Which letter represents ventricular depolarization?
E
D
B
The Correct Answer is C
Correct answer: B.
B: Ventricular depolarization is the electrical activation of the ventricles that triggers ventricular contraction. It occurs after the impulse travels from the sinoatrial . On an electrocardiogram (ECG), ventricular depolarization is represented by the QRS complex, labelled as B in the diagram.
D: artrial depolarization - Atrial depolarization initiates atrial contraction, driven by impulses from the SA node. This electrical activity spreads across atrial myocardium, generating the P wave on the ECG and enabling ventricular filling.
E: ventricular repolarization - Ventricular repolarization restores the ventricles to their resting state after contraction. Represented by the T wave, it prepares the heart for the next depolarization, ensuring rhythmic cardiac cycles and effective pumping.
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Related Questions
Correct Answer is B
Explanation
A. Higher pressure in the atria than in the veins: While venous return contributes to atrial filling, blood flow from the atria into the ventricles during diastole is primarily driven by pressure gradients between the atria and ventricles, not just between veins and atria. Venous pressure alone does not account for the efficient filling of the ventricles.
B. Contraction of the atria: During atrial systole, the atria contract, increasing atrial pressure above ventricular pressure. This pressure gradient forces blood through the open atrioventricular valves (tricuspid and mitral) into the ventricles, completing the final phase of ventricular filling known as the “atrial kick,” which contributes approximately 20–30% of ventricular end-diastolic volume.
C. Higher pressure in the veins than in the atria: Although venous pressure drives passive filling of the atria, the actual movement of blood into the ventricles requires the atria to generate pressure higher than that in the relaxed ventricles. Without atrial contraction, ventricular filling would rely solely on passive flow, which is less efficient.
D. Contraction of the ventricles: Ventricular contraction occurs during systole, when ventricular pressure rises above atrial pressure. This causes the atrioventricular valves to close, preventing backflow into the atria. Ventricular contraction does not facilitate blood flow from atria to ventricles; it actually temporarily halts it.
Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. P: The P wave represents atrial depolarization. It reflects the electrical activity as the impulse spreads from the sinoatrial (SA) node across the atrial myocardium, causing atrial contraction. Because the atria are smaller than the ventricles, the electrical signal is smaller in amplitude.
B. QRS: The QRS complex represents ventricular depolarization. It corresponds to the rapid spread of electrical impulses through the ventricles via the bundle branches and Purkinje fibers, leading to ventricular contraction. Since the ventricles have significantly greater muscle mass than the atria, this depolarization produces a larger and stronger electrical signal on the ECG.
C. T: The T wave represents ventricular repolarization, the process by which ventricular muscle cells return to their resting membrane potential after contraction. It does not represent depolarization.
D. PR: The PR interval reflects the time required for the electrical impulse to travel from the atria through the atrioventricular (AV) node to the ventricles. It represents conduction delay, not ventricular depolarization itself.
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