My prof told me if anyone had a better way to teach this concept we were to tell him. I feel like emailing him the link to this video aha.. thank you so much. You're making a tired physiology student a lot less confused.
If I had been watching this in a mirror, I think I literally would have seen a light bulb turn on in my head. Please don't ever stop making these vids.
I liked you explanation for this. I'm in A&P I in college, but this topic in class confused me and the book didn't help at all. All in all, thank you for explaining this!!! I hope you continue making videos on various topics!!!
You are the BEST!!! I said I'd follow your videos and I am. You take all of the stress of learning off of us so that we can absorb the concept and move on. You are truely an answer to prayer. I hope you have videos on the reproductive system and the 28 day menstral cycle.
after an action potential is created (the 40mV to close the Na channel and open the K one) the Na voltage gated channel is closed for a short period of time regardless of the membrane potential (like 5ms or something) - this is called the Refractory Period (look it up if you want :P) the refractory period means that every action potential are seperated and they only move in one direction
Exitatory and inhibitory potentials are summed up at the axon hillock, like you mentioned. This is the location where the neuron 'decides' to continue the action potential. Of course, there is a potential difference across the entire neuron (otherwise there would be no charge to sum at the hillock), but the actual action potential itself begins at the axon hillock.
Wow! This was excellent! It was like a real field trip of the nervous system! Oh how I love youtube. 10 thumbs up! I will be back often until this soaks and I am able to explain. I hope this guy have other Anatomy & Physiology topics for discussion. You rocks!
The amount of Na and K that pass through the membrane during an action potential does not significantly alter the overall concentration. You could have 100s or 1000s of action potentials before significantly effecting concentration gradient. However ,the Na/K pump is ALWAYS running in the background which maintains the concentration gradient.
Good question. It is not the membrane becoming more positive that allows the Na+ channels to open. It's some sort of "outside stimulus" which basically means something in the body is happening and this cell is being told to start generating a signal
That took forever! The constant repetition made it tedious, more confusing for me, although I am very grateful for your work. Maybe more succinct might be more direct and to the point might make it easier to follow and more interesting. Much appreciated. Thank you.
I had to watch 4 videos on this before I finally got what's going on thanks to your video. I kept wondering why Na+ opens; its very hard to visualize because there's so many things going on at once and alternately as well. THank YOU!
My understanding is that we only want to maintain electric equilibrium insomuch as it allows for the propogation of action / electrotonic potentials. The existence of this positive feedback loop is part of the body's strategy to propagate signals electronically (a much faster and more precise method than hormones etc).
There can be a few things that can open/close a channel. A molecule or membrane potential (aka. membrane voltage) can open/close a channel. A molecule can open/close a channel by binding to the channel (well, actually it binds to a receptor which is located just beside the channel and this binding to the receptor allows opening of the channel).
whenever the lecture class starts..... somebody please give their thumbdrive to the lecturer and play it for 2 hours long.... AND YOU WILL GET A++++.....
EXCELLENT VIDEO! Khan (or anyone else) at the core of this discussion, can you confirm whether it would be a good or bad thing to have some form of constant electrical stimulus which would result in the sodium and potassium gates being open all the time? I assume that would be a bad thing over time due to the constant need to try and rebalance and the energy it would require? What might such a scenario lead to in terms of complications or benefits?
each neuron will have different numbers so that they can respond to stimuli differently. There is a 'typical' set of numbers that textbooks use, but it's really just an average of the many different neurons you would find in the human body.
Analogy: (hot day) classroom = no AC....Hallway = AC....Class full of students. Temp keeps going up in room to point where student can take it anymore while some have more tolerance to the heat. if enough students leave class, teacher scrambles to get AC going in classroom. Temp goes down, students re-enter class......Kinda like a gated action potential! just a way to remember an extremely basic understanding of this process. I lived it! lol! Ha!
A small depolarization caused by Na+ cations. If the amount of Na+ is large enough and exceeds the treshold-level (usually -55mV) the Na+-channels open and allow for a further depolarization. If it doesn't exceed the threshold-level, the there isn't any depolarization. Watch at 07:40.
