The multifidus is innervated by which nerves?

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

Answer: (B)

The key idea is that deep intrinsic back muscles like the multifidus receive their motor supply from the dorsal rami of the spinal nerves. The dorsal (posterior) rami branch near each vertebra and send motor fibers to the deep back muscles, including the multifidus, while also providing sensory innervation to the skin of the back in that region. The ventral rami go to the anterior and lateral trunk and to the limbs, not the deep back muscles. Cranial nerves control muscles of the head and neck, and the sympathetic chain provides autonomic fibers, not skeletal muscle innervation. So the multifidus is innervated by the dorsal rami of spinal nerves.