Serratus posterior superior is innervated by which nerves?

• A. Intercostal nerves 2-4 and ventral rami spinal nerves
• B. Dorsal scapular nerve
• C. Long thoracic nerve
• D. Subscapular nerve

Answer: (A)

The muscle is supplied by the ventral rami of the upper thoracic spinal nerves via the intercostal nerves. In practical terms, the nerves that travel in the intercostal spaces around levels two to four provide the motor input to serratus posterior superior, which fits its location on the upper back and its role in elevating the upper ribs during inspiration. The other nerves listed don’t innervate this muscle: the dorsal scapular nerve serves rhomboids and levator scapulae; the long thoracic nerve innervates serratus anterior; and the subscapular nerves innervate subscapularis (and teres major).