009 Depolarization: Phase 1 of the Action Potential

009 Depolarization: Phase 1 of the Action Potential

The action potential can be a complicated thing to understand, unless you are dealing with little white plusses on a table :)

In this video, I help you visualize the first phase of the action potential – the Depolarization phase.

Go ahead and watch the video and you should get a clear understanding of the events that cause depolarization of the neuron.

– Leslie Samuel

Transcript of Today’s Video

Hello and welcome to Interactive Biology TV, where we’re making biology fun! In this episode, we’re going to be talking about depolarization, which is the first phase of the action potential. We’re going to go into some more detail than we’ve been doing in the past when it comes to the action potential. It’s going to be a little different. You’re not going to be looking at me talking about something. You’re actually going to be looking at another one of my elaborate set-ups, and I’m going to call this set-up the “Action Potential Simulator.” I hope that gets you excited about it.

Alright, so what we have here is, this side represents outside the cell, outside the axon, and this side represents inside the axon. Here we have a bunch of pluses, and these pluses are representing sodium ions. Now, sodium ions have a positive charge, and that’s why I chose these very attractive pluses to represent sodium ions.

Now, here in the center, we have what we’re going to refer to as voltage-gated sodium channels. What happens is, you have all these sodium ions on the outside of the cell, and these sodium ions want to get into the cell, but they cannot get into the cell. Why can’t they get into the cell? Because the voltage-gated sodium channels are closed. In order for them to get into the cell, this channel needs to open.

Now, why does sodium want to get into the cell? Well, if you go back to Episode 6, this can refresh your memory a little bit, we spoke about Donnan equilibrium. And we spoke about the fact that the membrane potential at rest is somewhere between -50 to -70, -80 millivolts. At that negative charge, sodium ions are not happy. In order for these guys to be happy, the membrane potential needs to be around +58. And on the inside of the cell, we have a negative charge, so this is not something that sodium likes.

So how does sodium want to counteract this? Well, sodium wants to rush into the cell so that it can make the membrane potential more positive, which will be closer to the Donnan equilibrium potential for sodium ions. I hope that makes sense, if not, once again, go back to Episode 6 and refresh your memory on how the Donnan equilibrium works.

So, someone touches you or there’s some stimulation and there needs to be an action potential that’s sent along the axons of the neurons that are stimulated. What happens is, when the membrane potential reaches threshold, that is enough charge to cause voltage-gated sodium channels to open. Once those voltage-gated sodium channels open, sodium ions can then go into the cell.

Now, what is this going to do to the charge inside the cell? What is it going to do to the membrane potential? Well, now you see you have all these positives on the inside, so that’s going to make the membrane potential more positive. This is the process of depolarization. It is the first phase of the action potential, and this is how the charge starts that gets sent along the axon.

So once again, when the membrane potential reaches threshold, voltage-gated sodium channels open and once those open, sodium ions are going to rush into the cell, making the membrane potential more positive, and that is depolarization. I hope that makes sense to you. If you have any questions, as usual, feel free to ask them in the comments below, and I’ll be happy to answer your questions. And who knows, maybe even make a video answering your specific question. That’s it for this video, and I’ll see you in the next one.

198 comments
barbara r.
barbara r.

This has been super helpful, I swear I learned this before but every time I start up on the information again I realize I forgot again. Pharmacology is kicking my arse. I have googled, I have looked at old notes, I have watched other videos but this has been most helpful, great thanks to you

Ingrid
Ingrid

Hi Leslie! Thank you SO SO very much for these wonderfully composed and easy to understand lessons; the combination of visual video with simple, well-written transcripts increased my rate of learning and absorption by ten-fold (at least). I am an English major attempting to get into a Nursing program and thus am spending my summer filled to the gills with biology and physiology courses. I'd been pouring over my textbook, our class lab book, and website after website trying to understand the connections between concepts that you made so rapturously clear in your beautifully organized lessons all across your website. Keep up the good work, you're helping a great number of people, and I wish you the best of luck in whatever path you choose to take. Thanks again, Ingrid (Bethesda, Maryland USA)

leo
leo

Great videos !!!! just a question how can it reach the threshold if the voltage gated channel is closed? is that with the passive transport ? thans a lot

Bina Ch
Bina Ch

your videos are of great help to me as i have many of my doubts cleared.......thanks:)

James Bronson
James Bronson

its 5;00 AM!!!!!! WOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

teresa
teresa

You have been soooooo helpful. I am thankful for your videos. Really, because of them I have passed difficult tests in the last year! Thank you so very much <3

Akash Ahmed
Akash Ahmed

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Karen Peaden
Karen Peaden

thank you! I am 56 yrs old and taking ECG and need all the help I can get! the heart is very complicated and you are great at explaining things! you are great at teaching! thank you again!

Foxy Roxy
Foxy Roxy

I love your videos. As I read each chapter of my Anatomy & Physiology book I watch one of your videos for a clear understanding of what I'm reading. Your videos are easier to follow. Keep up the good work!!! You have been a great help.

lovely gamboa
lovely gamboa

i could see,the previous video's you are talking about,the equilibrium thing.please help!!