@Js5s141 Yeah. The only real difference is the density of ion gates. For electrotonic, the gates are farther apart so the effect (from weak stimulus) dissipates before it has a real chance to affect anything. For action potentials, the gates are densely packed so the influx of ions is guaranteed to affect another ion gate.
@khanacademy thankyou so much for these videos; they have been so helpful in first year biomedical science! a quick question, are electrotonic potentials the same as graded potentials? and also, are graded potentials basically action potentials that don't reach threshold (and hence comes in the spacial and temporal summation, and the fact that they're localised, etc.)? thankyou! :)
i dont really understand a certain aspect of the video...How does a more positive or less negative charge stimulate the opening of an ion gate which is about to let more positive ions in? Isn't that counterproductive in terms of maintaining electric equilibrium and resting membrane potential? Otherwise the rest of the video was perfect and i understood everything that all the med textbooks couldn't teach me, thank you so much!
What is the point of the potassium restablishing a positive charge outside for a short time, if sodium/potassium pumps regulate the differences in charge again anyways? I don't get why it has to balance out the charge before changing sides with sodium again
Where on the neuron does the electrical potential gradient begin? At the dendrite, soma, or axon? I am just a little confused about whether the gradient is triggered as soon as the signal is passed from the axon terminal to the next dendrite or if the signal builds up at the axon hillock and the gradient actually begins at the axon?
they open in response to stimulus,which changes the permeability of the membrane..i.e *voltage, *chemicals(hormones,neurotransmitters) *mechanical pressure *light(photo receptors of the eye)
Just a quick comment about this video....while describing these two processes, my text states definate numbers when it comes to thresholds and opening and closing of gates while you describe them as,"lets say" this and that number. It would be helpful to use the book numbers like....resting state is -70, stimulation occurs at -60 to +30 with a refractory of -80...etc. Unless you, of course, disagree with the numbers I am reading in my text, state the numbers as they are instead of arbitrarily.
No, depends on the time of duration of stimulus. And remember that in diet you gent more Na then K (what means always a bigger conservation of Na outside than inside the cell)
So is an electrotonic potential the same as a graded potential? In my biology class I learned about a graded potential and it had essentially the same characteristics as what was described with the electrotonic potential (fast, dissipates with distance)
so only one type of gate should be able to open according to its neighbors or you would have it bouncing between -55 and +40 because of the na+ gates rules... right?
I have a question. If the potassium pump opens at 40mV and stays open till the potential reaches -80mV, it means that it is open for the -80 to 40mV range right?? Then why would it not be open when the Na channel is open, say at the -55mV?? Isn't -55mV in the -80 to 40mV range?? Is it that it needs a 40mV potential to open and then just stays open until the potential gets too low??? Help pleasee...
To say that these videos are good would be an understatement, however as a student they take up too much time. Sal explains a little slow, and that time adds up to huge chunks. Please offer an option to watch in fast view. It is very very very necessary to allow the necessary amount of knowledge to be learned in an available time period so as a student we can be efficient. Thank you.
@ecaep86 just use what you have been blessed with and push yourself and you won't desire his brain, because you would have explored the corners of your own.
so i've never heard of elctrotonic potential. we only use graded potential and action potential. is Graded potential an other terminology for Electrotonic potential?
Often people talk as though somehow the only diffusion gradients/chemical gradients (they're the same right?) that matter are those of one type of molecule. In this case, there is a higher concentration of sodium outside the membrane. But isn't the tendency to move down a chemical gradient caused by the probability of collisions? If so, why don't we look simply at the concentration of molecules outside the membrane rather than the concentration of sodium outside the membrane?
I don't understand why the potential becomes positive when the Na+ gates open. I would think the flow of Na+ ions stops at 0 volt. Could you explain that?
