What structure contracts to help air move in and out of the lungs?

The diaphragm is the primary muscle involved in the process of breathing. When the diaphragm contracts, it flattens and moves downward in the thoracic cavity. This movement creates a negative pressure within the lungs, allowing air to flow in from the atmosphere—a process known as inhalation. When the diaphragm relaxes, it returns to its dome-shaped position, which reduces the volume of the thoracic cavity and pushes air out of the lungs during exhalation.

In contrast, the trachea is a tube that serves as a passageway for air to move to and from the lungs but does not actively contract or contribute to the mechanical ventilation process. The larynx, commonly known as the voice box, also does not play a direct role in breathing mechanics; it primarily functions in phonation and protecting the airway during swallowing. The bronchioles are small airways that branch from the bronchi and lead into the lungs, but like the trachea and larynx, they do not contract to facilitate airflow. Instead, they can change diameter to regulate airflow resistance but are not the primary drivers of air movement.