Ravneetu
Ravneetu

Hey! Could you please make a video on Cardiac action potentials, SA node,and ventricular action potentials? Along with Cardiac muscle contraction? Maybe even the Cardiac cycle if you have time! You would be a lifesaver!!!

Ray
Ray

Great vids, but can you Please remove the sign up box that pops up from the beginning of every window? Because even though I've signed up, it still pops up before every videos and it's hard to keep writing that info in when you're watching 40-50 videos and you have to write it in before each one. But other than that, amazing videos!!!

Hayah Bellatrix
Hayah Bellatrix

thanx a lot 4 ya video brother. May Allah reward u.. will u please guide me to ur episode 6... i'm unable to find it!

tey croco
tey croco

I really enjoy watching your video! Thanks for making biology fun! It's enjoyable!

vladbio
vladbio

Hi Leslie, great video - as usual. I was wondering what stimulus can create the initial difference sufficient to open Na gated channels? Thanks in advance.

Underground308
Underground308

When something "clicks", Its the best feeling in the world!!! I understand!!! After feeling hopelessly lost for so many night, I get it!!! l! You sir are awesome!! Thanks!!

Dragonflowi
Dragonflowi

Hey excellent video !!! I have a question. I dont understand why inside the membrane the charge is negative if it contains Potassium K+ that also has a positive charge ? Could you explain to me why is this ? Thx in advance

Bryce Daniel
Bryce Daniel

Very "Attractive" pluses. Haha. Thanks for making these videos.

Coco Duncan
Coco Duncan

A friend advised me to come check out your videos and I am understanding so much from you than my own anatomy&physiology professor. Your videos are a great study tool. Thank you for your expertise.

main126
main126

Thank you for making this video ~

AM loki
AM loki

i thought that was a black duct tape

caxsmith
caxsmith

Is there food you can eat that will affect the threshold? I'm thinking of people with gluten reactive disorders, not celiac disease as such. And is this related to the threshold of pain a person has?

mohib ullah
mohib ullah

Nice method and very easy to understand thanx

Bubble Batth
Bubble Batth

we appreciate your time and expertise greatly!

erikaj13
erikaj13

Thanks so much for all your videos. You are really helping me through my anatomy & physiology course :)

Tan Run Yu
Tan Run Yu

2:46 how to make the membrane potential reaches threshold ? is it by increasing the amount of Na ions outside the cell ?

zmerka1
zmerka1

I want to sincerely thank you for this fountain of knowledge. Your videos have gotten me thru A&P classes and biochemistry classes. I am always amazed at the generosity of people like you who put so much time and effort bringing something like this to the world.

ASternTravesty
ASternTravesty

you sound so excited in the beggining, almost like your trying not to laugh.

TheAdmiston
TheAdmiston

hey! sorry a have a dilema.,i see that you respownd at this question..how is possible that one small stimulation at the one part of neuron can be transmited to oposite part ..neurons can be very long..over 30 cm.. i don't underestand how ions chanels is opened..i understand the first chanel is open by the stimulation but after that? i look all over the youtube but i find smth like this.."the signal is transmited afther that to all over the cel.."how more exactly?who opens the others ion chanels?

NaniiStarlight
NaniiStarlight

I'm from The Netherlands and I'm studying Psychology and the English Biology books we have to use are soooo hard but this is amazing!! it makes it really easy to understand, thank you!

kittykaaboom
kittykaaboom

This makes everything much easier to understand. Thank you so much!

OriginalRipndip
OriginalRipndip

West Indians apply a simple approach and logic to learning. feel free to merge the 2 vids on this subject we don't have the attention span of a neuron we are here to learn for our intense classes. thx doc do u have playlists grouped by systems?

Tasha Tolbert
Tasha Tolbert

Wow! You are an EXCELLENT teacher!!! I have been watching your videos all day going over some of the subjects that I did not understand in class. Your videos have made me more interested in the material, and I have actually been understanding the information as well!! I haven't gotten bored at all!! You are a truly gifted man. God bless you:-) You are quite handsome as well:-) Thank you.

luvlyvero14
luvlyvero14

I love the first line of all his videos.. "Hello and Welcome to interactive biology tv. Where we're making biology fun!" lol.. sounds like he really enjoys his subject matter. Pleasant voice for learning..

Bruno Balbino
Bruno Balbino

What an amazing video! I've looked for the next chapter in yt, but I couldn't find that! I wanna watch all of them.

InteractiveBiology
InteractiveBiology

Yes. Please check our channel to see a list of all the videos we have posted. Have fun!

SplashFlip
SplashFlip

Just wondering if there is a chapter 8? i couldn't find it in youtube though i searched. I don't wanna miss any of these awesome videos!

bautista1
bautista1

At rest, the action potential is negative due to more Sodium ions flowing out of the axon correct? And it is less Potassium that flows inside, correct?

DrMythology
DrMythology

Hi, i understand why the entry of Na will cause depolarization for example from -90mV to -10mV the polarity 'negativity of the cell' is being lost.. this is totally understandable but here is where i get mixed up >>> when the cell is in a depolarizing state when it reaches to '''+'' mV for example +10mV isn't that being also polarizing to the other side ?? why is it still called depolarizing?? can anyone explain to me .. Thank you