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Whether or not eyes are the windows to the soul... scientifically, pupils are the windows of the eyes.
不论眼睛是不是灵魂的窗户...科学上来讲，瞳孔是眼睛的窗户。
And sometimes, those windows are more open than usual, like when you've taken a medication that causes pupil dilation.
有时，那些窗户会放大，比如当你服用了一种会导致瞳孔扩张的药物。
Or when people use certain recreational drugs.
或是服用某种娱乐性药物
It all comes down to how different chemicals can cause changes throughout your whole body, which can affect little muscles in your eyes.
这一切都要归结于不同化学物质会如何导致整个身体的变化，也会影响到眼部的一些肌肉。
The pupils are openings that let light into the rest of your eye. And the colored part of your eye, the iris, controls how much light makes it in.
瞳孔张开是为了让光进入眼睛的剩余部分。并且眼睛有颜色的部分，虹膜，控制光线的进入量。
The balance of two muscle groups in the iris changes how big your pupils are, like a camera aperture.
虹膜中两组肌肉的平衡改变眼睛瞳孔的大小，就像是取景框。
The iris dilator is arranged like bicycle spokes around the center of your eye. And when it contracts, it pulls your pupils open wider.
虹膜扩张器的排列像是眼睛中心排成的自行车。当它收缩时，会让你的瞳孔放大。
The iris sphincter, on the other hand, is in a ring around your pupil and acts like most of the sphincter muscles in your body.
另一方面，虹膜括约肌呈环状围绕瞳孔，就像体内大部分括约肌一样。
It constricts your pupils down to little dots. So now you know that you've got a sphincter in your eye. That's just a fact for you.
它会将你的瞳孔缩成小点。现在你该知道你的眼睛里有一个括约肌了。这是一个事实。
Anything that blocks or stimulates either muscle can knock that balance out of whack and cause some really noticeable changes.
任何阻碍或刺激肌肉的东西都能让銮其平衡并造成一些显著的变化。
For example, drugs that block receptors for the neurotransmitter acetylcholine can cause impressive dilation.
例如，阻碍乙酰胆碱接收器的药物会造成显著扩张。
These medications are designed to inhibit the parasympathetic nervous system,
这些药物被用于抑制副交感神经系统，
which controls the involuntary muscle contractions that keep things moving in your body, like your lungs, or the plumbing that gets rid of waste.
副交感神经系统是控制无意识性肌肉收缩保持体内物质流动，比如肺或处理废物的管道系统。
This system also controls the iris sphincter muscle.
这个系统还控制着虹膜括约肌。
So when it's inhibited, the iris sphincter can't counteract the pull from the iris dilator — and you get wide open, 'blown out' pupils.
所以当被抑制时，虹膜括约肌无法抵消虹膜扩张器的牵引力—并且你的视野变得开阔，瞳孔‘要爆了’。
Some drugs, like ones for overactive bladders or excessive sweating, target the entire parasympathetic nervous system.
一些药物，比如用于膀胱过度活动症或出汗过多的药物，是以整个副交感神经系统为目标的。
They often have dilated pupils or blurry vision as side effects, but those aren't the goal.
瞳孔放大或视力模糊常常成为服用这些药物的副作用，但是那些副作用并不是这些药物的目标。
Others, like the drops used to dilate pupils for eye exams, are more targeted and don't throw your whole body off.
其他的，比如用于眼睛检查的瞳孔放大滴剂则更有针对性且不会对你的整个身体造成影响。
Now, other drugs can stimulate the sympathetic nervous system, responsible for your body's 'fight-or-flight' response. And these too can cause dilation.
现在其他药物可以刺激交感神经系统，对你身体的‘逃跑还是战斗’反应负责。这些也会引起扩张。
Take adrenaline, which floods your bloodstream when you're scared but is also a medication for extreme allergic reactions — it's what's in the EpiPen.
以肾上腺素为例，当你感到害怕时，肾上腺素涌入血流之中，但是这也是极端的过敏反应的一种药物疗法—肾上腺素注射药Epipen中就含有这个物质。
Adrenaline can bind to nerve receptors connected to the iris dilator, making it contract and pull your pupils open wide.
肾上腺素可以绑在神经感受器上与虹膜扩张器相连接，使其收缩、扩张。
If people use drugs like cocaine, amphetamines, or even weed, their brains have more dopamine and norepinephrine floating around.
如果有人使用像可卡因、安非他命或除草剂这些药物，他们的大脑会产生更多的多巴胺以及降肾上腺素。
Usually, either extra neurotransmitters get released, or receptors that naturally suck them away get blocked by those drugs.
通常，要么是释放额外的神经传导物质，要么是吸走被那些药物阻碍的接收器。
These chemicals are involved in the "high" feeling but also cause dilated pupils.
这些化学物质都会导致情绪“高涨”但是也会导致瞳孔扩张。
Scientists think that dopamine makes certain nerve cells release more norepinephrine, which works like adrenaline to make the iris dilator contract.
科学家们认为多巴胺会让某种神经细胞释放更多的去甲肾上腺素，其功能就像是肾上腺素一样，让虹膜扩张器收缩。
So wide pupils can be caused by a lot of things. But they're a hint that certain chemicals — illicit or not — are bubbling through your body.
所以瞳孔扩张的起因有很多。但是它们都有一个暗示—某些化学物质—不论正当与否—都在持续流通于你的身体之中。
Thanks to our Patreon on patrons for asking us great questions like this!
感谢Patreon赞助人们的提问！
If you want to support us and send us questions, and get some other cool stuff you can go to patreon.com/scishow.
如果想要支持我们、向我们提问以及了解超酷的知识，请登录patreon.com/scishow
And if you want to learn more about human eyes, check out our video where I explain what those pesky little eye floaters actually are.
如果你想了解更多关于人类眼睛的知识，请观看解释飞蚊症的视频。
