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.