Which of the following sequences of events best describes inspiration?

Options

A. Contraction of diaphragm and external intercostals `to` increase in size of thoracic cavity `to` decrease in thoracic and alveolar pressure
B. Relaxation of diaphragm and external intercostals `to` decrease in size of thoracic cavity `to` increase in thoracic and alveolar pressure
C. Relaxation of diaphragm and external intercostals`to` increase in size of thoracic cavity `to` increase in thoracic and alveolar pressure
D. Contraction of diaphragm and external intercostals `to` decrease in size of thoracic cavity `to` decrease in thoracic and alveolar pressure

Explanation

**Step-by-Step Solution:**

1. **Understanding Inspiration**: Inspiration is the process of inhaling air into the lungs, which is essential for gaseous exchange. This process allows oxygen to enter the body and carbon dioxide to be expelled.

2. **Role of the Diaphragm**: The diaphragm is a dome-shaped muscle located beneath the lungs. It plays a crucial role in the breathing process by contracting and relaxing.

3. **Contraction of Muscles**: During inspiration, the diaphragm contracts, and the external intercostal muscles (muscles between the ribs) also contract. This contraction increases the volume of the thoracic cavity.

4. **Increase in Thoracic Volume**: As the diaphragm and intercostal muscles contract, the thoracic cavity expands. This increase in volume leads to a decrease in pressure within the thoracic cavity and the lungs.

5. **Creation of Negative Pressure**: The decrease in pressure inside the lungs creates a negative pressure relative to the atmospheric pressure outside the body.

6. **Air Rushes In**: Due to the pressure difference, air from the outside rushes into the lungs to equalize the pressure, completing the process of inspiration.

7. **Conclusion**: The correct sequence of events for inspiration is:
- Contraction of the diaphragm and external intercostal muscles.
- Increase in the size of the thoracic cavity.
- Decrease in pressure within the lungs.
- Air rushing into the lungs.

**Final Answer**: The correct sequence of events that best describes inspiration is:
1. Contract the diaphragm and external intercostal muscles.
2. Increase the size of the thoracic cavity.
3. Decrease the pressure in the lungs.
4. Air rushes into the lungs.

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