Oligodendrocytes. Fluorescence light micrograph of proliferating oligodendrocyte progenitor cells amongst other nerve cells in a human brain tissue culture. The oligodendrocyte cells (red) form myelin sheaths (concentric layers of membrane) around nerve fibres (green) in the central nervous system. The myelin provides nutrients, structural support and insulation, allowing nerves to conduct impulses more quickly. One oligodendrocyte may be responsible for the myelination of up to 50 nerve fibres. Magnification unknown.