External Intercostals: which statement is true?

External Intercostals: which statement is true?

• A. Origin: inferior border of each rib
• B. Insertion: superior border of each rib
• C. Depresses ribs
• D. Action: elevates ribs during inspiration

Answer: (D)

The key idea is that the external intercostals help you inhale by lifting the rib cage. They run from the inferior border of the rib above to the superior border of the rib below, so when they contract they pull the ribs upward and outward, increasing the thoracic volume. That makes the statement about elevating the ribs during inspiration correct. The origin and insertion aren’t on the rib itself in the way some options describe (they originate on the rib above and insert on the rib below, not on the same rib’s borders), and they do not depress the ribs—depression of ribs is accomplished by other muscles during expiration.