Trapezius Muscle (Left)

Origin

The trapezius muscle originates from the:

- external occipital protuberance of occipital bone;

- superior nuchal line of occipital bone;

- nuchal ligament;

- spinous processes of seventh cervical and first to twelfth thoracic vertebrae;

- adjacent supraspinous ligaments.

Insertion

The fibers of the trapezius muscle travel laterally and converge to a tendon, which inserts onto the:

- posterior aspect of the lateral one third of clavicle;

- acromion of scapula;

- spine of scapula.

Key Features & Anatomical Relations

Overall, the trapezius muscle is an extrinsic muscle of the back and is found in the posterior cervical and upper back regions. It is a large, flat, triangular skeletal muscle that is composed of three parts:

- a descending part, which is the superior portion;

- a transverse part, which is the middle portion;

- an ascending part, which is the inferior portion.

The trapezius muscle is located:

- superficial to the semispinalis, spinotransversales, levator scapulae, rhomboid major, rhomboid minor, supraspinatus, and latissimus dorsi muscles;

- medial to the deltoid and infraspinatus muscles.

The trapezius muscle contributes to the formation of the:

- posterior cervical region, where the descending part of trapezius muscle forms its anterior boundary;

- lateral cervical region, where the descending part of trapezius muscle forms its posterior boundary;

- triangle of auscultation, where the ascending part of trapezius muscle forms its superomedial boundary.

Actions & Testing

Overall, the trapezius muscle is involved in multiple actions:

- elevates, depresses, retracts and upwardly rotates the pectoral (shoulder) girdle at the acromioclavicular and sternoclavicular joints;

- during unilateral contraction, it laterally flexes the head and neck to the same side;

- during bilateral contraction, it extends the head and neck.

Overall, the trapezius muscle can be tested by elevating the pectoral girdle (i.e., shrugging the shoulders) against resistance, during which the muscle can be seen and palpated (Moore, Dalley and Agur, 2009).

List of Clinical Correlates

- Contributes to the formation of the triangle of auscultation

References

Moore, K. L., Dalley, A. F. and Agur, A. M. R. (2009) Clinically Oriented Anatomy. Lippincott Williams & Wilkins.