your brain gets all the props.

你的大腦總是成為焦點。

And it deserves those props! It’s a complicated, and crucial, and sometimes crazy boss of an organ.

且它實至名歸！它是個既複雜且重要，有時候甚至是扮演瘋狂上司的一個器官。

But your brain would be pretty useless without a support team that kept it

雖然如此，你的大腦若是沒有一組支持小組

connected to the outside world.

幫助它與外界聯絡，也是英雄無用武之地而已。

Because frankly, like any leader, the more isolated your brain gets, the weirder it gets.

因為說實話，像任何領導者一樣，你的大腦越封閉，它就變得越奇怪。

Put a person in a watery, pitch-black sensory deprivation tank, and you’ll see the brain

把一個人關進一間充滿水，漆黑的、剝奪光線的水槽，你將會看見大腦

do some really weird stuff. Without a constant flood of external information, the brain starts

開始做一些奇怪的事。停止接收來自外界不斷湧入的訊息後一段時間後，大腦

to confuse its own thoughts for actual experiences, leading you to hallucinate the taste of cheeseburgers,

開始因為自身產生的想法和現實的經驗之間的差異而感到困惑，造成你產生幻覺像是嘗到起司漢堡

or the sound of a choir singing, or the sight of pink stampeding elephants.

或聽到合唱團唱歌的聲音，或者是看見一支粉紅大象慌張奔走的影像。

It’s your peripheral nervous system that keeps things real, by putting your brain in

這是你的周圍神經系統使事情感受為真，連結你的大腦

touch with the physical environment around you, and allowing it to respond. This network snakes

和外界物理環境周遭的接觸，且得以做出回應。這個網絡

through just about every part of your body, providing the central nervous system with

像蛇一般穿梭在幾乎身體的每個部分，提供中樞神經系統從溫度

information ranging from the temperature, to the touch of a hand on your shoulder, to a twisted ankle.

到有人把手放在你的肩膀，到扭傷腳踝等等資訊。

The peripheral nervous system’s sensory nerve receptors spy on the world for the central

周圍神經系統的感覺神經受器像個間諜般替中樞神經系統

nervous system, and each type responds to different kinds of stimuli.

監控著這個世界，並且各種不同的類型各司其職。

Thermoreceptors respond to changes in temperature. photoreceptors react to light, chemoreceptors

熱覺受器偵測溫度變化、光受器感測光線強弱，化學受器測量

pay attention to chemicals, and mechanoreceptors respond to pressure, touch, and vibration.

化學物質，而機械應力受器則對壓力、觸碰，和震動做出反應。

And then we’ve got specialized nerve receptors called nociceptors that, unlike those other

而特化神經受器，痛覺受器，不像其他受器，

receptors, fire only to indicate pain, which is the main thing I want to talk about today.

專責痛覺，也是我們今天討論主題的重點。

Because, as unpleasant as a stick in the eye or tack in the foot may be, pain is actually

因為，就如眼中刺、腳底針般的令人不悅，痛覺，

a great example of where everything we’ve talked about over the last few weeks all comes together,

其實是我們這幾週課程內容整合起來後最好的一個例子。

as we trace a pain signal through your nervous system, from the first cuss to the Hello Kitty band aid.

當我們在神經系統中追蹤痛覺訊號，從第一次詛咒到凱蒂貓繃帶。

By the end of this episode of Crash Course Anatomy & Physiology you’ll never think

等到了這節"速成課程：解剖與生理學"尾聲的時候，從此你會對

of a stubbed toe, pounding headache, or burned tongue the same way again.

被螫到腳的時候、頭痛愈烈時或者燙到舌頭這些事情有全新的看法。

Most people go to great lengths to avoid pain, but really, it’s an incredibly useful sensation,

大部分的人用盡辦法避免疼痛，但其實，這是一個極有用的感官，

because it helps protect us from ourselves, and from the outside world.

因為它幫助我們保護自己，不致受自己與外界的傷害。

If you’re feeling physical pain, it probably means that your body is under stress, damaged,

如果你感到身體的疼痛，可能是由於受到壓力、損傷或

or in danger, and your nervous system is sending a cease and desist signal to stop twisting

處於危險當中，你的神經系統正給出一個訊號告訴你該停止去

your arm like that, or to back away from that bonfire, or please seek medical attention, like, RIGHT NOW.

