the neuron resting membrane potential, which we often

神經元的靜止膜電位

just call the resting potential for short.

也就我們常簡稱的靜止電位

So first, let me just draw a neuron that'll

所以一開始，讓我先畫一個神經元細胞示意圖

be a little distorted, just so I have room to draw.

也許比例不對，但這樣才有空間畫

So we'll draw this soma here and a really big axon coming out

我先畫細胞體和一個大的軸突從細胞體

of the soma-- and normally an axon

延伸出來，一般來說軸突

is a thin, long process coming out of the soma,

是薄、長的細胞延伸自細胞本體

but I just need a little room to draw.

但我就只有這點空間畫

So I'll draw a big, thick one.

所以我會畫的大又粗

And this will be the other part of the soma, or the cell body.

而這會是另一部分的細胞體或者稱為細胞本體

And then I'll just draw one really big dendrite.

我會畫一個很大的樹突

And like the axon, of course, these

跟軸突一樣

are normally just these little thin processes coming out

實際上是細細的分支自

of the soma.

細胞體延伸出來

But I just need some space.

但我需要一點空間

So most neurons at rest, meaning when they're not

大部分的神經元在休息的意思就是它們

receiving any input, have a stable separation

並沒有收到任何的資訊，細胞膜內外的

of charges across the cell membrane called

電荷分布、電位差穩定

the resting potential.

所以稱為靜止電位

And that consists of more positive charges in a layer

而正電荷在細胞膜外側比較多

on the outside of the membrane, and more negative charges

膜內則是負電荷

in the layer along the inside of the membrane.

比較多

And these charges are ions.

這些電荷都是離子

So the negatively charged ions that

帶負電荷的離子

are in a layer along the inside of the membrane we also

位在膜內

call anions.

也稱作陰離子

And the positively charged ions in a layer

而帶正電的離子在

on the outside of the membrane we call cations.

膜外層稱作陽離子

And this layer of anions on the inside

神經元細胞膜各處

and cations on the outside goes all over the neuron cell

都是呈現陽離子分布在膜外

membrane.

陰離子在膜內的架構

All through the membrane of the dendrite,

從樹突

and the soma, and all along the membrane of the axon.

胞體到軸突都是如此

And just to be clear, there is a mix

而要澄清一點，細胞膜內外

of anions and cations on both sides of the membrane.

都含有陰、陽離子

And I've just drawn plus signs on the outside of the membrane

我在膜外標上十字記號

to represent that in the layer against the outside

來表示膜外環境帶正電

of the membrane, there are more cations and anions.

就是說膜外的陽離子多過陰離子

And I have drawn negative signs on the inside of the membrane

而我將膜內標記了減號

to represent that in that layer, there

表示負離子較多

are more anions than cations.

帶負電

And talk about the size of the difference in the separation

來看這些電荷規模

of charges, the convention is to call the outside zero.

傳統上稱膜外電位為零

So we just say the outside is zero,

我們直稱外面為零

and we just kind of set that as the reference.

將膜外當參考電位

And then we just refer to a single number

如此一來

on the inside of the membrane, which

就只有膜內電位有值

is the difference between the voltage on the outside

表示內外膜電位差值

and the inside, or the difference in the strength

或稱膜內外電位差的

of the charge separation.

位勢能

And this difference can vary between neurons,

這個電位差在神經元之間可能有點差異

but around negative 60 millivolts

大差不多在約負六十毫伏特

would be a really common resting potential for a neuron.

這是最普遍的神經元靜止電位

So I'll just write a little m and a big V for millivolts.

我會用mV表示毫伏特

That's the value we use to quantify

這是我們用來量化

this difference in charge separation.

電荷間電位差的數值

And around negative 60 would be a really common

可以發現幾乎所有神經元

resting membrane potential for a neuron.

的靜止電位都在約負六十毫伏特

The resting potential of neurons is

神經元的靜止電位代表

related to concentration differences, which are also

膜內外離子濃度差

called gradients, of many ions across the cell membrane.

也叫做離子濃度梯度

So there's lots of different ions

所以在細胞內外

that have high concentrations outside the neuron compared

含有許多不同的離子

to lower concentrations inside the neuron, or vice versa.

內外離子濃度隨著狀態變化而有時內大外小，有時相反

But a few of these ions are the most important

但是有少數的離子在神經元的運作上

for neuron function.

扮演著很重要的角色

The cations, or the positive charged ions that are most

陽離子或者帶正電的離子在神經元運作中

important for neuron function are potassium--

最重要的是鉀離子

and I'll just write that as a K+, sodium,

我寫成 K+ ，而鈉離子

which I'll write as an Na+, and calcium,

寫成 Na+，而鈣離子

which I'll write as a Ca2+.

寫成Ca2+

Because each calcium ion has two positive charges.

標記2的意思是因為每個鈣離子帶有兩個正電荷

And the most important anions for neuron function,

而神經元運作中最重要的陰離子

or negatively charged ions, are chloride,

或者為帶負電荷的離子是氯離子

which I'll write as Cl-, and then there are multiple organic

寫成Cl-，其次是許多個有機

anions.

陰離子

And so I'll just write OA- to stand for organic anions.

我會直接寫成OA-代表有機陰離子

And there a bunch of different organic

而在神經元和其他種細胞內

anions inside neurons and other cells.

都有許多種不同的有機陰離子

Most of these are proteins that carry a net negative charge.

大多數為帶有負電荷的蛋白質

Now, these five kinds of ions are

這類的五種離子分別

going to have concentration differences across the cell

在細胞膜內外有不同的濃度

membranes, which we also call concentration gradients.

