INTERCOSTAL MUSCLES Inhalation and exhalation make up 1 breath Internal intercostal muscles External intercostal muscles Sternum Inhalation ? Also termed inspiration ? Diaphragm contracts and flattens. ? Internal intercostal muscles relaxes ? While the external intercostal muscles contract ? The rib cage moves up and out. ? Enlarging the thoracic cavity and decreases the air pressure within. ? Air from the surrounding enters the lungs Exhalation ? Also termed expiration ? Diaphragm relaxes and arch upwards. ? Internal intercostal muscles contracts ? While the external intercostal muscles relaxes ? The rib cage moves down and in. ? Air is forced out of the lungs Summary