Say you're at the beach, and you get sand in your eyes.

假設你在海灘上，沙子進了眼睛

How do you know the sand is there?

你怎麼知道有沙子呢？

You obviously can't see it, but if you are a normal, healthy human,

顯然你看不到，但若你是個正常、健康的人

you can feel it,

你可以感覺到有沙子

that sensation of extreme discomfort, also known as pain.

這種極不舒服的感覺叫做「疼痛」

Now pain makes you do something,

疼痛要你採取行動

in this case, rinse your eyes until the sand is gone.

此例中是要你沖洗眼睛，直到沙子消失

And how do you know the sand is gone? Exactly. Because there's no more pain.

你怎麼知道沙子不見了？ 沒錯，因為不痛了

There are people who don't feel pain.

有人感覺不到疼痛

Now, that might sound cool, but it's not.

聽起來很酷，但其實一點也不酷

If you can't feel pain, you could get hurt, or even hurt yourself

如果感覺不到疼痛，你可能會受傷，甚至可能傷到自己

and never know it.

卻完全不知道

Pain is your body's early warning system.

疼痛是你身體的早期預警系統

It protects you from the world around you, and from yourself.

可保護你不受到周圍世界或自己的傷害

As we grow, we install pain detectors in most areas of our body.

隨著我們長大，疼痛感測器會安裝在身體的大多數地方

These detectors are specialized nerve cells

這些感測器是特殊的神經細胞

called nociceptors.

稱為「痛覺感受器」

that stretch from your spinal cord to your skin, your muscles, your joints,

分布在脊髓、皮膚、肌肉、關節

your teeth and some of your internal organs.

牙齒和一些內臟

Just like all nerve cells, they conduct electrical signals,

就像所有的神經細胞，它們用電傳送信號

sending information from wherever they're located back to your brain.

從它們所在之處，送訊號回大腦

But, unlike other nerve cells,

不像其他神經細胞

nociceptors only fire if something happens that could cause or is causing damage.

痛覺感受器只在可能、或正在造成傷害時才會作用

So, gently touch the tip of a needle.

所以，輕摸針尖

You'll feel the metal, and those are your regular nerve cells.

你可以感覺到金屬，一般神經細胞給你這種感覺

But you won't feel any pain.

但你不會感到任何疼痛

Now, the harder you push against the needle,

但你越用力推針尖

the closer you get to the nociceptor threshold.

越接近痛覺感受器的閾值 (譯註：閾值指的是生物上產生神經脈衝的門檻。)

Push hard enough, and you'll cross that threshold and the nociceptors fire, telling your body to stop doing whatever you're doing.

很用力的話，就會超過閾值，痛覺感受器啟動，告訴你的身體停止目前的行為

But the pain threshold isn't set in stone.

痛覺感受器的門檻，並非一成不變

Certain chemicals can tune nociceptors,

某些化學物質可以調節感受器

lowering their threshold for pain.

降低痛覺的閾值

And when cells are damaged, they and other nearby cells

細胞受損時，受損細胞及鄰近細胞

start producing these tuning chemicals like crazy,

開始瘋狂生產這些調節化學物質

lowering the nociceptors' threshold to the point where just touch can cause pain.

降低痛覺感受器的門檻，直到連觸摸都會疼痛

And this is where over-the-counter painkillers come in.

這時非處方的止痛藥就可以大展身手了

Aspirin and ibuprofen

阿斯匹靈和布洛芬

block production of one class of these tuning chemicals,

可阻止一種調節化學物質的生產

called prostaglandins.

稱為「前列腺素」

Let's take a look at how they do that.

我們來探討一下原理

When cells are damaged, they release a chemical called arachidonic acid.

當細胞損傷，會釋放一種化學物質 叫做「花生油酸」

Now, two enzymes called COX-1 and COX-2

有兩種酵素 COX-1 和 COX-2

convert this arachidonic acid into prostaglandin H2,

可將花生油酸轉換成前列腺素 H2

which is then converted into a bunch of other chemicals that do a bunch of things,

再將其轉換成一系列化學物質 產生一連串效果

including raise your body temperature, cause inflammation

包括升高體溫、引起發炎、

and lower the pain threshold.

降低疼痛閾值

Now, all enzymes have an active side.

所有的酵素有特定的活性部位

That's the place in the enzyme where the reaction happens.

也就酵素反應發生的地方

The active sites of COX-1 and COX-2

COX-1 和 COX-2 的活性部位

fit arachidonic acid very cozily.

非常適合花生油酸

As you can see, there is no room to spare.

正如你看到的，也沒有多餘的空間

Now, it's in this active site that aspirin and ibuprofen do their work.

阿斯匹靈和布洛芬，就是在這個 活性部位發揮作用

So, they work differently -- aspirin acts like a spine from a porcupine.

它們的工作原理不同： 阿斯匹靈像豪豬的刺

It enters the active site and then breaks off,

進入活性部位，然後脫落

leaving half of itself in there,

留下一半在那裡

totally blocking that channel and making it impossible for the arachidonic acid to fit.

完全阻斷通道，讓花生油酸進不來

This permanently deactivates COX-1 and COX-2.

永久停用 COX-1 和 COX-2

Ibuprofen, on the other hand,

另一方面，布洛芬

enters the active site, but doesn't break apart or change the enzyme.

進入活性部位，但不破壞或改變酵素

COX-1 and COX-2 are free to spit it out again,

COX-1 和 COX-2 可把它再吐出來

but for the time that ibuprofen is in there,

但布洛芬在那裡的期間

the enzyme can't bind arachidonic acid,

酵素無法結合花生油酸

and can't do its normal chemistry.

因此無法進行正常的化學反應

But how do aspirin and ibuprofen know where the pain is?

阿斯匹靈和布洛芬 怎麼知道哪裡痛？

Well, they don't.

噢，它們並不知道

Once the drugs are in your bloodstream,

一旦藥物進入血液中

they are carried throughout your body,

就會被帶往全身

and they go to painful areas just the same as normal ones.

不但會到疼痛部位，也會到正常部位

So that's how aspirin and ibuprofen work.

這就是阿斯匹靈和布洛芬的原理

But there are other dimensions to pain.

還有其他種類的疼痛

Neuropathic pain, for example,

例如神經性疼痛

is pain caused by damage to our nervous system itself;

是神經系統本身受損所引起的疼痛

there doesn't need to be any sort of outside stimulus.

不需要任何形式的外界刺激

And scientists are discovering that the brain controls how we respond to pain signals.

科學家們發現，大腦控制了我們對疼痛信號的反應

For example, how much pain you feel can depend on

例如，疼痛的程度取決於

whether you're paying attention to the pain, or even your mood.

你對疼痛的在意程度 甚至是你的心情

Pain is an area of active research.

疼痛是個活躍的研究領域

If we can understand it better, maybe we can help people manage it better.

如果能更了解疼痛，或許就更能有效的處理疼痛