What is the major muscle involved in respiration?

The diaphragm is the primary muscle involved in respiration. It is a dome-shaped muscle located at the base of the thoracic cavity, separating the thoracic and abdominal cavities. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and causing a decrease in pressure within the lungs. This pressure difference allows air to flow into the lungs, facilitating inhalation.

During exhalation, the diaphragm relaxes and moves back to its dome shape, which helps to push air out of the lungs. Its critical role in the breathing process makes it the major muscle responsible for respiration.

While the external intercostal muscles assist with inhalation by expanding the rib cage and the sternocleidomastoid may help during forced inhalation by elevating the sternum, they are not the most significant muscles for routine breathing. The rectus abdominis primarily aids in forced exhalation and does not play a central role in the inhalation process. Thus, the diaphragm stands out as the essential muscle for effective and efficient respiration.