Select the statement that is correct related to movement of diaphragm and intercostal muscles for the process of effortless exhalation.

Options

A. Diaphragm relax and external intercostal muscles relax
B. Diaphragm relax and external intercostal muscles contracts.
C. Diaphragm contracts and external intercostal muscles show no movement
D. Diaphragm contracts and external intercostal muscles relax

Answer

To solve the question regarding the movement of the diaphragm and intercostal muscles during effortless exhalation, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Exhalation**: Exhalation is the process of expelling air from the lungs. It occurs after inhalation, where air is drawn into the lungs.

2. **Role of the Diaphragm**: The diaphragm is a dome-shaped muscle located below the lungs. During inhalation, it contracts and flattens, increasing the volume of the thoracic cavity and allowing air to flow into the lungs. Conversely, during exhalation, the diaphragm relaxes and returns to its dome shape, which decreases the volume of the thoracic cavity and pushes air out of the lungs.

3. **Role of Intercostal Muscles**: The intercostal muscles are located between the ribs. The external intercostal muscles assist in inhalation by contracting and lifting the rib cage. During exhalation, these muscles relax, allowing the rib cage to fall back into its resting position, which also helps push air out of the lungs.

4. **Identifying the Correct Statement**: For effortless exhalation, both the diaphragm and the external intercostal muscles must relax. This allows the thoracic cavity to decrease in volume, leading to a natural expulsion of air.

5. **Conclusion**: The correct statement regarding the movement of the diaphragm and intercostal muscles during effortless exhalation is that both the diaphragm and the external intercostal muscles relax.

### Final Answer:
The correct statement is: "Diaphragm relaxes and external intercostal muscles relax."

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