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  • In this video, I want to provide an overview of neuron function,

    在這部影片中,我要給你一個神經元功能的概觀

  • which I think of sort of like how a gun functions.

    我個人覺得這有點像一把槍的運作方式

  • And we'll go into a lot more detail

    而我們會在之後的影片深入瞭解

  • on how a neuron functions in later videos.

    神經元運作的細節

  • But in this video.

    但在這部影片

  • I just want to give a bird's eye overview of it.

    我就只希望給你們一個鳥瞰方式綜觀全局

  • The function of neurons is to process and transmit

    神經元的功能是處理和傳遞

  • information.

    資訊

  • Without input, most neurons have a stable electrical charge

    在沒有訊號輸入時,大多數神經元在它們細胞膜內外

  • difference across their cell membrane,

    維持一個穩定的電荷比例

  • where it's more negative inside the cell membrane

    細胞膜內側的電性是偏負的

  • and more positive outside the cell membrane.

    而膜外是偏正的

  • And we call this the resting membrane potential or just

    我們稱這個為靜止膜電位或簡稱

  • resting potential for short.

    為靜止電位

  • And this resting potential is really

    而這個靜止電位

  • how the neuron is going to be able to be

    在神經元因外在刺激而激發和回應

  • excitable and respond to input.

    扮演了關鍵角色

  • And I think of this as similar to loading

    我個人認為這有點像是

  • a gun by putting a bullet in it.

    將一把槍上膛、裝進子彈

  • Neurons receive excitatory or inhibitory input

    神經元從其他細胞那或者外界的物理性刺激

  • from other cells or from physical stimuli

    接收到興奮型或者抑制型的輸入

  • like odorant molecules in the nose.

    就如我們鼻子裡的氣味分子一樣

  • Input information usually comes in through the dendrites.

    通常經由樹突接收到訊息

  • Although less often, it'll come in through the soma

    偶而還是可能從細胞體或軸突接收到訊息

  • or the axon.

    但很少

  • The information from the inputs is transmitted

    外界輸入的資訊會傳遞

  • through dendrites or the soma to the axon

    經過樹突或者細胞體到軸突

  • with membrane potential changes called graded potentials.

    同時細胞膜電位產生改變,稱作graded potentials

  • These graded potentials are changes

    這些graded potentials是由

  • to the membrane potential away from the resting potential,

    小規模以及短暫的電荷停留產生的

  • which are small in size and brief in duration,

    維持在細胞膜上,規模和膜電位差很多

  • and which travel fairly short distances.

    通常只能傳遞很小一段距離

  • The size and the duration of a graded potential

    graded potential的規模和持續時間

  • is proportional to the size and the duration of the input.

    與輸入資訊的規模和持續時間成正比關係

  • Summation, or an adding together of all the excitatory

    加成,或者把一段時間內所有發生在

  • and inhibitory graded potentials at any moment in time

    trigger zone、軸突初始片段

  • occurs at the trigger zone, the axon initial segment

    的興奮性和抑制性

  • right here.

    graded potential加總起來

  • This summation of graded potentials

    這個 graded potential 的加總機制

  • is the way neurons process information from their inputs.

    是神經元處理輸入資訊的一種方式

  • If the membrane potential at the trigger zone

    如果在trigger zone的膜電位

  • crosses a value called the threshold potential,

    達到所謂的閾值電位時

  • information will then be fired down the axon.

    資訊就會由軸突傳出去

  • So I like to think of this process of summation

    所以我喜歡把這個在trigger zone之

  • of the excitatory and inhibitory graded potentials

    興奮和抑制graded potential加總的過程

  • at the trigger zone as analogous to the trigger of a gun.

    比喻成一把槍的擊發過程

  • In fact, that's why it's called the trigger zone.

    事實上這就是為什麼這被稱作 trigger zone

  • I think of the graded potentials as being

    我把graded potential 看做

  • like the finger on the gun, that may be squeezing

    槍的板機,可能因為擠壓或放鬆

  • a little harder or relaxing.

    而變緊繃或鬆散

  • But once the trigger of the gun is pulled back

    但一旦板機被往後拉

  • past a certain threshold distance,

    到超過一個既定的閾值距離

  • a bullet will be fired down the barrel of the gun,

    槍膛裡的子就會被擊發

  • just like if the membrane potential of the trigger zone

    就跟trigger zone的膜電位

  • crosses a threshold value, information

    超過閾值時,資訊

  • will be fired down the axon.

