Which muscles are primarily responsible for exhalation?

• A. Diaphragm and abdominal muscles
• B. Intercostal muscles and neck muscles
• C. Diaphragm and intercostal muscles
• D. Abdominal muscles and back muscles

Answer: (C)

The diaphragm and intercostal muscles play crucial roles in the mechanics of ventilation, particularly during exhalation. While inhalation primarily involves the contraction of the diaphragm and external intercostal muscles to expand the chest cavity, exhalation can be viewed in two phases: passive and active.

During passive exhalation, which occurs during normal, restful breathing, the diaphragm relaxes, and the elasticity of the lungs and the thoracic cage allows air to be expelled without the need for additional muscular effort. However, during active breathing (such as during exercise or other physical exertion), the internal intercostal muscles become involved. These muscles help pull the ribs downward and inward, which decreases the volume of the thoracic cavity and further assists in expelling air from the lungs.

Therefore, the combination of diaphragm and intercostal muscles is fundamental to both inhalation and the mechanics of forced exhalation, making them the primary contributors to this process.