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The Temporomandibular Joint (TMJ) Quiz
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Which muscle is primarily responsible for protrusion (forward movement) of the mandible at the temporomandibular joint?
- A Suprahyoid muscle group You picked ✕
- B Lateral pterygoid muscle You picked ✓
- C Medial pterygoid muscle acting alone You picked ✕
- D Posterior fibres of temporalis muscle You picked ✕
- E Masseter muscle You picked ✕
Correct!
Incorrect
The answer is B: Lateral pterygoid muscle
Explanation
Why B is correct
See Movements of the TMJ. Option B is correct. The lateral pterygoid is a small, triangular muscle that runs almost horizontally from the sphenoid bone (a bone at the base of the skull) to the neck of the mandible and the joint disc. Because its fibres run horizontally, contracting both sides pulls the mandibular head and disc forwards, so it is the major protractor of the mandible (protrusion means pushing the jaw forwards). Both sides together also depress the chin, helping the mouth to open. Like all the muscles of mastication (chewing), it is supplied by the mandibular nerve (V3), a branch of the trigeminal nerve. The medial pterygoid assists with protrusion, but its main job is elevation, and the posterior fibres of temporalis do the opposite by retracting the jaw. A simple way to link muscle to movement is to picture the direction of the fibres: horizontal fibres move the jaw forwards, vertical fibres move it up.
- Muscle: The lateral pterygoid is the major protractor of the mandible.
- Fibre direction: Its fibres run horizontally, so contracting both sides pulls the mandibular head and disc forwards.
- Nerve supply: The mandibular nerve (V3), like all the muscles of mastication.
Why the other options are incorrect
- A. Suprahyoid muscle group: The suprahyoid muscles lie above the hyoid bone and help to depress the mandible when the mouth opens against resistance. They do not move the jaw forwards. Your answer
- C. Medial pterygoid muscle acting alone: Medial pterygoid assists protrusion, but it mainly elevates the mandible and it is the lateral pterygoid that is the major protractor. The option says 'acting alone', which makes it the wrong choice for the primary mover. Your answer
- D. Posterior fibres of temporalis muscle: The posterior fibres of temporalis pull the mandible backwards, so they perform retraction, the opposite of protrusion. They would be the answer to a question about retraction. Your answer
- E. Masseter muscle: Masseter is a powerful elevator of the mandible, closing the mouth and biting hard. It does not drive the jaw forwards. Your answer
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More questions from this set. Start the quiz to answer them and see each explanation.
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1
Which clinical feature is most characteristic of temporomandibular joint (TMJ) disorder?
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2
During wide opening of the mouth while yawning, which movement occurs at the temporomandibular joint after the initial hinge phase?
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