Which muscles are responsible for contraction during normal inspiration?

The external intercostals play a crucial role during normal inspiration by facilitating the expansion of the thoracic cavity. When these muscles contract, they elevate the ribs and increase the volume of the thoracic cavity. This expansion reduces the pressure inside the pleural cavity and allows air to flow into the lungs, following the principle of airflow from areas of higher pressure to lower pressure.

During normal breathing, this contraction is primarily involuntary and occurs alongside the diaphragm, which also contracts and moves downward to further enlarge the thoracic cavity. While other muscles, such as the scalene muscles and internal intercostals, may assist in breathing or become active during forced respiration, the external intercostals are specifically involved in the typical process of inhalation at rest.