If parasympathetic nerve of the rabbit is cut then heart beat

Options

A. Unaffected
B. Decreases
C. Increases
D. Stop

Answer

### Step-by-Step Solution:

1. **Understanding the Role of the Parasympathetic Nervous System**:
- The parasympathetic nervous system (PNS) is responsible for promoting the "rest and digest" state in the body. It generally works to decrease heart rate and promote relaxation.

2. **Identifying the Effect of Cutting the Parasympathetic Nerve**:
- If the parasympathetic nerve is cut, the inhibitory signals that normally decrease heart rate are disrupted. This means that the heart is no longer receiving signals to slow down.

3. **Analyzing the Options**:
- **Unchanged Heartbeat**: This option is incorrect because cutting the nerve will affect the heart's regulation.
- **Heartbeat Stops**: This option is also incorrect as the heart will continue to beat, but its rate will change.
- **Heartbeat Decreases**: This option is incorrect because the inhibitory effect of the parasympathetic system is lost, leading to an increase in heart rate.
- **Heartbeat Increases**: This is the correct option because without the parasympathetic influence, the heart rate will increase due to the dominance of sympathetic nervous system activity.

4. **Conclusion**:
- The cutting of the parasympathetic nerve leads to an increase in heart rate because the heart is no longer receiving signals to slow down.

### Final Answer:
- **The heartbeat will increase.**

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