Sternocleidomastoid Muscle: Function, Movement, and Anatomy

Rotation of the head to the opposite side and flexion of the neck to the same side.

The sternocleidomastoid muscle is a paired muscle that runs from the sternum and clavicle to the mastoid process of the temporal bone. It is innervated by the accessory nerve (cranial nerve XI) and the branches of the cervical plexus. The sternocleidomastoid muscle is responsible for rotating the head to the opposite side and flexing the neck to the same side.