This is going to be on glial cells, full name neuroglia cells, and just a real quick recap is their function is to support and nourish neurons, and they make up the majority of the nervous tissue cells. So there's going to be six glial cells, four in the central nervous system, two different types in the peripheral nervous system. What we're looking at right now is a... abstract picture of the central nervous system.
So this right here, this whole area would be from the brain. So the piamator, this is a membrane that covers the brain and the ventricles is basically going to be a hole in your brain. So if we went and looked at this picture right here, the piamator is going to surround the outer edges of the brain and we're seeing all of the cells the bulk of the brain until we hit this empty space which is the ventricles.
So we are going to start off talking about oligodendrocytes. So oligodendrocytes basically just means lots of projections that's what the word oligo means a lot. Dendro means dendrites or extensions, and then site means cell. These are the cells that myelinate, so they actually create that lipid protein layer on the axon in the central nervous system. Oligodendrocytes myelinate in the central nervous system.
That is their function. So we can see right here, if you follow the extensions, You'll notice that it's wrapping around the axon multiple times, and when it does that, it creates the myelin sheet, so it myelinates the axons. I want you to also look at this picture.
Here is one oligodendrocyte. Here is a second oligodendrocyte. So here's the first one.
Here's the second one. If you follow the projections, This projection is going to this neuron. This projection is going to a different neuron. So this is something that makes oligodendrocytes relatively unique. They can myelinate more than one axon at a time.
Oligodendrocytes can myelinate more than one axon at a time. That makes them unique. Now the downfall is, if an oligodendrocyte gets damaged, it will not be able to regenerate. So damage oligogen......it.
dendrocyte will not be able to regenerate. The myelin sheath that the illegal dendrocyte creates helps insulate the neuron, protect it, and speed up action potentials, those electrical signals. The next glial cell of the central nervous system are going to be astrocytes.
Astrocytes get their names, they kind of have that star appearance. Astrocytes have multiple functions, but you'll notice that as astrocytes appeared, so did blood vessels or capillaries. Astrocytes will actually form around and wrap around capillaries in the brain.
What astrocytes do is they help form the blood brain barrier. So astrocytes will wrap around capillaries in the brain and form the BBB, the blood-brain barrier. They help decide what will enter and exit the bloodstream.
So capillaries are basically like a door, or you can think of it as a doorman or a bouncer. They decide what goes in and out of the brain's capillaries. The other thing astrocytes do...
is that they will actually wrap around axons that may have been damaged previously. And when they do this, they basically are beginning to make scar tissue. So if an oligodendrocyte gets damaged or if an axon gets damaged, astrocytes will move in and wrap around those axons or that area to help support it. But when they do this, they're actually forming scar tissue, so it's more like fibrosis, so it becomes unfunctional. The next cell?
going to be the ependymal cells. Ependymal cells, if you look at this picture, are going to be similar to columnar shaped shells. They're not as columnar, they're a little bit cuboidal shape, but what's important is that they're gonna have microvilli on them as well as cilia.
So they'll have these unique structure where they have both microvilli and cilia. They're not quite columnar, they're not quite cuboidal, so they're unique glial cells. When we look at ependymal cells, we will find them lining ventricles in the brain. So what we see here is that we see we have this big opening in the brain.
Basically, this is an area in the brain where fluid is going to circulate, and this fluid circulates throughout the brain, all the way down through the spinal cord, back into the brain. These ventricles are going to be lined with the ependymal cells. The epidemal cells are going to have these microvilli and cilia, and they're going to help aid in production of your cerebrospinal fluid, also known as CSF. So the epidemal cells, they help produce as well as circulate.
the cerebrospinal fluid. The epidemial cells are found lining the ventricles of the brain. Now the last neuroglia cell that we find in the central nervous system are called the microglial cells.
I refer to these as either the trash cans or you can think of them as pac-man. Microglial cells are tiny cells that are phagocytic. Basically, they eat debris, bacteria, old cells. So they're the cleanup crew of your central nervous system.
So just to recap, we have four cells in the central nervous system. Oops, let me change colors. We have oligodendrocytes. Main function is to myelinate.
