The intercostal muscles are a group of muscles located between the ribs. They play a crucial role in the respiratory process by helping to expand and contract the chest cavity during breathing. There are three main types: external, internal, and innermost intercostal muscles, each serving different functions in inhalation and exhalation. These muscles work together to facilitate the movement of the rib cage. When the external intercostal muscles contract, they lift the ribs, allowing the lungs to fill with air. Conversely, the internal intercostal muscles assist in forced exhalation by pulling the ribs downward, expelling air from the lungs.