National Consortium for Health Science Education Practice Test

The sternocleidomastoid is the primary muscle located in the neck that is responsible for several important functions. It plays a key role in the rotation and flexion of the head and neck. This muscle originates from two points: the manubrium of the sternum and the clavicle, and it inserts at the mastoid process of the temporal bone of the skull.

When one side of the sternocleidomastoid contracts, it rotates the head to the opposite side and tilts it forward. When both sides contract simultaneously, they help to flex the neck forward. This muscle is also significant in maintaining posture and assisting in movements such as nodding or looking up and down.

In contrast, the other muscles listed, such as the deltoid, trapezius, and supraspinatus, are located in different areas of the body and are involved in different movements and functions. The deltoid is primarily responsible for shoulder movements, the trapezius supports the shoulders and upper back, and the supraspinatus is involved in shoulder abduction. These muscles, therefore, do not serve the same functions as the sternocleidomastoid in the neck region.