What is the primary action of the upper fibers of the trapezius?

What is the primary action of the upper fibers of the trapezius?

• A. Depresses the scapula
• B. Retracts the scapula
• C. Protracts the scapula
• D. Elevates the scapula and assists in upward rotation of the scapular glenoid

Answer: (D)

The upper fibers of the trapezius primarily elevate the scapula. When they contract, they lift the medial part of the scapula toward the ear, which is the action of elevation. They also contribute to upward rotation of the scapula, helping orient the glenoid fossa for overhead movements. This combined action enables raising the arm above shoulder level. The other options describe actions mainly produced by different parts or muscles: lowering the scapula (depression) is the role of the lower fibers, retracting the scapula is mainly the middle fibers, and protracting the scapula is a primary action of serratus anterior (not the upper trapezius). Thus, elevating the scapula with a contribution to upward rotation best matches what the upper fibers do. Innervation of the trapezius is the spinal accessory nerve (with proprioceptive input from C3–C4), and the upper fibers attach from the skull and nuchal ligament to the clavicle, explaining their ability to lift the shoulder girdle.

The upper fibers of the trapezius primarily elevate the scapula. When they contract, they lift the medial part of the scapula toward the ear, which is the action of elevation. They also contribute to upward rotation of the scapula, helping orient the glenoid fossa for overhead movements. This combined action enables raising the arm above shoulder level. The other options describe actions mainly produced by different parts or muscles: lowering the scapula (depression) is the role of the lower fibers, retracting the scapula is mainly the middle fibers, and protracting the scapula is a primary action of serratus anterior (not the upper trapezius). Thus, elevating the scapula with a contribution to upward rotation best matches what the upper fibers do. Innervation of the trapezius is the spinal accessory nerve (with proprioceptive input from C3–C4), and the upper fibers attach from the skull and nuchal ligament to the clavicle, explaining their ability to lift the shoulder girdle.