ACTION POTENTIALS: Depolarization and repolarization on an axon, Includes All or nothing principle

Watch this video for help undertading what an action potential is and how it is generated. I explain what the all-or-nothing principle and refractory period are and why both are important for survival. This links to AQA A-level topic 6.
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[@aaminahthekilla]

i swear it gets so hard to pay attention and understand things in class because of the amount of information thats constantly thrown at me, and the way they make things more complicated than they actually are - but your videos are so straightforward it takes a lot of the pressure away! thank you so much!! :)

[@shazmeertv44]

Nobody asked

[@laithjadallah6061]

you are an amazing person. you are honestly going to help me achieve a good grade with your explanations and simple diagrams. Im gonna cry i swear thank you so much

[@MissEstruchBiology]

Aww thank you. I'm so pleased the videos have helped you understand and have given you confidence. Good luck with your studies!

[@alaamorad8687]

you have saved my life in this topic you don't know how much I have struggled I got my teacher to explain this topic about five times and I also got a tutor for it but that also didn't work out thank you so much for everything you are amazing with you nice and simple explanations and the diagrams are also amazing thank you again

[@MissEstruchBiology]

Ahh amazing!!! It is such a tough topic and it took me a while to get my head around it when I first learnt it and then again when I first had to teach it so I am really pleased that you found it understandable the way I explained it :D

[@aflan8109]

Thank you so so much for this video, it was explained so clearly I understood it the first time!

[@MissEstruchBiology]

Hello, It is a tough topic so I'm really glad you found my explanation clear enough ☺

[@ethancheung114]

so much clearer than a text book or my lecturer. thank you

[@MissEstruchBiology]

yay so pleased 😁😁

[@sumayabusur7034]

Thank you so much for your amazing explanation it really helped me

[@MissEstruchBiology]

Hi Sumaya, I'm really glad it helped! :)

[@imaanmudassar5181]

Thank you so much! your video helped me tons:)

[@MissEstruchBiology]

aww I'm so pleased you've found them helpful ☺

[@saminaamin6808]

Omg you've made topics so easy for us !! I wonder what would have i done if your videos weren't here... THANKYOU SO MUCH LOVE❤ I don't know how to thank you🥺🥺❣️

[@MissEstruchBiology]

I'm so pleased!!! So happy it had helped you to understand it 😊😊

[@ramrad5905]

U explain perfect,thank u so much

[@MissEstruchBiology]

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[@keb7686]

You’re legend !! I’m subscribing now

[@MissEstruchBiology]

aww thank you and welcome ☺

[@dilprotiva2992]

You always have the answer to my confusion😫😫 I love you miss❤❤Never stop with your work👍👍

[@MissEstruchBiology]

I'm so please the video helped you to understand the topic!! :D

[@simdicool5438]

Your videos are honestly SO HELPFUL thanks so much

[@MissEstruchBiology]

Glad you like them!

[@shuaybhussein8282]

These are sooooo good

[@MissEstruchBiology]

Thank you so much ☺ So glad you found it helpful

[@Sanchoo25]

This is good ...thanks am subscribing right now

[@MissEstruchBiology]

Thanks for the sub! So glad that you like the video. I hope the others help you too!

[@anthonyyau9315]

This video is a masterpiece

[@MissEstruchBiology]

oh wow thank you!

[@reemamin1584]

hi miss Estruch , could you please make a video about the scientific article ( ial edexel oct/nov exam) and your expectations 😘

[@gamingspotlight6194]

Your definitely a god send when it comes to a level biology !! I’m not sure if it’s covered in your spec but do you know what happens when drugs block the gated potassium channels in the axon membrane ? Like how it would affect the action potential trace

[@MissEstruchBiology]

Hello, This could be an application question on the specification, where you would be given information to use to work out the outcome. Drugs tend to affect the synapses rather than axon, as this is where neurotransmitters (chemicals) diffuse. Some drugs prevent the neurotransmitter from detaching from the receptor and some can bind and block the receptor. So this can result in either the action potential continuously being triggered without any stimulus and this can cause muscles to remain contracting where as others, like pain killers, that block there receptors prevent the action potential travelling further and therefore preventing a response or preventing the action potential travelling the the CNS. Hope that helps.

