Florida Basic Recruit Training Program High Liability (First Aid) Practice Exam

The diaphragm is a dome-shaped muscle located at the base of the thoracic cavity and is the primary muscle responsible for breathing. When you inhale, the diaphragm contracts and moves downward, creating a vacuum effect that allows air to be drawn into the lungs. As the diaphragm relaxes, it moves back to its original position, allowing air to be expelled from the lungs during exhalation. This movement is essential for normal breathing and highlights the critical role of the diaphragm in respiratory function.

Other muscles, while involved in the breathing process, do not play as central a role as the diaphragm in the mechanics of air movement. The intercostal muscles, for example, work alongside the diaphragm to help expand and contract the rib cage during breathing. However, the diaphragm is the main driver of the airflow into and out of the lungs. The sternocleidomastoid and trapezius muscles are primarily associated with head movement and neck stabilization rather than directly facilitating air movement in the lungs. Therefore, while interconnected in overall respiratory mechanics, the diaphragm is unequivocally the key muscle for moving air in and out of the lungs.