Which muscles act as agonists in left rotation of the neck?

• A. Right SCM, Right Scalenes, Right Trapezius, Left Levator Scapulae
• B. Left SCM, Left Scalenes, Left Trapezius, Right Levator Scapulae
• C. Pectoralis Major
• D. Latissimus Dorsi

Answer: (A)

Rotating the neck to the left is produced mainly by muscles that pull the head toward the right, creating leftward rotation. The primary mover on that side is the sternocleidomastoid on the right; when it shortens, it pulls the head to the right at the same time that the skull rotates to the left, making it the key agonist for left rotation.

The scalene muscles on the right contribute as well, aiding the contralateral rotation and helping stabilize the neck as rotation occurs. The upper fibers of the trapezius on the right can also assist by influencing the atlas and occiput to promote rotation to the left. On the left side, the levator scapulae can help with ipsilateral rotation when the shoulder girdle is stabilized, further supporting leftward turning.

Pectoralis major and latissimus dorsi don’t primarily rotate the neck; they act on the shoulder girdle and trunk, so they aren’t considered agonists for neck rotation.