trapezius (cowl muscle)

Origin

• medial 1/3 of superior nuchal line
• external occipital protuberance
• ligamentum nuchae
• spinous processes of C7 & thoracic vertebrae & corresponding supraspinous ligaments

Insertion

• lateral 1/3 of posterior surface of clavicle
• anterior side of acromion
• upper & medial border of the spine of the scapula

Action

• when scapulae are fixed, parts of the muscle can act independently
• cervical part elevates scapula
• thoracic part contributes to depression of scapula
• upper & lower parts act simultaneously to rotate glenoid fossa superiorly
• when the entire muscle contracts, the scapulae retract
• draws head to one side or backward

Superior fibers

• elevate the scapula (e.g., when squaring the shoulders)

Middle fibers

• retract the scapula (i.e., pull it posteriorly)

Inferior fibers

• depress the scapula & lower the shoulder

Innervation

• motor: accessory nerve (CN XI)
• sensory: cervical plexus

Notes

[Greek, trapezium = irregular 4-sided figure]

More general terms

• skeletal muscle (voluntary muscle)