015 Saltatory Conduction

015 Saltatory Conduction

Leslie Samuel IBTV, The Nervous System 61 Comments

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.

Comments 61

  1. nicodube23

    but why would the steps be bigger in myelinated vs unmyelinated axons? that’s the real question… what is the conceptual explanation for insulation increasing speed of conduction?

  2. nicodube23

    but why would the steps be bigger in myelinated vs unmyelinated axons? that’s the real question… what is the conceptual explanation for insulation increasing speed of conduction?

  3. InteractiveBiology

    Great question. I answered your question with a video. Check out the video I just posted – Episode 24. Hope that helps!

  4. LUNurses

    Why would saltatory conduction occur as opposed to waiting for the next voltage gated sodium channel to open? What triggers saltatory conduction?

    1. Post
      Author
  5. IHateSarsi

    Hmm so the Na+ that comes in from the channels in a previous node travels down thru the myelin to the next node very quickly right?

  6. juhidgenius

    are the only ion channels working in the neuron?? whether it is saltatory or contiguous conduction..is it like we have less channels in the saltatory conduction??

  7. Bas

    Hello Leslie, is there a decrease in amplitude while traveling down the axion? or do the nodes of ranvier act like a “traject amplifier”?

    if yes, becouse you explaned that the voltage-gated sodium channels are much slower, does that not influence the travel time down the axion to the axion terminals?

    1. Post
      Author
      Lrsamuel

      Yes, the v-gated channels do act like little amplifiers at the Nodes of Ranvier. Yes, they are a little slower, but it’s a trade off between their relative slowness and the decreasing altitude of electrotonic conduction. Keep in mind though that slow is relative. We’re still talking about milliseconds here.

  8. NeedsAHardOne

    OH!
    I’ve known that AP travels fastest in myelinated axons, and I was always told it was because it jumps from node to node.
    But FINALLY someone gives me a more thorough explanation.

  9. alexharrison101

    this is brilliant – thanks. i couldn’t figure what it was about saltatory conduction that made it faster, but you’ve really helped!

  10. Uchchash

    it’s really simple…the myelin sheath actually prevents wastage of resources which would have been spent in formation of Na/K ATPase pumps all along the axon.During depolarisation,the Na+ conc just below the pumps gets really high and so by simple diffusion,they travel laterally along the axoplasm,wrapped in myelin,until it reaches adjacent Node and causes threshold.The behind node cant get depolarised since it’s in refractory period and resting potential hasn’t established there yet.

  11. Uchchash

    it’s really simple…the myelin sheath actually prevents wastage of resources which would have been spent in formation of Na/K ATPase pumps all along the axon.During depolarisation,the Na+ conc just below the pumps gets really high and so by simple diffusion,they travel laterally along the axoplasm,wrapped in myelin,until it reaches adjacent Node and causes threshold.The behind node cant get depolarised since it’s in refractory period and resting potential hasn’t established there yet.

  12. Hasan Dilhan Bingöl

    Thanks for your these videos, but I’m having really big troubles with the understanding of the physics part of the action potential and the other membrane stuff.What I mean is that I have some troubles about properties of the cell membrane.One of the properties of the membrane is that membrane is a capacitor to separate electrical charges and this feature affects its length constant and tau value.Therefore, it affects the velocity of the action potential along the axon.I guess my knowledge is so superficial for a medical student.I gave my e-mail adress. Could you help me about this problem by sending me an e-mail or making a video please ?

    1. Post
      Author
    1. Post
      Author
  13. ninjaofginga

    WOW you make all these concepts soo much easier to understand. Thank you very much, its seriously helping with my study :) hope you’re getting paid the big bucks, cause you really are a talented teacher and communicator!

  14. ninjaofginga

    WOW you make all these concepts soo much easier to understand. Thank you very much, its seriously helping with my study :) hope you’re getting paid the big bucks, cause you really are a talented teacher and communicator!

  15. ApparentlyNick

    Thanks this helped a lot! A question: Why are there still nodes of ranvier, would the proces not be even faster if there was only myeline sheaths? So basically, what is the purpose of the nodes of ranvier, is it necessary to regenerate an AP repeatedly for some reason?
    Thanks a lot!

  16. ApparentlyNick

    Thanks this helped a lot! A question: Why are there still nodes of ranvier, would the proces not be even faster if there was only myeline sheaths? So basically, what is the purpose of the nodes of ranvier, is it necessary to regenerate an AP repeatedly for some reason?
    Thanks a lot!

  17. kmarie923kb

    You are the best! I have been watching a lot of your videos and I feel well prepared for my huge exam tomorrow! Thank you!

  18. wendyhirschi

    Now why can’t other teachers, who you pay lots of money in college classes, explain it that way!!!!! That is such a great way to explain it!!!

  19. anita

    Thank you SO much! I love your videos and have recommended them to all of my classmates. You are making my life in anatomy & physiology SO much easier to understand.

  20. Duh Dun

    A better example will be having a messenger travel the entire distance from point A to B versus, lighting beacons that are over vast distances but close enough to be seen from one another (like in LOTR where Gondor asks Rohan for help).

    Thank you this made much more sense than I have been taught in the past.

  21. Christina Kresge

    I love u. I was so stressed about my lack of confidence on this chapter… Thank you so very much. I am touched by your kindness to share!

  22. Brittany

    I second what anita said! I’ve recommended my students watch your videos as well to supplement what I am teaching in class. Keep up the great work!

  23. Emily

    Great video, really helpful, especially as you give a transcript. I was wondering about neurons and I can’t seem to find an answer anywhere – is there a specific reason why sensory neurons have short axons and long dendrites, whereas motor neurons have long axons and short dendrites?

Leave a Reply

Your email address will not be published. Required fields are marked *