[@gamingspotlight6194]

@@MissEstruchBiology Hi miss, thanks a lot for your detailed reply. I'm still confused about what happens when drugs block the gated potassium channels in the axon membrane and how it would affect the action potential trace

[@gamingspotlight6194]

@@MissEstruchBiology I've written down that it slows down the action potential since K+ channels are blocked but that's it :(

[@adamrose6809]

Loving the videos miss, hope you had a nice Christmas. Just a question, what’s the point of having unmyelinated neurones then if the myelinated ones are much faster?

[@MissEstruchBiology]

Thank you 😊 Hardly any are unmyelinated, but this site goes through why some are www.ncbi.nlm.nih.gov/books/NBK554461/

[@raisadrawss4190]

you're a lifesaver

[@MissEstruchBiology]

Happy to help ☺️

[@daaragoodluck]

I’ve said this before imma say it again you are a God Send! Awesome vid as usual 💥

[@MissEstruchBiology]

Aww thank you so much 😊

[@markdean6174]

Hi really good video. Do we need to know about what determines the speed of action potentials and the difference between non-myelinated and myelinated neurones for aqa? Thanks

[@MissEstruchBiology]

Hello, Yes you do need to know that. I thought I'd made a video on this already, but doesn't seem so.

[@markdean6174]

@@MissEstruchBiology thats fine i just wasnt sure

[@missgirl7879]

I think im gona cry, hate biology so much. Been blank and sleepy past couple of lessons uderstanding nothing and u literally summarised it to a level my brain could comprehended 😭😭 this whole channel... thank u so much fr

[@MissEstruchBiology]

Oh no, sorry you have been finding it so hard. I hope my videos can make you start to enjoy the subject again 😊

[@rocksyantonygnaneswaran8595]

What's the difference between a generator potential and an action potential?

[@khaled-ig1hz]

hi, Mrs @9.25 in the refractory period how does the axon ensure that the impulse is unidirectional and so prevents the backflow of the impulse where there is a more negative charge so surely the Na+ ions are attracted to the opposite charge? I'm confused how its kept 1 way thank you !

[@MissEstruchBiology]

Hello, This is because the ions can only pass through the voltage gated protein channels, so at that point the gates are closed. Hope that helps 😊

[@benstorey8085]

Hi miss, I’m a bit confused on how it triggers the next impulse along the neurone. In one book it’s saying sodium diffuses sideways but in the other it’s saying it makes localised currents so it can jump from node to node

[@phoebemay7550]

Hi its a bit late but isn't that the difference between myelinated and non-myelinated neurones? I think in myelinated neurones the impulse 'jumps' whereas in non-myelinated neurones the sodium diffuses sideways in the wave of depolarisation?

[@benstorey8085]

@@phoebemay7550 nah in this book was saying that sodium diffuses sideways but then can only make the action potentials In the breaks of the myelin

[@mxrcy03]

Hi Miss, does this video explain how the action potential passes along the UNmyeliated axon?

[@MissEstruchBiology]

Hello, this would be the case for both. I have another video - factors affecting the speed of conductance, which goes through unmyelinated v myelinated too.

[@galefray]

Hi Miss Estruch, really awesome video as always. I was just curious however; are the K+ channel proteins which open and close also voltage-gated like the Na+ ones? Thanks so so much

[@MissEstruchBiology]

Hello, Some of them are where as some a permanently open, which is one of the reason why the membrane is more permeable to K+

[@salenaakram2436]

I love you, Miss Estruch.

[@MissEstruchBiology]

I hope the video helps your studies 😀

[@MatT-vf7qo]

at repolarisation, does the na+/k+ pump and Na+ ion channel close

[@MissEstruchBiology]

As this is a movement is due to active transport, this pump is constantly in action, as long as it has energy for the active transport to occur.

