What is the main muscle involved in respiration that separates the chest cavity from the abdominal cavity?

The diaphragm is the main muscle involved in respiration and plays a crucial role in the process of inhalation and exhalation. It is a thin, dome-shaped sheet of muscle that separates the thoracic (chest) cavity from the abdominal cavity. When the diaphragm contracts, it moves downward, increasing the volume of the thoracic cavity and creating a negative pressure that allows air to flow into the lungs. During exhalation, the diaphragm relaxes and moves back to its resting position, which reduces the thoracic cavity's volume and pushes air out of the lungs.

Understanding this muscle's function is essential for comprehending how breathing works mechanically. The intercostal muscles, while also involved in respiration by aiding with the expansion and contraction of the ribcage, do not function as the primary divider between the abdominal and thoracic cavities. Abdominal muscles contribute to forced exhalation but are not responsible for the inhalation process and the structural separation. Costal muscles refer to those associated with the ribs but do not denote a specific muscle or group of muscles in standard anatomical terminology. Therefore, the diaphragm is distinctly recognized as the primary muscle facilitating respiration.