Which muscles open and close the valves that prevent backflow?

• A. Papillary Muscles
• B. Pectinate Muscles
• C. Purkinje Fibers
• D. Myocardial Fibers

Answer: (A)

Papillary muscles are responsible for opening and closing the valves that prevent backflow. They attach to the valve leaflets (mitral and tricuspid) via the chordae tendineae. When the ventricles contract, the papillary muscles also contract, pulling on the chordae to tense the leaflets so they stay closed and don't prolapse into the atria. This prevents regurgitation during systole. The other options don’t perform this valve-tensing role: pectinate muscles help atrial contraction, Purkinje fibers coordinate electrical timing, and general myocardial fibers are the muscle tissue that contracts but don’t specifically control valve closure.