Circulatory Pathways

1. Joint Diastole: During this phase, both atria and ventricles are in a relaxed state, leading to the opening of the atrioventricular valves (the tricuspid and bicuspid/mitral valves).
2. Blood Flow: As a result of the lower pressure in the ventricles compared to the atria, blood flows passively from the atria into the ventricles.
3. Role of Semilunar Valves: During joint diastole, the semilunar valves (located between the ventricles and the arteries) remain closed to prevent the backflow of blood from the arteries into the ventricles.

An action potential's conduction pathway through the heart follows specific stages that involve sequentially activating different regions of the heart's electrical system to coordinate a proper heartbeat. Here's the correct sequence:

1. SA node (Sinoatrial node): Initiates the electrical impulse as the natural pacemaker, which causes the atria to contract.
2. AV node (Atrioventricular node): Receives the impulse from the SA node and introduces a delay, allowing time for the ventricles to fill with blood before they contract.
3. AV bundle (Bundle of His): Transfers the impulse from the AV node to the ventricles, acting as a bridge.
4. Bundle branches: Conduct the impulse through the septum, dividing the signal towards the left and right ventricles.
5. Purkinje fibres: Spread the impulse throughout the ventricles, causing them to contract.

Thus, the correct sequence matching the provided options is E-C-A-D-B, which corresponds to SA node, AV node, AV bundle, Bundle branches, Purkinje fibres.