Acetylcholine causes

Options

A. Bradycardia
B. Tachycardia
C. Both
D. None

Answer

### Step-by-Step Solution:

1. **Understanding Acetylcholine**: Acetylcholine is a neurotransmitter that plays a crucial role in the nervous system, particularly in the transmission of signals between neurons and muscles.

2. **Effects of Acetylcholine**: When released, acetylcholine can have various effects on the body, particularly on the heart. It is known to influence heart rate.

3. **Bradycardia**: Bradycardia refers to a slower than normal heart rate. It is defined as a heart rate of fewer than 60 beats per minute. Acetylcholine can cause bradycardia by acting on the heart's pacemaker cells, leading to a decrease in heart rate.

4. **Tachycardia**: In contrast, tachycardia refers to a faster than normal heart rate, typically over 100 beats per minute. Acetylcholine does not cause tachycardia; rather, it has the opposite effect.

5. **Evaluating the Options**:
- **Option 1: Bradycardia** - Correct, as acetylcholine causes a decrease in heart rate.
- **Option 2: Tachycardia** - Incorrect, as acetylcholine does not cause an increase in heart rate.
- **Option 3: Both** - Incorrect, since acetylcholine does not cause both conditions.
- **Option 4: None** - Incorrect, as acetylcholine does have a specific effect (causing bradycardia).

6. **Conclusion**: The correct answer is that acetylcholine causes bradycardia.

### Final Answer:
Acetylcholine causes bradycardia.

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