anatomy 1

	Sternocleidomastoid muscle
	In human anatomy, the sternocleidomastoid muscle also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the anterior portion of the neck. It acts to flex and rotate the head. It also acts as an accessory muscle of inspiration, along with the scalene muscles of the neck. Etymology 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. Origin and insertion The sternocleidomastoid passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end. The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed superiorly, laterally, and posteriorly. The lateral or clavicular head, composed of fleshy and aponeurotic fibers, arises from the superior border and anterior 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, 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 function of this muscle is to rotate the head to the opposite side or obliquely rotate the head. It also flexes the neck Innervation The sternocleidomastoid is innervated by the ipsilateral accessory nerve.  It supplies only motor fibres. The cervical plexus supplies sensation, including proprioception, via the dorsal primary rami of C2 and C3 Latin musculus sternocleidomastoideus Origin manubrium sterni, medial portion of the clavicle Insertion    mastoid process of the temporal bone, superior nuchal line Artery occipital artery and the superior thyroid artery Nerve motor: accessory nerve sensory: cervical plexus Actions Acting alone, tilts head to its own side and rotates it so the face is turned towards the opposite side. Acting together, flexes the neck, raises the sternum and assists in forced inspiration.