The sternocleidomastoid (sternocleidomastoideus; sternomastoid) muscle is located in the neck. It is a thin, broad muscle that narrows at the center. It originates from two heads, one from the sternum and and one from the clavicle , and runs upward, inserting into the mastoid process. The sternocleidomastoid muscle is innervated by the accessory nerve and the cervical plexus. It is supplied by the occipital arteryans the superior thyroidartery. This muscle is used to tilt the head from side to side. Research Sternocleidomastoid