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Video transcript
In this video, I want to talk about oligodendrocytes. Oligodendrocytes are glia of the central nervous system, derived from neural stem cells and named from Greek words for cells with a few branches. To show the structure of oligodendrocytes, let me first draw a few neurons. I'll just draw their somas and axons and I'll leave off their dendrites. I'll draw the somas for a couple of oligodendrocytes, one here and one here. And each oligodendrocyte will extend a few processes, maybe up to a few dozen processes each, towards the axons of neurons. And the structures at the end of these oligodendrocyte processes will be the myelin sheath for neurons that have a myelin sheath on their axons. And you can see that each oligodendrocyte can be creating segments of myelin sheath for the axons of multiple neurons. And the different segments of myelin sheath can be from different oligodendrocytes on any particular neuron's axon. This material of myelin is composed mostly of lipid, which is the same kind of substance that makes up fat. So this is kind of a fatty sheath around some of the axons of certain neurons. So let's take a little closer look at this over here. And what we'll do is we'll kind of cut through the soma and the process in one of these segments of myelin sheath, kind of like this. And then we're going to look at it end-on, like we're looking down from the end of the axon. So here, I'll draw the axon. And we've cut it. So we're looking at it end-on. So we're looking down the tube of the axon. And the myelin sheath is just the membrane at the end of the process of the oligodendrocyte, that's wrapped very thinly around the axon many, many, many times, like a roll of tape. And I like to think of these like the rubber coating on a wire, kind of insulating the axon. And we'll get into how information is transmitted along axons in other videos. But basically, this makes the transmission of information faster and more efficient. And the myelin sheath is still connected by the process to the soma of the oligodendrocyte to maintain it. So each oligodendrocyte process forms one segment of myelin on an axon. And each oligodendrocyte may myelinate multiple axons. In addition to this function of creating the myelin sheath, oligodendrocytes also appear to influence neurons and other glia, and vice versa, through exchange of a variety of substances. There are also some variably-shaped nonmyelinating oligodendrocytes in parts of the central nervous system. But their function is not yet entirely clear.