Coloured transmission electron micrograph (TEM) showing an unmyelinated nerve fibre located among several myelinated nerve fibres. In the unmyelinated nerve fibre, the axons (yellow) are located in invaginations of the Schwann cell that show the nucleus (brown). In myelinated fibres, axons are light magenta. In both fibres, the Schwann cell cytoplasm is light green and the basement membrane pink.