What is the action of Serratus posterior superior?

• A. Protracts the scapula
• B. Elevates the clavicle
• C. Elevates ribs 2-5; assists in proprioception; acts as an accessory muscle of respiration
• D. Depresses the ribs 2-5

Answer: (C)

The action being tested is what serratus posterior superior does to the rib cage during breathing. This muscle attaches to the upper thoracic spine and inserts on the second through fifth ribs, so its primary job is to pull those ribs upward. Elevating ribs 2–5 helps expand the thoracic cavity during inspiration. In addition to moving the ribs, it provides proprioceptive feedback about rib motion and functions as an accessory muscle of respiration, assisting with deeper or more forceful breathing when needed.

That combination—elevating ribs 2–5, with a proprioceptive role and function as an accessory muscle of respiration—fits the muscle’s true action best. Protracting the scapula is the job of serratus anterior, not serratus posterior superior. Elevating the clavicle isn’t a recognized action of this muscle, and depressing the ribs 2–5 is what serratus posterior inferior does, not the superior.