What happens when the pacemaker becomes nonfunctional ?

Options

A. Only ventricle will contract rhythmically
B. Only the Atria will contract rhythmically
C. Atria and ventricles contract simultaneously
D. The cardiac muscles do not contract in a coordinated manner rhythmically

Answer

### Step-by-Step Solution:

1. **Understanding the Pacemaker's Role**: The pacemaker of the heart is primarily the Sinoatrial (SA) node. It generates electrical impulses that initiate the heartbeat and regulate the rhythm of the heart.

2. **Function of the SA Node**: The SA node sends electrical impulses through the heart's conduction system, which includes the inter-atrial pathways, the Atrioventricular (AV) node, the bundle of His, bundle branches, and Purkinje fibers. This ensures that the atria contract first, followed by the ventricles, allowing for efficient blood flow.

3. **Consequences of a Non-Functional Pacemaker**: If the SA node becomes non-functional, it can lead to a lack of coordinated electrical impulses. This means that the heart will not beat in a synchronized manner.

4. **Analyzing the Options**:
- **Option A**: "Only ventricle will contract rhythmically" - This is incorrect because the ventricles rely on signals from the atria to contract.
- **Option B**: "Only the atria will contract rhythmically" - This is also incorrect as the atria need the SA node to initiate their contraction.
- **Option C**: "Atria and ventricles contract simultaneously" - This is incorrect because simultaneous contraction would not allow for effective blood flow.
- **Option D**: "The cardiac muscle does not contract in a coordinated manner rhythmically" - This is the correct answer, as the loss of the SA node's function leads to uncoordinated contractions.

5. **Conclusion**: When the pacemaker (SA node) becomes non-functional, the heart's contractions become uncoordinated, leading to ineffective pumping of blood.

### Final Answer:
The correct answer is **Option D**: The cardiac muscle does not contract in a coordinated manner rhythmically.

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