The trapezius muscle is a large muscle in the back that extends from the base of the skull to the mid-back, attaching to the scapula (shoulder blade), clavicle (collarbone), and the length of the spine. There is one trapezius on each side of the back.
The trapezius is a superficial muscle that serves a number of important functions for movement. Daily use involves shrugging the shoulders and overhead movements. As a whole, it provides support to the spine and neck and enables arm, neck and shoulder movement. It also serves to stabilize, raise, retract (bring together) and rotate the scapulae. Another function of the trapezius is as a breathing muscle. Though not as powerful as the diaphragm for this use, it can help to open the upper chest area to allow a small amount of breathing room.
The three regions of the trapezius are the superior (upper), intermediate (middle) and inferior (lower) fibers. The superior region works to elevate the scapula, or shrugging the shoulders upward. The middle fibers raise, rotate and pull the shoulder blades back and together. The lower region helps to arch the upper back, move the shoulder blades, and enable lateral raising and rowing movements.
The trapezius has a complex origin along the back of the vertebral column extending from the base of the skull to the last thoracic vertebra. It attaches at the medial third of the superior nuchal line, the nuchal ligament, the spinous processes of C7-T12 - the seventh cervical vertebrae and all (T1-T12) the thoracic vertebrae, and the supraspinous ligament above C7-T12.
The trapezius has a complex insertion at the back of the shoulder, where it attaches to the scapula (shoulder blade) and the clavicle (collar bone). The upper fibers insert at the lateral third of posterior border of the clavicle. The lower fibers insert at the medial acromion process and the superior lip of the spine of scapula.
The name trapezius comes from the trapezoidal shape made by the right and left triangular-shaped sides.