Na+/K+-Pump has acutally nothing to do with the afterhyperpolarisation and how the cell returns to its resting potential, because its kinetic is too slow to act wihtin milliseconds. Other channels are responsible for that. doi:10.1038/nrn2148
this is a complex topic. No one can explain it more briefly and understandably than sal. You've done it again man. cheers.
Khan, you are currently one of my favorite human beings.
My prof told me if anyone had a better way to teach this concept we were to tell him. I feel like emailing him the link to this video aha.. thank you so much. You're making a tired physiology student a lot less confused.
dude all of these videos literally have made me twice as smart. thank you so much!
If I had been watching this in a mirror, I think I literally would have seen a light bulb turn on in my head. Please don't ever stop making these vids.
I remember watching this for my high school and exams and here I am in second year in college and still watching
Oh my goodness same. But you've long since graduated
Thanks for posting these videos! It's a great way to review for my physiology exams when I'm sick and tired of looking at the book!
11:34 that stutter though,
very clear communications of the topics....good teaching
I liked you explanation for this. I'm in A&P I in college, but this topic in class confused me and the book didn't help at all. All in all, thank you for explaining this!!! I hope you continue making videos on various topics!!!
Nice Video That You Share , So Very Nice Thanks You How electrotonic and action potentials propagate down cells
You are the BEST!!! I said I'd follow your videos and I am. You take all of the stress of learning off of us so that we can absorb the concept and move on. You are truely an answer to prayer. I hope you have videos on the reproductive system and the 28 day menstral cycle.
this voice got me through college
after an action potential is created (the 40mV to close the Na channel and open the K one) the Na voltage gated channel is closed for a short period of time regardless of the membrane potential (like 5ms or something) - this is called the Refractory Period (look it up if you want :P)
the refractory period means that every action potential are seperated and they only move in one direction
This video explains so much. I was really struggling to understand this part. I could never thank you enough, but THANK YOU!!!!!!!!!!!!!!!!!!!!!
Exitatory and inhibitory potentials are summed up at the axon hillock, like you mentioned. This is the location where the neuron 'decides' to continue the action potential. Of course, there is a potential difference across the entire neuron (otherwise there would be no charge to sum at the hillock), but the actual action potential itself begins at the axon hillock.
You're so good at explaining!
you are a legend!! every video of yours ive watched has made mud clear!!
Khan, you're the bomb. Thank you for your work.
you are absolutely incredible. if I ever make it through these exams I have you to thank!
Other than the confusion of Na+ and K+ names, its really good :D
you deserve a nobel peace prize for ending the struggle of millions of biology students with their text books, why cant all teachers explain that well
Love it! That's amazing.
Wow! This was excellent! It was like a real field trip of the nervous system! Oh how I love youtube. 10 thumbs up! I will be back often until this soaks and I am able to explain. I hope this guy have other Anatomy & Physiology topics for discussion. You rocks!
god bless your soul khan academy your going to heaven for this
The amount of Na and K that pass through the membrane during an action potential does not significantly alter the overall concentration. You could have 100s or 1000s of action potentials before significantly effecting concentration gradient. However ,the Na/K pump is ALWAYS running in the background which maintains the concentration gradient.
This man is a life saver :)
Thank you very much for your illustration!
brilliant videos..so helpful,thanks!
Nothing better than learning in High Definition.
Good question. It is not the membrane becoming more positive that allows the Na+ channels to open. It's some sort of "outside stimulus" which basically means something in the body is happening and this cell is being told to start generating a signal
That took forever! The constant repetition made it tedious, more confusing for me, although I am very grateful for your work. Maybe more succinct might be more direct and to the point might make it easier to follow and more interesting. Much appreciated. Thank you.
2 years later,I'm watching this video again for my college course,&Sal is still saving my ass.
Great video.
I had to watch 4 videos on this before I finally got what's going on thanks to your video. I kept wondering why Na+ opens; its very hard to visualize because there's so many things going on at once and alternately as well. THank YOU!
he confused me so much by mixing Na+ with K+, it happened multiple times...
