A, Dorsal view of lumbar spinal segment with lamina and facets removed. On left side, dura and root exiting at that level remain. On right side, dura has been resected and root is elevated. Sinuvertebral nerve with its course and innervation of posterior longitudinal ligament is usually obscured by nerve root and dura. B, Cross-sectional view of spine at level of endplate and disc. Note that sinuvertebral nerve innervates dorsal surface of disc and posterior longitudinal ligament. Additional nerve branches from ventral ramus innervate more ventral surface of disc and anterior longitudinal ligament. Dorsal ramus arises from root immediately on leaving foramen. This ramus divides into lateral, intermediate, and medial branches. Medial branch supplies primary innervation to facet joints dorsally.