Which of the following does NOT contract during inspiration?

During inspiration, the primary muscles that facilitate the expansion of the thoracic cavity to draw air into the lungs include the diaphragm, parasternal muscles, and external intercostal muscles. The diaphragm is the primary muscle responsible for breathing and contracts to flatten and increase the volume of the thoracic cavity. The parasternal and external intercostal muscles assist by elevating the rib cage, which further expands the thoracic cavity.

In contrast, the internal intercostal muscles primarily play a role during expiration rather than inspiration. They function to depress the ribs and decrease the volume of the thoracic cavity, which aids in pushing air out of the lungs. Therefore, during the act of inspiration, the internal intercostal muscles do not contract as their role is not required in this phase of respiration. This is why they are the correct choice for the question regarding which structure does not participate in the contraction associated with inhalation.