Oligodendrocytes are identified as the cells that produce myelin, the insulating wrap around axons. A single oligodendrocyte sends out multiple branches that reach and wrap around many different axons at once, rather than pairing one cell to one axon, and electron microscopy later revealed myelin's layered, wrap-around structure. This one-to-many arrangement means damage to a single oligodendrocyte can affect many axons simultaneously, and it underlies the classic gray matter versus white matter distinction in the brain, where gray matter holds cell bodies and white matter is made up of myelinated axon tracts.
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The oligodendrocyte was first identified around 1921 by a Spanish neuroanatomist using Golgi silver staining techniques.
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Researcher Betty Ben Geren showed in 1954 that myelin forms from a single cell spiraling around the axon, proving it is living tissue rather than a substance secreted by the neuron itself.
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The myelin sheath does more than speed up signals through capacitance, it also supplies the axon with energy and helps remove metabolic waste.
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The gray matter versus white matter distinction was already noted by Italian anatomists dissecting brains as early as the 1500s, including Michelangelo, long before its link to myelination was understood.
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17:46Okay, so the let's talk about the myelin now in a more cellular level. What is the cell that is responsible for that myelin? It's something called the oligodendrite. Okay. This was identified by Spanish neuroanatomist um I'm can you >> P Rio Ortega. >> Nice. Yeah. Around 1921. So that guy he stained using the GGI silver staining techniques. And he found that there's these cells that have a few branches that branch out and reach out to a bunch of neurons. A key discovery here is that a single cell can actually branch out to a bunch of neurons and wrap its
18:28processes around those neurons. So you know those myin sheets that I was talking about where the the wrapping around that's not a single cell. There's a there's one cell that is going around and reaching out to a bunch of axons around it. kind of like Venom >> in in Spider-Man like and it goes around and wraps around all of these axons nearby. >> Interesting. Okay. >> Which is which is kind of cool to think about. It's not a one one sort of mapping. It's a single cell that's doing like 50 different >> electrical wires. >> It has this distributed >> um placement of its that Oh, that's actually very >> Yeah. >> intriguing. And so this maybe foreshadows some of the stuff that we're going to talk about which is if there's
19:08a problem with these oligodendrites. >> Yeah. >> It's like not a single neuron problem. >> It's it it becomes a single point of failure across multiple end points. >> Exactly. And that's what we're we're sort of building towards. That makes sense. Okay. So the precise ultra structure of this myelin was only sort of revealed in the 1950s with the advent of electron microscopy. Here's an electron microscope image where you can see this is a cross-section of a neuron. So that's the axon in the middle. There's a little mitochondria. You see the circle? That's a mitochondria. The neurons have a bunch of mitochondria. >> Powerhouse of the cell. >> It is the powerhouse of the cell. And neurons need a lot of powerhouses of the cell because they need to maintain this
19:50um this voltage difference which means they need to pump ions against like you know if there's a bunch of calcium ions on one side it takes a lot of energy to pump even more calcium ions over there right and so >> even even with the milein sheet you still need power >> you still need a lot of power and the myelin sheets actually it's not just something that um provides this capacitance trade-off of like speed the myin sheath is is something that provides energy for the cell and provides like metabolic waste removal from the cell. It's kind of like a maintainer. >> One of the key things that it does is wrap around the cell and you can see the little layers, right? >> You can see the layers of the myelin
20:31sort of wrapping around to create a bunch of capacitors in parallel. But it does way more than just this physics argument. >> That that makes sense. And for the those who are listening, if you've ever eaten Nerd's rope and took a bite out of it and looked at the inside um or like the Twizzler things where there's an inside that's a little bit then there's outer layer. It looks like when you've taken a bite and look at it long ways. So >> yeah. No, you know what I would say it was? It's like a Twizzler on the inside and then fruit roll up. >> Yeah. On the on the Yeah. Like wrapped wrapped around. Yeah. It's like fruit roll up. >> Yeah, that's a great point. >> Yeah. Yeah. We should have some fruit roll up in the studio >> actually. Anyways, so um Betty Bengarin, she graduated from Washington University
21:12and then later went to Harvard Medical School where she was doing a lot of her research. She showed in 1954 that myelin is formed from spiral wrapping of a single cell. So this oligo dendrite wraps around and that's a single cell that's doing it. It's a living tissue. That's the main finding from this paper. Before then it was thought that it was just like >> it it was something that maybe the neurons secreted cuz we don't know, right? You don't know. But she definitively showed that there's a single cell that goes around. This oligo dendrite goes around and wraps around >> and all of that is a single process that's doing it. >> The venom analogy is very visually compelling in the context of like the the how to kind of visualize what that
21:54would mean. >> Yeah. >> Right. Like the movement of it and anyway. >> Exactly. And and as we started learning more about the brain, we started realizing that this dichotomy between the gray matter and the white matter, >> right? That was already known from like the 1500s. There were like these Italian surgeons who were dissecting brains, um, Michelangelo being one of them. And they had already noticed that there were parts of the brain on the outside where there was gray matter and then on the inside there was this white matter. It turns out that gray matter, white matter difference has to do with mileelination. >> Okay. Um, you've got the gray matter on the outside. That's mostly where the cell bodies are. >> Okay? >> And then the white matter are the axons
22:34that connect different parts of the brain. >> And a lot of the myelin is in the axons because that's where the signal propagation is happening. >> It's like that's the superighway and the gray matter are these islands. Yeah. >> That are connected by the white matter of this the superighway system. >> Exactly. Exactly. So this is where we get into MS. Okay. 1868 French neurologist Jean Martin Charott I believe >> and people might it might be charcoal. >> Yeah, maybe. Anyways, um he documented evidence of plaques in the white matter. >> Okay. And he showed that there's a
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