How do parasympathetic neural signals affect the working of the heart?

Options

A. Reduce both heart rate and cardiac output
B. Heart rate is increased without affecting the cardiac output.
C. Both heart rate and cardiac increase
D. Heart rate decreases but cardiac output increases

Answer

**Step-by-Step Solution:**

1. **Understanding the Parasympathetic Nervous System**: The parasympathetic nervous system is a part of the autonomic nervous system that generally promotes a "rest and digest" state. It is responsible for conserving energy and slowing down the heart rate.

2. **Effects on Heart Rate**: When parasympathetic neural signals are activated, they release neurotransmitters like acetylcholine. This neurotransmitter binds to receptors in the heart, leading to a decrease in heart rate. This is known as a negative chronotropic effect.

3. **Effects on Cardiac Output**: Cardiac output is determined by both heart rate and stroke volume (the amount of blood pumped by the heart with each beat). While the heart rate decreases due to parasympathetic stimulation, the stroke volume may remain relatively unchanged in moderate conditions. Therefore, a decrease in heart rate can lead to a decrease in cardiac output, but not necessarily in all situations.

4. **Conclusion**: Given that the parasympathetic stimulation leads to a decrease in heart rate and can also reduce cardiac output, the correct answer to the question is:
- **Option A**: Reduce both heart rate and cardiac output.