Depression of the mandible includes which muscles (and gravity)?

• A. Lateral pterygoid, digastric, geniohyoid, mylohyoid
• B. Temporalis
• C. Masseter
• D. Medial pterygoid

Answer: (A)

Depression of the mandible occurs when the mouth opens, mainly through the action of muscles that pull the mandible downward or forward, aided by gravity. The lateral pterygoid (inferior head) helps depress and protrude the mandible by pulling the condyle and articular disc forward. The digastric (anterior belly), mylohyoid, and geniohyoid are suprahyoid muscles that pull the mandible downward when the hyoid is stabilized, enabling opening of the mouth. Gravity also assists this process, especially as the jaw opens.

The other listed muscles are primary jaw closers. Temporalis, masseter, and medial pterygoid elevate the mandible, not depress it, so they do not contribute to opening the jaw.