Volume of thoracie chamber increases in atheroposterior and dorso-ventral axis by

Options

A. Contraction of diaphragm and eternal intercostal musles respetively
B. Relaxation of diaphragm and external intecostal muscles erspectively
C. Relaxation of diaphragm and abdominal musles respectively
D. Contraction of abdominal muscles and relaxation of external intecostal muscles respectively

Answer

To solve the question regarding how the volume of the thoracic chamber increases in the anterior-posterior and dorso-ventral axes, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Thoracic Chamber**: The thoracic chamber is the space within the rib cage that houses the lungs and is involved in the process of breathing. The volume of this chamber can change during the respiratory cycle.

2. **Breathing Mechanism**: Breathing consists of two main phases: inspiration (inhaling) and expiration (exhaling). During inspiration, the volume of the thoracic chamber increases, allowing air to flow into the lungs.

3. **Role of the Diaphragm**: The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic chamber in the anterior-posterior axis (front to back).

4. **Role of External Intercostal Muscles**: The external intercostal muscles are located between the ribs. When these muscles contract, they lift the ribs and sternum, which increases the volume of the thoracic chamber in the dorso-ventral axis (top to bottom).

5. **Pressure Gradient**: The increase in volume during inspiration leads to a decrease in intrapulmonary pressure (pressure inside the lungs). When the pressure inside the lungs becomes lower than atmospheric pressure, air flows into the lungs.

6. **Conclusion**: Based on the roles of the diaphragm and external intercostal muscles during inspiration, we can conclude that the volume of the thoracic chamber increases in the anterior-posterior axis due to the contraction of the diaphragm and in the dorso-ventral axis due to the contraction of the external intercostal muscles.

### Final Answer:
The correct answer is **Option A**: "Volume of thoracic chamber increases in anterior-posterior and dorso-ventral axis by a contraction of diaphragm and external intercostal muscles respectively."

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