過度扭轉你的手臂，或是遠裡那熊熊營火，或者立即去尋求醫療協助。

So in that way, pain is actually good for you -- that’s why it exists. I’m not saying

所以以這個方面而言，疼痛其實對你益處，也是它為何存在。並不是說，

it’s pleasant, but if you’ve ever wished for an X-Men-like power to be impervious to

它是另人愉悅的，但如果你曾經希望擁有X戰警的超能力，而能夠

pain, I’ve gotta say, that is one foolish monkey’s paw of a wish.

免於受疼痛，我需要說，那就只是個愚蠢的心願罷了。

Just ask Ashlyn Blocker. She’s got a genetic mutation that’s given her a total insensitivity

就只要問艾許琳‧布拉克。她因為具有一組基因突變，所以她完全感受不到

to any kind of pain. And as a result, she’s absent-mindedly dunked her hands in pots of

任何的疼痛。結果就是，她把手放進了滾燙的熱水裡面

boiling water, run around for days without noticing broken bones, and nearly chewed off her own tongue.

骨折卻不知道還趴趴走了好多天，還幾乎差點把自己的舌頭給咬了下來。

Luckily, such congenital conditions are very rare. The rest of us have a whole nervous

幸好，這種先天性的狀況非常罕見。撇開罕見狀況不談，我們都有完整的

system dedicated to making sure our bodies react with a predictable chain of events at the first sign of damage.

神經系統盡責地去確定我們的身體對於外界危險的第一個徵兆做出一連串預測，然後回應

Like say you just wake up and you’re extraordinarily hungry for some reason, so you run downstairs

就像你剛起床因為某些原因感覺到超級餓，你就跑下樓

to grab some clam chowder, but you didn’t put any shoes on and suddenly you’re like, “YOWW!”

去喝一些蛤蜊巧達湯，但你並沒有穿鞋，而突然間感到，"哇！"

There’s a tack, fell out of the wall, and you stepped right on it -- of course.

有個圖釘耶，從牆上掉下來的，而你正踩在上頭 -- 當然。

Your foot immediately lifts off the ground, and then you’re assuring your dog that you’re

你的腳立刻就抬起，離開地面，之後你確認你躲開了，而也不是針對

not yelling at her, you’re just yelling, and then you limp over to the couch, and sit

對她失控大吼，你就只是想大叫罷了，然後就靠在椅子上，坐下

down, and you pull up your foot, and remove that spiny devil from your flesh.

你拉起你的腳，把帶刺的惡魔從你的肉中拔除。

You want to talk physiology? So what exactly just happened in your body?

你想要知道其中的生理學？到底這段時間你的身體經歷了些什麼？

Well, the first step was a change in your environment -- that is, a stimulus that activated

嗯哼，第一步就是環境中的改變，也就是說，一個刺激

some of your sensory receptors.

你感覺受器的改變出現。

In this case, it was a change from the probably completely ignored feeling of bare skin on

在這個例子中，大概就是從完全忽略掉自己赤腳踩在平滑的地板上，

a smooth floor to a distinct feeling of discomfort -- the sharp metal tack piercing your skin.

轉變到一股部舒服的感受 -- 尖銳的金屬至圖釘刺穿你的皮膚。

Your peripheral nervous system’s mechano- and nociceptors provided that base sensation,

你的周圍神經系統的機械應力受器和痛覺受器提供了基礎的感官

or awareness that something had changed.

或者是對於某種變化的覺知。

Then it went to your central nervous system -- first to the spinal cord that caused the

而那個覺知走到中樞神經系統 -- 首先到達了脊髓觸發了

immediate reflexive action of pulling up your foot, and then your brain eventually interpreted that

立即的反射動作拉起你的腳，然後你的大腦終於了解

awareness into the perception of pain, and decided to pull the tack out and probably say an expletive or two.

因疼痛而生的警覺，而決定要把腳抽開，順帶一兩句髒話。

Pain itself is a pretty subjective feeling, but the fact is, we all have the same pain threshold.

