Question

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

Explanation:

During inspiration, the process begins with the contraction of the diaphragm (moving downward) and the external intercostal muscles. This contraction increases the thoracic cavity volume. As a result, the intra - alveolar pressure decreases (due to Boyle's law \(P_1V_1 = P_2V_2\), when \(V\) increases, \(P\) decreases if \(T\) is constant). Then, because of the pressure gradient (atmospheric pressure > intra - alveolar pressure), air is forced into the respiratory tract, and finally, the lungs inflate. So the first event is the muscle contraction.

Answer:

The diaphragm moves downward and the external intercostal muscles contract.