Semispinalis innervation is which of the following?

• A. Dorsal rami spinal nerve
• B. Ventral rami spinal nerve
• C. Occipital nerve
• D. Phrenic nerve

Answer: (A)

Semispinalis is part of the deep back muscle group that receives motor input from the dorsal rami of the spinal nerves. These dorsal rami provide the segmental innervation to the intrinsic back muscles, including the transversospinalis group, which includes semispinalis, and also supply the skin over the back. The ventral rami supply most of the trunk and limb muscles on the front and sides, not these deep back muscles. The occipital nerve is mainly a sensory branch to the scalp and does not motor-innervate the semispinalis, and the phrenic nerve controls the diaphragm. So the dorsal rami spinal nerves are the correct innervation.