The trapezius muscle suspends the shoulder girdle from the skull and spinal column. The upper fibers elevate the scapula. The middle fibers retract the scapula. The lower fibers pull the medial border of the scapula downward so that the glenoid cavity faces upward and forward. Knowing that the scapula rotates around the point of attachment of the coracoid process to the clavicle by the coracoclavicular ligament, it can be appreciated that the superior and inferior fibers of the trapezius assist the serratus anterior muscle in rotating the scapula when the arm is raised above the head.
Anatomy of the trapezius
OriginThe trapezius arises from the medial third of the superior nuchal line of the occipital bone, the external occipital protuberance, and the posterior border of the ligamentum nuchae; from the spine of the seventh cervical vertebrae and the spines and supraspinous ligaments of all the thoracic vertebrae.
InsertionThe upper fibers are directed downward and laterally into the lateral third of the clavicle; the middle fibers are directed horizontally into the acromion and the upper border of the spine of the scapula; the lowest fibers are directed upward and laterally and are inserted on the medial end of the spine of the scapula.
Nerve supplyMotor functions are supplied by fibers from the spinal part of the accessory nerve; sensory functions are supplied by fibers from the third and fourth cervical nerves.
Related entries• posterior triangle
• skeletal muscle groups
Related category• ANATOMY AND PHYSIOLOGY
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