A2 Biology - Resting potential and action potential (OCR A Chapter 13.4)

A cell membrane normally is maintained at a resting potential of -70mV. When the receptors detect a stimulus, the membrane will generate an action potential to transmit the signal to the brain/spinal cord. In this video, we will look at the mechanisms of how the resting potential is maintained and re-established, and what happens to the membrane for an action potential to be generated.
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[@BioRach]

Glad to be of help! Thanks for watching :)

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Your videos are a total lifesaver! Got an A in my CAIE AS just for u and targetting an A* now in A2. THANK YOU SO SO MUCH.

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This video (and your other videos) are total lifesavers! Thank you so much!

[@BioRach]

Aww glad you find it helpful! Thanks for watching :)

[@gracex3]

@@BioRach during depolarization is the potassium channel close

[@putyourfaithinthelight749]

@@gracex3 The non-voltage-gated potassium ion channels remain open throughout the process (hence the leakage of K+ ions out), however the voltage- gated ion channels only open during repolarisation and begin to close at hyperpolarisation. This is because it is a slow process to close the voltage-gated potassium ion channels, therefore causing the charge to go beyond -70mV. Edit: Typo

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[@BioRach]

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[@BioRach]

I'm glad you find it helpful! Thanks for watching :D

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[@BioRach]

I'm glad you found the videos helpful! Yes, it's always good to repeat something so much that you hook your memory onto specific parts :)

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[@BioRach]

Glad it helped! Thanks for watching :D

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[@BioRach]

Thank you! :D Glad it helped!

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I was soo confused bout this, now i feel better! Thanks it was really helpful

[@BioRach]

Haha this can be confusing, glad you find the video helpful! Thanks for watching :)

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[@BioRach]

I'm really glad you found it helpful :) thanks for watching!

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[@BioRach]

haha really glad it helps! :D All the best in uni and thanks for watching!

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[@BioRach]

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[@gracex3]

This is great and understandable

[@thusharihemanthika3959]

i'm doing cambridge exams but still this is helpful...there's just some changes in the threshold potential (-50mV) and the action potential value (+30mV) in my syllabus...but perfect explanation...thank you very much...

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[@Astarlevels]

great video!

[@ruwahameed1275]

Thankyou so much!

[@BioRach]

Thanks for watching! :)

[@arusaabid4981]

This was so helpful! I just wanted to know, where does the refractory period come in?

[@BioRach]

Glad it was helpful! Do you mean the hyperpolarised period? That happens right after the end of action potential :)

[@abdulminhas1397]

Whenever the sodium ion channels are closed for example during both hyper and repolarisation

[@JjGabrielPianist]

thankiuuu so much

[@aayushimishra7528]

Great explanation 👍👍👏👏

[@BioRach]

Glad you found it helpful! Thanks for watching :)

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[@BioRach]

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[@BioRach]

haha glad it was of help to you :D Thanks for watching!

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SO SO helpful!!! Please do more of these vids!! THANK YOU

[@BioRach]

Hahaha glad you find it helpful! And will do when I have more time! Thanks for watching :)

[@jochadwick4890]

hi this was so useful to watch thank u!! i just have a q abt the relative proportions of charges in the short bit after hyperpolarisation? u said the Na/K pump will bring it back to resting mem potential. if the Na/K pump is transporting net 1 positive ion out, so the inside goes from negative to even more negative, why isnt it hyperpolarising further away from resting mem potential?

[@munaaliii]

Hello miss, can you make a video covering the nervous system- the transmission of nerve impulses in neurones to synapse to role of drugs in synapses. Thank u for ur work!

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[@bananabird7584]

This is a very good video, but why do our nerve cells do this? What's the point in constantly pumping in and out Sodium and Potassium ions?

[@oswin4715]

Please do more vids!!

[@BioRach]

Haha will do! Thanks for watching :)

[@smejgaming3352]

Great video thanks. What is the music? It would be great for revision.

[@abdelrahmanshams6016]

The video is outstanding as always. Easily understandable explanation which is amazing, can you explain saltatory conduction and impulse propagation in another video

[@BioRach]

Glad you found the video helpful :) I can do, though it's not much extra on top of what's already covered in this video. Saltatory conduction is referring to the fact that the sodium ions diffuse from one node of Ranvier to the next, rather than having every ion channel opening in between the nodes, therefore the impulse transmission is extremely quick. Impulse propagation is pretty much referring to the same thing, unless I interpreted your question wrong? In which case then please let me know and I'll cover it in a bit more detail :) Thanks for watching!

[@abdelrahmanshams6016]

@@BioRach what I meant by impulse propagation was the several changes in potential difference across membrane that let the impulse to move across neurone in one direction. I want to know what happens in the membrane to let that happen

[@BioRach]

@@abdelrahmanshams6016 Ah I see. That would be due to the opening/closing of the ion channels along the membrane due to it reaching the threshold potential of -55mV. 1.) When an action potential is initiated, the sodium ion channels open, which increases the membrane's PD from -70mV to -55mV. 2.) At that point, the voltage-gated sodium ion channels nearby will then open to allow more sodium ions to come in (reaching 40mV). 3.) These ions then diffuse along the membrane, which then causes the "next area" to also increase its PD (as more positive ions inside than outside). 4.) Then the same thing happens - the channels in the "next area" open due to reaching -55mV. 5.) The membrane in the "previous area" will then experience a drop in PD (due to the "loss" of sodium ions) and the voltage-gated potassium ion channels will then open, which helps further decrease the PD (ie. repolarisation), even beyond -70mV, which is then called hyperpolarisation... before the sodium/potassium ion pumps work again to regenerate the PD to -70mV. If you use the OCR A textbook, there is a really good diagram that shows this on p.13 (in 13.4 Nervous transmission).

