The

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valve prevents backflow of blood into the right atrium when the right ventricle contracts.

Correct answer: False

The relative refractory period occurs during the latter part of the cardiac action potential, specifically during phase 3 (repolarization) of ventricular muscle cells. During this period, the myocardial cell has partially repolarized but has not yet fully returned to its resting membrane potential. While the cell can respond to a stronger-than-normal stimulus, normal stimuli will not trigger a contraction. Anatomically, this period applies to cardiac myocytes throughout the atria and ventricles, ensuring coordinated contractions while preventing premature or tetanic contractions, which could compromise effective cardiac output.

Correct answer: False

The atrioventricular (AV) node, located in the lower portion of the interatrial septum near the tricuspid valve, functions as a critical electrical relay between the atria and ventricles. While the SA node sets the normal heart rhythm, the AV node limits the number of impulses transmitted to the ventricles, providing a protective delay that allows adequate ventricular filling. Under extreme SA node stimulation, impulses exceeding 220 per minute can overwhelm the AV node, resulting in ineffective ventricular contractions, reduced cardiac output, and compromised heart function. The AV node’s intrinsic conduction limits are essential for maintaining coordinated and efficient cardiac performance.