5.2 Ion channels and membrane potentials II

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来自 Peking University 的课程

Advanced Neurobiology I

248 个评分

Peking University

Advanced Neurobiology I

248 个评分

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!

从本节课中

Signaling within neurons & Ion channels and membrane potentials

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

5.1 Ion channels and membrane potentials I15:03

5.2 Ion channels and membrane potentials II5:58

5.3 Ion channels and membrane potentials III10:54

5.4 Ion channels and membrane potentials IV6:23

5.5 Ion channels and membrane potentials V10:36

5.6 Ion channels and membrane potentials VI10:02

5.7 Ion channels and membrane potentials VII15:17

5.8 Ion channels and membrane potentials VIII14:28

与讲师见面

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

And so how can Huxley,

Understand the mechanism

of action potential?

In fact, there are at least technical breakthroughs and

imaginative usage of various special samples, and

there are insights in understanding the circuit issue.

So they were using the squid giant axon.

This axon is a huge cell that allow them to manipulate and

record the voltage and current across

the squid membrane, it's a nerve cell.

And this illustrates their setup, okay?

So they were using the so-called voltage clamp invented by Casey Clamp.

So voltage clamp was not invented by Hodgkin-Huxley, but

by an American scientist.

So what I do here is that you can

put the electrode into the squid, okay?

And what it actually to measure the current, and

one is actual is to deliver, sorry,

one is actually to measure voltage inside of the cell,

and one is actually is to deliver the current.

And what you can do is you can put external

command voltage into this amplifier.

So this electrical circuit, whenever you have a command voltage and

if there is a difference between the voltage

inside of the cell and this command voltage,

then this amplifier is going to generate current

into this axon to make sure that this voltage

here will follow the command voltage.

So this is so called voltage clamp, that is, you can artificially through feedback

system to inject the currents to keep the cell's membrane potentially constant.

That's the reason it's called voltage clamp, okay?

So in this experiment, they can

control the voltage across the membrane.

And therefore, they can study how the different ion channel or

the conductance, is regulated as

a function of voltage difference, as a function of time.

So this is one of their experiments in 1950s,

that reported in 1952, okay?

So here is one of the experiment.

And then I hoped you guys can travel with me, time travels back

into the early 1950s to understand how those things are working, okay?

So on the top is the voltage clamp, that is,

they used their circuitry to control

voltage across the squid axon membrane.

So at the beginning, the intracellular membrane potential is -50 millivolt, okay?

And then through voltage clamp,

they can control a membrane potential

jumping to plus 15 millivolt, okay?

So what will happen in the membrane?

You have a voltage step.

This initially minus, so

this is a positive membrane potential that you apply.

Initially, it is -50 millivolt and

then go to plus 15 millivolt, for example.

And this is a cell or a squid membrane.

If the squid membrane does not have any active component,

the active component will be those specific battery or specific ion channel.

What will be the response of the current?

So let me just rephrase the discussion.

We already have a piece of membrane, a biological membrane,

and then we can artificially apply a membrane potential

that is following initially -50 millivolt.

Put it a little bit longer.

And then jump into plus 15.

What will be the current?

Or what will be the waveform of the current looks like?

If you have the electrode like Hodgkin-Huxley does,

you have one measure of voltage and the other one to deliver the current, okay?

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