Omg yes! I thought I was going crazy the first time I watched it!
you are so right
I didn't know I could learn so much so fast. My head has exploded.
i wish my teacher could explain this half as well as you.. she didnt even go in this but still tested from it on the midterms
you saved my life khanacademy
My understanding is that we only want to maintain electric equilibrium insomuch as it allows for the propogation of action / electrotonic potentials. The existence of this positive feedback loop is part of the body's strategy to propagate signals electronically (a much faster and more precise method than hormones etc).
Great work
Thank you!
There can be a few things that can open/close a channel. A molecule or membrane potential (aka. membrane voltage) can open/close a channel. A molecule can open/close a channel by binding to the channel (well, actually it binds to a receptor which is located just beside the channel and this binding to the receptor allows opening of the channel).
really informative and interesting
I like it!
you are right about hyperpolarization of the K+ gate but it is at "undershoot". not "overshoot".
whenever the lecture class starts..... somebody please give their thumbdrive to the lecturer and play it for 2 hours long.... AND YOU WILL GET A++++.....
god bless your soul
thank you so much!
EXCELLENT VIDEO! Khan (or anyone else) at the core of this discussion, can you confirm whether it would be a good or bad thing to have some form of constant electrical stimulus which would result in the sodium and potassium gates being open all the time? I assume that would be a bad thing over time due to the constant need to try and rebalance and the energy it would require? What might such a scenario lead to in terms of complications or benefits?
each neuron will have different numbers so that they can respond to stimuli differently. There is a 'typical' set of numbers that textbooks use, but it's really just an average of the many different neurons you would find in the human body.
Analogy: (hot day) classroom = no AC....Hallway = AC....Class full of students. Temp keeps going up in room to point where student can take it anymore while some have more tolerance to the heat. if enough students leave class, teacher scrambles to get AC going in classroom. Temp goes down, students re-enter class......Kinda like a gated action potential! just a way to remember an extremely basic understanding of this process. I lived it! lol! Ha!
A small depolarization caused by Na+ cations. If the amount of Na+ is large enough and exceeds the treshold-level (usually -55mV) the Na+-channels open and allow for a further depolarization. If it doesn't exceed the threshold-level, the there isn't any depolarization. Watch at 07:40.
I wish i was your student :) Great Video Thanks
@Js5s141 Yeah. The only real difference is the density of ion gates. For electrotonic, the gates are farther apart so the effect (from weak stimulus) dissipates before it has a real chance to affect anything. For action potentials, the gates are densely packed so the influx of ions is guaranteed to affect another ion gate.
@khanacademy thankyou so much for these videos; they have been so helpful in first year biomedical science! a quick question, are electrotonic potentials the same as graded potentials? and also, are graded potentials basically action potentials that don't reach threshold (and hence comes in the spacial and temporal summation, and the fact that they're localised, etc.)? thankyou! :)
i dont really understand a certain aspect of the video...How does a more positive or less negative charge stimulate the opening of an ion gate which is about to let more positive ions in? Isn't that counterproductive in terms of maintaining electric equilibrium and resting membrane potential? Otherwise the rest of the video was perfect and i understood everything that all the med textbooks couldn't teach me, thank you so much!
haha ur a legend i actually might pass neuroscience now lol
physiology ayyyye
Would you say it is a kind of ripple effect?
Thank YOU!!!
thank you
I hate the fact that K is called potassium and Na is called sodium. It just makes it all the more confusing
robbert593 potassium was called kalium and sodium was called nadium. This is the reason for the elemental symbols.
Does this guy know everything?
YES!!
Yes he knows everything!! HE IS A SCIENCE GOD/GODDESS.
yep! he is Salman Khan ☺😍😌❤
what is with 👅✌💀👹😎😎
What is the point of the potassium restablishing a positive charge outside for a short time, if sodium/potassium pumps regulate the differences in charge again anyways?
I don't get why it has to balance out the charge before changing sides with sodium again
I am in exactly the same position, if that makes you feel any better. I'm at university in the UK.
