Which of the following structure is having maximum autorhytmicity in the normal human heart ?

Options

A. Purkinje fibres
B. Bundle of His
C. AV node
D. SA node

Answer

To determine which structure in the normal human heart has the maximum autorhythmicity, we need to analyze the different components of the heart's conduction system.

### Step-by-Step Solution:

1. **Identify the Structures**: The options given are Purkinje fibers, bundle of His, AV node, and SA node. Each of these structures plays a role in the heart's electrical conduction system.

2. **Understand Autorhythmicity**: Autorhythmicity refers to the ability of certain cardiac cells to generate action potentials spontaneously without external stimuli. This property is crucial for maintaining the heart's rhythm.

3. **Locate the SA Node**: The Sinoatrial (SA) node is located in the right atrium and is known as the natural pacemaker of the heart. It is responsible for initiating the electrical impulses that trigger heartbeats.

4. **Evaluate Other Structures**:
- **AV Node**: Located at the junction of the atria and ventricles, it conducts impulses from the atria to the ventricles but does not generate impulses at a higher rate than the SA node.
- **Bundle of His**: This structure transmits impulses from the AV node to the ventricles but also does not have a higher rate of impulse generation compared to the SA node.
- **Purkinje Fibers**: These fibers distribute the electrical impulse throughout the ventricles but are not the primary pacemaker.

5. **Determine the Structure with Maximum Autorhythmicity**: Since the SA node generates the highest number of action potentials per minute (about 60-100 beats per minute), it has the maximum autorhythmicity among the given options.

6. **Conclusion**: Therefore, the structure with maximum autorhythmicity in the normal human heart is the **SA node**.

### Final Answer:
The correct option is **SA node**.

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