The stimulation for heart contraction initiates in

Options

A. SA-node
B. AV-node
C. Medulla
D. Purkinje fibres

Answer

To answer the question "The stimulation for heart contraction initiates in," we will analyze the options provided and identify the correct one step by step.

### Step-by-Step Solution:

1. **Understanding Heart Contraction**: The heart contracts due to electrical impulses that stimulate the heart muscles. This process is crucial for maintaining the heart's rhythm and pumping blood effectively.

2. **Identifying the Pacemaker**: The primary structure responsible for initiating the electrical impulses in the heart is known as the sinoatrial (SA) node. It is often referred to as the "pacemaker" of the heart because it sets the pace for heartbeats.

3. **Evaluating the Options**:
- **Option 1: SA Node**: This is the correct answer. The SA node generates electrical impulses that cause the atria (the upper chambers of the heart) to contract.
- **Option 2: AV Node**: This option is incorrect. The atrioventricular (AV) node does not initiate heart contractions; instead, it receives impulses from the SA node and transmits them to the ventricles.
- **Option 3: Medulla**: This option is also incorrect. The medulla oblongata is part of the brain that regulates autonomic functions such as heartbeat and respiration but does not initiate heart contractions.
- **Option 4: Purkinje Fibers**: This option is incorrect as well. Purkinje fibers are responsible for conducting impulses throughout the ventricles after the AV node has transmitted the signal, but they do not initiate the contraction.

4. **Conclusion**: Based on the analysis, the correct answer is **Option 1: SA Node**. This is where the stimulation for heart contraction initiates.