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PN1 (Midha) Microanatomy of Peripheral Nerves-Part1.Pdf

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PN1 (Midha) Microanatomy of Peripheral Nerves-Part1.Pdf Peripheral Nerve Basics • Consist of processes of cell bodies found in the DRG, anterior horn, and autonomic ganglia • Organized by several distinct connective tissue layers – the epineurium, perineurium, and endoneurium • Vascular supply provided by the vasa nervorum Peripheral Nerve Basics • Neuronal processes bound into fascicles by perineurium • Fascicles bound into nerves by epineurium • Endoneurium is a division of the perineurium which form thin layers of connective tissue surrounding neuronal fibers in a fascicle Sural nerve in cross-section Epineurium • Loose areolar tissue with sparse, longitudinally-oriented collagen fibers • Some elastic fibers where epineurium abuts perineurium • Able to accommodate a significant amount of nerve stretching and movement • Increases in thickness where nerves cross joints • Constitutes an increasing proportion of nerves as they increase in size • Epineurial fat helps cushion nerves from compressive injury • Decreased epineurial fat found in patients with diabetes Perineurium • Cellular component composed of laminated fibroblasts of up to 15 layers in thickness which are bounded by a basal lamina • Semi-permeable: inner lamellae have tight junctions, providing a barrier to intercellular transport of macromolecules – Tight junctions can be loosened with topical anaesthetics and with osmotic change Perineurium • Exhibits a slightly positive internal pressure – Fascicular contents herniate upon perineurial injury • Under tension longitudinally – Nerve segment shortens upon transection – may complicate surgical repair as nerve can be stretched only approximately 10% before being inhibited by collagen Endoneurium • Intrafascicular connective tissue consisting of a collagenous matrix in the interstitial space • Develops into partitions of dense connective tissue between diverging fascicles and eventually becomes perineurium when the fascicles separate • Collagen fibers are longitudinally-oriented and run along nerve fibers and capillaries.
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