Which of the following events do not occur during joint diastole ?
I. All 4 chambers of heart are in relaxed state
II. Tricuspid and bicuspid valves open
III. Action potential is conducted from SAN to AVN
IV. Blood from the pulmonary veins and venae cavae flows into the left and right ventricles respectively through the left and right atria
V. The semilunar valves are closed

Options

A. Only V
B. Only III
C. Only IV
D. Only I and II

Answer

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

1. **All 4 chambers of heart are in relaxed state**:
- During joint diastole, all four chambers of the heart (the left and right atria and the left and right ventricles) are indeed in a relaxed state. This allows for the filling of the chambers with blood.
- **Conclusion**: This statement is **correct**.

2. **Tricuspid and bicuspid valves open**:
- The tricuspid valve (between the right atrium and right ventricle) and the bicuspid valve (or mitral valve, between the left atrium and left ventricle) open during joint diastole to allow blood to flow from the atria into the ventricles.
- **Conclusion**: This statement is **correct**.

3. **Action potential is conducted from SAN to AVN**:
- The sinoatrial node (SAN) generates an action potential that spreads through the atria, causing them to contract. However, during joint diastole, the heart is in a relaxed state, and while the SAN is still functioning, the conduction of the action potential primarily leads to the next contraction phase (systole) rather than during diastole itself.
- **Conclusion**: This statement is **incorrect** as it implies that action potential conduction is a primary event during joint diastole.

4. **Blood from the pulmonary veins and venae cavae flows into the left and right ventricles respectively through the left and right atria**:
- During joint diastole, blood does flow from the pulmonary veins into the left atrium and from the venae cavae into the right atrium, and subsequently into the ventricles as the valves are open.
- **Conclusion**: This statement is **correct**.

5. **The semilunar valves are closed**:
- The semilunar valves (pulmonary and aortic valves) are indeed closed during joint diastole to prevent backflow of blood into the ventricles from the arteries.
- **Conclusion**: This statement is **correct**.

### Final Answer:
The event that does not occur during joint diastole is **III. Action potential is conducted from SAN to AVN**.