Question

multiple choice question
which event enlarges the thoracic cavity?
o relaxing the external intercostal muscles
o contracting the external intercostal muscles
o relaxing the diaphragm

Explanation:

When the external intercostal muscles contract, they lift the ribs upward and outward. This action increases the anteroposterior and transverse dimensions of the thoracic cavity. Relaxing the external intercostal muscles would reverse this (decrease thoracic cavity size). Relaxing the diaphragm causes it to dome upward, decreasing the vertical dimension of the thoracic cavity. Contracting the diaphragm (not an option here) would flatten it and increase the vertical dimension. But among the given options, contracting the external intercostal muscles is the event that enlarges the thoracic cavity.

Answer:

contracting the external intercostal muscles