what are the intercostal muscles
Intercostal muscles are several groups of muscles that run between the ribs, and help form and move the chest wall. The intercostal muscles are mainly involved in the mechanical aspect of breathing.These muscles help expand and shrink the size of the chest cavity to facilitate breathing. The external intercostals are responsible for the elevation of the ribs and bending them more open, thus expanding the transverse dimensions of the thoracic cavity. 2  Internal intercostal muscles aid in forced expiration (quiet expiration is a passive process).