Friede R L, Beuche W
J Neuropathol Exp Neurol. 1985 Jan;44(1):60-72. doi: 10.1097/00005072-198501000-00005.
The thickness of the myelin sheath is known to increase with axon caliber, but there is also a superimposed, slight variation in sheath thickness depending on whether a fiber of a given caliber has very long or very short internodes. This relationship between myelin sheath thickness and the geometric proportion of the internode has been shown in subserial sections of isolated nerve fibers. It allows a prediction of sheath thickness from the quotient internode length/axon caliber, or conversely, a prediction of internode foreshortening from sheath thickness. We applied this new approach to the analysis of sciatic fiber populations of frogs, mice, rats and cats. The geometric proportions of these fibers were defined by the quotient internode length/fiber caliber. This quotient was compared with minor variation in sheath thickness as determined with a computer-assisted technique measuring large numbers of fibers in low-power electron micrographs. The method also calculated fiber shrinkage and recalculated all data for circular fiber profiles. The data obtained confirmed previous electron microscopic measurements showing that there is a slight reduction in sheath thickness when a fiber of a given caliber has relatively short internodes, and vice versa. A population of very thin, thinly myelinated fibers was also revealed. Sheath thickness and the geometric proportions of internodes in frogs differed markedly from those in mammals.
已知髓鞘厚度会随着轴突直径增加，但根据给定直径的纤维节间是很长还是很短，髓鞘厚度还存在叠加的细微变化。髓鞘厚度与节间几何比例之间的这种关系已在分离神经纤维的亚连续切片中得到证实。这使得可以根据节间长度/轴突直径的商来预测髓鞘厚度，反之，也可以根据髓鞘厚度来预测节间缩短情况。我们将这种新方法应用于青蛙、小鼠、大鼠和猫的坐骨神经纤维群体分析。这些纤维的几何比例由节间长度/纤维直径的商来定义。将该商与通过计算机辅助技术在低倍电子显微镜下测量大量纤维所确定的髓鞘厚度的微小变化进行比较。该方法还计算了纤维收缩情况，并对圆形纤维轮廓的所有数据进行了重新计算。所获得的数据证实了先前的电子显微镜测量结果，即当给定直径的纤维节间相对较短时，髓鞘厚度会略有减小，反之亦然。还发现了一群非常细的薄髓鞘纤维。青蛙的髓鞘厚度和节间几何比例与哺乳动物的明显不同。
