Trigeminal nerve and TMJ
Muscles of Mastication, TMJ, Mandible and Trigeminal Nerve
Mastication and the trigeminal nerve for FCPS Part 1: the four chewing muscles, temporomandibular joint and dislocation, mandible and its nerves, and the three divisions of V with their nuclei and reflexes. Covers dental blocks, neuralgia and fractures.
Muscles of mastication
All derive from the first pharyngeal arch and are supplied by the mandibular nerve (V3).
| Muscle | Main action | Note |
|---|---|---|
| Masseter | Elevates (closes) the jaw | Facial artery and vein cross the mandible at its anterior border (pulse point) |
| Temporalis | Elevates; posterior fibres retract | Attached to coronoid process |
| Medial pterygoid | Elevates; helps protrusion and side-to-side grinding | Nerve to medial pterygoid also supplies tensor tympani and tensor veli palatini |
| Lateral pterygoid | Opens the mouth (with gravity and digastric), protrudes; pulls condyle and disc forward | The only muscle of mastication that depresses the jaw |
- Other first-arch muscles on V3: tensor tympani, tensor veli palatini, mylohyoid, anterior belly of digastric.
- Side-to-side chewing: lateral and medial pterygoids of one side act alternately with those of the other side.
- Depressors of the mandible: lateral pterygoids, digastric, geniohyoid and mylohyoid. The depressor anguli oris (lowers the angle of the mouth) is a facial muscle supplied by VII.
Temporomandibular joint
- Synovial joint between the mandibular condyle and the mandibular fossa and articular eminence of the temporal bone, divided by a fibrocartilaginous articular disc into upper (gliding) and lower (hinge) compartments; articular surfaces are fibrocartilage, not hyaline.
- Opening: hinge rotation in the lower compartment, then the condyle and disc glide forward onto the eminence.
- Lateral (temporomandibular) ligament: main stabiliser; prevents posterior and excessive lateral displacement. Sphenomandibular (to the lingula) and stylomandibular ligaments are accessory.
- Dislocation is anterior: after a wide yawn the condyles slide in front of the articular eminence and spasm of the elevators (masseter, temporalis, medial pterygoid) holds them there; the mouth cannot close. Reduce by pressing down on the molars, then backwards.
- Nerve supply: auriculotemporal and masseteric nerves; TMJ pain is often felt in the ear.
Mandible and dental nerves
- Fractures are often bilateral (angle, condylar neck, body): look for a second fracture. A condylar fracture makes the jaw deviate towards the injured side on opening.
- Inferior alveolar nerve enters the mandibular foramen (lingula in front), runs in the mandibular canal, and exits as the mental nerve at the mental foramen below the second premolar. A fracture across the canal numbs the lower teeth, chin and lower lip.
- Inferior alveolar nerve block: injection near the mandibular foramen also catches the lingual nerve (tongue numb). Pitfalls:
| Problem | Explanation |
|---|---|
| Buccal gum beside the lower molars still painful | Supplied by the long buccal nerve (V3), a sensory nerve needing a separate block; not the motor buccal branch of VII |
| Temporary facial palsy (cannot close eye, mouth droops) | Needle placed too far back: anaesthetic deposited in the parotid gland reaches the facial nerve; protect the eye until it wears off |
- The lingual nerve lies against the lingual plate near the lower third molar; wisdom tooth extraction can leave a numb tongue and lost taste (chorda tympani fibres travel with it).
Trigeminal nerve (V)
| Division | Exit | Sensory territory | Motor |
|---|---|---|---|
| V1 Ophthalmic | Superior orbital fissure | Forehead, upper eyelid, cornea, dorsum and tip of nose | None |
| V2 Maxillary | Foramen rotundum | Lower eyelid, cheek, upper lip, upper teeth, palate, nasal cavity | None |
| V3 Mandibular | Foramen ovale | Lower lip, chin, lower teeth, temple (auriculotemporal), anterior two-thirds of tongue (lingual) | Mastication and other first-arch muscles |
- The trigeminal (semilunar) ganglion lies in Meckel's cave, a dural pouch at the petrous apex in the middle cranial fossa. A lesion there numbs the whole half-face and weakens chewing. A cavernous sinus lesion affects V1 and V2 but spares V3 and chewing, because V3 leaves the ganglion directly downwards through foramen ovale. The ganglion is reached for neuralgia procedures through the foramen ovale.
