Mechanism of Breathing III: The Accessory Muscles

Accessory muscles activate when a person breathes deeply or struggles to breathe, enhancing lung expansion beyond what primary muscles alone can achieve. The sternocleidomastoid lifts the sternum, the scalene muscles elevate the second and third ribs, and the pectoralis minor lifts the third, fourth, and fifth ribs. These coordinated actions maximize air intake and ensure sufficient oxygen reaches the bloodstream.

The sternocleidomastoid, positioned in the neck, lifts the sternum during deep breathing or respiratory effort. This action facilitates increased expansion of the chest cavity, allowing greater lung expansion and enhancing inhalation capacity. The muscle is a key accessory muscle activated when additional respiratory effort is required.

Scalene muscles, located in the neck, assist in elevating the second and third ribs during intensive breathing efforts. This elevation contributes to chest expansion and increases lung capacity during deep inhalation. These muscles work as accessory muscles to optimize lung function when additional respiratory effort is needed.

During forced exhalation, such as vigorous physical activity or coughing, abdominal muscles actively contract to push up against the diaphragm. This action helps expel air more forcefully from the lungs. In normal exhalation, the diaphragm and intercostal muscles relax to facilitate passive air expulsion.

During exhalation, the diaphragm and intercostal muscles relax, reducing the space in the chest cavity and pushing air out of the lungs. This passive process occurs during normal, quiet breathing. When forced exhalation is required, accessory muscles like the abdominal muscles contract to enhance air expulsion.

The pectoralis minor, located in the upper chest and front of the shoulders, elevates the third, fourth, and fifth ribs during deep breathing. The scalene muscles elevate the second and third ribs, while the sternocleidomastoid lifts the sternum. These coordinated rib elevations enhance chest expansion and increase lung capacity.

Understanding accessory muscle function is crucial for comprehending breathing mechanics and diagnosing respiratory conditions. Detailed insights into how these muscles work allow healthcare professionals to develop targeted therapeutic strategies and improve respiratory health interventions. This knowledge enhances the effectiveness of respiratory assessment and treatment planning.