During inspiration in mammals the sternum moves

Options

A. forward and upward
B. backward and upward
C. forward and downward
D. backward and downward

Answer

**Step-by-Step Solution:**

1. **Understanding Inspiration:**
- Inspiration is the process of taking air into the lungs. It involves the contraction of certain muscles, primarily the diaphragm and the external intercostal muscles.

2. **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 volume of the thoracic cavity.

3. **Role of External Intercostal Muscles:**
- The external intercostal muscles are located between the ribs. When these muscles contract, they pull the ribs upward and outward. This movement also causes the sternum (the breastbone) to move.

4. **Movement of the Sternum:**
- During inspiration, the combined action of the diaphragm and the external intercostal muscles causes the sternum to move forward and upward. This movement increases the volume of the thoracic cavity.

5. **Pressure Changes:**
- According to Boyle's Law, an increase in volume leads to a decrease in pressure. As the volume of the thoracic cavity increases, the pressure inside the lungs decreases, allowing air to flow in from the atmosphere where the pressure is higher.

6. **Conclusion:**
- Therefore, during inspiration in mammals, the sternum moves forward and upward.

**Final Answer:**
- The correct option is: **Forward and Upward.**

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