- The motor root joins V3 below the ganglion.
Trigeminal nuclei and reflexes
| Nucleus | Function |
|---|---|
| Main (principal) sensory | Touch, pressure |
| Spinal nucleus | Pain and temperature |
| Mesencephalic nucleus | Proprioception from muscles of mastication; contains the cell bodies of primary sensory neurons inside the CNS (the only such exception) |
| Motor nucleus (pons) | Muscles of mastication |
- Jaw jerk: afferent and efferent both V3; afferent cell bodies in the mesencephalic nucleus. A brisk jaw jerk means an upper motor neurone lesion above the pons (pseudobulbar palsy).
- Corneal reflex: afferent V1 (nasociliary), efferent VII. Touching the right cornea with no blink in either eye, but a normal response from the left, means the right V1 is damaged; an early sign of acoustic neuroma.
Clinical conditions
- Trigeminal neuralgia: brief electric-shock pains in V2 or V3 triggered by chewing, talking or touching the lip; normal examination; often vascular compression of the root. First-line carbamazepine.
- Herpes zoster ophthalmicus: V1 (forehead, upper lid, side and tip of nose); Hutchinson's sign predicts eye involvement. Herpes zoster, not herpes simplex, causes this.
- Referred pain: dental pain felt in the ear (auriculotemporal) and the reverse.
- Pierre Robin sequence: small mandible (micrognathia), glossoptosis and cleft palate, with airway obstruction in newborns.
Remember Lateral pterygoid opens and protrudes; the other three close; temporalis posterior fibres retract.
Exam trap TMJ dislocation is anterior: the condyle is trapped in front of the articular eminence.
Exam trap Jaw jerk afferent cell bodies lie in the mesencephalic nucleus, not in the trigeminal ganglion.
How FCPS asks about this
- Muscle that opens the mouth and protrudes the mandible: lateral pterygoid.
- Bony feature trapping the condyle in dislocation: articular eminence; lateral ligament is the main stabiliser.
- Facial palsy after inferior alveolar block: anaesthetic in the parotid gland.
- Buccal gum still painful after inferior alveolar block: long buccal nerve.
- Site of the trigeminal ganglion: Meckel's cave at the petrous apex; cavernous sinus lesions spare V3.
- Cell bodies for the jaw jerk: mesencephalic nucleus of V.
- Electric-shock jaw pain on chewing: trigeminal neuralgia (V3); carbamazepine.
Test yourself on this topic
5 of the 40 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
A woman with a trigeminal ganglion schwannoma has numbness of the whole left face and weak chewing. Where does this ganglion lie?
Answer: Meckel's cave at the petrous apex
The trigeminal (semilunar) ganglion lies in a pouch of dura called Meckel's cave (trigeminal cave), over the trigeminal impression near the apex of the petrous temporal bone in the middle cranial fossa. Its sensory branches V1, V2 and V3 leave its anterior border, and the motor root passes beneath it to join V3. A lesion here can affect all three sensory divisions and the muscles of mastication together.
Trigeminal ganglion
- In Meckel's cave
- Over the petrous apex
- Gives V1, V2, V3
- Motor root runs beneath it
Remember All three divisions plus chewing weakness: think Meckel's cave.
Exam trap A lesion in the cavernous sinus spares V3 and chewing.
Why the other options are wrong
- Lateral wall of the cavernous sinus Only V1 and V2 run in the cavernous sinus wall, beyond the ganglion.
- Pterygopalatine fossa Contains the maxillary nerve and pterygopalatine ganglion.
- Cerebellopontine angle cistern The trigeminal root crosses here, but the ganglion lies further forward.
- Infratemporal fossa Contains branches of V3 after it leaves the skull.
After surgical removal of an impacted lower left third molar, a 24-year-old man has numbness and loss of taste over the left anterior two-thirds of his tongue. Sensation of the lower lip and chin is normal. Which of the following nerves has been injured?
Answer: Lingual nerve
The lingual nerve lies directly against the lingual cortical plate of the mandible next to the third molar, where it is at risk during third molar surgery. It carries general sensation from the anterior two-thirds of the tongue and, after receiving the chorda tympani, taste fibres from the same area. Normal lip and chin sensation shows the inferior alveolar nerve is intact.
