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.

74 comments
Emily
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?

Brittany
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!

Christina Kresge
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!

Duh Dun
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.

anita
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.

Zoelis17
Zoelis17

wow! you are really good..thanks

wendyhirschi
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!!!

Luke Cutts
Luke Cutts

I have a question why and how does the action potential seem to "jump". Thanks

kmarie923kb
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!

ApparentlyNick
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!

sottroll
sottroll

Wow, thanks! It really did make sense now.. Great work, your brilliant !! :)

ninjaofginga
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!

Donna
Donna

I love the flow of the video and thank you so much your videos have help me greatly in A&P

Hasan Dilhan Bingöl
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 ?

afiste
afiste

I'm already falling for you!!! You definitely rock and makes life much easier!!!

afiste
afiste

I'm already falling for you!!! You definitely rock and makes life much easier!!!

Uchchash
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.

Uchchash
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.

alexharrison101
alexharrison101

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

alexharrison101
alexharrison101

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

InteractiveBiology
InteractiveBiology

Glad to know we've cleared that one out for you :) DO stay tuned! There are more fun Biology videos coming very soon!

NeedsAHardOne
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.

InteractiveBiology
InteractiveBiology

@NeedsAHardOne Glad to know we've cleared that one out for you :) DO stay tuned! There are more fun Biology videos coming very soon!

InteractiveBiology
InteractiveBiology

@NeedsAHardOne Glad to know we've cleared that one out for you :) DO stay tuned! There are more fun Biology videos coming very soon!

InteractiveBiology
InteractiveBiology

Glad to know we've cleared that one out for you :) DO stay tuned! There are more fun Biology videos coming very soon!

NeedsAHardOne
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.

NeedsAHardOne
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.

Bas
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?

Bas
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?

InteractiveBiology
InteractiveBiology

It's not that you have less, but they are blocked by the Myelin Sheaths.

InteractiveBiology
InteractiveBiology

@juhidgenius It's not that you have less, but they are blocked by the Myelin Sheaths.

InteractiveBiology
InteractiveBiology

@juhidgenius It's not that you have less, but they are blocked by the Myelin Sheaths.

InteractiveBiology
InteractiveBiology

It's not that you have less, but they are blocked by the Myelin Sheaths.

InteractiveBiology
InteractiveBiology

@IHateSarsi It doesn't go through the myelin, it travels down the axon.

InteractiveBiology
InteractiveBiology

@IHateSarsi It doesn't go through the myelin, it travels down the axon.

juhidgenius
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??

juhidgenius
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??

juhidgenius
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??

IHateSarsi
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?

IHateSarsi
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?

IHateSarsi
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?

Leslie Samuel
Leslie Samuel

You are very much welcome. Glad the videos are helping you.

Leslie Samuel
Leslie Samuel

Glad you are finding value in the videos. Unfortunately, I'm not able to answer specific questions due to time limitations.

Lrsamuel
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.

Lrsamuel
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.