[@marcocasali8434]

Hi. How is a potassium concentration gradient created. Potassium is constantly being diffused out of the axon

[@ItsTheEddemundos]

inside of axon is negative so K+ wants to diffuse in (down electrochemical gradient) - it also wants to diffuse out as conc. of K+ is higher inside axon (down conc. gradent). Equilibrium is reached at -70mV so there is no net movement of K+ at that point (resting potential).

[@user-tz5pz8ev7u]

can Na+ travel both ways through the channel? I thought that Na+ can only move into the axon and not move the other way.

[@MissEstruchBiology]

Hello, If you have a look at the image on this link it may help.en.m.wikipedia.org/wiki/Resting_potential Na+ moves out due to the Na+/K+ pump, but then diffuses back into the axon through the Na+ channel. So it does travel both ways, but through different proteins. Hope that helps ☺

[@tahakarim1901]

I wanted to ask, how does the refractory period ensure that the action potential only travels in one direction? I was a bit confused on this.

[@ashmartyr6392]

The refractory period stops the action potential from generating another one in the backwards direction (Mexican wave) because the refractory period causes that part of the axon that has just fired an action potential to be unresponsive as voltage-gated channels are closed. This means the next action potential can’t trigger another action potential backwards as it is unresponsive. This only allows the action potential to travel unidirectionally from the dendrite to the axon terminal :)

[@curtishagen6840]

Hi, I wonder if you can help me, I bought a second hand Action Potential Stimulation) Therapy machine - MK 1.1 but I don’t know how to used it. Please can you advice me where to get instructions Manual book or website were I can download video . Thanks

[@MissEstruchBiology]

Hello, Oo afraid I can't help on that. I've never used one. Sorry!

[@Mozzie7920]

Wait so how does the refractory period ensure they travel in one direction?

[@MissEstruchBiology]

Because at -80mV a lot of Na+ is needed to trigger an action potential, whereas the next part of the axon moving forward will be in the -70mV resting potential and therefore as Na+ enters the axon this part will meet the threshold and cause the action potential to continue to move forwards in one direction along the axon. Hope that helps

[@juliettecurran3173]

Hi I was just wondering if you're allowed to refer to sodium as Na+ and potassium as K+ in the exam?

[@Caller8194]

in the exam refer to them as sodium IONS. IONS you must says ions

[@jafwonta]

@@Caller8194 Na+ ions?

[@Caller8194]

@@jafwonta Na+ is already an ion. Saying Na+ ions is like saying Na ions ions

[@jafwonta]

@@Caller8194 many textbooks refer to hydrogen ions as H+ ions. I don't get why it would be any different here

[@Caller8194]

@@jafwonta H+ ions is wrong. Ask anyone with more than A level knowledge and they’ll agree

[@miaxx3929]

Hi, thanks for the video, I’m slightly confused on which voltage gated channels are open at the different stages of an action potential In an exam I wrote that the sodium ion channels are closed at resting potential, open at depolarisation and closed at repolarisation which was correct However when I wrote that potassium ion channels are open at resting, open at depolarisation and open at repolarisation it was marked incorrectly The mark scheme stated that the potassium ion channels are closed at resting, closed at depolarisation and open at repolarisation If you could give me any help with this I’d really appreciate it as I am slightly confused by this 😊

[@lionqueen19]

I think it’s because some potassium ion channels are voltage gated and some aren’t, so some stay open all the time and the ones which are voltage gated require a particular environment to open for example the voltage gated channels open at +40 mV allowing potassium ions back into the cell which is why repolarisation occurs. The question was probably asking about voltage gated potassium ion channels so when you said they were open at resting potential, while the potassium ions that are not voltage gated are open because as the concentration of potassium ions increases inside the cell they want to diffuse out (so you were technically right there) but the voltage gated one’s remain closed? I’m sorry if that was confusing😭

[@ozairmuddasir8578]

maam u beauty

[@MissEstruchBiology]

I hope the video helped!

[@ozairmuddasir8578]

@@MissEstruchBiology it did ma'am really very kind of u❤️