What muscles between the ribs contract during breathing?

The intercostal muscles are located between the ribs and play a crucial role in the breathing process, specifically during inhalation. When we breathe in, the intercostal muscles contract, causing the rib cage to expand. This expansion increases the volume of the thoracic cavity and reduces the pressure within, allowing air to flow into the lungs.

While other muscle groups are involved in breathing, such as the diaphragm, which is the primary muscle responsible for inhalation, and abdominal muscles that assist during forceful exhalation, the direct action of contracting between the ribs during regular breathing is the function of the intercostal muscles. Thus, this option accurately represents the specific muscles involved in the mechanics of breathing between the ribs.

It's important to distinguish that the sternocleidomastoid primarily assists in elevating the sternum and is more active during deep or labored breathing rather than normal, relaxed breathing, and abdominal muscles typically engage more during exhalation, particularly in forced breathing scenarios.