January 13, 2011

015 Saltatory Conduction

The action potential travels rapidly down the axon. Why? Because of the process of saltatory conduction.

In this video, I talk about how that process works.

Question? Comments? Leave them below 🙂

– Leslie Samuel

Transcript of Today’s Episode

Hello and welcome to Interactive Biology TV, where we’re making biology fun! My name is Leslie Samuel, and in this episode, I’m going to be talking about saltatory conduction. We’re going to look at how this process is responsible for having the action potential move quickly down the axon.

We’ve been talking about the action potential, and we’ve shown that in order for an action potential to happen, voltage-gated sodium channels need to open. And once those voltage-gated sodium channels open, sodium ions rush in, causing the membrane potential to become more positive and initiating the action potential.

Now, there’s something that you need to understand here. The process of voltage-gated sodium channels opening is significantly slower than sodium rushing along the axon once it’s in the axon. So sodium moving along the axon happens much quicker than the voltage-gated sodium channels opening.

You can think about it like this: if you’re in your car, and you’re trying to get into your garage, you can do that really quickly. However, in order to get into the garage, you have to wait for the garage door to open. And it’s a similar concept: voltage-gated sodium channels need to open, and that’s a little slower than the movement of the ions along the axon. Keep that in mind as we look at the example that I’m going to give right now.

To illustrate this, I am going to step back all the way back here. What I’m going to do is I’m going to take 4 steps forward. And I’m going to just go 1, 2, 3, 4. Now, those were 4 very small steps, and I’m going to take 4 steps backwards now again. 1, 2, 3, 4, and I’m in the starting position. Now, what I’m going to do is I’m going to repeat the same process but I’m going to take bigger steps. 1, 2, 3, 4, and you can see I’m much closer to the camera. I’m going to do the same thing and go back now. 1, 2, 3, 4.

Now, which one of these is faster motion? Of course, you’re going to say the second time, when I took the bigger steps, I was moving significantly faster. If we look at the axon, and let’s just look at a picture of an axon right now. What you will see is that we have Schwann cells that cause myelin sheaths to wrap around the axon. What you will notice by looking at this is you will see that there are little spaces between the myelin sheaths. These spaces are called the nodes of Ranvier. At these nodes, this is where we have voltage-gated sodium channels and voltage-gated potassium channels, but here is where the channels can open and allow ions to come in.

Because these channels are concentrated in these nodes of Ranvier, these are the places along the axons where the channels are going to open to allow sodium to come in. Once sodium comes in, it can jump from that node to the next node very rapidly. And then when sodium comes in at this point, it can go from that node to the next node very rapidly.

In other words, it’s as if the signal is jumping from one node to the next node to the next node, and that causes it to go faster, because it doesn’t have to wait for voltage-gated sodium channels to open all along the axon. It’s just like I was showing before. When I took bigger steps, I moved significantly faster.

Saltatory conduction is like taking these bigger steps, jumping from one node to the next node to the next node, and that helps the action potential to travel significantly faster. I hope that makes sense. As usual, if you have any questions, you can go ahead and leave your questions or your comments in the comments section below, and I’d be happy to answer your questions. That’s it for this video, and I’ll see you in the next one.

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