Which of the following statements about thoracic diaphragm is true?

Options

A. The thoracic diaphragm relaxes during inhalation and exhalation
B. The thoracic diaphragm contracts during inhalation,
C. The thoracic diaphragm contracts during inhalation and exhalation
D. The thoracic diaphragm relaxes during inhalation

Answer

### Step-by-Step Solution:

1. **Understanding the Thoracic Diaphragm**:
- The thoracic diaphragm is a dome-shaped muscle located beneath the ribs that separates the thoracic cavity from the abdominal cavity.

2. **Function During Breathing**:
- During inhalation, the diaphragm contracts and flattens. This contraction increases the volume of the thoracic cavity, which decreases the pressure inside the cavity, allowing air to flow in from the outside (inhalation).
- During exhalation, the diaphragm relaxes and returns to its dome shape. This relaxation decreases the volume of the thoracic cavity, which increases the pressure inside, forcing air out (exhalation).

3. **Evaluating the Statements**:
- **Option A**: "Thoracic diaphragm relaxes during inhalation and exhalation."
- This statement is incorrect because the diaphragm contracts during inhalation and relaxes during exhalation.
- **Option B**: "Thoracic diaphragm contracts during inhalation."
- This statement is correct as the diaphragm indeed contracts during inhalation.
- **Option C**: "Thoracic diaphragm contracts during inhalation and exhalation."
- This statement is incorrect because the diaphragm only contracts during inhalation, not during exhalation.
- **Option D**: "Thoracic diaphragm contracts during inhalation."
- This statement is also correct but is a repetition of Option B.

4. **Conclusion**:
- The true statement about the thoracic diaphragm is that it contracts during inhalation (Option B).