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AN33.1-5 | Temporal and Infratemporal regions — Gate Quiz
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All muscles of mastication are supplied by which division of the trigeminal nerve?
Correct! All four muscles of mastication (temporalis, masseter, medial pterygoid, lateral pterygoid) are supplied by the mandibular division of the trigeminal nerve (CN V3) — specifically the anterior division.
CN V3 (mandibular) = only mixed (sensory + motor) branch of CN V. Motor fibres supply all 4 muscles of mastication via the anterior division. V1 and V2 are purely sensory.
Incorrect. All muscles of mastication are innervated exclusively by CN V3 (mandibular division) — the only division of the trigeminal nerve that carries motor fibres.
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Among the four muscles of mastication, which is the ONLY one that depresses (opens) the mandible?
Correct! The lateral pterygoid is the only muscle of mastication that opens the mouth (depresses the mandible), along with protracting the jaw. All others close (elevate) the jaw.
Muscles of mastication and jaw movement: Elevation (closing) — masseter, medial pterygoid, temporalis. Depression (opening) — lateral pterygoid. Protraction — lateral and medial pterygoid. Retraction — posterior temporalis. Mnemonic: Lateral pterygoid is the Lone Opener.
Incorrect. The lateral pterygoid is the ONLY muscle of mastication that opens the mouth. Masseter, temporalis, and medial pterygoid all close (elevate) the jaw.
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The articular surfaces of the temporomandibular joint are lined with fibrocartilage rather than hyaline cartilage. This is because the TMJ develops from:
Correct! The mandibular condyle develops from secondary cartilage (a secondary ossification centre, not a primary cartilage precursor). Secondary cartilage produces fibrocartilage rather than hyaline cartilage, which is why the TMJ articular surfaces are fibrocartilaginous.
TMJ is the only joint in the body lined with fibrocartilage (not hyaline cartilage). This is due to development from secondary cartilage. Fibrocartilage has better resistance to compressive and shear forces from mastication.
Incorrect. The TMJ is unique — it develops from secondary cartilage (condylar cartilage), not primary cartilage (Meckel's cartilage). Secondary cartilage produces fibrocartilage. This is why the TMJ can remodel under mechanical stress.
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During mouth opening, the initial rotation of the condyle occurs in the lower (discoidal) compartment, followed by forward gliding in the upper (temporodiscal) compartment. Which muscle is primarily responsible for the forward gliding phase?
Correct! The lateral pterygoid (especially the lower head) protracts the condyle during the gliding phase in the upper compartment. The upper head attaches to the articular disc and helps stabilise the disc during condylar movement.
TMJ opening: Phase 1 — rotation in lower compartment (hinge). Phase 2 — translation (gliding) in upper compartment, driven by lateral pterygoid. The articular disc is attached anteriorly to the lateral pterygoid, preventing disc prolapse.
Incorrect. Forward gliding (translation) in the upper compartment = lateral pterygoid action. Masseter and medial pterygoid elevate the jaw; posterior temporalis retracts it.
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A patient develops high fever, proptosis, ophthalmoplegia, and chemosis one week after an untreated periapical abscess of the upper second molar. The most likely intracranial complication is:
Correct! Dental infections (especially upper molars) can spread via the pterygopalatine fossa → pterygoid venous plexus → emissary veins through foramen ovale → cavernous sinus. The triad of proptosis + ophthalmoplegia + chemosis with sepsis = cavernous sinus thrombosis.
Dental infection → cavernous sinus thrombosis pathway: Upper molar/premolar → pterygopalatine fossa → pterygoid venous plexus → emissary vein through foramen ovale → cavernous sinus. Signs: fever, proptosis, chemosis, ophthalmoplegia (CN III, IV, VI), facial pain (CN V1/V2), papilloedema.
Incorrect. The pterygoid venous plexus connects to the cavernous sinus via emissary veins (through foramen ovale and foramen spinosum). Dental sepsis spreading along this route causes cavernous sinus thrombosis, not extradural haematoma (which requires trauma).
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The pterion is the thinnest region of the skull. It overlies the anterior branch of which artery, making it vulnerable in head trauma?
