Innervation of the canine thoracolumbar vertebral column

Abstract

The pattern of innervation of the caudal thoracic and cranial lumbar vertebral column of the dog is described. Frozen sections stained with Schofield's silver impregnation method show that the dorsal longitudinal ligament is profusely innervated, while the anulus fibrosus contains a few nerves limited to its outermost layers; no nerves are present in the nucleus pulposus. Following injection of horseradish peroxidase (HRP) into the anulus fibrosus of the thoracolumbar intervertebral disc and subsequent removal and staining of dorsal root ganglia, the reaction product is found in ganglia as far as two segments cranially as well as caudally, demonstrating that the disc is innervated by nerves arising from several spinal cord segments. A meningeal ramus, which innervates the discs of man, could not be found by gross dissection. Dissections show each vertebral articular facet innervated by the medial branches of two contiguous spinal nerves, a pattern further confirmed by injections of HRP into facet joints with subsequent staining of dorsal root ganglia. The dorsal rami of spinal nerves often divide into medial, intermediate, and lateral branches rather than the traditionally described division into only medial and lateral branches.

Functional anatomy

“…Intervertebral discs have a poor blood supply; nutrients gain access by diffusion. The anulus fibrosus is supplied with pain fibers, mainly in the outer laminae (Forsythe and Ghoshal, 1984). Sacrum L7 1.27 Sagittal MRI of a dog to show that the intervertebral foramen of L7 (arrows) extends much more cranially than it does in other vertebrae (L6/7 and L7/S1 disc spaces shown by arrowheads).…”

“…It is continuous with the joint capsules of the articular processes, and may be significantly thickened in some disease conditions, particularly lumbosacral disease and cervical spondylomyelopathy (CSM). The fibers of the dorsal longitudinal ligament (1.33, 1.34) merge with those of the anulus fibrosus of the intervertebral disc; both carry pain fibers (Forsythe and Ghoshal, 1984). The presence of the intercapital ligament (1.34) Functional anatomy 13 1.…”

“…The origin of the branches varies between the regions of the spine (1.36-1.39) (Forsythe and Ghoshal, 1984).…”

Sparse substance P-like immunoreactivity in intervertebral discs: Nerve fibers and endings in the rat

“…Sympathetic post-ganglionic and sensory afferents are the only nerve fibers whose presence is anatomically expected in the lumbar disc (Bogduk et al 1981, Bogduk 1983, Forsythe and Ghoshal 1984, Kojima et al 1990, McCarthy et al 1992. Of these 2 innervations, at least in the rat, SP-LI is only found in the soma and fibers of sensory afferent neurons (Lee et al 1985, Ju et al 1987.…”

“…Retrograde labeling experiments in dogs have confirmed the presence of sensory fibers to the disc (Forsythe and Ghoshal 1984). The neuropeptide substance P is an important compound in this respect as it has been linked with both pain and neurogenic effects, such as plasma extravasation and vasodilation (Maggi and Meli 1988).…”