Which set of muscles is primarily responsible for raising the ribs during inspiration?

The external intercostal muscles play a crucial role during the process of inspiration by assisting in the elevation of the ribs. When these muscles contract, they pull the ribs upward and outward, expanding the thoracic cavity. This increase in the volume of the thoracic cavity leads to a decrease in pressure within the lungs, allowing air to flow in.

In contrast, the diaphragm is also an essential muscle involved in respiration but is primarily responsible for the downward movement during inhalation rather than the raising of the ribs. The internal intercostal muscles mainly assist with forced expiration by depressing the ribs. The abdominal muscles are involved in forced expiration and help expel air from the lungs, but they do not contribute to raising the ribs during inspiration.

Thus, the external intercostal muscles are the primary muscles that facilitate the elevation of the ribs when breathing in, making them the correct choice for this question.