Question

18 which of the following occurs first, causing inspiration? multiple choice intra - alveolar pressure decreases the lungs inflate the diaphragm moves downward and the external intercostal muscles contract. atmospheric pressure forces air into the respiratory tract.

Explanation:

Inspiration (inhalation) begins with the contraction of the diaphragm (moving downward) and external intercostal muscles. This increases the thoracic cavity volume. As per Boyle's law ($P_1V_1 = P_2V_2$, where pressure and volume are inversely related at constant temperature), an increase in volume leads to a decrease in intra - alveolar pressure. Then, atmospheric pressure (higher than the now - lower intra - alveolar pressure) forces air into the respiratory tract, and the lungs inflate. So the first event is the contraction of the diaphragm and external intercostal muscles.

Answer:

The diaphragm moves downward and the external intercostal muscles contract.