The rate of the heart and their conduction is represented in the pathway :

Options

A. AVN- Bundle of His - Network of Purkinje fibres
B. Network of Purkinje fibres - AVN-SAN- Bundle of His
C. AVN-SAN-Bundle of His- Purkinje fibres
D. SAN-AVN - Bundle of His - Purkinje fibres

Answer

To answer the question regarding the pathway of heart rate and conduction, we will break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Heartbeat**:
- A heartbeat represents one complete cardiac cycle. This means that each heartbeat consists of a sequence of events that occur in the heart.

**Hint**: Remember that a heartbeat is synonymous with a cardiac cycle.

2. **Initiation of the Heartbeat**:
- The heartbeat begins at the **Sinoatrial (SA) Node**, which is often referred to as the heart's natural pacemaker. This node generates electrical impulses that initiate the contraction of the heart.

**Hint**: The SA node is crucial as it sets the rhythm for the heartbeat.

3. **Conduction to the Atrioventricular Node**:
- Once the impulse is generated by the SA node, it travels to the **Atrioventricular (AV) Node**. The AV node is located in the right atrium and acts as a gatekeeper, slowing down the impulse before it moves to the ventricles.

**Hint**: The AV node ensures that the atria have time to contract before the ventricles do.

4. **Transmission through the Bundle of His**:
- After the AV node, the impulse moves to the **Bundle of His** (also known as the AV bundle). This bundle is responsible for conducting the electrical signal from the AV node into the ventricles.

**Hint**: The Bundle of His is essential for transmitting signals to the ventricles.

5. **Division into Purkinje Fibers**:
- The Bundle of His then divides into right and left bundle branches, which further branch into **Purkinje Fibers**. These fibers spread throughout the ventricles and ensure that the contraction occurs in a coordinated manner.

**Hint**: Purkinje fibers help in spreading the impulse quickly across the ventricles.

6. **Final Contraction of the Heart**:
- Finally, the electrical signal reaches the outer walls of the heart, leading to the contraction of the ventricles and pumping blood out of the heart.

**Hint**: The coordinated contraction of the ventricles is crucial for effective blood circulation.

### Conclusion:
The correct sequence of the heart conduction pathway is:
1. SA Node
2. AV Node
3. Bundle of His
4. Purkinje Fibers

Thus, the answer to the question is option D: SA Node → AV Node → Bundle of His → Purkinje Fibers.