When considering the inspiration/expiration cycle that occurs with pulmonary ventilation, the internal intercostal muscles have a role in the process of while external intercostals are important in the process of .

Internal intercostal muscles have a role in the process off exhalation while the external intercostal muscles are important in the process of inhalation.

Explanation:

Internal and external intercostal muscles both function in respiration, each muscle having its specified function.

Internal intercostal muscles depress the ribs. These muscles function in exhalation, particularly forced exhalation as they depress the ribs and decrease the space in the chest.

External intercostal muscles are responsible for both forced and quiet inhalation. They raise the ribs, expanding the chest cavity, creating space for air to fill the lungs.

The external intercostal muscles shorten in areas of the ribcage during passive inhalation while the internal intercostals lengthen. The external intercostal muscles therefore, are shown to be more implicated in the inspiratory mechanism while the internal intercostal muscles are implicated in the expiatory mechanism.