Question

Exhalation begins when the elastic recoil of the chest wall and lungs occurs. internal intercostal muscles contract. inspiratory muscles relax. elastic recoil of the chest wall and lungs occurs and internal intercostal muscles contract. elastic recoil of the chest wall and lungs occurs, internal intercostal muscles contract, and inspiratory muscles relax.

Answer 1

I believe that ,Exhalation begins when the internal intercostal muscles contract.
Exhalation happens due to elastic properties of the lungs as well as the internal intercostal muscles which lower the rib cage and decrease the thoracic volume. As the thoracic diaphragm relaxes during exhalation it causes the tissue it has depressed to rise superiorly and put the pressure on the lungs to expel the air.