What is the dome-shaped muscle under the lungs that flattens during inspiration?

The diaphragm is the dome-shaped muscle located beneath the lungs and plays a crucial role in the respiratory process. During inhalation, the diaphragm contracts and flattens, creating a larger space in the thoracic cavity. This change in pressure allows air to flow into the lungs. The diaphragm is essential for efficient breathing and is the primary muscle involved in inspiration.

While the intercostal muscles also assist in the process of breathing by elevating the rib cage, it is the diaphragm that is primarily responsible for the change in shape that leads to lung expansion. The rectus abdominis and transversus abdominis are involved in abdominal movements and stability but do not directly contribute to the act of inhaling. Therefore, the diaphragm is correctly identified as the muscle that flattens during inspiration, making it the appropriate answer to the question.