during inspiration

Options

A. Diaphragm and external intercostal muscles contract
B. Diaphragm relaxes and external intercostal muscles contract
C. Both diaphragm and external intercostal muscles relax
D. Diaphragm and internal intercostal muscles contract

Answer

**Step-by-Step Solution:**

1. **Understanding Inspiration**: Inspiration is the process of taking air into the lungs. It involves specific muscular actions that increase the volume of the thoracic cavity.

2. **Diaphragm Contraction**: The diaphragm, a dome-shaped muscle located below the rib cage, contracts during inspiration. This contraction causes the diaphragm to flatten and move downward, which increases the volume of the thoracic cavity.

3. **External Intercostal Muscles**: The external intercostal muscles, which are located between the ribs, also contract during inspiration. This contraction lifts the ribs upward and outward, further expanding the thoracic cavity.

4. **Increase in Lung Volume**: As the thoracic cavity expands due to the contraction of the diaphragm and external intercostal muscles, the volume of the lungs increases. This decrease in pressure within the lungs allows air to flow in from the atmosphere.

5. **Conclusion**: The correct description of what happens during inspiration is that both the diaphragm and external intercostal muscles contract, leading to an increase in lung volume and air intake.

**Final Answer**: During inspiration, both the diaphragm and external intercostal muscles contract.

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