Which muscle is primarily involved in inspiration?

Which muscle is primarily involved in inspiration?

• A. Diaphragm
• B. Rectus Abdominis
• C. External Oblique
• D. Internal Oblique

Answer: (A)

The primary muscle driving inspiration is the diaphragm. When it contracts, it moves downward and flattens from its dome shape, increasing the vertical size of the thoracic cavity. This expansion lowers intrathoracic pressure, so air flows into the lungs. The abdominal muscles listed—rectus abdominis and the obliques—are mainly involved in increasing intra-abdominal pressure and pushing the diaphragm upward during forced expiration; they act to expel air rather than pull air in. They, along with the internal and external obliques, contribute to expiration rather than inspiration. In quiet breathing, the diaphragm supplies most of the tidal volume, with accessory muscles only coming into play during heavy breathing.

The primary muscle driving inspiration is the diaphragm. When it contracts, it moves downward and flattens from its dome shape, increasing the vertical size of the thoracic cavity. This expansion lowers intrathoracic pressure, so air flows into the lungs. The abdominal muscles listed—rectus abdominis and the obliques—are mainly involved in increasing intra-abdominal pressure and pushing the diaphragm upward during forced expiration; they act to expel air rather than pull air in. They, along with the internal and external obliques, contribute to expiration rather than inspiration. In quiet breathing, the diaphragm supplies most of the tidal volume, with accessory muscles only coming into play during heavy breathing.