What happens to the volume of the thoracic cavity when the diaphragm contracts during inspiration?

When the diaphragm contracts during inspiration, it moves downward and becomes flatter. This action increases the volume of the thoracic cavity because the diaphragm forms the floor of the thoracic cavity. As the volume of the thoracic cavity increases, it causes a decrease in the pressure within the cavity, allowing air to flow into the lungs from the higher atmospheric pressure outside the body. This process is crucial for proper ventilation and gas exchange within the respiratory system. Thus, the correct answer emphasizes the role of the diaphragm in expanding the thoracic cavity to facilitate breathing.