The volume of thoracic chamber increases in dorso-ventral axis due to the contraction of

Options

A. Phrenic muscles
B. External intercostal muscles
C. Abdominal muscles
D. Internal intercostal muscles

Answer

To solve the question regarding the increase in the volume of the thoracic chamber in the dorso-ventral axis due to contraction, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Thoracic Chamber**:
- The thoracic chamber, or thoracic cavity, is the space within the chest that houses the lungs and heart. It plays a crucial role in the respiratory process.

2. **Identifying the Axes of Expansion**:
- The question specifies an increase in volume in the "dorso-ventral axis." This refers to the front-to-back dimension of the thoracic cavity.

3. **Muscle Contraction During Breathing**:
- The increase in volume of the thoracic cavity during inhalation is primarily due to the contraction of specific muscles.

4. **Key Muscles Involved**:
- The diaphragm is the main muscle responsible for increasing the volume of the thoracic cavity. When the diaphragm contracts, it moves downward, increasing the space in the thoracic cavity.
- Additionally, the external intercostal muscles, which are located between the ribs, also play a role in expanding the thoracic cavity by lifting the rib cage.

5. **Conclusion**:
- Therefore, the volume of the thoracic chamber increases in the dorso-ventral axis primarily due to the contraction of the diaphragm and the external intercostal muscles. However, since the question asks specifically for the dorso-ventral axis, the diaphragm is the most relevant muscle.

### Final Answer:
The volume of the thoracic chamber increases in the dorso-ventral axis due to the contraction of the diaphragm.