The Distribution of Nerve Endings in the sheath of Human Cervical Nerve Roots, with a Focus on Free Nerve Endings

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The presence and distribution of nerve endings in the dural sheath of cervical nerve roots (dural root-sheaths) was investigated histopathologically using 39 cervical root-dorsal root ganglion specimens obtained from 18 postmortem examinations within 12 hours after death. Ages ranged from 4 months to 88 years, with a mean of 58 years. Microscopic investigation was conducted using 20 mum serial sections of various parts of the dural root-sheath, stained by the Suzuki silver impregnation method or Kluver-Barrera method. Free nerve endings were identified in each of the dural root-sheaths of the anterior root, posterior root and dorsal root ganglia (DRG), including the septum, and two types of sensory corpuscles were identified in each of the dural root-sheaths of the dorsal root ganglia and the septum. The fiber diameters of free nerve endings corresponded to those of either Adelta-fibers or C-fibers. The distribution of free nerve endings was greater in the proximal and distal portions of the DRG sheath than in other parts of the dural root-sheath. The largest population of free nerve endings with C-fibers in the DRG sheath was 12 in a tissue cylinder with a volume of 0.01 mm^3 (0.16mm^2*0.06mm), with an average of 3.7. These nerve endings were found to follow either of two centripetal routes, one through a sinuvertebral nerve and the other through small nerves which penetrated directly into the DRG from nerve endings. The number of free nerve endings in the dural root-sheath increased with ages (gamma=0.75). In addition, the number of free nerve endings in subjects below the age of sixty was lower than that of subjects above sixty with a statistical significance (p=0.019). These free nerve endings in the dural root-sheath, especially those in the DRG sheath, are thought to play an important role in the mediation of cervical radicular pain.