4.2 The resting potential

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En provenance du cours de Peking University

Advanced Neurobiology I

241 notes

Peking University

Advanced Neurobiology I

241 notes

Hello everyone! Welcome to advanced neurobiology! Neuroscience is a wonderful branch of science on how our brain perceives the external world, how our brain thinks, how our brain responds to the outside of the world, and how during disease or aging the neuronal connections deteriorate. We’re trying to understand the molecular, cellular nature and the circuitry arrangement of how nervous system works. Through this course, you'll have a comprehensive understanding of basic neuroanatomy, electral signal transduction, movement and several diseases in the nervous system. This advanced neurobiology course is composed of 2 parts (Advanced neurobiology I and Advanced neurobiology II, and the latter will be online later). They are related to each other on the content but separate on scoring and certification, so you can choose either or both. It’s recommended that you take them sequentially and it’s great if you’ve already acquired a basic understanding of biology. Thank you for joining us!

À partir de la leçon

Signaling within neurons & Ion channels and membrane potentials

Let's switch to the electrical properties of the neuron.

4.1 Overview9:36

4.2 The resting potential13:33

4.3 The resting potential and the Nernst equation13:39

4.4 The Nernst Equation11:57

4.5 Biological and electrical proporties of neurons I15:04

4.6 Biological and electrical proporties of neurons II4:44

4.7 Biological and electrical proporties of neurons III.18:30

Rencontrer les enseignants

Yan Zhang
Professor
School of Life Sciences, Peking University
Yulong Li
Research Fellow
School of Life Sciences, Peking University

All right, let's start with a cell, okay?

We have a way, using an amplifier, to amplify small

voltage signals to record those cell membrane potentials.

And then we generate this apparatus that

through this fine electrical or

class electrical we can insert into a cell to measure a cell's electrical property.

For example, if the electrical is fine enough that

you can insert into the cell without disrupting

cell's property, and we can measure the voltage from the cell.

Magically, when you measure that,

the voltage is frequently -80 mV, or -70 mV.

In fact, historically people have done that and

then imagine, they call it a funny name.

Okay, they call it a funny name as angel potential.

Okay, as if [FOREIGN] They got not human potential.

They don't understand why this is such an active membrane potential to the cell.

They some how injure this cell and then you get a potential so

they call you injured potential.

And interestingly the most skillful people trying to

make this recording a subsequent found.

If you put in more fine tips most likely will not

injure the cell that you got more negative okay?

Close to -18 [INAUDIBLE] if you make a pretty big [INAUDIBLE] okay.

Then sometimes the membrane potential would be -40 millivolt.

People doesn't understand why there's such a membrane potential, okay?

Well, since we have in the modern days we have some physics background, right?

Then when you have a different member potential, in this case,

we count the internal side of the cell, zero which is a ground.

And so you get a ground, okay?

Inside, it's a -18 meter roll.

That indicates that there must be a charter separation, okay?.

There's more negatively charge inside the cell comparing

with outside the cell, okay?

So why this is the case?

Why the opia negatively charge inside the cells, okay.

This actually is because of the different

concentration of the ions in the interior.

Was the outerior of the cell, okay.

we have a different iron concentration irons

having the different amount of charge, and

then they will have different charges separation okay.

So for example, what is the charge of potassium?

Plus one.

The charge for a potassium ion will be plus one.

What will be the charge of?

Class one. >> Class one.

>> Minus one.

>> Minus one, right, chloride.

Right?

And what is the charge of calcium ion?

>> Class two.

>> Class two, okay.

So If one people measuring

those different ions and their concentration for a typical self.

You can see that the chart

ends the concentration is different.

Okay, an active charged chloride, positive charged potassium but for a typical cell.

Usually what you'll find is that the inside of

the cell has a higher concentration of potassium,

lower concentration of a sodium, okay.

And outside of the cell has a higher concentration of sodium,

lower concentration of potassium, okay?

