During inspiration in man,

Options

A. the internal intercostal muscles relax
B. due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity increases
C. due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity decreases
D. the abdominal muscles contract

Answer

**Step-by-Step Solution:**

1. **Understanding Inspiration**: Inspiration is the process of taking air into the lungs. It involves several muscles and changes in the thoracic cavity.

2. **Muscle Contraction**: During inspiration, the external intercostal muscles contract. This contraction lifts the rib cage upwards and outwards.

3. **Diaphragm Movement**: Simultaneously, the diaphragm, which is a dome-shaped muscle at the base of the thoracic cavity, contracts and flattens.

4. **Volume Change in Thoracic Cavity**: The contraction of the external intercostal muscles and the flattening of the diaphragm lead to an increase in the volume of the thoracic cavity.

5. **Pressure Change**: As the volume of the thoracic cavity increases, the pressure inside the cavity decreases, creating a vacuum that allows air to flow into the lungs.

6. **Conclusion**: Therefore, during inspiration in man, the correct statement is that due to the contraction of the external intercostal muscles and the flattening of the diaphragm, the volume of the thoracic cavity increases.

**Correct Answer**: Option 2 - Due to contraction of external intercostal muscles and flattening of diaphragm, the volume of thoracic cavity increases.

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