Contraction of diaphragm increases the volume of the thoracic chamber in the ....(A).... axis while the contraction of external intercostal muscles increases the volume of the thoracic chamber in the ..... (B).... axis.

Options

A. (A) : antero-posterior, (B) : antero-posterior
B. (A) : dorso-ventral, (B) : dorso-ventral
C. (A) : antero-posterior, (B) : dorso-ventral
D. (A) : dorso-ventral, (B) : antero-posterior

Answer

To solve the question, we need to understand the mechanics of breathing, specifically how the diaphragm and external intercostal muscles contribute to the changes in the thoracic chamber's volume during inhalation.

### Step-by-Step Solution:

1. **Understanding the Role of the Diaphragm:**
- The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity. When it contracts, it moves downward, increasing the vertical dimension of the thoracic cavity.
- This increase in volume occurs primarily along the **anterior-posterior axis** (front to back).

2. **Understanding the Role of External Intercostal Muscles:**
- The external intercostal muscles are located between the ribs. When these muscles contract, they lift the rib cage upward and outward.
- This action increases the volume of the thoracic cavity primarily along the **dorsal-ventral axis** (back to front).

3. **Combining the Effects:**
- During inhalation, the contraction of the diaphragm increases the volume of the thoracic chamber in the anterior-posterior axis.
- Simultaneously, the contraction of the external intercostal muscles increases the volume of the thoracic chamber in the dorsal-ventral axis.

4. **Final Answer:**
- Therefore, the correct completion of the statement is:
- (A) anterior-posterior
- (B) dorsal-ventral

### Answer:
Contraction of diaphragm increases the volume of the thoracic chamber in the **anterior-posterior** axis while the contraction of external intercostal muscles increases the volume of the thoracic chamber in the **dorsal-ventral** axis.

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