Correct! The anterior branch of the middle meningeal artery (a branch of the maxillary artery that enters through foramen spinosum) runs in a groove immediately deep to the pterion. Fracture at the pterion tears this artery → extradural haematoma.
Pterion = junction of frontal + parietal + temporal + sphenoid bones. Thinnest skull point. Overlies anterior branch of middle meningeal artery. Classic extradural haematoma: lucid interval + deterioration. Treatment: burr hole at pterion.
Incorrect. The middle meningeal artery (anterior branch) runs in a groove on the inner surface of the temporal bone, directly beneath the pterion. Pterion fracture = middle meningeal artery tear = extradural haematoma.
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In the Hippocratic manoeuvre to reduce an anterior TMJ dislocation, the operator's thumbs are placed on the lower molar teeth. The direction of force applied is:
Correct! In the Hippocratic manoeuvre, the thumbs press the molar region downward (to free the condyle from anterior to the articular tubercle) while the fingers lift the chin upward and backward — net movement is downward + backward for the condyle to slip back into the mandibular fossa.
Hippocratic manoeuvre: Thumbs on lower molars (padded with gauze — to prevent biting injury). Push downward and backward. Fingers lift chin anteriorly. The condyle descends past the articular tubercle and glides back into the mandibular fossa. Feel/hear the "clunk" of reduction.
Incorrect. The Hippocratic manoeuvre applies downward pressure on the molars (thumbs) + upward lift on the chin (fingers) = the condyle moves downward first (clears the articular tubercle) and then backward into the mandibular fossa.
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The superficial head of masseter originates from:
Correct! The superficial head of masseter originates from the lower border of the zygomatic arch (anterior 2/3 of the arch). The deep head originates from the medial surface (deep surface) of the zygomatic arch.
Masseter origin: Superficial head = lower border, anterior 2/3 of zygomatic arch. Deep head = medial surface of zygomatic arch. Insertion: both into lateral surface of ramus and coronoid process. The masseter is the most powerful elevator of the jaw per unit volume.
Incorrect. Masseter has two heads: Superficial — lower border of zygomatic arch (anterior 2/3); Deep — medial surface of zygomatic arch. Both insert into the lateral surface of the mandibular ramus.
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Which ligament of the TMJ runs from the spine of the sphenoid to the lingula of the mandible and is an accessory (extracapsular) ligament?
Correct! The sphenomandibular ligament is an accessory extracapsular ligament of the TMJ running from the spine of the sphenoid to the lingula of the mandible (the bony projection guarding the mandibular foramen). It is a remnant of Meckel's cartilage.
TMJ ligaments: (1) Temporomandibular/lateral ligament — capsular thickening; limits posterior condyle movement. (2) Sphenomandibular — spine of sphenoid to lingula of mandibular foramen; extracapsular; Meckel's cartilage remnant. (3) Stylomandibular — styloid to mandible angle; separates parotid and submandibular glands.
Incorrect. Sphenomandibular ligament: spine of sphenoid → lingula of mandible; extracapsular; derived from Meckel's cartilage. Not to be confused with the temporomandibular (lateral) ligament, which is the primary capsular thickening.
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Trismus (inability to open the mouth) following a third molar (wisdom tooth) extraction is most likely caused by:
Correct! After lower third molar extraction, the inferior alveolar nerve block (medial pterygoid is adjacent to the injection site) and surgical trauma to the medial pterygoid (which lies in the pterygomandibular space) causes spasm → trismus. The medial pterygoid closes the jaw; its spasm prevents opening.
Trismus after dental extraction: most commonly from medial pterygoid spasm/haematoma. The medial pterygoid lies in the pterygomandibular space — directly adjacent to the inferior alveolar nerve block injection site. Injection trauma, haematoma, or infection causes spasm → inability to open the jaw.
Incorrect. Trismus post-lower molar extraction = medial pterygoid spasm. The medial pterygoid lies immediately medial to the ramus in the pterygomandibular space, making it vulnerable to needle trauma or haematoma from the inferior alveolar nerve block.
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