The muscular wall essential to respiration is the _________.

• A. Diaphragm
• B. Intercostal muscles
• C. Abdominals
• D. Latissimus dorsi

Answer: (A)

The diaphragm is the main muscle responsible for respiration. It forms the floor of the thoracic cavity and, when it contracts, moves downward and flattens, expanding the chest cavity and drawing air into the lungs. When it relaxes, air is expelled as the chest cavity narrows. Intercostal muscles help by lifting the rib cage during deeper breaths, but they are secondary to the diaphragm’s essential role in inspiration. Abdominal muscles assist with forced expiration by increasing intra-abdominal pressure, and latissimus dorsi isn’t a primary breathing muscle.