Transmission electron micrograph (TEM) of a cross-sectioned peripheral myelinated nerve fibre. At centre is the axon with many cross-sectioned neurofilaments. Around the axon, the laminated structure of myelin appears as alternating dark lines (protein layers) separated by unstained zones (the lipid hydrocarbon chains). Outside the myelin, the Schwann cell cytoplasm (showing the mesaxon) surrounded by a basement membrane, can be seen.