[@BioRach]

I appreciate this is confusing - I can go over it with the diagrams that I drew in front of me maybe in a Q&A livestream? :)

[@abdelrahmanshams6016]

@@BioRach Finally I have understood it really thank you and I appreciate your work

[@ProJamesO]

Very helpful video! shame you didn't do more videos on neurones/synapeses/etc but thanks so much anyways

[@BioRach]

Haha working my way through the spec! Definitely will be covering those at some point in the next academic year so keep an eye out for the new videos :) thanks for watching!

[@muniroloko3584]

At what point do the voltage-gated potassium ion channels close? what mV?

[@arwazain8860]

What is the use of the potassium ions that come in the resting potential bcz it goes out again right? so whats the use of it?

[@rasheede.o4824]

If you have a larger stimulus does that mean a large amount of energy from the stimulus (but not all the energy) is transferred but that is not enough to open the subsequent voltage gated channels but opens more sodium channels than if it were a smaller stimulus.

[@BioRach]

Yes. We think of something a larger stimulus based on us feeling it more. That implies that more receptors are trigger in the beginning, hence more initial sodium ion channels are opened to reach the threshold potential, which then opens more of the subsequent voltage-gated channels.

[@rasheede.o4824]

@@BioRach Thanks make sense

[@rasheede.o4824]

Another question Biorach you said at 5:58 the 'first sodium' channels by that did you mean the first voltage gated channels or the normal sodium ion channels. I thought that the voltage gated channels only opened at -55mv

[@chloeb6093]

how is the impulse passed along the axon after this?

[@sherjazrawi4510]

is there a difference between just Na+ channels and Na+ voltage gated channels since they were labelled differently or are they supposed to be the same thing?

[@BioRach]

There are different versions of Na+ channels. Some are voltage gated, meaning they're sensitive to changes in potential difference. Some are stretch mediated, such as the ones found in the Pacinian corpuscles, which are literally stretched apart for sodium influx.

[@myavehniwal9374]

Hi, thank you for this video! So do potassium ion channels open during resting potential, close during repolarisation, and open again during hyperpolarisation?

[@BioRach]

Yes, correct!

[@Bella-we2sq]

I swear the Na/K pump was always active?

[@maheknadeem1193]

Great Video! I have a question though. Why are the NVG potassium ion channels opened at resting potential. Don't we want K+ to remain within the membrane that's why it's actively transported into the membrane in the first place?

[@BioRach]

We want K+ out! At resting potential K+ are actively transported into the neurone to facilitate Na+ going out, but we want to maintain -70mV by moving most positive ions out, so the K+ ion channels are open to allow any K+ to diffuse back out after active transport.

[@maheknadeem1193]

@@BioRach thank you for your fast reply! I get it now. K+ must go away to keep the inside negative! Got it😄btw I love the oxford revise workbook it’s been really helpful

[@jjsupermegabye3913]

Very good video with lots of diagrams and explanations but could speak a bit slower sometimes.

[@shahadmerani3116]

fvcking hell i’ve studied this subject for 1 whole year and i was always confused bc so much is said about Na but almost nothing about K now i understand what actually happens 🤦‍♀️

[@Big_Impact_Historics]

07:55 - so am I right in saying, that hyperpolarisation initiates the reactivation of the sodium-potassium pump?

[@BioRach]

Yes :)

[@yebany9662]

Would they ever ask "Define resting potential" in an exam? If so what would be a suitable answer?

[@Emzy17]

mate thats not even a gcse question(ud expect foundation to have that) not a level standard🤣

[@kazishahjalal6852]

So are you trying to say that during an action potential that both the sodium potassium pump and non-voltage potassium channels are deactivated in the earlier stages. Am I correct?

[@BioRach]

Yes.

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Just from your hands I can tell you're fit.. and thanks for the revision seshh!

[@jlc5271]

Lol

[@shinzoshiratori2223]

Whats the difference between voltage and non-voltage channels?

[@BioRach]

Voltage-gated channels are those that open due to a change in the potential difference in the membrane. They are mostly involved in triggering an action potential, or in any situation where the release of a substance is regulated (eg. insulin). Whereas non-voltage channels (so normal protein channels) are not necessarily involved in regulation of any substance release - examples include protein channels for water absorption, which happens all the time and isn't controlled to only occur at certain moments. Hope this make sense!

[@hannah6444]

Sounds like Minecraft music in the background but thank you it was vvv helpful x

[@BioRach]

Not sure if Minecraft uses music from the same artist? 😂 Just got it off KZbin music library! But glad you found the video helpful :)

[@arjunpatel8247]

Is this the membrane of the axon ?

[@BioRach]

Yes it is :)

[@nathantorresstanevil6958]

Yeah but won't Na+ run out? It's constantly being pumped out and nit being replenished here

[@BioRach]

They are replenished through active transport during hyperpolarisarion. The Na-K pump will re-establish the Na+ concentration gradient.

[@fatimaab5931]

can you make videos for module 2 please :(

[@BioRach]

Any particular chapters? I've made quite a few videos on various chapters on module 2 so check it out! They should be organised in chapter playlists in the AS playlists :)

[@fatimaab5931]

@@BioRach ahhh iv just checked thankyou ! could you make a video cofactors and enzyme inhibition please x

[@tousifhabib7868]

are the negative ions cl-

[@BioRach]

Yes they are usually large chloride ions :)

[@alevelzah117]

BioRach I thought the negative charge inside the cell membrane was of negatively charged proteins ?

[@torikujawa8887]

have you got any videos on the refractory period? I'm really stuck on that

[@phoebesmith7496]

slow down