痛覺是相當主觀的感受，但事實上，我們對痛覺都有相同的閾值。

That is, the point where a stimulus is intense enough to trigger action potentials in those

也就是說，每個人身體內的痛覺受器在受到刺激而引發動作電位

nociceptors is the same for everybody. But, you and I might have different tolerances for discomfort.

所需要的強度是相同的。但，每個人對於痛覺的耐受程度卻不一。

In general, most doctors think of pain as the perception of pain -- whatever any given brain says pain is.

一般而言，大部分的醫生覺得痛覺就是對疼痛的認知與否 -- 不論大腦說有多痛。

So, you’ve got the stimulating event -- foot meets tack -- and then the reception of that

所以，你有了刺激事件 -- 腳踩圖釘 -- 當你腳上的痛覺受器感受到那刺激

signal, as the nociceptors in your foot sense that stimulus, and then the transmission of

訊號接收到並透過你的神經傳遞

that signal through your nerves to your spinal cord and eventually up to the brain.

到你的脊髓，最終傳至大腦。

Now remember back how every neuron in your body has a membrane that keeps positive and negative

現在要學習你體內神經元是如何以細胞膜分隔正、負電荷與兩側

charges separated across its boundaries, like a battery sitting around waiting for something to happen?

像個電池般等待某事發生一般？

Well that tack in your flesh is that something. And it snaps those nociceptors to attention.

你踩到圖釘就是那個事件。而它引起那些痛覺受器的注意。

Some neurons have mechanically-gated receptors that respond to a stretch in their membranes

某些神經元有機械性門控受器對其細胞膜受到拉伸時做出反應

-- in this case, that happens when the tack punches through them.

-- 在這個例子當中，當它們被圖釘扎到時就產生反應。

Meanwhile, other neurons have ligand-gated receptors that open when the damaged skin

同時，其他的神經元有著配體性門控受器會對受傷的皮膚組織

tissue releases chemicals like histamine or potassium ions.

所釋出的組織胺或鉀離子做出反應。

These channels allow sodium ions to flood into the neuron, causing a graded potential,

這些通道讓那離子得以湧進神經元內，形成階梯電位，

if that hits the right threshold, it activates the electrical event that sends the signal

如果這個電位達到正確閾值，就會激發電流的活動傳遞出訊號

all the way up the axon and gets one neuron talking to another -- the action potential.

一直到軸突端與另一個神經元做訊息傳遞溝通 -- 即動作電位。

When that action potential races down the length of its axon to the terminal, the message

當動作電位一路衝刺到軸突的末端，訊息

hits the synapse that then flings it over that synaptic gap to another neuron that’s in your spinal cord.

到達突觸且被拋擲過突觸間隙到彼端的另一個在你脊髓內的神經元上。

Remember, signals travel between neurons either by electrical or chemical synapses.

記住，訊號在神經元經的傳遞機制不是透過電的就是化學的突觸來傳遞。

The electrical ones send an electrical impulse, while the chemical ones -- the ones I’m

電突觸發出電脈衝，而化學突觸則 -- 現在要討論的

talking about now -- first convert that signal from electrical to chemical, by activating

-- 首先轉換訊號從電至化學性的，

neurotransmitters to bridge the synaptic gap, before the receiving neuron converts that

在接受訊號的神經元把訊號從化學性的

chemical signal back into an electrical one.

轉換回電性的之前，透過神經傳導物質來橋接突觸間隙

In this case, news of the tack-attack is carried by specific neurotransmitters whose sole job

這個例子中，由專司痛覺信息的特定神經傳導物質將圖釘攻擊的新訊息

is to pass along pain messages.

承載著。

Now, so far, your body’s response to the stimulus has been handled by the sensory,

到此，你的身體對刺激的反應已經被感覺端處理當中

or afferent, division of your peripheral nervous system. This is the part that’s involved

，或者說向內傳遞途徑路段，是你周邊神經系統的一個分支。這是個涉入快速

expressly in collecting data and sending it to the central nervous system.

收集資訊和傳遞至中樞神經系統的部份。

But at this point, the responsibility changes hands. The torch is passed.

