During inspiration, the volume of thoracic cavity increases because of

Options

A. Contraction of diaphragm and external intercosta muscles
B. Relaxation of diaphragm and external ntercosta muscles
C. Contraction of diaphragm and relaxation of eternal intercostal museles
D. Relaxation of diaphragm and external intrcostal muscles

Answer

**Step-by-Step Solution:**

1. **Understanding Inspiration**: During inspiration, the process of drawing air into the lungs occurs. This is essential for gas exchange, where oxygen is taken in and carbon dioxide is expelled.

2. **Role of Thoracic Cavity**: The thoracic cavity is the space within the chest that houses the lungs. For air to flow into the lungs, the volume of this cavity must increase.

3. **Pressure and Volume Relationship**: According to Boyle's Law, there is an inverse relationship between pressure and volume. If the volume of a container increases, the pressure inside decreases.

4. **Muscle Contraction During Inspiration**: The primary muscles involved in increasing the volume of the thoracic cavity during inspiration are:
- **Diaphragm**: When the diaphragm contracts, it moves downward, increasing the vertical dimension of the thoracic cavity.
- **External Intercostal Muscles**: These muscles contract to lift the ribs and sternum, which increases the volume of the thoracic cavity in the anterior-posterior and lateral dimensions.

5. **Resulting Pressure Change**: As the volume of the thoracic cavity increases due to the contraction of the diaphragm and external intercostal muscles, the intrapulmonary pressure decreases. This pressure becomes lower than the atmospheric pressure, allowing air to flow into the lungs.

6. **Conclusion**: Therefore, during inspiration, the volume of the thoracic cavity increases because of the contraction of the diaphragm and the external intercostal muscles. The correct answer is option A.

**Final Answer**: A) Contraction of diaphragm and external intercostal muscles.

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