The diagram shows the electrical coordination pathway of the mammalian heart, where PPP, QQQ, RRR, and S S\,S represent specific structures.
Which of the following statements correctly explains how structures Q Q\,Q and S S\,S coordinate the mammalian cardiac cycle?
SSS acts as an electrical pathway that conducts impulses directly from the atria to the apex of the ventricles, while QQQ initiates the cardiac impulse to ensure the ventricles contract first.
SSS physically prevents blood from backflowing from the ventricles into the atria, while QQQ speeds up conduction to ensure the semilunar valves open before atrial systole begins.
SSS prevents the electrical wave of excitation from spreading directly from the atria to the ventricles, while QQQ delays the impulse to allow the ventricles to fill completely before they contract.
SSS conducts the myogenic impulse generated by PPP to the left atrium, while QQQ ensures that ventricular contraction begins at the base (top) of the ventricles to pump blood towards the apex.
