Choose the correct pathway of the transmission of impulses in the heart beat `:`

Options

A. Av node `rarr` S A node `rarr ` Bundle of His `rarr` Purkinje fibre
B. SA node `rarr` AV node `rarr` Bundle of His `rarr` Purkinje fibres
C. SA node `rarr` Bundle of His `rarr` AV node `rarr` purkinje fibre
D. AV node `rarr` Bundle of His `rarr ` SA node `rarr ` Purkinje fibres

Answer

### Step-by-Step Solution:

1. **Identify the Starting Point of Impulse Transmission**:
- The heartbeat begins with the **Sinoatrial (SA) node**, which is located in the upper right corner of the right atrium. This node generates electrical impulses that initiate the heartbeat.

2. **Transmission Through the Atria**:
- The electrical impulse generated by the SA node spreads through the atria, causing them to contract. This contraction pushes blood into the ventricles.

3. **Reaching the Atrioventricular (AV) Node**:
- After the atria contract, the impulse reaches the **Atrioventricular (AV) node**. The AV node is located at the junction of the atria and ventricles. It serves as a gatekeeper, allowing the impulse to pass into the ventricles while providing a brief delay to ensure that the atria have fully contracted and the ventricles are filled with blood.

4. **Transmission Through the Bundle of His**:
- From the AV node, the impulse travels down to the **Bundle of His** (also known as the atrioventricular bundle). This bundle divides into left and right bundle branches that extend into the ventricles.

5. **Purkinje Fibers**:
- The impulse then spreads through the **Purkinje fibers**, which are specialized fibers that distribute the electrical signal throughout the ventricular walls, causing the ventricles to contract and pump blood to the lungs and the rest of the body.

6. **Correct Pathway**:
- The correct pathway of impulse transmission in the heartbeat is: **SA node → AV node → Bundle of His → Purkinje fibers**.

### Conclusion:
The correct option for the pathway of impulse transmission in the heartbeat is **SA node → AV node → Bundle of His → Purkinje fibers**.

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