The sternocleidomastoid is a prominent muscle located in the neck. It plays a crucial role in head movement, allowing the head to rotate and tilt. This muscle originates from two points: the sternum and the clavicle, and it inserts at the mastoid process of the skull, which is located just behind the ear. When the sternocleidomastoid contracts, it can flex the neck or turn the head to the opposite side. It is also involved in activities such as looking up or down. This muscle is easily identifiable as it runs diagonally along the side of the neck.