Which of the following represents the correct events of a cardiac cycle beginning from the firing of an impulse from the pacemaker of the heart ?

Options

A.
B.
C.
D.

Answer

To solve the question regarding the correct sequence of events in a cardiac cycle starting from the firing of an impulse from the pacemaker of the heart, we can break it down into several steps:

### Step-by-Step Solution:

1. **Understanding the Cardiac Cycle**: The cardiac cycle consists of a series of events that occur during one heartbeat. It can be divided into three main phases: atrial systole, ventricular systole, and joint diastole.

2. **Starting Point - Pacemaker Activity**: The cycle begins with the firing of an electrical impulse from the sinoatrial node (SAN), which is known as the pacemaker of the heart. This initiates atrial systole.

3. **Atrial Systole**: This phase lasts approximately 0.1 seconds. During atrial systole, the atria contract, pushing blood into the ventricles. This is the first event in the cardiac cycle.

4. **Ventricular Systole**: Following atrial systole, the next phase is ventricular systole, which lasts about 0.3 seconds. During this phase, the ventricles contract and pump blood out of the heart to the lungs and the rest of the body.

5. **Joint Diastole**: The final phase is joint diastole, which lasts around 0.4 seconds. During this time, both the atria and ventricles relax, allowing the heart chambers to fill with blood.

6. **Sequence of Events**: Therefore, the correct sequence of events in the cardiac cycle starting from the firing of the impulse from the pacemaker is:
- Atrial Systole (0.1 seconds)
- Ventricular Systole (0.3 seconds)
- Joint Diastole (0.4 seconds)

7. **Identifying the Correct Option**: Based on the descriptions given in the options, we need to find the one that matches the sequence:
- Atrial Systole (0.1s) → Ventricular Systole (0.3s) → Joint Diastole (0.4s).

After analyzing the options, the correct answer is **Option C**, which accurately reflects the sequence of events.