Which muscle is primarily 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 and plays a crucial role in the breathing process. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and causing air to be drawn into the lungs. This contraction is essential for inhalation. During exhalation, the diaphragm relaxes, allowing the thoracic cavity to decrease in volume and push air out of the lungs.

While the intercostal muscles and abdominal muscles also play a role in respiration, particularly during forced breathing or physical exertion, they are not the primary muscles responsible for the act of breathing under normal conditions. The rectus femoris, a muscle in the thigh, is not involved in respiration at all. Thus, the diaphragm stands out as the key muscle necessary for effective breathing.