The Diaphragm: Primary Muscle of Respiration

The diaphragm is a large, dome-shaped muscle separating thoracic and abdominal cavities.

• Contraction: Flattens, expands chest cavity → negative pressure → air inflow (inspiration).
• Relaxation: Returns to dome → elastic recoil → air outflow (expiration).

Also generates pressure for coughing, sneezing, vomiting, and defecation.