Trapezius muscle

The trapezius muscle (m. trapezius) is flat, triangular in shape, with a wide base facing the posterior midline. The muscle occupies the upper part of the back and the posterior region of the neck. It begins with short tendinous bundles from the external occipital protuberance, the medial third of the superior nuchal line of the occipital bone, from the nuchal ligament, the spinous islands of the seventh cervical and all thoracic vertebrae and from the supraspinous ligament. From the points of origin, the muscle bundles are directed, noticeably converging, in the lateral direction and are attached to the bones of the shoulder girdle. The upper bundles of the muscle pass downward and laterally, are attached to the posterior surface of the outer third of the clavicle. The middle bundles are oriented horizontally outward and are attached to the acromion and the scapular spine. The lower bundles of the muscle follow upward and laterally, pass into the tendinous plate, which is attached to the scapular spine. The tendinous origin of the trapezius muscle is more pronounced at the level of the lower border of the neck, where the muscle has the greatest width. At the level of the spinous process of the 7th cervical vertebra, the muscles of both sides form a well-defined tendinous area, which is found as an indentation in a living person.

The trapezius muscle is located superficially throughout its length, its upper lateral edge forms the back of the lateral triangle of the neck. The lower edge of the trapezius muscle covers the upper part of the latissimus dorsi and the medial edge of the scapula, forming the medial border of the so-called auscultation triangle. The lower border of this triangle runs along the upper edge of the latissimus dorsi, and the lateral border runs along the lower edge of the rhomboid major muscle (the size of the triangle increases when the arm is bent forward at the shoulder joint, when the scapula is displaced laterally and anteriorly).

Function: When all parts of the trapezius muscle contract simultaneously with the spine fixed, the scapula approaches the spine. The upper bundles of the muscle elevate the scapula. The upper and lower bundles of the muscle, when contracting simultaneously, rotate the scapula around the sagittal axis: the lower angle of the scapula shifts forward and laterally, and the lateral angle moves upward and medially. When the scapula is fixed and contracted on both sides, the trapezius muscles extend the cervical spine and tilt the head back. When contracting unilaterally, the muscle turns the face to the opposite side.

Innervation: accessory nerve, cervical plexus (CIII-CIV).

Blood supply: transverse cervical artery, suprascapular, occipital arteries, posterior intercostal arteries.