What is the function of accessory muscles in respiration?

The role of accessory muscles in respiration is primarily to assist in increasing the effort of breathing when the body requires greater ventilation, such as during exercise or respiratory distress. These muscles, which include the sternocleidomastoid, scalene, and pectoralis major, help elevate the rib cage and expand the chest cavity. This additional muscular assistance allows for deeper and quicker breaths, facilitating increased air intake when metabolic demands are heightened. Their activation typically occurs when the primary respiratory muscles—the diaphragm and intercostal muscles—are insufficient to meet the body's oxygen needs.