Lingual nerve injury
- Lies on lingual plate at third molar
- General sensation anterior 2/3
- Carries chorda tympani taste
Remember Third molar surgery plus numb tongue: lingual nerve.
Exam trap Taste loss with lingual injury comes from chorda tympani fibres it carries.
Why the other options are wrong
- Inferior alveolar nerve Would numb the lower lip, chin and teeth.
- Glossopharyngeal nerve Serves the posterior third of the tongue.
- Hypoglossal nerve Motor only; would cause tongue deviation, not numbness.
- Long buccal nerve Supplies the cheek and buccal gum, not the tongue.
After a successful inferior alveolar nerve block, a lower first molar is numb, as are the lip and tongue. However, the patient still feels pain when the buccal gum beside the tooth is incised. Which nerve needs a separate block?
Answer: Long buccal nerve
The long buccal nerve, a sensory branch of the anterior division of the mandibular nerve, supplies the skin and mucosa of the cheek and the buccal gingiva of the lower molars. It runs on the anterior border of the ramus, away from the mandibular foramen, so a standard inferior alveolar block does not reach it. A separate buccal infiltration is needed before cutting the buccal gum of the lower molars.
Long buccal nerve
- Sensory branch of V3 anterior division
- Supplies buccal gum of lower molars
- Missed by IANB
Remember Long buccal (V3) feels; buccal branch (VII) moves.
Exam trap Do not confuse the sensory long buccal nerve with the motor buccal branch of the facial nerve.
Why the other options are wrong
- Mental nerve Terminal branch of the inferior alveolar; already numb.
- Lingual nerve Already blocked, as the tongue is numb.
- Buccal branch of facial nerve Motor to buccinator; no sensory supply to the gum.
- Mylohyoid nerve Motor to mylohyoid and anterior digastric.
A woman with acute maxillary sinusitis has aching in her healthy upper molar teeth on that side. Which of the following nerves explains the toothache?
Answer: Superior alveolar branches of maxillary nerve
The posterior, middle and anterior superior alveolar nerves, branches of the maxillary nerve and its infraorbital continuation, run in the walls of the maxillary sinus to supply the upper teeth and the sinus lining. Inflammation of the sinus mucosa irritates these nerves, so maxillary sinusitis often presents as pain in the upper molars and premolars. Conversely, an upper dental abscess can cause maxillary sinusitis.
Sinus toothache
- Superior alveolar nerves in sinus walls
- Branches of maxillary nerve (V2)
- Sinusitis felt as upper molar pain
Remember Upper toothache with healthy teeth: think sinusitis.
Exam trap Lower teeth are never involved in maxillary sinus pain.
Why the other options are wrong
- Inferior alveolar branch of mandibular nerve Supplies the lower teeth.
- Greater palatine nerve Supplies the hard palate mucosa, not teeth.
- Nasopalatine nerve Supplies the anterior palate behind the incisors.
- Buccal branch of facial nerve Facial nerve branches are motor to facial muscles.
A 32-year-old woman who grinds her teeth has earache on the right. The ear canal and drum are normal, but the right temporomandibular joint is tender and clicks. Which of the following nerves best explains why the joint pain is felt in the ear?
Answer: Auriculotemporal nerve
The auriculotemporal nerve, a branch of the mandibular nerve, supplies the temporomandibular joint and also the skin of the external acoustic meatus, the outer tympanic membrane and the front of the auricle. Pain from the joint is therefore readily felt as earache. A normal ear examination with a tender, clicking joint is a typical picture of TMJ dysfunction.
TMJ earache
- Auriculotemporal (V3) supplies TMJ
- Also supplies ear canal and drum
- Normal ear: look at the joint
Remember Earache with a normal ear: check TMJ, teeth and throat.
Exam trap Always examine the throat and larynx in an adult with otalgia and a normal ear.
Why the other options are wrong
- Great auricular nerve Supplies the lower auricle and parotid skin, not the joint.
- Lesser occipital nerve Supplies the scalp behind the ear.
- Chorda tympani Carries taste and secretomotor fibres; not pain from the joint.
- Greater petrosal nerve Carries secretomotor fibres to the lacrimal gland.
Where this sits in the CPSP syllabus
- Paper 1: Head, neck and back, Muscles of mastication, TMJ, mandible and trigeminal nerve
- Surgery & Allied, Paper 2: Head and neck, Muscles of mastication, TMJ, mandible and trigeminal nerve