Expiration involves

Options

A. Relaxation of diaphragm and intercostal muscles
B. Contraction of diaphragm and intercostal muscles
C. Contraction fo diaphragm muscles
D. Contraction of intercostal muscles

Answer

**Step-by-Step Solution:**

1. **Understanding Expiration**: Expiration is the process of breathing out, which involves the expulsion of carbon dioxide from the lungs. It is the opposite of inspiration, where oxygen is inhaled.

2. **Role of Diaphragm**: The diaphragm is a dome-shaped muscle located below the lungs. It plays a crucial role in the breathing process. During expiration, the diaphragm relaxes, which helps to decrease the volume of the thoracic cavity.

3. **Role of Intercostal Muscles**: Intercostal muscles are located between the ribs. They assist in the breathing process by helping to expand and contract the rib cage. During expiration, these muscles also relax, contributing to the decrease in thoracic volume.

4. **Mechanics of Expiration**: When the diaphragm and intercostal muscles relax, the volume of the thoracic cavity decreases. According to Boyle's law, when the volume decreases, the pressure inside the lungs increases. This increased pressure forces air (containing carbon dioxide) out of the lungs.

5. **Conclusion**: Therefore, expiration involves the relaxation of both the diaphragm and intercostal muscles. This leads to the expulsion of air from the lungs, making option A (relaxation of diaphragm and intercostal muscles) the correct answer.

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