During inspiration, the volume of thoracic caity
increases because of

Options

A. Contraction of diaphragm and external intercostal muscles
B. Relaxation of diaphragm and external intercostal muscles
C. Contraction of diaphragm and relaxation of external intercostal muscles
D. Relaxation of diaphragm and contraction of external intercostal muscles

Answer

**Step-by-Step Solution:**

1. **Understanding Inspiration**: During the process of inspiration (inhalation), the body takes in air, and this involves changes in the thoracic cavity.

2. **Role of the Diaphragm**: The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. When we inhale, the diaphragm contracts and moves downward. This contraction increases the volume of the thoracic cavity.

3. **Role of Intercostal Muscles**: The external intercostal muscles are located between the ribs. When these muscles contract, they pull the ribs upward and outward, further expanding the thoracic cavity.

4. **Volume and Pressure Changes**: As the volume of the thoracic cavity increases due to the contraction of both the diaphragm and the external intercostal muscles, the pressure inside the thoracic cavity decreases. This pressure difference allows air to flow into the lungs.

5. **Conclusion**: Therefore, the increase in the volume of the thoracic cavity during inspiration is primarily due to the contraction of both the diaphragm and the external intercostal muscles.

**Final Answer**: The volume of the thoracic cavity increases because of the contraction of the diaphragm and the external intercostal muscles.

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