What is the driving force for inspiration during breathing?

The driving force for inspiration during breathing is primarily related to atmospheric pressure. When we inhale, the diaphragm and intercostal muscles contract, causing the thoracic cavity to increase in volume. This expansion results in a decrease in the intrapulmonary pressure (the pressure within the lungs) relative to the outside atmosphere. Since atmospheric pressure is higher than the pressure within the expanded lungs, air rushes into the lungs to equalize the pressure. Thus, the difference between atmospheric pressure and intrapulmonary pressure is what drives air into the lungs during inspiration.

While diaphragm contraction plays a crucial role in creating the initial change in lung volume, it is the difference between atmospheric and intrapulmonary pressures that ultimately determines the flow of air into the respiratory system. Similarly, although chest cavity expansion is caused by muscle contractions, it is atmospheric pressure that acts as the primary force that facilitates the movement of air into the lungs.