[3] It is given the name sternocleidomastoid because it originates at the manubrium of the sternum (sterno-) and the clavicle (cleido-) and has an insertion at the mastoid process of the temporal bone of the skull.

[4] It travels obliquely across the side of the neck and inserts at the mastoid process of the temporal bone of the skull by a thin aponeurosis.

The clavicular head is composed of fleshy and aponeurotic fibers, arises from the upper, frontal surface of the medial third of the clavicle; it is directed almost vertically upward.

The two heads are separated from one another at their origins by a triangular interval (lesser supraclavicular fossa) but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.

The accessory nerve nucleus is in the anterior horn of the spinal cord around C1-C3, where lower motor neuron fibers mark its origin.

The movement of troponin and tropomyosin is key in facilitating the myosin head to move along the thin filament, resulting in a contraction of the sternocleidomastoid muscle.

[9] Many important structures relate to the sternocleidomastoid, including the common carotid artery, accessory nerve, and brachial plexus.

[9] The triangle formed by the clavicle and the sternal and clavicular heads of the sternocleidomastoid muscle is used as a landmark in identifying the correct location for central venous catheterization.

Congenital torticollis can have an unknown cause or result from birth trauma that gives rise to a mass or tumor that can be palpated within the muscle.