    就會從軸突擊發出去一般

  • The way information is fired down

    從軸突極發出去的資訊的形式

  • the axon is with a different kind of change

    與膜電位的形式有點不同

  • to the membrane potential called an action potential.

    稱為動作電位

  • An action potential is usually large in size and brief

    動作電位通常規模比較大

  • in duration.

    且持續時間短

  • But it's usually conducted the entire length of the axon,

    但它通常能傳導過整段軸突

  • no matter how long it is, so that it can travel

    且不論軸突有多長,也就是說動作電位在

  • a very long distance, just like a bullet usually

    軸突上可以傳遞很長一段距離,就像子彈通常

  • has no trouble making it down the barrel of the gun.

    不可能連槍管的距離都到達不了一樣

  • And like a bullet traveling through the barrel of a gun,

    且像子彈行經過槍管般

  • action potentials tend to travel very quickly down

    動作電位傾向快速行經

  • the length of the axon.

    整段軸突

  • Action potentials are different than graded potentials

    動作電位與graded potential不同

  • because they're usually the same size and duration

    因為動作電位通常規模和持續時間上

  • for any particular neuron, as opposed

    在任何神經元上都差不多,而與

  • to the graded potentials, whose size and duration

    graded potential相反,graded potential在規模和持續時間上

  • depends on the size and the duration of the inputs.

    都會隨著輸入資訊的規模和持續時間而改變

  • Action potentials are conducted faster along

    動作電位在比較大的軸突

  • larger axons, axons with a larger diameter,

    直徑較粗的軸突中傳遞速度較快

  • and along axons that have a myelin sheath, that I've

    且在附有隨鞘的軸突中亦是如此

  • drawn in yellow here.

    隨鞘我用黃色畫

  • When an action potential reaches the axon terminals

    當動作電位抵達軸突終端

  • at the end of the axon, information

    軸突的底端,資訊

  • will then cross, usually a small gap,

    會跨越一個小的間隙

  • to the target cell of the neuron.

    到達彼岸的目標神經元

  • And the way this happens for most synapses

    在這裡軸突終端藉由釋放出

  • where an axon terminal makes contact with the target cell

    能與目標細胞上受器鍵結的

  • is by release of molecules called neurotransmitters

    神經傳遞物質分子

  • that bind to receptors on the target cell

    與目標細胞接觸

  • and which may change its behavior.

    來改變其行為

  • Neurotransmitter is then removed from the synapse.

    神經傳遞物質之後會從突觸上被移除

  • So it's reset to transmit more information.

    進而清除上次傳遞的資訊以供更多新的資訊傳遞使用

  • And I think of this part as similar to the bullet leaving

    而我認為這部份就像是子彈離開

  • the gun, to hit the target.

    槍枝,擊中目標

  • The input information that was converted

    輸入資訊會被轉換成

  • into the size and the duration of graded potentials

    graded potential的規模和持續時間

  • is then converted into the temporal pattern of firing

    然後轉換成暫時的觸發型態

  • of action potentials down the axon.

    以動作電位的形式由軸突傳遞下去

  • And this information is then converted

    然後這資訊會被轉換成

  • to the amount and the temporal pattern of neurotransmitter

    暫時的神經傳遞物質形式

  • release at the synapse.

    從突觸釋放

  • These steps are how neurons transmit information,

    這些步驟是關於神經元如何

  • often over long distances.

    把資訊長距離地傳送

  • This is the general way that neurons usually function.

    這是神經元運作的基本形式

  • But there are multiple functional types of neurons.

    但是神經元的種類繁多,功能也各不相同

  • So let's take a look at some of those.

    我們來看看其中一些

  • Here I've drawn a few different neurons,

    我在這畫了幾個不同的神經元

  • with their somas in red, their axons in green,

    把細胞體用紅色畫,軸突用綠色

  • and their dendrites in blue.

    樹突用藍色

  • And I've drawn a line here to separate

    我畫一條線在這做區隔

  • between the central nervous system on this side--

    中樞神經系統在這側

  • so I'll just write CNS for short--

    簡寫CNS

  • and the peripheral nervous system on this side--

    周圍神經系統在另一側

  • so I'll just write PNS for short.

