Frey's syndrome. Cut auriculotemporal parasympathetics regenerate into skin sweat-gland fibres → sweating while eating.
👩⚕️ *Jaw deviates toward the weak side on opening = ipsilateral lateral pterygoid palsy.* Intact contralateral pterygoid pushes the mandible across.
👩⚕️ Trigeminal neuralgia — paroxysms of lancinating V2/V3 pain triggered by light touch. Usually vascular compression by the superior cerebellar artery. First-line: carbamazepine.
👩⚕️ Reflexes: Corneal — afferent V1 (nasociliary), efferent VII. Jaw jerk — afferent + efferent V3; absent is normal, brisk implies UMN lesion above the pons.
Innervation of the tongue
| Region | General sensation | Taste | Motor |
|---|---|---|---|
| Anterior 2/3 | Lingual (V3) | Chorda tympani (VII) | Hypoglossal (XII) |
| Posterior 1/3 | Glossopharyngeal (IX) | Glossopharyngeal (IX) | Hypoglossal (XII) |
| Palatoglossus | — | — | Vagus (X) |
XII supplies 7 of 8 tongue muscles; palatoglossus (the exception) is vagus.
[Image: MCQs banner]
Test yourself
A 22-year-old woman has lost sensation over the tip of her nose. Where else is sensation likely to be lost?
- ((Hard palate::Greater palatine n. (V2) — wrong division.))
- ((Soft palate::Lesser palatine (V2) and CN IX — wrong division.))
- ((Ear pinna::Mixed supply (great auricular, lesser occipital, auriculotemporal) — not paired with nasal tip.))
- ((Cornea::☑️ Both supplied by nasociliary (V1) — cornea via long ciliary, nasal tip via external nasal.))
👩⚕️ Nasal tip + cornea = nasociliary nerve. Same fact underlies Hutchinson's sign in shingles.
A patient presents with numbness of the cheek, upper teeth and lateral nose following facial trauma. Which nerve is most likely injured?
- ((Infraorbital::☑️ Terminal branch of V2; classically injured in zygomatic and orbital floor fractures.))
- ((Infratrochlear::V1 branch — medial canthus and nasal bridge only.))
- ((Supratrochlear::V1 branch — medial forehead, not cheek.))
- ((Anterior superior alveolar::A branch of the infraorbital — would only numb upper incisors.))
👩⚕️ Cheek + upper teeth + lateral nose = infraorbital nerve. The orbital floor is its roof — fracture it and the nerve goes with it.
A 21-year-old undergoes removal of an impacted lower third molar. Post-op he has anaesthesia of the anterolateral tongue. Which nerve was injured?
- ((Marginal mandibular::Motor branch of VII — depressor labii inferioris, not tongue.))
- ((Hypoglossal CN XII::Motor only — would cause deviation, not numbness.))
- ((Glossopharyngeal CN IX::Supplies the posterior third.))
- ((Inferior alveolar::Lower teeth, lip and chin — not tongue.))
- ((Lingual::☑️ Runs medial to the third molar; high-risk in lower 3rd molar extraction.))
👩⚕️ Taste preserved — chorda tympani joins lingual proximal to the surgical field.
During submandibular gland excision, which nerve is most at risk during mobilisation of the duct?
- ((Hypoglossal CN XII::Lies deeper, below the duct.))
- ((Marginal mandibular::At risk during skin incision, not duct mobilisation.))
- ((Inferior alveolar::Inside the mandibular canal — distant.))
- ((Lingual::☑️ Loops under the duct from lateral to medial — easily injured during duct dissection.))
- ((Glossopharyngeal CN IX::Posterior tongue — not in this field.))
👩⚕️ The lingual crosses deep to the duct then loops medially around it — the "two old men hugging" image.
During parotidectomy, the facial nerve is transected. Which would not result?
- ((Numbness over the cheek::☑️ Facial sensation is trigeminal (V2/V3) — VII is motor only.))
- ((Loss of corneal reflex::Efferent of corneal reflex = VII (orbicularis oculi).))
- ((Lower lip drop::Marginal mandibular branch of VII supplies depressor labii inferioris.))
- ((Droop at angle of mouth::Buccal + marginal mandibular of VII supply depressor anguli oris.))
👩⚕️ Corneal reflex: cornea → long ciliary → nasociliary V1 → spinal V nucleus → VII nucleus → orbicularis oculi. A V1 lesion abolishes the reflex bilaterally; a VII lesion only the ipsilateral blink.
A 60-year-old has paroxysms of lancinating right cheek and upper jaw pain triggered by shaving. The most likely division involved is:
- ((V1::Forehead and scalp — not the described area.))
- ((V2::☑️ Cheek and upper jaw = maxillary. V2 + V3 are the commonest sites of trigeminal neuralgia.))
- ((V3::Lower jaw and chin — not described.))
- ((Facial nerve::Motor; not a sensory pain nerve.))
👩⚕️ First-line treatment: carbamazepine. Microvascular decompression of the superior cerebellar artery is curative in refractory cases.
Revision summary
- Three divisions, three foramina: V1 → SOF, V2 → rotundum, V3 → ovale (Standing Room Only).
- V1 and V2 sensory only. V3 mixed — the only motor division.
- Motor (V3): masseter, temporalis, medial + lateral pterygoid; mylohyoid, anterior belly digastric, tensor tympani, tensor veli palatini.
- Sensory: face, scalp to vertex, cornea, dura (anterior + middle fossae), nasal/oral cavities, sinuses, teeth, anterior 2/3 tongue (general only).
- Taste anterior 2/3 = chorda tympani (VII), not V.
- Parasympathetics: trigeminal carries only; fibres from III (ciliary g.), VII (pterygopalatine, submandibular g.), IX (otic g.).
- Ganglion: trigeminal (Gasserian) in Meckel's cave.
- Reflexes: corneal — afferent V1, efferent VII. Jaw jerk — afferent + efferent V3 (absent normal).
- Pearls: nasal tip + cornea → nasociliary V1 (Hutchinson's sign). Cheek + upper teeth → infraorbital V2 (orbital floor #). Anterolateral tongue numb, taste intact → lingual V3 (3rd molar). Gustatory sweating post-parotidectomy → Frey's. Jaw deviates toward weak side → ipsilateral lateral pterygoid palsy. Trigeminal neuralgia → V2/V3, carbamazepine first-line.