Which one of the following process does not occur during inspiration in humans ?

Options

A. Contraction of internal intercostal muscles
B. Contraction of phrenic muscles
C. an overall increase in the volume of the thoracic chamber
D. the intra-pulmonary pressure decreases than atm . Pressure

Answer

To solve the question "Which one of the following processes does not occur during inspiration in humans?", we will analyze each option provided in the context of the physiological events that take place during the process of inspiration (inhalation).

### Step-by-Step Solution:

1. **Understanding Inspiration**:
- Inspiration is the process of inhaling air into the lungs. It involves several muscular and pressure changes in the thoracic cavity.

2. **Analyzing the Options**:
- **Option 1: Contraction of the internal intercostal muscles**:
- This statement is correct. During inspiration, the internal intercostal muscles actually relax, while the external intercostal muscles contract to help expand the thoracic cavity.
- **Option 2: Contraction of the phrenic muscles**:
- This statement is incorrect. During inspiration, the diaphragm (which is innervated by the phrenic nerve) contracts and moves downward, increasing the volume of the thoracic cavity.
- **Option 3: An overall increase in the volume of the thoracic chamber**:
- This statement is correct. As the diaphragm contracts and the external intercostal muscles lift the ribs, the volume of the thoracic cavity increases, allowing air to flow into the lungs.
- **Option 4: Intrapulmonary pressure decreases than the atmospheric pressure**:
- This statement is also correct. During inspiration, the increase in thoracic volume leads to a decrease in intrapulmonary pressure, allowing air to flow into the lungs.

3. **Conclusion**:
- The process that does not occur during inspiration is the contraction of the internal intercostal muscles. Therefore, the correct answer is **Option 1**.

### Final Answer:
**Option 1: Contraction of the internal intercostal muscles does not occur during inspiration in humans.**