A hormone responsible for normal sleep- wake cycle is

Options

A. epinephrine
B. gastrin
C. melatonin
D. insulin

Answer

To solve the question regarding which hormone is responsible for the normal sleep-wake cycle, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Options**: The options given are:
- A) Epinephrine
- B) Gastrin
- C) Melatonin
- D) Insulin

2. **Understand the Function of Each Hormone**:
- **Epinephrine**: This hormone is primarily involved in the fight-or-flight response and is not directly related to the sleep-wake cycle.
- **Gastrin**: This hormone stimulates the secretion of gastric acid in the stomach and is involved in digestion, not sleep regulation.
- **Melatonin**: This hormone is produced by the pineal gland and is known to regulate sleep patterns and the circadian rhythm.
- **Insulin**: This hormone regulates glucose levels in the blood and is not involved in sleep regulation.

3. **Focus on Melatonin**:
- Melatonin is secreted in response to darkness and helps signal to the body that it is time to sleep. It plays a crucial role in the regulation of the sleep-wake cycle by synchronizing the body’s internal clock with the external environment.

4. **Conclusion**: Based on the functions of the hormones listed, the hormone responsible for the normal sleep-wake cycle is **C) Melatonin**.

### Final Answer:
The hormone responsible for the normal sleep-wake cycle is **C) Melatonin**.