Sternocleidomastoid
Latin: M. sternocleidomastoideus
Location: Neck
View the sternocleidomastoid in 3DOrigin
Sternal head: manubrium of the sternum. Clavicular head: superior surface of the medial third of the clavicle.
Insertion
Mastoid process and superior nuchal line of the temporal bone.
Action
Acting alone: rotates the head to the opposite side and tilts it to the same side (the 'look over the shoulder' muscle). Acting together: flexes the neck and, against resistance, assists forced inspiration by elevating the sternum.
Nerve supply
Spinal accessory nerve (CN XI) motor; C2–C3 proprioceptive.
Blood supply
Occipital and superior thyroid arteries.
Clinical relevance
Congenital torticollis fibroses and shortens the muscle, tilting the head toward and rotating away from the lesion. It is the key landmark for central venous cannulation — the internal jugular vein lies deep to the triangle between its sternal and clavicular heads.
Educational anatomy reference, not medical advice. About this content.