也稱之為濃度梯度

And it's different for the different ions

而若它們在神經元細胞膜內外的

if they have a higher concentration

離子濃度不相等時造成濃度梯度出現

inside or outside the neuron.

且不同種離子有不同的濃度梯度

The organic anions and the potassium ions

有機陰離子和鉀離子

have a higher concentration inside the neuron than outside.

在神經元細胞內的濃度比外面高

So I'll just represent that by having these letters written

所以我就在細胞膜內側

large inside the neuron.

寫上比較大的標記

And then I'll write a small OA- to show

我會在細胞膜外寫上比較小的OA-來表示

that there's a smaller concentration of organic anions

有機陰離子在細胞膜外的濃度

outside the neuron than inside.

比較小

And the same for potassium.

鉀離子也一樣

I'll write a small K+ outside the neuron compared to a large

膜外的K+比較小

K+ inside, because the concentration of potassium is

膜內的比較大，因為其在神經元細胞膜內的濃度

higher inside the neuron that outside the neuron.

比較高

And the opposite is true for these other three ions.

而其他的三種離子

So the concentration of sodium is much higher

狀況正好相反

outside the neuron than inside the neuron,

所以鉀離子在內側標記比較小

as is the concentration of calcium.

外側比較大，鈣離子也是一樣

There's much more calcium outside the neuron than inside.

鈣離子在膜外的數量比膜內多

And the concentration of chloride ions

氯離子也

is also much higher outside the neuron than inside the neuron.

在神經元細胞膜外濃度比內要高

Each of these ions, therefore, is

因此每一種離子

going to be acted on by two forces that

都受到兩種力量驅動

try to drive them into or out of the neuron.

進出神經元內外

The first is an electrical force from the membrane potential.

第一個是細胞膜電位造成的電力

Because each ion will be attracted

因為每個離子都被

to the side of the membrane with the opposite charge,

膜的另一邊的相反電荷

opposite charges attract each other and like charges

吸引著，或相同電荷

repel each other.

排斥著

So if we look at each of these ions in turn,

我們來一一看這些離子

the organic anions are negatively charged,

有機陰離子帶負電荷

so they will be attracted to the outside of the neuron

所以它們會被神經元細胞膜外濃度高的正電荷

where there are more positive charges.

給吸引

So the electrical force acting on the organic anions

所以施加在有機陰離子上的的電力

will try to drive them out of the neuron.

驅使它們流出神經元

Potassium is the opposite.

鉀離子則相反

It's positively charged.

它帶正電荷

So it will be attracted to the inside of the membrane

所以它會被膜內較多的

where it's more negative.

負電荷

So it's electrical force will try

給吸引驅使其

to drive it into the neuron.

往神經元內部移動

Sodium is the same as potassium.

鈉離子和鉀離子一樣

It's positively charged, so it will

都帶正電

be attracted to the more negative inside of the neuron.

會被膜內帶有較多的負電荷給吸引

Chloride is an anion like the organic anions,

氯離子和有機陰離子一樣

so its electrical force will try to drive it out of the neuron.

所以它是被電力驅使流出神經元的

Calcium is a cation like potassium and sodium,

鈣離子則是和鉀、鈉離子一樣

so it's electrical force will also

所以受到電力驅使

try to drive it into the neuron.

像神經元內部流動

But now the second force acting on these ions

第二個作用在這些離子上的力量

can be thought of as a diffusion force,

是擴散力

or it's often called a chemical force, related

或者叫做化學驅力

to the concentration gradients across the neuron membrane.

與神經元內外離子濃度梯度有關

Because particles in solution will always

這是由於溶液中的粒子總是

try to move from an area of higher concentration

會從濃度高的區域

to an area of lower concentration.

往濃度低的區域流動

So if we look at the organic anions,

我們來看有機陰離子

they're in a higher concentration

它們在膜內濃度

inside the neuron than outside.

比膜外高

So their diffusion force will be trying to drive them out

所以其所受之擴散力為由神經元內部

of the neuron, just like their electrical force is.

往外移動，就跟它們所受之電力驅動方向一樣

Now, potassium is a little confused.

現在，討論鉀離子這個有點複雜的狀況

Its electrical force is trying to drive it into the neuron,

它所受的電力試圖驅使其進入神經元

but it has a higher concentration

但是它卻在神經元內部有

inside the neuron.

比較高的濃度分布

So it's diffusion force is actually

所以其所受之擴散力事實上

trying to drive it out of the neuron.

是將其驅離往神經元外部的

Sodium has matched electrical and diffusion forces,

鈉離子受的電力和擴散力是一致的

because it has a higher concentration

因為其在神經員外的濃度

outside the neuron than inside.

比較高

Chloride's electrical force is trying

氯離子受之電力試圖

to drive it out of the neuron.

將其驅離出神晶圓

But because it has a higher concentration

但由於它在神經元外部

outside the neuron, it's diffusion force

的濃度比較高，所以它所受的擴散力

will be trying to drive it into the neuron.

是驅使其進入神經元的

And calcium is just like sodium.

然後鈣離子和鈉離子的情形一樣

Both its electrical and its diffusion force

兩者所受的電力和擴散力

are trying to drive calcium into the neuron.

都驅使它們進入神經元

These forces we often call electrochemical driving forces

這些力我們通常

for short.

簡稱為電化學驅力

And neurons are going to use these forces to perform

而神經元們則利用這些驅力來執行

their functions.

它們的功能

But before we talk about that, in the next video,

在進入下一部影片之前

let's talk about how the resting membrane potential is created

我們要談論關於靜止膜電位是如何產生的

and how it's related to the concentration

以及與某些關鍵的離子的膜內外

differences of some of these key ions.

濃度差又有什麼樣的關係