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 and understand how they contribute to the increase in thoracic volume.

### Step-by-Step Solution:

1. **Understanding the Thoracic Chamber**:
- The thoracic chamber, or thoracic cavity, is the space within the rib cage that houses the lungs and heart. Its volume can change to facilitate breathing.

2. **Option 1: Contraction of the Diaphragm**:
- The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. When it contracts, it flattens and moves downward, increasing the vertical dimension of the thoracic cavity. This contraction creates a negative pressure that allows air to flow into the lungs.
- **Conclusion**: This mechanism increases the volume of the thoracic chamber.

3. **Option 2: 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, expanding the ribcage. This action increases the anteroposterior and lateral dimensions of the thoracic cavity, further enhancing its volume.
- **Conclusion**: This mechanism also increases the volume of the thoracic chamber.

4. **Option 3: Uplifting of the Sternum**:
- The sternum, or breastbone, can be lifted during inhalation. This movement, often referred to as the "pump handle" effect, contributes to the expansion of the thoracic cavity by increasing the anterior-posterior dimension.
- **Conclusion**: This mechanism increases the volume of the thoracic chamber as well.

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