What is the primary muscle used in inhalation?

The diaphragm is the primary muscle used in inhalation because it is the main muscle responsible for expanding the thoracic cavity during the respiratory process. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and decreasing the pressure within the lungs. This pressure differential allows air to flow into the lungs from the outside environment, completing the inhalation process.

While the intercostal muscles assist in breathing by elevating the rib cage and expanding the chest, their role is supportive compared to that of the diaphragm. The abdominal muscles are primarily involved in forced expiration rather than inhalation, and the pectoral muscles may aid in respiratory effort during deep or labored breathing, but they are not the primary muscle responsible for the initial phase of inhalation. Hence, the diaphragm is essential for normal, quiet breathing and plays a crucial role in the mechanics of inhalation.