Descending Part of Trapezius Muscle

Origin

The descending part of trapezius muscle originates from the:

- external occipital protuberance of occipital bone;

- superior nuchal line of occipital bone;

- nuchal ligament;

- spinous process of seventh cervical vertebra.

Insertion

The fibers of the descending part of trapezius muscle travel inferolaterally along the posterior cervical region. They converge to a tendon, which inserts onto the:

- posterior aspect of the lateral one third of the clavicle;

- anterior half of acromion of scapula.

Key Features & Anatomical Relations

Overall, the trapezius muscle is an extrinsic muscle of the back and is found in the posterior neck 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.

With regard to the descending part of trapezius muscle specifically, it 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.

Actions & Testing

The descending part of trapezius muscle is involved in multiple actions:

- elevates the pectoral (shoulder) girdle at the acromioclavicular and sternoclavicular joints;

- retracts the pectoral girdle at the acromioclavicular and sternoclavicular joints;

- upwardly rotates the pectoral 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).

References

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