Which of the following is not an involuntary action?

Options

A. Vomiting
B. Salivation
C. Heart beat
D. Chewing

Explanation

To determine which of the following is not an involuntary action, we need to understand the difference between involuntary and voluntary actions.

### Step-by-Step Solution:

1. **Define Involuntary Actions**: Involuntary actions are those that occur without conscious control. They are regulated by the autonomic nervous system and are essential for survival. Examples include heartbeat, digestion, and reflex actions.

2. **Identify Examples of Involuntary Actions**: Common involuntary actions include:
- Heartbeat: The heart beats automatically without our conscious effort.
- Peristalsis: The wave-like muscle contractions that move food through the digestive tract.
- Vomiting: The body's automatic response to expel harmful substances.
- Salivation: The production of saliva, which occurs without conscious effort.

3. **Identify Voluntary Actions**: Voluntary actions are those that we can control consciously. They are regulated by the cerebral cortex. An example is chewing food, which we can decide to do or not.

4. **Analyze the Options**: Given the options, we need to identify which action is voluntary:
- Option 1: Vomiting - Involuntary
- Option 2: Salivation - Involuntary
- Option 3: Heartbeat - Involuntary
- Option 4: Chewing - Voluntary

5. **Conclusion**: The action that is not involuntary is chewing, as it is a voluntary action controlled by the brain.

### Final Answer:
The action that is not an involuntary action is **chewing** (Option 4).