Which of the following events do not occur during joint diastole ?
(A) All four chamber of heart are in relaxed state
(B) Atrial repolarization valve open
(C ) Action potential is conducted from SAN to AVN
(D) Blood from the pulmonary veins and vena cava flows into the left and right ventricles respectively through the left and right atria
(E ) The semilunar valves are closed

Options

A. Only E
B. Only C
C. Only D
D. Only A and B

Answer

To determine which of the following events do not occur during joint diastole, let's analyze each option step by step:

1. **Understanding Joint Diastole**: Joint diastole is the phase of the cardiac cycle where all four chambers of the heart are in a relaxed state, allowing for the filling of the heart with blood. During this phase, the atria fill with blood from the veins, and the ventricles fill with blood from the atria.

2. **Evaluating Each Option**:
- **(A) All four chambers of the heart are in a relaxed state**: This statement is true. During joint diastole, all chambers (both atria and ventricles) are relaxed.
- **(B) Atrial repolarization valve open**: This statement is also true. During diastole, the atria are repolarizing, and the atrioventricular (AV) valves (tricuspid and mitral) are open, allowing blood flow from the atria to the ventricles.
- **(C) Action potential is conducted from SAN to AVN**: This statement is false. While the sinoatrial node (SAN) does initiate the heartbeat, the conduction of the action potential to the atrioventricular node (AVN) occurs during the depolarization phase, not during joint diastole.
- **(D) Blood from the pulmonary veins and vena cava flows into the left and right ventricles respectively through the left and right atria**: This statement is true. During joint diastole, blood flows from the pulmonary veins into the left atrium and from the vena cava into the right atrium, and subsequently into the ventricles.
- **(E) The semilunar valves are closed**: This statement is true. During diastole, the semilunar valves (aortic and pulmonary) are closed, preventing backflow of blood into the ventricles.

3. **Conclusion**: The only statement that does not occur during joint diastole is (C) "Action potential is conducted from SAN to AVN".

**Final Answer**: (C) Action potential is conducted from SAN to AVN.

---