The longissimus thoracis is innervated by which nerves?

• A. Ventral rami of spinal nerves
• B. Cranial nerves
• C. Sacral nerves
• D. Dorsal rami of spinal nerves

Answer: (D)

The innervation of deep back muscles comes from the dorsal rami of spinal nerves. After a spinal nerve exits the intervertebral foramen, it splits into ventral and dorsal rami. The dorsal (posterior) rami supply the intrinsic back muscles, including the longissimus thoracis, and the overlying skin along the vertebral column. Cranial nerves don’t innervate these deep back extensors, ventral rami supply most trunk and limb muscles (anterior and lateral aspects), and sacral nerves mainly serve the pelvis and lower limb regions. So, the longissimus thoracis is innervated by the dorsal rami of spinal nerves.