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  • In this video, I want to describe

    這部影片中,我要來談談

  • 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

In this video, I want to describe

這部影片中,我要來談談

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B2 中高級 中文 美國腔 離子 神經元 濃度 細胞膜 電荷 電力

神經元靜息電位描述 (Neuron resting potential description)

  • 117 15
    Alvin He   發佈於 2021 年 01 月 14 日
影片單字