Plasma membranes of axon-wrapping glial cells develop specific cylindrical bilayer membranes that surround thin individual axons or axon bundles. Axons are wrapped with single layered glial cells in lower organisms whereas in the mammalian nervous system, axons are surrounded with a characteristic complex multilamellar myelin structure. The high content of lipids in myelin suggests that lipids play crucial roles in the structure and function of myelin. The most striking feature of myelin lipids is the high content of galactosylceramide (GalCer). Serological and genetic studies indicate that GalCer plays a key role in the formation and function of the myelin sheath in mammals. In contrast to mammals, Drosophila lacks GalCer. Instead of GalCer, ceramide phosphoethanolamine (CPE) has an important role to ensheath axons with glial cells in Drosophila. GalCer and CPE share similar physical properties: both lipids have a high phase transition temperature and high packing, are immiscible with cholesterol and form helical liposomes. These properties are caused by both the strong headgroup interactions and the tight packing resulting from the small size of the headgroup and the hydrogen bonds between lipid molecules. These results suggest that mammals and Drosophila wrap axons using different lipids but the same conserved principle.

轴突包裹的神经胶质细胞的质膜形成特定的圆柱形双层膜，围绕着薄的单个轴突或轴突束。轴突被低等生物中的单层神经胶质细胞包裹，而在哺乳动物的神经系统中，轴突被特有的复杂多层髓鞘结构包围。髓磷脂中脂质的含量高表明脂质在髓磷脂的结构和功能中起关键作用。髓磷脂脂质的最显着特征是半乳糖神经酰胺（GalCer）含量高。血清学和遗传学研究表明，GalCer在哺乳动物髓鞘的形成和功能中起关键作用。与哺乳动物相反，果蝇缺乏GalCer。代替GalCer，神经酰胺磷酸乙醇胺（CPE）在果蝇的神经胶质细胞中包裹轴突具有重要作用。GalCer和CPE具有相似的物理特性：两种脂质都具有较高的相变温度和高堆积度，与胆固醇不混溶并形成螺旋脂质体。这些性质是由于头基团的小分子和脂质分子之间的氢键所引起的，强烈的头基相互作用和紧密堆积所引起的。这些结果表明哺乳动物和果蝇使用不同的脂质但保留相同的原理包裹轴突。