Which muscle rotates the head and flexes the head?

Which muscle rotates the head and flexes the head?

• A. Frontalis
• B. Masseter
• C. Sternocleidomastoid
• D. External Intercostals

Answer: (C)

Rotating the head and flexing the head require a muscle that crosses the neck and can act on the skull. The sternocleidomastoid fits this perfectly: when both sides contract, it flexes the head forward; when it contracts on one side, it rotates the head to the opposite side. Its attachments—originating from the sternum and clavicle and inserting on the mastoid process—place it in the right position to influence head movement. The other muscles listed do not move the head: the frontalis raises the eyebrows, the masseter elevates the jaw, and the external intercostals lift the ribs during breathing. Therefore, the sternocleidomastoid is the one that can both rotate and flex the head.

Rotating the head and flexing the head require a muscle that crosses the neck and can act on the skull. The sternocleidomastoid fits this perfectly: when both sides contract, it flexes the head forward; when it contracts on one side, it rotates the head to the opposite side. Its attachments—originating from the sternum and clavicle and inserting on the mastoid process—place it in the right position to influence head movement. The other muscles listed do not move the head: the frontalis raises the eyebrows, the masseter elevates the jaw, and the external intercostals lift the ribs during breathing. Therefore, the sternocleidomastoid is the one that can both rotate and flex the head.