The first element of the spinal nerve, which reacts to the mechanical action is its vascular system. Compression of the spine prevents the flow of blood in the compressed nerve segment; the degree of ischemization is proportional to the level of pressure that is being made under compression. The circulation of blood in the spine with some form of mechanical damage – such as the tension has showed a complete loss of conduction at 15% of tension that allows you associate the loss of conductivity in the spine with the development of ischemia in it. Also, in addition to intravascular changes in mechanical damage, extravascular violations in circulation occur. They are associated with increased vascular permeability, experiencing high pressure compression or subjected by prolonged or repeated mechanical damage.
As the result the destruction of the blood barrier that is nerve and formation of endonevral edema. Subsequent changes in the ionic balance in the endoneurium and increasing pressure of endonevral fluid influence on the microcirculation in the nerve bundles and cause the development of posttraumatic ischemia of the damaged area. This damaging mechanism acts towards the ganglio-radicular site root – at the level of radicular canal, where the dura becomes epineurium and tightly fused with the periosteum, and increased – in comparison with the peripheral nerves – the permeability of microvessels ganglion easily provokes it swelling even with a slight mechanical damage. Long inneural swelling that occurs in chronic stimulation of the nerve root, causing accumulation of fibroblasts and formation of inneural fibrous of scar tissue.
Inside dural part of the spine, including radicular nerve Nazhotta, does not have perineurium and is surrounded by cerebrospinal fluid. Edema in this part of the roots does not lead to endonevral increase of pressure, because the excess liquid is drained quickly in the cerebrospinal fluid surrounding root due to the absence of diffusion barriers in the roots.
Violation of circulation and the development of edematous and fibrous inflammatory processes in the trunk of the spine have the damaging affect on the structural unit of the nerve fibers that is to say axon. The resulting in this type of damage to the segmental demyelination is more expressed, the more intense and prolonged pressure factor are.
The increased compression causes deformation of the nerve fibers directly, with those most – on the edges of the compressed segment. It was found that Ranvier nodes in the compression shift toward the uncompressed part of the nerve – both distal and proximal ones. Being next to the nodal displacement, segmental demyelination causes local conduction block in this area. Qualitatively different changes in the axons occur at rough mechanical impact: changing the number of fibers, some fibers are exposed by wallerian degeneration. Damage to nerve root fibers as a result of mechanical influence on it with herniated disc is probably often mixed: some of fibers are subjected with segmental demyelination, the other part is wallerianly degenerated.
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