Which of the following mechanism /s help to increase the volume of the thoracic chamber ?

Options

A. The contraction of diaphragm
B. Contraction of external intercostal muscle
C. The uplifting of sternum
D. All of the above

Answer

To solve the question "Which of the following mechanisms help to increase the volume of the thoracic chamber?", we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Thoracic Chamber**:
- The thoracic chamber is the space within the rib cage that houses the lungs and heart. Increasing its volume is essential for inhalation (inspiration) as it allows air to flow into the lungs.

2. **Analyzing Option A: The contraction of diaphragm**:
- The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. When the diaphragm contracts, it flattens and moves downward, increasing the vertical dimension of the thoracic cavity. This action increases the volume of the thoracic chamber, allowing air to be drawn into the lungs.

3. **Analyzing Option B: Contraction of external intercostal muscles**:
- The external intercostal muscles are located between the ribs. When these muscles contract, they pull the ribs upward and outward, which increases the volume of the thoracic cavity in the lateral (dorsal-ventral) direction. This also contributes to the inhalation process.

4. **Analyzing Option C: The uplifting of sternum**:
- The sternum (breastbone) can be lifted during inhalation, which is facilitated by the contraction of certain muscles (including the external intercostal muscles). This action further increases the volume of the thoracic chamber, allowing for more air to enter the lungs.

5. **Conclusion**:
- All three mechanisms (contraction of diaphragm, contraction of external intercostal muscles, and uplifting of sternum) contribute to increasing the volume of the thoracic chamber. Therefore, the correct answer is:
- **D. All of the above**.

### Final Answer:
D. All of the above