mellkasüreg

Mellkasüreg, also known as the *sternocleidomastoid muscle*, is a prominent paired muscle located in the human neck. It extends from the sternum and clavicle (hence its name, derived from Latin and Greek roots meaning "sternum," "clavicle," and "sleeve" or "muscle") to the mastoid process of the temporal bone near the ear. This muscle plays a crucial role in head movement and posture.

The sternocleidomastoid is responsible for rotating and flexing the neck. When both muscles contract simultaneously, they flex the neck, bringing the chin closer to the chest. If only one muscle contracts, it rotates the head toward the opposite shoulder while tilting it slightly. This muscle also aids in lateral flexion, tilting the head sideways.

Anatomically, the sternocleidomastoid is superficial, making it easily visible and palpable beneath the skin. It is innervated by the accessory nerve (cranial nerve XI) and branches of the cervical plexus, which provide sensory input. The muscle is covered by the superficial layer of the cervical fascia and is separated from deeper structures by a layer of fat and connective tissue.

Conditions affecting the sternocleidomastoid can include muscle strains, spasms, or torticollis, a condition where the muscle contracts abnormally, causing the head to tilt and rotate involuntarily. Overuse or poor posture may contribute to discomfort or dysfunction in this muscle. Proper stretching and ergonomic practices can help maintain its health and function.