Study: Oligodendrocytes play key role in the distribution of energy-rich molecules The human brain has about as many neurons as glial cells. These are divided into four major groups: the microglia, the astrocytes, the NG2 glial cells, and the oligodendrocytes. Oligodendrocytes function primarily as a type of cellular insulating tape: They form long tendrils, which consist largely of fat-like substances and do not conduct electricity. These wrap around the axons, which are the extensions through which the nerve cells send their electrical impulses. This prevents short circuits and accelerates signal forwarding. Astrocytes, on the other hand, supply the nerve cells with energy: Through their appendages they come into contact with blood vessels and absorb glucose from these. They then transport it to the interfaces between two neurons, the synapses. Before that, they partially convert the sugar into other energy-rich molecules.