Myelin and Saltatory Conduction

by Jason Amores Sumpter
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neurons generate their electric currents by moving ions across the membrane and down along the ax on to propagate their action potentials. Now the diameter of an ax on will actually influence the speed of propagation of an action potential. Basically, the larger diameter is the lower the resistance, meaning faster action potentials, so larger diameter, faster action potential. But diameter is not the on leeway to speed up in action potential. In fact, our axons are almost all covered in Milan now. This is a fatty substance that insulate the ax on and actually speeds up the action potential. And this is very similar to how wires, for example, are wrapped in plastic or rubber to insulate their electric currents and cause them thio. Move with lower resistance. Move faster. No, the myelin sheath, as it's called, this fatty covering over axons, is generated by glial cells, but not by a single goal. I'll sell, and it's also not continuous. It has thes gaps that we call nodes of Rhonda, named after the guy who discovered them, and it actually takes multiple glial cells to cover the ax on of a neuron. So here you can see the glial cell of the central nervous system responsible for Milo Nation. That's Ah, just another way of saying a knacks on being covered in Milan. Write it down for you, Milo Nation. These are a Liga dangerous sites and you can see one right here. This isn't a leg, a dangerous site. It will actually multi mile innate multiple axons. And you can see that it is currently myelin aiding in this image. 123 different acts ons. And this stands in contrast to Schwann cells, which are glial cells of the peripheral nervous system responsible for Milo Nation. However, they Meilin ate a single acts on and I'm just gonna jump out of the way here. You can see that we have Schwann cells along or acts on right, and it actually takes multiple Schwann cells. 2,000,008, the ax on of this neuron. And you can also see the gap there. That is a note of Ron via. We also have nodes of Rhonda here. It's another node of Ron V a. So this mylan helps speed up action potentials. But hopefully you're thinking and you're saying Wait, if we're covering the ax on, how do we have ion channels there that can exchange ions with the extra cellular fluid. The answer is those ion channels air packed in the nodes of Rhonda. And this basically leads us to the crux of how an action potential moves along the ax on. Now it's termed salt hitori conduction. And basically, this is just a fancy way of saying that the action potential more or less jumps between thes nodes of Ron va along the ax on, and it essentially moves from one note of Ron via to the next. And what this sort of looks like is here. So here we have our open open ion channels, Right? Are action potential is currently here, and it's moving this way now because of these open ion channels, which are, if you concede here at a node, right, this is a node right here this opening in the Mylan. So here we have the action potential, right? Uh, the interior of the cell has become positive, the exteriors negative. That is our action potential. And it's moving along so literally, these sodium ions are going to defuse down the membrane to carry this action potential. Those ions air moving right electric current is flow of electric charges ions air moving. And when they get to the next note of Ron, Va. They're gonna cause deep polarization that will open the ion channels there and allow those sodium ions to rush in so that the action potential can keep moving along the axon. Now what's really cool that gets back to that whole concept of inactivation of the sodium channels is if you think about this, there's nothing preventing the action potential from moving backward, right? Nothing except inactivated sodium channels. You see where the action potential has just been. There are going to be inactivated sodium channels where the action potential is headed. Those sodium channels are Onley closed. They're not inactivated, meaning that even though as these sodium ions Russian at the location where the action potential currently is in the ax on and because there's nothing preventing them from diffusing in either direction. Even though we want the action potential moving this way, there's nothing preventing them from diffusing in either direction in the ax on. However, even if they get over here, these channels are inactivated, meaning, uh, these sodium ions causing deep polarization, aren't going thio do anything. The action potential. Can Onley move this way? Because Onley closed sodium channels will open when stimulated by a deep polarization by those sodium ions moving along the ax on. So again, this results in salt hitori conduction, which is basically just the propagation of the action potential along Meilin ated axons, where it hops from one road of note of Rhonda to the next. So with that, let's go ahead and flip the page.