UPT Aerospace Physiology Practice Test

The contraction of the diaphragm and external intercostal muscles is primarily responsible for inspiration, or inhalation. When the diaphragm contracts, it moves downward, expanding the thoracic cavity and creating a negative pressure that pulls air into the lungs. Simultaneously, the external intercostal muscles contract, elevating the rib cage, which further increases the volume of the thoracic cavity and aids in drawing air in. This process is essential for allowing oxygen to enter the lungs, making it a crucial step in the respiratory cycle.

While exhalation involves the relaxation of these muscles and the passive expulsion of air from the lungs, it is important to clarify that contraction of the diaphragm and external intercostal muscles directly facilitates the phase of inhalation rather than exhalation. Circulation pertains to the movement of blood and is not directly related to the mechanical action of breathing. Respiration often encompasses both the physiological process of breathing and the cellular exchange of gases, but in the context of this question, the specific action described relates clearly to the act of inspiration.