Which of the following pairs of muscles undergo contraction during the process of inspiration in human ?

Options

A. Phrenic muscle of diaphragm and external inter - costal muscles
B. Phrenic muscle of diaphragm and internal inter - costal muscles
C. External inter - costal and internal inter - costal muscles
D. Abdominal muscles and external inter- costal muscles

Answer

To determine which pairs of muscles undergo contraction during the process of inspiration in humans, we can analyze the options provided and understand the mechanics of breathing.

### Step-by-Step Solution:

1. **Understanding Inspiration**:
- Inspiration is the process of drawing air into the lungs. It occurs when the volume of the thoracic cavity increases, leading to a decrease in intrapulmonary pressure compared to atmospheric pressure.

2. **Identifying Key Muscles**:
- The primary muscles involved in inspiration are the diaphragm and the external intercostal muscles.
- The diaphragm is a dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. When it contracts, it flattens, increasing the volume of the thoracic cavity.
- The external intercostal muscles are located between the ribs. When they contract, they lift the ribs upward and outward, further increasing the thoracic cavity's volume.

3. **Evaluating the Options**:
- **Option A**: Phrenic muscles of diaphragm and external intercostal muscles.
- **Correct**: Both muscles contract during inspiration.
- **Option B**: Phrenic muscles of diaphragm and internal intercostal muscles.
- **Incorrect**: Internal intercostal muscles are primarily involved in expiration, not inspiration.
- **Option C**: External intercostal and internal intercostal muscles.
- **Incorrect**: Internal intercostal muscles do not contract during inspiration.
- **Option D**: Abdominal muscles and external intercostal muscles.
- **Incorrect**: Abdominal muscles are not involved in the contraction during inspiration.

4. **Conclusion**:
- The correct answer is **Option A**: Phrenic muscles of diaphragm and external intercostal muscles undergo contraction during the process of inspiration in humans.