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. Author manuscript; available in PMC: 2021 Jan 1.

Published in final edited form as: Toxicol Pathol. 2019 Jun 10;48(1):152–173. doi: 10.1177/0192623319854326

Regions of non-compact myelin that are affected earliest during axonal degeneration. (a) Longitudinal section of plastic-embedded toluidine blue-stained rat sciatic nerve showing Schmidt-Lanterman incisures (arrows) distributed along the internode. These structures consist of non-compact myelin that provide a cytoplasmic pathway connecting the Schwann cell cytoplasm adjacent to the axon to that on the external myelin sheath. A mast cell (*) is present in the endoneurium. (b) Transverse section through the paranodal region of a large myelinated fiber. The axon (ax) is constricted and contains a high density of neuroflaments and organelles. The compact myelin has opened to form folded myelin (fm) and microvilli (mv) that contact the axolemma.

Regions of non-compact myelin that are affected earliest during axonal degeneration. (a) Longitudinal section of plastic-embedded toluidine blue-stained rat sciatic nerve showing Schmidt-Lanterman incisures (arrows) distributed along the internode. These structures consist of non-compact myelin that provide a cytoplasmic pathway connecting the Schwann cell cytoplasm adjacent to the axon to that on the external myelin sheath. A mast cell (*) is present in the endoneurium. (b) Transverse section through the paranodal region of a large myelinated fiber. The axon (ax) is constricted and contains a high density of neuroflaments and organelles. The compact myelin has opened to form folded myelin (fm) and microvilli (mv) that contact the axolemma.