Question

question 45
normal, resting inspiration is due to:
a the diaphragm muscle pushes down
b atmospheric pressure increases
c contraction of the intercostals
d elastic recoil of the lung tissue

Explanation:

During normal, resting inspiration, the diaphragm muscle contracts and moves downward (it does not "push" down in an incorrect sense; contraction causes its dome - shaped structure to flatten and move inferiorly). This increases the volume of the thoracic cavity. The intercostal muscles (external intercostals) also contract, elevating the ribs and further increasing the thoracic volume. As the volume of the thoracic cavity (and thus the lungs) increases, the intrapulmonary pressure decreases below the atmospheric pressure, and air flows into the lungs.
Atmospheric pressure does not increase during normal inspiration (it is relatively constant in the local environment for the short duration of a breath). Elastic recoil of the lung tissue is involved in expiration (when the muscles relax, the elastic fibers in the lung tissue help the lungs return to their original, smaller volume).

Answer:

A. The diaphragm muscle pushes down, C. Contraction of the intercostals