P.Normal activities of the heart are regulated extrinsically i. e auto regulated by specialized muscles.
Q. A special neural center in the medulla oblongata can moderate the cardiac function through the autonomic nervous function ( ANS) .
R. Parasympathetic mental signals decrease the rate of heartbeat.
S. Adrenal medullary hormones increase cardiac output.
How many of the given statements are incorrect about the regulation of cardiac activities ?

Options

A. None
B. One
C. Two
D. Three

Answer

To determine how many of the given statements about the regulation of cardiac activities are incorrect, let's analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement P**: "Normal activities of the heart are regulated extrinsically, i.e., auto-regulated by specialized muscles."
- **Analysis**: This statement is incorrect. The normal activities of the heart are primarily regulated intrinsically by the heart's own pacemaker cells (sinoatrial node), which generate impulses for contraction. While there are extrinsic factors (like the autonomic nervous system) that can influence heart rate, the heart's intrinsic regulation is fundamental.
- **Conclusion**: Incorrect.

2. **Statement Q**: "A special neural center in the medulla oblongata can moderate the cardiac function through the autonomic nervous system (ANS)."
- **Analysis**: This statement is correct. The cardiovascular center located in the medulla oblongata does indeed regulate heart function through the autonomic nervous system, which includes both sympathetic and parasympathetic pathways.
- **Conclusion**: Correct.

3. **Statement R**: "Parasympathetic mental signals decrease the rate of heartbeat."
- **Analysis**: This statement is correct. The parasympathetic nervous system, primarily through the vagus nerve, releases acetylcholine, which decreases the heart rate.
- **Conclusion**: Correct.

4. **Statement S**: "Adrenal medullary hormones increase cardiac output."
- **Analysis**: This statement is correct. Hormones such as adrenaline (epinephrine) and norepinephrine released from the adrenal medulla during stress or emergency situations increase heart rate and cardiac output.
- **Conclusion**: Correct.

### Summary of Findings:
- **Incorrect Statements**: 1 (Statement P)
- **Correct Statements**: 3 (Statements Q, R, and S)

### Final Answer:
Only **1 statement** (Statement P) is incorrect about the regulation of cardiac activities.