During exhalation the ribs move ________.

The correct completion of the statement is "During exhalation, the ribs move downward and inward."
1. Exhalation (Expiration):
o Exhalation is the process of breathing out air from the lungs.
o It is a passive process (in most cases) that occurs when the diaphragm relaxes and moves upward, and the intercostal muscles (muscles between the ribs) relax as well.
2. Movement of the Ribs During Exhalation:
o The ribs move in a downward and inward direction during exhalation.
o The relaxation of the external intercostal muscles causes the rib cage to move downward and inward, reducing the volume of the thoracic cavity and helping to push air out of the lungs.
3. Mechanism:
o As the diaphragm relaxes and moves upward and the intercostal muscles relax, the volume of the chest cavity decreases. This causes an increase in pressure within the lungs, which forces the air out of the lungs through the trachea and out of the body.
During exhalation, the ribs move downward and inward to help expel air from the lungs.