Trapezius muscle

Last revised by Wilson Tao on 24 Jun 2024

The trapezius muscle is a large, broad superficial muscle of the posterior neck and back. It gains its name from its diamond shape. Along with sternocleidomastoid muscle, it is invested by the superficial layer of the deep cervical fascia, which splits around it. 

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It has many origins due to its large size:

  • medial third of superior nuchal line

  • inion and external occipital protuberance

  • nuchal ligament

  • spinous processes of C7-T12 vertebrae and the corresponding supraspinous ligaments

  • clavicle: occipital fibers insert onto the posterior aspect of the lateral third of clavicle

  • scapula: occipital fibers insert onto the medial acromion and superior lip of scapular spine, while the lower fibers from the T6-T12 spinous processes insert onto the medial end of the spine

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  • spinal part (C1-C5 or C6) of the accessory nerve (cranial nerve XI) provides motor supply

  • branches of cervical plexus (C3 and C4 spinal nerves) supply pain and proprioceptive fibers

  • all fibers: retract the scapula medially

  • upper fibers only: elevate and rotate scapula up to aid in shoulder abduction

  • middle fibers only: retract scapula

  • lower fibers only: depress and rotate scapula down

  • upper and lower fibers together: rotate spinous process of scapula superiorly

  • with the shoulders fixed:

    • bilateral contraction extends neck

    • unilateral contraction produces ipsilateral flexion

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