Aguayo A J, Bray G M, Terry L C, Sweezey E
J Neuropathol Exp Neurol. 1976 Mar;35(2):136-51. doi: 10.1097/00005072-197603000-00002.
The technique of serial-section electron microscopy and diagrammatic three dimensional reconstructions has been used to assess normal and pathological unmyelinated nerve fibers from a peripheral autonomic nerve: the rat cervical sympathetic trunk. Within this predominantly unmyelinated nerve, there is a complex arrangement of axons into longitudinally oriented bundles brought together by chains of Schwann cells. Each bundle is subdivided into smaller components by the cytoplasmic processes of Schwann cells; such subdivisions, which are basal lamina-enclosed masses of Schwann cell cytoplasm, when viewed on cross-sectional electron micrographs, are termed Schwann cell units. The size and shape of each Schwann cell unit varies along the length of fibres, but the diameter of individual axons shows little variation over the segments studied. Axonal branching was not observed in normal unmyelinated nerves. Crush injury and x-irradiation produces different patterns of alteration in the axon-Schwann cell relationships of unmyelinated nerves. Following crush injury, Schwann cell processes increase in diameter and contain numerous small diameter axonal sprouts. Many of the regenerating axons remain thin while others reacquire a normal diameter. X-irradiation affects Schwann cells leading to retraction of their processes and the appearance of naked axonal segments.
连续切片电子显微镜技术和三维重建示意图已被用于评估来自外周自主神经（大鼠颈交感干）的正常和病理状态的无髓神经纤维。在这条主要由无髓神经纤维组成的神经中，轴突通过雪旺细胞链聚集在一起，形成纵向排列的束状结构。每个束状结构又被雪旺细胞的细胞质突起细分为更小的部分；在横断面电子显微镜图像上观察时，这些被基膜包围的雪旺细胞细胞质团块组成的细分结构被称为雪旺细胞单位。每个雪旺细胞单位的大小和形状沿纤维长度变化，但单个轴突的直径在所研究的节段中变化很小。在正常无髓神经中未观察到轴突分支。挤压伤和X射线照射会导致无髓神经中轴突-雪旺细胞关系出现不同的改变模式。挤压伤后，雪旺细胞突起直径增大，并含有许多小直径的轴突发芽。许多再生轴突仍很细，而其他轴突则恢复到正常直径。X射线照射会影响雪旺细胞，导致其突起回缩，出现裸露的轴突节段。
