Which action at the mandible would shorten the fibers of the masseter?

• A. Elevation
• B. Depression
• C. Protraction
• D. Retraction

Answer: (A)

Elevating the mandible shortens the fibers of the masseter. The masseter runs from the zygomatic arch to the lower jaw, so when it contracts it pulls the mandible upward toward the cheekbone, bringing the teeth together. That contraction shortens the muscle fibers themselves.

Lowering the jaw would stretch the masseter rather than shorten it, and moving the jaw forward or backward (protraction or retraction) relies more on other muscles and doesn’t place the masseter in a shortened state. So, the action that makes the masseter fibers shorten is elevation.