Which muscle primarily opens the mouth (lowers the mandible)?

Which muscle primarily opens the mouth (lowers the mandible)?

• A. Lateral pterygoid
• B. Medial pterygoid
• C. Masseter
• D. Temporalis

Answer: (A)

Opening the mouth involves depressing the mandible. The muscle that does this primarily is the lateral pterygoid. Its inferior head attaches to the neck of the mandible and, when it contracts, it pulls the condyle and the articular disc forward and downward, effectively lowering the jaw to create opening, especially when the mouth is being opened wide or protruded. The other muscles listed mainly elevate the mandible to close the mouth: the masseter and medial pterygoid lift the jaw (with the latter assisting in some protrusion), and the temporalis elevates and can retract the jaw. So the lateral pterygoid is the best answer because its main action is to depress and protrude the mandible, enabling mouth opening.

Opening the mouth involves depressing the mandible. The muscle that does this primarily is the lateral pterygoid. Its inferior head attaches to the neck of the mandible and, when it contracts, it pulls the condyle and the articular disc forward and downward, effectively lowering the jaw to create opening, especially when the mouth is being opened wide or protruded. The other muscles listed mainly elevate the mandible to close the mouth: the masseter and medial pterygoid lift the jaw (with the latter assisting in some protrusion), and the temporalis elevates and can retract the jaw. So the lateral pterygoid is the best answer because its main action is to depress and protrude the mandible, enabling mouth opening.