Sternocleidomastoid muscle

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. ==Structure==

The sternocleidomastoid muscle originates from two locations: the manubrium of the sternum and the clavicle, hence it is said to have two heads: sternal head and clavicular head. 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 sternocleidomastoid is thick and narrow at its center, and broader and thinner at either end. The sternal head is a round fasciculus, tendinous in front, fleshy behind, arising from the upper part of the front of the manubrium. It travels superiorly, laterally, and posteriorly. 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 called '''Sedillot's triangle''' 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. Nerve supply The sternocleidomastoid is innervated by accessory nerve of the same side. It supplies only motor fibres. The cervical plexus supplies sensation, including proprioception, from the ventral primary rami of C2 and C3. Variation The clavicular origin of the sternocleidomastoid varies greatly: in some cases the clavicular head may be as narrow as the sternal; in others it may be as much as in breadth. When the clavicular origin is broad, it is occasionally subdivided into several slips, separated by narrow intervals. More rarely, the adjoining margins of the sternocleidomastoid and trapezius are in contact. This would leave no posterior triangle. The supraclavicularis muscle arises from the manubrium behind the sternocleidomastoid and passes behind the sternocleidomastoid to the upper surface of the clavicle. ==Function==

The function of this muscle is to rotate the head to the opposite side or obliquely rotate the head. Anatomical landmark labelled. The sternocleidomastoid is within the deep fascia of the neck, along with the trapezius muscle, with which it shares its nerve supply (the accessory nerve). It is thick and thus serves as a primary landmark of the neck, as it divides the neck into anterior and posterior cervical triangles (in front and behind the muscle, respectively) which helps define the location of structures, such as the lymph nodes for the head and neck. Many important structures relate to the sternocleidomastoid, including the common carotid artery, accessory nerve, and brachial plexus. ==Clinical significance==

Examination of the sternocleidomastoid muscle forms part of the examination of the cranial nerves. It can be felt on each side of the neck when a person moves their head to the opposite side. Contraction of the muscle gives rise to a condition called torticollis or wry neck, and this can have a number of causes, including rheumatic, reflex or congenital causes. Torticollis gives the appearance of a tilted head on the side involved. Treatment involves physiotherapy exercises to stretch the involved muscle and strengthen the muscle on the opposite side of the neck. 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. ==References==