Questions: Which causes most of the pressure changes that result in inhalation and exhalation? a.) Contraction and relaxation of the intercostal muscles only b.) Contraction and relaxation of the diaphragm only. c.) Contraction and relaxation of the diaphragm and intercostal muscles d.) Contraction and relaxation of the lungs.

The answer is c.) Contraction and relaxation of the diaphragm and intercostal muscles.

Explanation for each option:

a.) Contraction and relaxation of the intercostal muscles only: This option is incorrect because while the intercostal muscles do play a role in changing the pressure within the thoracic cavity, they work in conjunction with the diaphragm to facilitate breathing.

b.) Contraction and relaxation of the diaphragm only: This option is incorrect because the diaphragm alone is not solely responsible for the pressure changes. It is the primary muscle involved in breathing, but the intercostal muscles also contribute significantly.

c.) Contraction and relaxation of the diaphragm and intercostal muscles: This option is correct because both the diaphragm and the intercostal muscles work together to change the volume of the thoracic cavity, which in turn changes the pressure and results in inhalation and exhalation.

d.) Contraction and relaxation of the lungs: This option is incorrect because the lungs themselves do not contract or relax. Instead, they expand and recoil passively in response to the changes in pressure created by the diaphragm and intercostal muscles.

In summary, the combined action of the diaphragm and intercostal muscles is responsible for the pressure changes that lead to inhalation and exhalation.