Trapezius Muscle Anatomy

Overview
Origin Superior nuchal line
External occipital protuberance
Nuchal ligament
Spinous processes of C7 to T12 vertebrae
Insertion Lateral third of clavicle
Acromion
Spine of scapula
Action Elevates scapula
Depresses scapula
Scapula adduction
Scapula rotation
Neck extension and lateral flexion.
Nerve Spinal accessory nerve (cranial nerve XI) (motor fibres)
C3, C4 cervical spinal nerves (pain and proprioceptive fibres)
Artery Cervical artery
Dorsal scapular artery
Posterior intercostal arterial branches

Location & Overview

The trapezius muscle is a large back muscle and resembles a trapezoid shape (which gives it its name). It is one of the most superficial muscles (closest to the skin’s surface) of the trunk and upper back[1]. The trapezius is generally broken down into three segments of fibres. It consists of superior, intermediate and inferior regions.

Because the fibres of the superior trapezius descend downwards from the top of the neck to the clavicle, the superior trapezius is sometimes referred to as the descending portion. The intermediate fibres extend horizontally from the spine outwards to the medial border of the acromion. Due to this, the intermediate trapezius is sometimes referred to as the horizontal fibres. Finally, because the inferior portion of the trapezius’s fibres ascend in a superior direction, sometimes the inferior portion is referred to as the ascending fibres. These descriptions can be easily mixed up because the name refers to the direction the fibres move, rather than the muscle’s location[2].

Muscle Fibre Summary:
Superior fibres = descending trapezius
Intermediate fibres = horizontal trapezius
Inferior fibres = ascending trapezius

Here we can see the trapezius muscle in isolation from a posterior view.

Origin & Insertion

The trapezius originates on the superior nuchal line and external occipital protuberance. These are located near the base of the skull. The origins then continue down the nuchal ligament, which runs down the posterior of the neck. It then continues to originate from the spinous processes of C7 to T12 vertebrae. These fibres then go on to insert onto the lateral third of clavicle, acromion and spine of scapula[3].

nuchal ligament

Here we can see the nuchal ligament. It is one of the origin points of the trapezius muscle.

superior nuchal line and external occipital protuberance

Here we can see the superior nuchal line and external occipital protuberance. They are origin points of the trapezius muscle.

trapezius origin marked in red

Here we can see the origin of the trapezius muscle marked in red. The trapezius originates at the superior nuchal line, external occipital protuberance, nuchal ligament and spinous processes of C7 – T12 vertebrae.

insertion of the trapezius marked in blue

Here we can see the insertion of the trapezius muscle marked in blue. The trapezius inserts on the lateral third of the clavicle, acromion and spine of scapula.

Actions

The actions of the trapezius are elevation and depression of the scapula. The superior fibres contribute to elevation whereas the inferior fibres contribute to depression. The trapezius also can contribute to scapula adduction/retraction (primarily the intermediate fibres). The inferior and superior fibres of the trapezius can also work together to assist in scapula rotation, to angle the glenohumeral joint of the scapula upwards. The superior fibers can rotate the scapula medially whereas the inferior fibers can rotate it laterally [4]. The trapezius can also cause neck extension and lateral flexion (tilting the head back and side to side) [5].

Innervation

The trapezius muscle is innervated by the spinal accessory nerve (CN XI) (motor fibres) and C3, C4 cervical spinal nerves (pain and proprioceptive fibres)[6].

Blood Supply

Blood is suppled to the trapezius by the transverse cervical artery, dorsal scapular artery (superior portion) and posterior intercostal arterial branches(deep portions)[7].

Want some flashcards to help you remember this information? Then click the link below:
Trapezius Muscle Flashcards

References

References
1 Johnson G, Bogduk N, Nowitzke A, House D. Anatomy and actions of the trapezius muscle. Clin Biomech (Bristol, Avon). 1994 Jan;9(1):44-50. doi: 10.1016/0268-0033(94)90057-4. PMID: 23916077.
2, 4 Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.
3, 5, 6 Ourieff J, Scheckel B, Agarwal A. Anatomy, Back, Trapezius. [Updated 2021 Jul 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK518994/
7 Netterville JL, Wood DE. The lower trapezius flap. Vascular anatomy and surgical technique. Arch Otolaryngol Head Neck Surg. 1991 Jan;117(1):73-6. doi: 10.1001/archotol.1991.01870130079020. PMID: 1986765.