但在這個時間點，責任交棒發生了。聖火火把傳遞給下一棒。

Because the pain signal has just triggered an action potential in a neuron in the spinal

由於痛覺訊號只觸發脊髓內的神經元產生動作電位

cord, which is part of the central nervous system, and there it reaches an integration center.

也就是中樞神經系統的一部分，而在那裡，訊號進入資訊整合中心。

From here, the response is taken over by the motor, or efferent division.

從這，訊號就進入了運動端，或是向外傳遞路段。

Once the integration center interprets the signal, it transmits the message to motor

一旦資訊整合中心轉譯完訊息，它就將信息交給運動

neurons, which send an action potential back down your leg, where it reaches an effector.

神經元們，它門就以傳遞動作電位的方式把指令傳至你的腿，也就是受動器端。

And an effector is just any structure that receives and reacts to a motor neuron’s

受動器就是任何接收來自運動神經元指令並做出回應

signal, like a muscle contracting or a gland secreting a hormone.

的結構，就如肌肉收縮或是腺體釋出賀爾蒙。

From here, the motor neurons complete the whole foot-lifting response until the rest

至此，運動神經元完成了整個抬腳的回應直到

of your nervous system gets engaged in the complicated tasks of figuring out what the

你神經系統其餘部份去做更複雜的任務，如了解

problem is, and fixing it.

到底出了什麼問題，和去修復它。

Those are the five steps that your highly specific neural pathways go through to produce

以上是你體內高度特化的神經路徑們完成有名的

what’s known as a reflex arc.

反射弧動作的五個步驟。

A lot of your body’s control systems boil down to reflexes just like this -- immediate

你身上的控制系統簡化性反射動作如剛才的例子 -- 立即的

reactions that can either be innate or learned, but don’t need much conscious processing in the brain.

回應可能是天生的或者是後天學習得來的，但不需要大腦太多的意識處理過程就可完成。

Lifting your foot when you step on a tack is an innate, or intrinsic, reflex action

你本能地、內化地做出反射動作，在腳踩圖釘時抬腳

-- a super fast motor response to a startling stimulus.

-- 對初始刺激產生一個超級快速的運動反應。

These reflexes are so invested in your self-preservation that you actually can’t think about them

這些反射能力深植在你的自我保護機制當中以至於你在做出動作前

before you respond.

根本不需要思考。

All this processing happens in the spinal cord, so that the control of muscles can be

這全部的過程都發生在脊髓，所以所有的肌肉控制

initiated before the pain is actually perceived by the brain.

就可以在被大腦察覺之前就完成了。

Learned, or acquired reflexes on the other hand, come from experience. Like how you learn

另一方面，學習而得或者的反射，從經驗而來。像你

to dodge obstacles while riding a bike or driving a car. That process is also largely

如何學會在騎車或開車時閃避障礙物。那個過程也是打部分

automatic, but you learn those reflexes by spending time behind the wheel, or behind the handlebars.

為自動化過程，但你在那之前要花時間去學騎車或學開車去訓練那些反射動作經驗。

And reflex arcs stimulate some muscles, while inhibiting others. For example, the tack in

而反射弧在刺激某些肌肉的同時也抑制某些肌肉。舉例來說，

your right foot ended up activating the motor neurons in your right hip flexors and hamstring,

腳踩圖釘啟動了你右腳大腿的屈肌和腿筋，

causing that knee to bend and your foot to lift up.

致使膝蓋彎曲而讓腳抬起。

But it also told the quad muscles in your left leg to extend and stand tall, allowing

但這也同時告訴左腳的四頭肌去伸長而站立挺直，使

you to shift your body’s weight off the tack.

你可以將體重移離踩到圖釘那一側。

Of course not all reflexes come from pain, as you’ve probably experienced when a doctor

當然不是所有的反射都來自於疼痛，就像你一定有被醫生用小鎚子

tapped your knee and your foot kicked.

敲擊膝蓋測試膝跳反射而產生的腳踢的動作。

Your muscles and tendons are very sensitive to being stretched too far, or too fast, because

你的肌肉和肌腱對於延展過快或過長都非常的敏感，

that kind of movement can cause injury.

