Which of the following changes occur in diaphragm and intercostal muscles when expiration of air takes place ?

Options

A. Internal intercostal muscles relex and diaphragm contracts
B. External intercostal muscles and diaphragm relax
C. internal intercostal muscles contract and diaphragm ralax
D. External intercostal muscles and diaphragma contract

Explanation

To answer the question regarding the changes that occur in the diaphragm and intercostal muscles during expiration, we can break down the process step by step:

### Step-by-Step Solution:

1. **Understanding Expiration**:
- Expiration is the process of breathing out, where air is expelled from the lungs.

2. **Muscle Actions During Expiration**:
- During expiration, the **internal intercostal muscles** contract. This contraction pulls the ribs downward and inward.
- Simultaneously, the **diaphragm** relaxes. When the diaphragm relaxes, it moves upward and becomes more convex.

3. **Effect on Thoracic Cavity**:
- The contraction of the internal intercostal muscles and the relaxation of the diaphragm lead to a decrease in the volume of the thoracic cavity.
- As the volume decreases, the pressure inside the thoracic cavity increases relative to the atmospheric pressure outside.

4. **Air Movement**:
- The increase in pressure inside the thoracic cavity compared to the outside pressure causes air to be pushed out of the lungs, completing the process of expiration.

5. **Conclusion**:
- Therefore, the correct changes during expiration are that the internal intercostal muscles contract while the diaphragm relaxes.

### Final Answer:
- The correct option is: **Internal intercostal muscles contract and diaphragm relax.**