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  • Have you ever noticed that when you use eye drops

  • or put on mascara, your mouth hangs open?

  • Although there aren't any hard numbers on how many people

  • experience thismascara mouthphenomenon, it's definitely pretty common.

  • Just watch next time you're around someone putting in their contacts.

  • So why is it that messing with our eyes often leaves our mouth agape?

  • No one knows for sure, but there are some best guesses as to what might be causing it.

  • We can start by looking at the nerves that control facial movements

  • of which there are quite a few.

  • The trigeminal nerve is a large, complex nerve that controls

  • the lateral pterygoid muscle, which along with other muscles,

  • opens and closes your mouth.

  • And the oculomotor nerve is responsible for controlling a wide range of muscles

  • in and around the eye -- including the muscle that raises and lowers your upper eyelid.

  • Although these nerves do pretty different things,

  • they originate close to one another in the brain stem.

  • So one hypothesis to explain mascara mouth is

  • that the two nerves are so close together, they get their signals crossed.

  • When you activate your oculomotor nerve and open your eyes wide,

  • this might also accidentally trigger your trigeminal nerve,

  • causing your mouth to open.

  • Some researchers have made a connection to this response with

  • a very rare genetic disorder called Marcus Gunn syndrome.

  • This syndrome causes one eyelid to move rapidly every time the jaw moves.

  • It's thought to be caused by an abnormal connection between the trigeminal and oculomotor nerves.

  • And researchers aren't totally sure why yet.

  • But some think that it's a more extreme version of thismascara mouth

  • response that most of us seem to have.

  • Which could help explain why individuals who don't have this syndrome

  • will still open their mouths while poking around their eyes.

  • Another interesting connection between our eyes and

  • our mouths shows itself in a reaction called the corneomandibular reflex.

  • This is an automatic, completely involuntary movement of the jaw

  • which happens when touching the cornea, the transparent front layer of the eye.

  • Touching the cornea makes you blink, and the jaw movement seems to happen in response to that.

  • It almost always shows up in patients with brain related damage or diseases,

  • like those with Parkinson's or ALS.

  • It's well known in comatose patients, suggesting it can happen when you're totally unconscious.

  • It's thought that this reflex is present when there is either a brain stem dysfunction,

  • or structural damage to nerve pathwayspossibly another mixed message between

  • the oculomotor and trigeminal nerves.

  • So while there are definitely a number of connections

  • between our eye and mouth movements, we're still really not sure what exactly

  • is happening to cause your mouth to hang open when you're trying to convince your stubborn

  • contact lens to stick to your eyeball.

  • What we do know is that it's hard to avoid looking silly.

  • Thanks to our patron Katy for sending in this question,

  • and thanks to everyone who voted in our Patreon question poll.

  • If you want a shot at getting your questions answered

  • or just want to vote in the polls, head on over to patreon.com/scishow.

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B1 中級

目を触った時にできる変な顔とは? (What's the Weird Face We Make When We Touch Our Eyes?)

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    林宜悉 に公開 2021 年 01 月 14 日
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