What is the primary muscle responsible for inspiration during quiet breathing?

The diaphragm is the primary muscle responsible for inspiration during quiet breathing. This dome-shaped muscle sits beneath the lungs and separates the thoracic cavity from the abdominal cavity. When a person inhales, the diaphragm contracts and moves downwards, which increases the volume of the thoracic cavity. This change in volume creates a negative pressure relative to the outside atmosphere, causing air to flow into the lungs.

The importance of the diaphragm in quiet respiration cannot be overstated; it accounts for the majority of the air intake during normal breathing at rest. While other muscles, such as the intercostal muscles, may assist in breathing - particularly during more vigorous activities or forced breathing - they are not the primary movers for inspiration in a resting state like the diaphragm. Thus, selecting the diaphragm reflects an understanding of its essential role in the mechanics of respiration.