因為這種的動作通常都會導致受傷。

So for this we have receptors called muscle and tendon spindles that specifically sense

對此，我們有叫做肌肉束和肌腱束的受器專門

stretching. If triggered by an over-stretch, they generate a reflex arc that contracts

感受拉伸的力量。一旦有過度拉伸時就啟動，產生一個反射弧告訴

the muscle to keep it from stretching further.

肌肉收縮以停止更多的拉伸。

So, when does the brain actually get involved in all this?

所以，大腦到底何時才介入這個過程呢？

Well, when your spinal cord sent impulses down the motor neurons, it also sent signals

嗯，當你的脊髓給脈衝到運動神經元，它也同時給訊息

up your spinal cord toward the brain.

到大腦。

News of the tack arrived first at your thalamus, the information switchboard that then split

視丘是當你踩到圖釘的事件發生後第一個到達的在腦部的區域，這個資訊轉繼站

the message and sent it to the somatosensory cortex -- which identifies and localizes the

在將訊息分出，傳送到體感覺皮質 -- 區分和定位

pain, like: “sharp, and foot”; as well as the limbic system, which registers emotional

疼痛的腦區，像是："尖銳，還有腳"；也跟邊緣系統一樣，標定情緒上

suffering -- like, “why tack? Why me?!” And it also went to the frontal cortex, which

的痛苦的腦區 -- 像是："為什麼是圖釘？為什麼是我踩到？！"訊息也會傳到額葉，

made sense of it all, assigning meaning to the pain -- like, “oh, I see this tack fell

是釐清一切事情的腦區，對疼痛賦與意義 -- 像是，"喔，我看到這個圖釘從這牆上貼的

from the Crash Course poster on the wall here.”

速成課程的海報上掉落下來"

So basically, although your body has been reacting all along, it’s not until those

所以基本上，儘管你的身體做出了這麼多事情，在痛覺傳到腦部

pain signals hit the brain that you have the conscious thoughts of both “dang, that hurt,”

理出如"該死，好痛"和"喔，因為我踩到某個特別間的東西所以好痛"這些有意識的想法之前

and “oh, that hurt because I stepped on a specific pointy thing.“

躲避的動作早就都已以做完了。

And this is where I want to point out that we here at Crash Course cannot be held responsible

而這裡先聲明，任何因為持有速成課程海報所導致的傷害

for any injuries sustained in the process of owning a Crash Course poster. Enjoy them

速成課程在此做出免責聲明。請享受，

at your own risk.

風險自負。

Today you got your first look at the peripheral nervous system, by learning how the afferent

今天，藉由學習到對於疼痛反應向外和向內傳遞訊息的神經路徑機制

and efferent divisions provide information about, and responses to, pain. You learned

得以一窺周圍神經系統奧秘。你學到

about the five steps of the reflex arc, the different kinds of reflexes you have, and

關於反射弧的五個傳導階段，人體上不同的神經反射的形式，

what your brain has to say about all that pain, once the news is finally broken to it.

還有當你的大腦認知到受傷之前，需要對疼痛所做的一切動作。

Crash Course is now on Patreon! Big thanks to all of our supporters on Patreon who make

"速成課程"已在Patreon上架囉！感謝所有在Patreon上的支持者，他們每個月的貢獻

Crash Course possible for themselves and for the whole rest of the world through their

讓"速成課程"得以實現不僅讓他們自己也讓全世界的朋友們得以

monthly contributions. If you like Crash Course and you want to help us keep making great

收看這個節目。如果你喜歡"速成課程"且你想要幫助我們持續製作像這部影片般

new videos like this one, you can check out Patreon.com/CrashCourse

更新、更好的的影片，你可以去Patreon.com/CrashCourse上看看。

This episode was written by Kathleen Yale. The script was edited by Blake de Pastino,

這集影片寫自凱瑟琳‧耶魯。劇本由布雷克‧狄‧帕司提諾編輯

and our consultant, is Dr. Brandon Jackson. It was directed by Nicholas Jenkins, edited

顧問為布蘭登‧傑克森博士。由尼可拉司‧傑金司執導，由

by Nicole Sweeney, and our graphics team is Thought Café.

尼可‧史雲妮編導，動畫團隊為點子咖啡。