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

  • How do you know the sand is there?

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

  • you can feel it,

  • that sensation of extreme discomfort, also known as pain.

  • Now pain makes you do something,

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

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

  • There are people who don't feel pain.

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

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

  • and never know it.

  • Pain is your body's early warning system.

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

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

  • These detectors are specialized nerve cells

  • called nociceptors.

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

  • your teeth and some of your internal organs.

  • Just like all nerve cells, they conduct electrical signals,

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

  • But, unlike other nerve cells,

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

  • So, gently touch the tip of a needle.

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

  • But you won't feel any pain.

  • Now, the harder you push against the needle,

  • the closer you get to the nociceptor threshold.

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

  • But the pain threshold isn't set in stone.

  • Certain chemicals can tune nociceptors,

  • lowering their threshold for pain.

  • And when cells are damaged, they and other nearby cells

  • start producing these tuning chemicals like crazy,

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

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

  • Aspirin and ibuprofen

  • block production of one class of these tuning chemicals,

  • called prostaglandins.

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

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

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

  • convert this arachidonic acid into prostaglandin H2,

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

  • including raise your body temperature, cause inflammation

  • and lower the pain threshold.

  • Now, all enzymes have an active side.

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

  • The active sites of COX-1 and COX-2

  • fit arachidonic acid very cozily.

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

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

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

  • It enters the active site and then breaks off,

  • leaving half of itself in there,

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

  • This permanently deactivates COX-1 and COX-2.

  • Ibuprofen, on the other hand,

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

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

  • but for the time that ibuprofen is in there,

  • the enzyme can't bind arachidonic acid,

  • and can't do its normal chemistry.

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

  • Well, they don't.

  • Once the drugs are in your bloodstream,

  • they are carried throughout your body,

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

  • So that's how aspirin and ibuprofen work.

  • But there are other dimensions to pain.

  • Neuropathic pain, for example,

  • is pain caused by damage to our nervous system itself;

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

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

  • For example, how much pain you feel can depend on

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

  • Pain is an area of active research.

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

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B1 US TED-Ed pain cox ibuprofen aspirin threshold

【TED-Ed】How do pain relievers work? - George Zaidan

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    Ashley Chen posted on 2014/11/20
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