Which muscles elevate the sternum during inspiration to create more space in the thoracic cavity?

The external intercostal muscles play a crucial role in the process of inspiration by elevating the ribs and the sternum, thereby expanding the thoracic cavity. During inhalation, these muscles contract, resulting in lateral and anterior elevation of the ribs. This elevation increases the volume of the thoracic cavity, which decreases intrathoracic pressure and allows air to flow into the lungs.

By contrast, while the diaphragm is also essential for respiration, its primary function is to create a downward movement of the thoracic cavity, increasing volume during inspiration. The internal intercostal muscles mainly assist with forced expiration rather than elevation of the sternum. The rectus abdominis is primarily involved in flexion of the trunk and expiration, thus not directly influencing the elevation of the sternum during inhalation. Understanding the specific roles of these muscles clarifies why the external intercostal muscles are the key muscles involved in elevating the sternum during inspiration.