The primary muscle responsible for inspiration during quiet breathing is the:

The primary muscle responsible for inspiration during quiet breathing is the:

• A. Diaphragm
• B. External intercostals
• C. Internal intercostals
• D. Abdominal muscles

Answer: (A)

The main muscle driving quiet (resting) breathing is the diaphragm. When it contracts, the diaphragm flattens and moves downward, increasing the vertical dimension of the thoracic cavity. This expansion lowers intrapleural pressure and draws air into the lungs. The external intercostals assist by lifting the rib cage to add a bit more volume, but their role is secondary during quiet breathing. The internal intercostals and the abdominal muscles are more involved in forced expiration or active breathing maneuvers, not the passive inspiration of normal, restful breathing. So, the diaphragm is the primary muscle responsible for inspiration at rest.

The main muscle driving quiet (resting) breathing is the diaphragm. When it contracts, the diaphragm flattens and moves downward, increasing the vertical dimension of the thoracic cavity. This expansion lowers intrapleural pressure and draws air into the lungs. The external intercostals assist by lifting the rib cage to add a bit more volume, but their role is secondary during quiet breathing. The internal intercostals and the abdominal muscles are more involved in forced expiration or active breathing maneuvers, not the passive inspiration of normal, restful breathing. So, the diaphragm is the primary muscle responsible for inspiration at rest.