Trapezius Muscle Anatomy

The trapezius muscle is a triangular muscle covers the posterior aspect of the neck and the superior half of the trunk. It provides a direct attachment of the pectoral girdle to the trunk. The trapezius was given its name because the muscles of the two sides form a trapezium (G. irregular four-sided figure).

The trapezius muscle attaches the pectoral girdle to the cranium and vertebral column and assists in suspending the upper limb. The fibers of the trapezius are divided into three parts, which have different actions at the physiological scapulothoracic joint between the scapula and thoracic wall.

Trapezius Muscle Anatomy

The Trapezius Muscle has multiple origins, it originates from the medial third of superior nuchal line, external occipital protuberance, nuchal ligament and spinous processes of C7 – T12 vertebrae. It also has 3 different insertions on the lateral third of clavicle, the acromion and spine of scapula.

See Also: Scapula Anatomy

There are three components of the trapezius muscle:

1. The superior portion attaches to the skull (external occipital protuberance and superior nuchal line) and neck (ligamentum nuchae). This portion of the muscle extends the head at the neck.
2. The middle portion attaches to the upper part of the spinous processes of C7-T12. This portion adducts (draws together) the two scapulae.
3. The inferior portion (lower part of C7-T12) depresses the scapula.

The innervation to the Trapezius Muscle comes from the spinal root of accessory nerve (CN XI) (motor) and cervical nerves (C3 and C4) (pain and proprioception) (XI, C3, C4). The blood supply comes from the transverse cervical artery.

Descending and ascending trapezius fibers act together in rotating the scapula on the thoracic wall in different directions, twisting it. The trapezius muscle also braces the shoulders by pulling the scapulae posteriorly and superiorly, fixing them in position on the thoracic wall with tonic contraction; consequently, weakness of the trapezius causes drooping of the shoulders.

See Also: Normal Shoulder Range of Motion

To test the trapezius muscle (or the function of the spinal accessory nerve [CN XI] that supplies it), the shoulder is shrugged against resistance (the person attempts to raise the shoulders as the examiner presses down on them). If the muscle is acting normally, the superior border of the muscle can be easily seen and palpated.

References & More

1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice
2. Clinically Oriented Anatomy – 8th Edition
3. Ourieff J, Scheckel B, Agarwal A. Anatomy, Back, Trapezius. [Updated 2023 Mar 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed