Sternocleidomastoid: Origin, Insertion, Nerve Supply & Action

The sternocleidomastoid muscle is also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the side of the neck. It is one of the most sizably voluminous and most superficial cervical muscles.

Attachments of the Sternocleidomastoid

Origin:
The anterior surface of the upper sternum
The inner part of the clavicle.

Insertion:
Mastoid process (behind the ear).

Function of the Sternocleidomastoid
Contraction on both sides: Neck flexion.
Contraction on one side only: Laterally flexes to the same side(side bends) and rotates to the other side.