Where on the neuron does the electrical potential gradient begin? At the dendrite, soma, or axon? I am just a little confused about whether the gradient is triggered as soon as the signal is passed from the axon terminal to the next dendrite or if the signal builds up at the axon hillock and the gradient actually begins at the axon?
What causes the sodium gate in electronic potential to open?
they open in response to stimulus,which changes the permeability of the membrane..i.e
*voltage,
*chemicals(hormones,neurotransmitters)
*mechanical pressure
*light(photo receptors of the eye)
Just a quick comment about this video....while describing these two processes, my text states definate numbers when it comes to thresholds and opening and closing of gates while you describe them as,"lets say" this and that number. It would be helpful to use the book numbers like....resting state is -70, stimulation occurs at -60 to +30 with a refractory of -80...etc. Unless you, of course, disagree with the numbers I am reading in my text, state the numbers as they are instead of arbitrarily.
is electrotonic potential another term referring to a graded potential?
thkns a lot
No, depends on the time of duration of stimulus. And remember that in diet you gent more Na then K (what means always a bigger conservation of Na outside than inside the cell)
Hey How does the inside of the membrane become positive enough for it to open Na+ channels?
Please don't ever take your videos down.
So is an electrotonic potential the same as a graded potential? In my biology class I learned about a graded potential and it had essentially the same characteristics as what was described with the electrotonic potential (fast, dissipates with distance)
Perhaps it's just me, but i don't really see the huge difference between action potentials and electrotonic potentials?
so only one type of gate should be able to open according to its neighbors or you would have it bouncing between -55 and +40 because of the na+ gates rules...
right?
So for electronic potential no ATP is used?
Could you do a video behind the electrophysics of action potentials? :)
I have a question. If the potassium pump opens at 40mV and stays open till the potential reaches -80mV, it means that it is open for the -80 to 40mV range right?? Then why would it not be open when the Na channel is open, say at the -55mV?? Isn't -55mV in the -80 to 40mV range?? Is it that it needs a 40mV potential to open and then just stays open until the potential gets too low??? Help pleasee...
To say that these videos are good would be an understatement, however as a student they take up too much time. Sal explains a little slow, and that time adds up to huge chunks. Please offer an option to watch in fast view. It is very very very necessary to allow the necessary amount of knowledge to be learned in an available time period so as a student we can be efficient. Thank you.
What is the title of the video previous to this one...
GOOD
Thanks! This is a great video! Maybe you could talk a little bit less quick.
I thought the overshoot/ hyperpolarization is a result of the K+ gate closing slower?
@ecaep86 just use what you have been blessed with and push yourself and you won't desire his brain, because you would have explored the corners of your own.
so i've never heard of elctrotonic potential. we only use graded potential and action potential. is Graded potential an other terminology for Electrotonic potential?
@bisoulula i believe so
Often people talk as though somehow the only diffusion gradients/chemical gradients (they're the same right?) that matter are those of one type of molecule. In this case, there is a higher concentration of sodium outside the membrane. But isn't the tendency to move down a chemical gradient caused by the probability of collisions? If so, why don't we look simply at the concentration of molecules outside the membrane rather than the concentration of sodium outside the membrane?
I love you
@noahnz Diffusion gradients and electrochemical gradients are not the same.
The Sodium's broke through the front gates!!! RUN FOR YOUR LIVES!!!!
I don't understand why the potential becomes positive when the Na+ gates open. I would think the flow of Na+ ions stops at 0 volt. Could you explain that?
The Na+ keeps entering the cell because of its chemical gradient (there' s approximately 5mM/L of Na+ in the cell and 135mM/L outside)
16:36 "...this first DUDE" xD
How it return to -70 from -80 ! 14:32
Sodium Potassium pumps brings it back to -70mV
Na+/K+-Pump has acutally nothing to do with the afterhyperpolarisation and how the cell returns to its resting potential, because its kinetic is too slow to act wihtin milliseconds. Other channels are responsible for that.
doi:10.1038/nrn2148
so where does electrotonic potential happen and why?
Electrotonic potential is the same as a graded potential, yeah?
On action Potential :)