Trapezius (Full Overview)

musculus trapezius overview

The trapezius covers the posterior neck and upper thorax. Its three parts coordinate scapular movement for full shoulder elevation — the lower trapezius depresses and rotates the scapula as the upper and middle elevate and retract it.

Nerve: Accessory nerve (CN XI) — motor; C3, C4… Blood Supply: Transverse cervical artery Region: Neck

Anatomical Data

Origin, Insertion & Supply

Origin	External occipital protuberance, superior nuchal line, nuchal ligament, spinous processes C7-T12
Insertion	Spine of scapula, acromion, lateral third of clavicle
Nerve Supply	Accessory nerve (CN XI) — motor; C3, C4 — proprioceptive
Blood Supply	Transverse cervical artery

Biomechanics

Function & Actions

Actions	Upper fibres: elevate scapula and extend head; Middle fibres: retract scapula; Lower fibres: depress scapula and rotate glenoid upward

Clinical Relevance

Clinical Notes

CN XI palsy causes shoulder droop, loss of retraction, and inability to elevate the arm above 90 degrees due to lost scapular upward rotation. Trapezius is frequently divided in posterior cervical surgery. Used as a musculocutaneous flap for posterior neck reconstruction.

Palpation

Upper fibres at neck-shoulder junction; middle at interscapular space; lower along lower thoracic spine during resisted shoulder movements.

Pathology

Common Injuries & Conditions

CN XI Palsy with Trapezius Weakness

Accessory nerve injury producing trapezius paralysis with shoulder drop, superior scapular winging, and loss of arm elevation, managed by CN XI repair or Eden-Lange transfer.