Which muscles are primarily contracted during a forced inspiration, such as when taking a deep breath to reach inspiratory reserve volume?

• A. Internal intercostal and abdominal muscles
• B. Only the abdominal muscles
• C. Diaphragm and external intercostal muscles
• D. Only the diaphragm

Answer: (C)

Verified step by step guidance

1. Understand the concept of forced inspiration: Forced inspiration occurs when a person takes a deep breath beyond normal tidal volume to reach inspiratory reserve volume. This requires the activation of specific muscles to expand the thoracic cavity.
2. Identify the primary muscles involved in normal inspiration: The diaphragm is the main muscle responsible for normal inspiration. It contracts and moves downward, increasing the volume of the thoracic cavity and reducing pressure to draw air into the lungs.
3. Recognize the role of external intercostal muscles: During forced inspiration, the external intercostal muscles contract to lift the ribs and sternum, further expanding the thoracic cavity and allowing for a greater intake of air.
4. Differentiate the roles of other muscles: Internal intercostal muscles and abdominal muscles are primarily involved in forced expiration, not inspiration. They help compress the thoracic cavity to expel air from the lungs.
5. Conclude that the diaphragm and external intercostal muscles are the primary muscles contracted during forced inspiration, as they work together to increase thoracic volume and facilitate deep breathing.