Which list correctly names the bones of the respiratory pump?

• A. diaphragm, external intercostals, scalenes, sternocleidomastoid, pectoralis major
• B. sternum, ribs, vertebrae
• C. internal intercostals, abdominals
• D. front of body

Answer: (A)

The respiratory pump relies on muscles that enlarge the thoracic cavity to draw air in and to help push blood back to the heart. The diaphragm contracts and lowers, increasing vertical space in the chest, while the external intercostals lift the ribs to broaden the thorax. Accessory inspiratory muscles like the scalenes lift the upper ribs, the sternocleidomastoid can elevate the sternum during heavy breathing, and the pectoralis major can assist when the arms are fixed and extra effort is needed. Together, these muscles expand the chest, create negative pressure to pull air in, and also promote venous return to the heart during respiration.

The other options don’t fit because they either list bones of the thorax, which don’t actively contract to drive breathing, or include muscles more related to expiration (like the internal intercostals and abdominal muscles), or are defined too vaguely to identify the muscles involved in the inhalation-driven pump.