Read the following statements :
A. The action potential generated by the SA node stimulates both ventricles to undergo simultaneous contraction.
B. The heart sound Lubb is associated with the closure of both semilunar valves.
C. The QRS complex in ECG represents the depolarization of the ventricles.
Select the appropriate option from the following :

Options

A. A and B are correct , C is incorrect
B. A, B are incorrect and C is correct
C. Only B and C are correct
D. Only A is correct

Answer

To solve the question, we need to analyze each statement provided about the heart's physiology and the ECG (electrocardiogram) readings. Let's go through the statements one by one.

### Step 1: Analyze Statement A
**Statement A:** "The action potential generated by the SA node stimulates both ventricles to undergo simultaneous contraction."

- The SA node (sinoatrial node) is responsible for initiating the heartbeat and generating action potentials that cause the atria to contract.
- The action potential does not directly stimulate the ventricles to contract simultaneously; instead, it first causes the atria to contract, and then the impulse travels through the AV node to the ventricles.
- **Conclusion:** This statement is **incorrect**.

### Step 2: Analyze Statement B
**Statement B:** "The heart sound Lubb is associated with the closure of both semilunar valves."

- The heart sound "Lubb" (S1) is actually associated with the closure of the atrioventricular (AV) valves (mitral and tricuspid valves) at the beginning of ventricular contraction.
- The closure of the semilunar valves (aortic and pulmonary valves) is associated with the second heart sound "Dubb" (S2).
- **Conclusion:** This statement is **incorrect**.

### Step 3: Analyze Statement C
**Statement C:** "The QRS complex in ECG represents the depolarization of the ventricles."

- The QRS complex on an ECG does indeed represent the depolarization of the ventricles, which leads to ventricular contraction.
- This is a well-established fact in cardiac physiology.
- **Conclusion:** This statement is **correct**.

### Final Evaluation
- **Statement A:** Incorrect
- **Statement B:** Incorrect
- **Statement C:** Correct

From our analysis, we find that statements A and B are incorrect, while statement C is correct. Therefore, the appropriate option that reflects this conclusion is:

**Correct Answer:** Option 2 (A and B are incorrect, C is correct).

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