Sternocleidomastoid muscle

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The sternocleidomastoid muscle (sternomastoid muscle) is a neck muscle that extends from the upper part of chest bones to the top of the neck along the side. There is one sternocleidomastoid muscle on each side of the neck. As the name implies, it has attachments to the sternum, clavicle and the mastoid process on the lower skull.

The sternocleidomastoid is easily visible at the base of the neck when the head is turned sharply to either side.

Contents

Origin

The sternocleidomastoid originates as two heads, one from the upper part of the sternum called the manubrium sterni and the other from the medial part of the clavicle.

Insertion

The sternocleidomastoid inserts on two bones of the skull - the mastoid process on the temporal bone and the occipital bone at the anterior half of the superior nuchal line.

Action

The sternocleidomastoid muscle has several actions. The muscle on each side of the neck helps in moving the head towards the same shoulder and rotating the head towards opposite side. Sternocleidomastoid muscles on both sides working together help in bending the neck forward and in forced inspiration.

Innervation

The sternocleidomastoid muscle is innervated by accessory nerves of C1-C5.

Word origin

The word sternocleidomastoid is built from the muscle's three attachment points:

See also

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