sternocleidomastoideuksen

The sternocleidomastoideus, often abbreviated as SCM, is a paired, superficial muscle of the anterior neck. It originates from the clavicle and the manubrium of the sternum and inserts onto the mastoid process of the temporal bone and the nuchal line of the occipital bone. This anatomical placement allows the SCM to perform a variety of crucial movements and stabilize the head.

When both sternocleidomastoideus muscles contract simultaneously, they flex the neck, bringing the chin towards the chest. Acting unilaterally, meaning one SCM contracts while the other relaxes, it causes ipsilateral lateral flexion of the head, tilting the head towards the same side. It also causes contralateral rotation of the head, turning the face towards the opposite side. In addition to these actions, the SCM plays a significant role in elevating the sternum and clavicle during forced inspiration, acting as an accessory muscle of respiration.

Innervation of the sternocleidomastoideus is primarily supplied by the accessory nerve (cranial nerve XI) and branches from the cervical plexus. Its function is vital for everyday activities such as looking around, maintaining posture, and breathing. Dysfunction or tightness in the SCM can lead to conditions like torticollis, also known as wryneck, characterized by a tilted head and limited range of motion.