How do parasympathertic neural signals affect the working the heart

Options

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

Answer

### Step-by-Step Solution:

1. **Understanding the Parasympathetic Nervous System**:
- The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system, which controls involuntary bodily functions. It is often referred to as the "rest and digest" system.

2. **Effects on Heart Rate**:
- When parasympathetic signals are activated, they primarily release the neurotransmitter acetylcholine. This neurotransmitter binds to receptors in the heart, particularly in the sinoatrial (SA) node, which is the natural pacemaker of the heart.
- The binding of acetylcholine slows down the firing rate of the SA node, leading to a decrease in heart rate.

3. **Impact on Cardiac Output**:
- Cardiac output is defined as the volume of blood the heart pumps per minute and is a product of heart rate and stroke volume (the amount of blood pumped with each beat).
- Since the parasympathetic signals reduce the heart rate, this will also lead to a reduction in cardiac output, assuming stroke volume remains constant or does not increase significantly.

4. **Conclusion**:
- Based on the effects of parasympathetic neural signals, we conclude that they reduce both heart rate and cardiac output. Therefore, the correct answer to the question is **Option B: Reduce both heart rate and cardiac output**.