Sternomastoid muscle

The sternocleidomastoid muscle (SCM) is a paired muscle in the superficial layers of the side of the neck. It is one of the largest and most superficial cervical muscles. The name derives from its three attachments: the sternum, the clavicle, and the mastoid process of the temporal bone.

Structure

The sternocleidomastoid muscle originates from the manubrium of the sternum and the medial portion of the clavicle. It inserts at the mastoid process of the temporal bone and the superior nuchal line of the occipital bone.

Innervation

The muscle is innervated by the accessory nerve (cranial nerve XI) and receives additional innervation from the cervical plexus (C2, C3).

Function

The primary actions of the sternocleidomastoid muscle are the rotation of the head to the opposite side and flexion of the neck. When both sides of the muscle act together, they flex the neck and extend the head. The muscle also plays a role in respiration by elevating the sternum and thus the rib cage.

Clinical significance

The sternocleidomastoid muscle can be involved in various clinical conditions. Torticollis, also known as "wry neck," is a condition where the muscle is contracted, causing the head to tilt to one side. This can be congenital or acquired. The muscle can also be affected in cases of muscle strain or spasms.

Additional images

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  The sternocleidomastoid muscle shown in red

See also

• Muscles of the neck
• Accessory nerve
• Torticollis

External links

• Sternocleidomastoid muscle on WikiMD