What happens when the pacemaker becomes nonfunctional ?

Options

A. Only auricles contract rhythmically
B. Only ventricles contract rhythmically
C. Cardiac muscles do not undergo co-ordinated rhythmic movements
D. Auricles and ventricles contract rhythmically

Explanation

### Step-by-Step Solution:

1. **Understanding the Role of the Pacemaker:**
- The pacemaker of the heart is primarily the Sinoatrial (SA) node. It is responsible for generating electrical impulses that initiate the heartbeat.

2. **Action Potential Pathway:**
- The action potential generated by the SA node travels through the heart in a specific sequence:
- From the SA node, it moves to the Atrioventricular (AV) node.
- Then, it travels to the Bundle of His.
- Finally, it reaches the Purkinje fibers, which are located in the ventricles.

3. **Consequences of a Nonfunctional Pacemaker:**
- If the SA node becomes nonfunctional, it means that there will be no generation of action potentials.
- This leads to the absence of coordinated rhythmic contractions of the cardiac muscles.

4. **Impact on Heart Function:**
- Without the SA node functioning, the heart will not contract in a coordinated manner. This can lead to arrhythmias or irregular heartbeats.
- The atria and ventricles may not contract together, which is essential for effective blood pumping.

5. **Conclusion:**
- The primary outcome of a nonfunctional pacemaker is that the cardiac muscles do not undergo coordinated rhythmic movements.

### Final Answer:
When the pacemaker (SA node) becomes nonfunctional, the cardiac muscles do not undergo coordinated rhythmic movements.

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