    簡寫PNS

  • And there's some different ways we

    且有一些不同的方法我們能用來

  • can categorize functional types of neurons.

    幫不同功能的神經元做分類

  • The first way is the direction of information flow

    第一個是它們在CNS和PNS之間的

  • between the CNS and the PNS.

    資訊流動方向

  • If a neuron like this pseudounipolar neuron

    如果有一個神經元像這個偽單極神經元

  • right here brings information from the periphery

    在這把資訊從周圍擷取

  • in toward the central nervous system,

    傳遞進入中樞神經系統

  • we call that an afferent neuron.

    的話我們稱之為傳入神經元

  • Afferent, meaning it's bringing information

    Afferent 意指把資訊

  • into the central nervous system.

    傳進中樞神經系統

  • We can also call this type of neuron

    我們也稱這類型的神經元

  • a sensory neuron because the information

    一個感覺神經元,因為它把

  • it's bringing into the central nervous system

    資訊帶入中樞神經系統

  • involves information about a stimulus.

    牽涉到資訊包括刺激來源訊號

  • And a stimulus is anything that can

    一個刺激源訊號是可以

  • be sensed in the internal or external environment, which

    在內部或外部環境中被感知的

  • is to say anything inside the body

    也就是說體內

  • or anything outside the body.

    或體外任何的訊息都是如此

  • These neurons are carrying information away

    這些神經元將這些資訊

  • from the central nervous system out into the periphery.

    從中樞神經系統往周圍神經系統傳遞

  • So instead of calling them afferent neurons,

    所以不叫做傳入神經元

  • we call them efferent neurons.

    而叫做傳出神經元

  • And there are two main kinds of efferent neurons.

    而主要有兩種傳出神經元

  • The first we call motor neurons.

    第一個叫做運動神經元

  • Motor, which means movement.

    運動代表著動作

  • These are efferent neurons that control skeletal muscle,

    這些是控制骨骼肌肉的傳出神經元

  • the main type of muscle that's attached

    是骨骼上附著的主要

  • to our skeleton, that moves us around.

    肌肉種類,讓我們得以行動

  • These motor neurons are also called somatomotor neurons

    這些運動神經元也稱作體運動神經元

  • or neurons of the somatic nervous system.

    或者為體神經系統

  • The other type of the efferent neurons

    另一種傳出神經元

  • are called autonomic neurons.

    叫做自主神經元

  • And these neurons control smooth muscle,

    這些是來控制平滑肌的

  • like the muscle around our blood vessels;

    像是附著在我們血管周圍的肌肉

  • cardiac muscle, the muscle of our heart; and gland cells,

    心臟肌肉,和腺體細胞

  • the cells of our glands that secrete hormones

    在腺體處釋放賀爾蒙進入血流

  • into the bloodstream.

    的那些細胞

  • These autonomic neurons are also called visceromotor neurons

    這些自主神經元叫做內臟運動神經元

  • or neurons of the autonomic nervous system.

    或者自主神經系統神經元

  • Most neurons of the central nervous system

    大多數的中樞神經系統神經元

  • aren't any of these types of neurons, however.

    都不是這些類型中的其中一種,然而

  • They're like this neuron, in that they

    它們像是這種神經元,這樣

  • connect other neurons together.

    與其他神經元連結在一起

  • So these are called interneurons,

    所以這些叫做中間神經元

  • neurons between neurons.

    就是連結神經元與神經元之間的那個

  • And there are many interneurons in the central nervous system,

    而在中樞神經系統中有許多中間神經元

  • forming very complex pathways for information to travel.

    形成非常複雜的訊息傳遞路徑

  • So that while an individual neuron

    所以當個別的神經元

  • is processing and transmitting information,

    處理並傳遞資訊時

  • these complex networks of neurons

    這些中樞神經系統中

  • in the central nervous system are

    有著複雜網絡的神經元們

  • doing even more complex processing

    正做著更複雜的處理

  • and transmitting of information.

    並解傳遞資訊

In this video, I want to provide an overview of neuron function,

在這部影片中,我要給你一個神經元功能的概觀

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