Which muscle depresses the ribs and originates from the superior border of each rib?

Which muscle depresses the ribs and originates from the superior border of each rib?

• A. External Intercostals
• B. Latissimus Dorsi
• C. Internal Intercostals
• D. Deltoid

Answer: (C)

Depressing the ribs to aid expiration is done by the internal intercostal muscles, which lie between the ribs. They attach along the superior border of the rib below and the inferior border of the rib above, so when they contract they pull the ribs downward and inward, reducing the thoracic volume. This action helps push air out of the lungs during forced expiration. In contrast, external intercostals elevate the ribs to expand the chest during inhalation. The latissimus dorsi and deltoid are shoulder and back muscles and do not participate in depressing the ribs during respiration.

Depressing the ribs to aid expiration is done by the internal intercostal muscles, which lie between the ribs. They attach along the superior border of the rib below and the inferior border of the rib above, so when they contract they pull the ribs downward and inward, reducing the thoracic volume. This action helps push air out of the lungs during forced expiration. In contrast, external intercostals elevate the ribs to expand the chest during inhalation. The latissimus dorsi and deltoid are shoulder and back muscles and do not participate in depressing the ribs during respiration.