Which statement is true about serratus posterior inferior?

Which statement is true about serratus posterior inferior?

• A. It inserts on ribs 2-5
• B. It is innervated by intercostal nerves T2-T5
• C. It originates from spinous processes of T11-L2
• D. It elevates the upper ribs

Answer: (C)

Serratus posterior inferior is a muscle of the back that helps with expiration by pulling the lower ribs downward. It originates from the spinous processes of the lower thoracic and upper lumbar spine, specifically T11 to L2, and it inserts along the inferior borders of ribs 9–12. It is innervated by the lower thoracic intercostal nerves (T9–T12). Its action is to depress the lower ribs, not elevate the upper ribs. So the true statement is that it originates from the spinous processes of T11–L2. The other options mix up its insertion (not on ribs 2–5), its innervation (not T2–T5), or its action (it depresses, not elevates, the ribs).

Serratus posterior inferior is a muscle of the back that helps with expiration by pulling the lower ribs downward. It originates from the spinous processes of the lower thoracic and upper lumbar spine, specifically T11 to L2, and it inserts along the inferior borders of ribs 9–12. It is innervated by the lower thoracic intercostal nerves (T9–T12). Its action is to depress the lower ribs, not elevate the upper ribs. So the true statement is that it originates from the spinous processes of T11–L2. The other options mix up its insertion (not on ribs 2–5), its innervation (not T2–T5), or its action (it depresses, not elevates, the ribs).