Which muscle aids in breathing by contracting and relaxing?

The diaphragm is the primary muscle responsible for breathing. It is a dome-shaped muscle located beneath the lungs and plays a crucial role in the respiratory process. When the diaphragm contracts, it flattens and moves downward, creating negative pressure in the thoracic cavity and allowing air to be drawn into the lungs. Upon relaxing, the diaphragm returns to its original dome shape, pushing air out of the lungs and facilitating exhalation.

While the intercostal muscles, abdominals, and pectoralis muscles do assist in the breathing process, particularly during forceful inhalation or exhalation, they are not the primary muscles responsible for the basic act of breathing. The intercostal muscles support the diaphragm by helping expand and contract the rib cage, while the abdominals can assist in forceful exhalation. The pectoralis muscles also play a minor role in respiration, primarily during deep breathing situations. However, the diaphragm remains the central player in the maintenance of normal breathing patterns.