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