Parasympathetic neural signal decreases cardiac put by -

Options

A. Decreasing the rate of heart beat
B. Decreasing the speed conduction of action potential
C. Both
D. Increasing adrenal medulla hormones secretion

Answer

### Step-by-Step Solution:

1. **Understanding Cardiac Output**: Cardiac output (CO) is defined as the amount of blood the heart pumps in one minute. It is determined by two main factors: stroke volume (SV) and heart rate (HR). The formula for cardiac output is:
\[ CO = SV \times HR \]

2. **Role of the Parasympathetic Nervous System**: The parasympathetic nervous system (PNS) is responsible for the 'rest and digest' functions in the body. It primarily decreases heart rate and can also affect the strength of heart contractions.

3. **Effect on Heart Rate**: When the PNS is activated, it releases neurotransmitters (like acetylcholine) that bind to receptors in the heart. This action leads to a decrease in heart rate (HR). A lower heart rate means fewer beats per minute, which directly reduces cardiac output.

4. **Effect on Stroke Volume**: The PNS can also influence the strength of the heart's contractions. If the strength of contraction decreases, the stroke volume (the amount of blood pumped with each beat) will also decrease. This further contributes to a reduction in cardiac output.

5. **Overall Impact on Cardiac Output**: Since both heart rate and stroke volume can decrease due to parasympathetic stimulation, the overall cardiac output will decrease. Therefore, the parasympathetic neural signal decreases cardiac output by reducing both heart rate and the strength of heart contractions.

6. **Conclusion**: The correct answer to the question is that the parasympathetic neural signal decreases cardiac output by:
- Decreasing the heart rate.
- Decreasing the strength of cardiac contractions (stroke volume).

### Final Answer:
The parasympathetic neural signal decreases cardiac output by decreasing the heart rate and the strength of heart contractions.

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