If we give an injection of acetylcholine to a person, rate of heart beat will

Options

A. Increase
B. Decrease
C. Increases first then decrease
D. No effect on heart beat

Answer

To answer the question about the effect of acetylcholine on heart rate, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Acetylcholine**: Acetylcholine is a neurotransmitter that plays a crucial role in the autonomic nervous system. It is involved in transmitting signals between nerve cells and can influence various bodily functions, including heart rate.

2. **Role of Acetylcholine in the Heart**: Acetylcholine primarily acts on the parasympathetic nervous system, which is responsible for promoting a "rest and digest" state. When acetylcholine is released, it binds to receptors in the heart, particularly the muscarinic receptors.

3. **Effect on Heart Rate**: The binding of acetylcholine to these receptors leads to a decrease in heart rate. This is because acetylcholine increases the activity of the vagus nerve, which slows down the heart's pacemaker activity in the sinoatrial (SA) node.

4. **Conclusion**: Therefore, if an injection of acetylcholine is administered to a person, the rate of heartbeat will **decrease**.

### Final Answer:
The rate of heartbeat will **decrease**.

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