Sternocleidomastoid muscle

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Description:

Origin:
Anterior upper margin of the manubrium of the sternum; superior aspect of the medial third of the clavicle

Insertion:
Lateral side of the mastoid process and lateral portion of the superior nuchal line

Actions:
Flexes and rotates the head

Nerve supply:
Accessory nerve

Blood supply:
Branches of the external carotid and subclavian arteries