But does that sufficient to its brain?

The, a lot of, memory potential that you record.

Okay, why the memory potential -80 millivolts rather than -40?

Okay what determines the [INAUDIBLE] member potential

meaning that there's no such a action potential

generation it just possibly recall the cell.

What determines it is determine by sodium, potassium chloride

or, maybe there some additional ions, and then they have different distribution.

Maybe the will determine the memory potential and

the resting memory potential.

What is the quantitive relationship between the ionic

concentration and the memory potential, okay.

Let's, what do you guys think, okay?

First let me just ask, looking at this image is chloride

determine the memory potential, chloride.

Okay, because outside the cell, there's a lower concentration of chloride.

Outside of the cell there's more concentration of chloride.

If chloride Is the determinant of the membrane potential.

That the membrane potential will be what?

Will be positive, right?

Will not be negative, okay?

Right?

Okay?

Then we can think about the sensing for

sodium and potassium.

Let's just do one-by-one.

If sodium is the main determinant of the memory potential.

Will the memory potential be minus 18?

See, sodium has a less concentration positive.

Less positive concentration inside.

Outside it's higher.

So at least the the sign is consistent with the membrane potential.

Low inside, right?

How about potassium?

How about potassium?

So likewise, potassium has a higher concentration inside, right?

And lower concentration outside in potassium determines here.

Do the synthesis interface, no.

Okay as you guys will see since my [INAUDIBLE] I'm expected okay.

So The story starts from 1990s-ish.

Bernstein, a great German scientist,

he proposed that excitable cells are,

they are resting membrane potential,

are determined by the potassium concentration, okay.

Big surprise, okay.

And he even proposed the mechanism

of action potential, okay, as we will discuss in detail later.

He said the action potential how you generate because in the 19th century,

people can already use the electro physiology recording outside of the cell.

It's called external recording to detect the generation of action potential.

And then That he proposed that dealing the action potentials,

this selectivity for potassium get transiently lost.

And he membrane are permeable to other ions.

So he proposed that how to the action potential is generated is,

in a resting condition is permeable to potassium and

during action potential somehow the membrane breakdown.

And then all eyes can freely pass in that case

the membrane potential will be 0 medieval.

As we also discussed, and this is the mechanism of action potential, okay?

He might not be right of the total membrane breakdown in this case but

at least, he's correct in the sense that he proposed

that [INAUDIBLE] determines the [INAUDIBLE] of a potential okay.

So how do we do that is [INAUDIBLE] to demonstrate

rather the potassium is a important determinate of memory potential.

Well, you can do the experiment, okay start with our sort experiment.

If you have a very skilled head, and you can recall your cell,

okay and what you can do is since you want to test

potassium determines the membrane potential.

All you can do is to disrupt or

altering the potassium concentration, right?

And then you match it what has

changed of the memory potential.

So in this case, if we do that spot experiment,

we into the cellular memory potential.

And then superfusion, or

changing the internal ionic concentration, you first change the sodium.

And then we thought that it doesn't matter what concentration of the sodium we use.

That's essentially not too much a difference

of the membrane potential, okay?

So you say, maybe I don't know the reason but

if I change in the sodium, the membrane potential does not change.

So it's unlikely as it is the outside sodium concentration

will control or will determine the memory potential.

But if you do so for example within a cell,

if the cell is long leaf cell, right.

Very skillful the cell that goes through all the tortures that you have

to change the solution It's still there, okay?

Then you change the potassium concentration, and what do you find?

Ha, ha!

If you change the potassium concentration,

actually the memory potential recall changes.

Okay?

If you are not so

skillful, well you can recall at least two cell looks identical, right?

You choose two sister cells, okay?

Or you choose a group of cells.

You do 10 cells with 1, condition and you do 10 cells with other conditions and

that can give you a simple of what's going on for the group cells, okay?

And then [INAUDIBLE] when you generate host that will you change

in the potassium will auto [INAUDIBLE]

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