Which of the following structure in the normal human heat generates action potential to initiate a cardiac cycle ?

Options

A. AV node
B. SA node
C. Purkinjefibres
D. Bundle ofHis

Answer

To solve the question regarding which structure in the normal human heart generates action potential to initiate a cardiac cycle, we can follow these steps:

### Step 1: Understand the Structures of the Heart
The heart has several key structures involved in its electrical conduction system, including:
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Bundle of His
- Purkinje fibers

### Step 2: Identify the Function of Each Structure
- **SA Node**: Known as the pacemaker of the heart, it generates electrical impulses that initiate the heartbeat.
- **AV Node**: Acts as a gatekeeper that slows down the electrical signal before it enters the ventricles.
- **Bundle of His**: Transmits impulses from the AV node to the ventricles.
- **Purkinje Fibers**: Distribute the electrical impulse throughout the ventricles to cause contraction.

### Step 3: Determine Which Structure Initiates the Cardiac Cycle
The SA node is responsible for generating the action potential that starts the cardiac cycle. It does this by spontaneously depolarizing and creating an electrical impulse.

### Step 4: Eliminate Incorrect Options
- **AV Node**: Does not initiate the cardiac cycle; it only relays signals.
- **Bundle of His**: Also does not initiate; it transmits signals.
- **Purkinje Fibers**: They conduct impulses but do not generate them.

### Conclusion
The structure that generates action potential to initiate a cardiac cycle is the **SA node**.

### Final Answer
The correct answer is **SA node** (Option 2).

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