Multiple axons from neurons in the central nervous system. We have astrocytes. Main function is to form the blood-brain barrier, the side that goes into and out of the blood vessels within the brain.
They can also help protect axons of oligodendrocytes, but they often form fibrosis tissue. We have ependymal cells. These are the cells that are going to line the ventricles and help produce and then circulate.
the CSF, cerebrospinal fluid. And the last, we have microglial cells, which are the cleanup crews. They're going to help us break down and eat any type of cellular debris or bacteria found within the area, microglial cells or phagocytic cells. Now, our next is going to be The cell is found in the peripheral nervous system.
We have two cells in the peripheral nervous system. The first cell is going to be the Schwann cell. The Schwann cell is going to have two major jobs, but we'll talk about what most people associate it with.
Most people think about the Schwann cell as the ability to myelinate. So that is its main job. Schwann cells myelinate axons in the peripheral nervous system, PNS only, in the central nervous system, it's oligodendrocytes.
Now there's quite a few differences. If you look on this particular picture, you'll notice that you're seeing lots of Schwann cells. One, two, three, all on one axon. What does this tell you about the Schwann cell?
It takes multiple Schwann cells to myelinate a single axon. Schwann cells can only myelinate small portions of an axon at a time. So if your axon's long, you could have hundreds of thousands of Schwann cells myelinating it. So Schwann cells can only myelinate small portions of an axon at a time. When they myelinate it, it helps protect, insulate, and speed up action potentials.
But Schwann cells aren't only used for myelination. Schwann cells are also used for protection. If you look in this picture right here, we still have multiple Schwann cells.
But we see more than one axon in this picture. One, two, three, four, five, six, seven axons are being surrounded by one schwan cell. If a schwan cell doesn't myelinate, what they'll do is they'll take a bundle of axons, wrap around them once just to give them some extra protection. So in this particular picture, what we're seeing is myelination.
It takes... Hmm. thousands of Schwann cells to myelinate a single axon because they can only myelinate one axon at a time. But in this picture, what we're seeing is that one Schwann cell can wrap around multiple axons at once, a single wraparound like a hug, to give extra protection to those cells. So each of these axons of the neuron cell are being protected very little by the single Schwann cell.
It's giving a little hug to each of these axons, giving it a little extra protection. It's not wrapping itself around multiple times like this, like it does on a myelinated axon. Instead, it's just one single circle.
So just a quick recap. Schwann cells can myelinate, or they can just help protect axons in the peripheral nervous. system. What's unique about Schwann cells is that they do have the capability to regenerate if this axon is not damaged. So if that, not the axon, sorry, if the nucleus is not damaged.
So if the nucleus stays intact, Schwann cells do have the capability to regenerate. This is again different from oligodendrocytes in that they are not capable of regenerating. The next cell is going to be the satellite cell. The satellite cell is also found only in the peripheral nervous system. And what I want you to notice is we're seeing one cell body in this picture.
It's attached to a unipolar, one projection here, neuron. And what we'll notice is that one cell body is going to be found in a ganglion. Remember that ganglions are bundles of cell bodies. in the peripheral nervous system. So what we're seeing is just one of the cell bodies that would be found within a ganglion.
And you'll notice that this cell body has lots of what I think look like little fried eggs laying all around it. These little fried eggs are called satellite cells. These satellite cells are different from the satellite cells found with muscles. In the peripheral nervous system, the glial cell called the satellite cell will surround and attach cell bodies in the peripheral nervous system. When the satellite cells surround a cell body, they're going to decide what enters and what exits that cell body.
So they are the gatekeeper of the cell body for the peripheral nervous system. Now, in the central nervous system, astrocytes are wrapping around blood capillaries. So they would determine what goes in and out of the bloodstream.
But in the peripheral nervous system, these satellite cells wrap around a cell body, and they determine what goes in and out. We can see here that we have Schwann cells on the axon. That also tells you that it is part of the peripheral.
So the two cells of the peripheral nervous system are Schwann cells and satellite cells. Then the four cells of the central nervous system are oligodendrocytes, astrocytes, microglial, and ependymal.