trapezius muscle

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.

Summary

• origin: superior nuchal line, inion, nuchal ligament, and spinous processes of C7-T12 vertebrae 
• insertion: clavicle and scapula
• innervation: accessory nerve (CN XI)
• action: complex movements of the scapula and neck

Gross anatomy

Origin 

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

Insertion

• clavicle: lateral third
• scapula: acromion and spine 

Relations

• it lies superficial (posterior) to multiple muscles (from superior to inferior):
  • semispinalis capitis
  • splenius
  • levator scapulae
  • rhomboid minor
  • rhomboid major
  • latissimus dorsi and thoracodorsal fascia

Innervation

• spinal part (C2, C3) of the accessory nerve (cranial nerve XI) provides motor supply
• C3 and C4 spinal nerves supply pain and proprioceptive fibers

Action 

• 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

Siehe auch:

• Nervus accessorius

und weiter:

• Scapula alata
• Schultergürtelmuskulatur