The atrial systole normally precedes the ventricular systole because the impulse takes time to pass from

Options

A. SA node to AV node
B. AV node to SA node
C. AV node to AV bundle
D. AV bundle to Purkinje fibres

Explanation

To answer the question: "The atrial systole normally precedes the ventricular systole because the impulse takes time to pass from...", we can break down the solution into the following steps:

### Step-by-Step Solution:

1. **Understanding Atrial and Ventricular Systole**:
- Atrial systole refers to the contraction of the atria, which pushes blood into the ventricles.
- Ventricular systole refers to the contraction of the ventricles, which pumps blood out of the heart.

2. **Sequence of Heart Contraction**:
- The heart contracts in a specific sequence to ensure efficient blood flow. Atrial contraction (systole) occurs before ventricular contraction (systole).

3. **Role of the Sinoatrial (SA) Node**:
- The SA node, located in the right atrium, is the natural pacemaker of the heart. It generates electrical impulses that initiate the heartbeat.

4. **Impulses Travel Pathway**:
- The electrical impulse generated by the SA node travels through the atria, causing them to contract.
- After the atria contract, the impulse moves to the atrioventricular (AV) node.

5. **AV Nodal Delay**:
- The AV node introduces a delay in the conduction of the electrical impulse. This delay is crucial because it allows time for the ventricles to fill with blood from the atria before they contract.
- This delay is known as the AV nodal delay.

6. **Conclusion**:
- Therefore, the reason atrial systole precedes ventricular systole is due to the time it takes for the impulse to pass from the SA node to the AV node, which is characterized by the AV nodal delay.

### Final Answer:
The impulse takes time to pass from the SA node to the AV node, which is known as AV nodal delay.

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