Mechanism of Breathing III: The Accessory Muscles

The breathing process starts with inhalation. The diaphragm, the primary respiratory muscle, contracts and descends, creating a negative pressure that facilitates the inhalation of air.

Simultaneously, the intercostal muscles between the ribs contract, causing the rib cage to expand and provide more space for lung expansion.

When a person breathes deeply or struggles to breathe, accessory muscles activate. The sternocleidomastoid in the neck lifts the sternum, allowing greater lung expansion.

The scalene muscles in the neck help elevate the second and third ribs, further facilitating chest expansion.

In the upper chest and front of the shoulders, the pectoralis minor lifts the third, fourth, and fifth ribs, aiding chest expansion during deep breaths.

As a person exhales, the diaphragm and intercostal muscles relax, reducing the space in the chest cavity and pushing air out of the lungs.

During forced exhalation, accessory muscles like the abdominal muscles may contract, pushing up on the diaphragm to expel air more forcefully.

This process continues, infusing oxygen into the bloodstream and facilitating optimal bodily function.