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trapezius (cowl muscle)
Origin:
1) medial 1/3 of superior nuchal line
2) external occipital protuberance
3) ligamentum nuchae
4) spinous processes of C7 & thoracic vertebrae & corresponding supraspinous ligaments
Insertion:
1) lateral 1/3 of posterior surface of clavicle
2) anterior side of acromion
3) upper & medial border of the spine of the scapula
Action:
1) when scapulae are fixed, parts of the muscle can act independently
2) cervical part elevates scapula
3) thoracic part contributes to depression of scapula
4) upper & lower parts act simultaneously to rotate glenoid fossa superiorly
5) when the entire muscle contracts, the scapulae retract
6) 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:
1) motor: accessory nerve (CN XI)
2) sensory: cervical plexus
Notes:
[Greek, trapezium = irregular 4-sided figure]
General
skeletal muscle (voluntary muscle)
References
- Stedman's Medical Dictionary 26th ed, Williams &
Wilkins, Baltimore, 1995.
- Clinically Oriented Anatomy, 4th edition, KL Moore &
AF Dalley (eds), Lippincott Williams & Wilkins, Philadelphia,
PA 1999.
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