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  • It's the first sense you use when you're born.

    嗅覺是你出生時頭一個使用的感官

  • One out of every fifty of your genes

    你每五十個基因裡

  • is dedicated to it.

    就有一個基因致力為嗅覺工作

  • It must be important, right?

    嗅覺一定很重要,對吧?

  • Okay, take a deep breath

    好,來個深呼吸

  • through your nose.

    用你的鼻子吸氣

  • It's your sense of smell,

    這就是你的嗅覺

  • and it's breathtakingly powerful.

    而且它強大地令人屏息

  • As an adult, you can distinguish

    成人可辨認出約一萬種不同的氣味

  • about 10,000 different smells.

    成人可辨認出約一萬種不同的氣味

  • Here's how your nose does it.

    你的鼻子是這麼作用的

  • Smell starts when you sniff molecules

    嗅覺從你聞到從空氣中

  • from the air into your nostrils.

    進入鼻孔的氣味分子開始

  • 95% of your nasal cavity

    在那分子到達肺部之前

  • is used just to filter that air

    95% 的鼻腔

  • before it hits your lungs.

    僅用來過濾空氣

  • But at the very back of your nose

    但在你鼻子的最後方

  • is a region called the olfactory epithelium,

    有個叫「嗅覺上皮」的區域

  • a little patch of skin

    那片小小的皮膚

  • that's key to everything you smell.

    是你聞到氣味的關鍵

  • The olfactory epithelium has a layer

    嗅覺上皮有一層

  • of olfactory receptor cells,

    嗅覺受體細胞

  • special neurons that sense smells,

    可以感受氣味的特殊神經元

  • like the taste buds of your nose.

    就像似你鼻子的味蕾

  • When odor molecules hit the back of your nose,

    當氣味分子達到你鼻子的後方

  • they get stuck in a layer of mucus

    附著在那包覆在

  • covering the olfactory epithelium.

    嗅覺上皮的黏液層上

  • As they dissolve,

    當氣味分子溶解時

  • they bind to the olfactory receptor cells,

    會與嗅覺受體細胞結合

  • which fire and send signals

    燃燒並透過嗅覺神經束

  • through the olfactory tract

    傳送訊號

  • up to your brain.

    至你的大腦

  • As a side note,

    附帶一提

  • you can tell a lot

    你可以很容易

  • about how good an animal's sense of smell is

    依動物嗅覺上皮的大小

  • by the size of its olfactory epithelium.

    來判斷牠們的嗅覺有多靈敏

  • A dog's olfactory epithelium

    狗的嗅覺上皮

  • is 20 times bigger

    比人類的大上二十倍

  • than your puny human one.

    比人類的大上二十倍

  • But there's still a lot we don't know

    但我們對於這一小塊的細胞群

  • about this little patch of cells, too.

    仍有許多的未知

  • For example, our olfactory epithelium is pigmented,

    例如,我們的嗅覺上皮是帶有色素的

  • and scientists don't really know why.

    而科學家們並不十分清楚為什麼

  • But how do you actually tell the difference

    但實際上,你如何分辨不同的氣味呢?

  • between smells?

    但實際上,你如何分辨不同的氣味呢?

  • It turns out that your brain has

    其實,你腦中有

  • 40 million different olfactory receptor neurons,

    四千萬個不同的嗅覺受體神經元

  • so odor A might trigger neurons 3, 427, and 988,

    氣味 A 可以觸發神經元 3、427 和 988

  • and odor B might trigger neurons 8, 76, and 2,496,678.

    而氣味 B 可以觸發神經元 8、76 和 2,496,678

  • All of these different combinations

    所有各式不同的組合

  • let you detect a staggeringly broad array of smells.

    讓你聞出數量驚人的各種氣味

  • Plus, your olfactory neurons are always fresh

    加上你的神經元總是常保清新

  • and ready for action.

    且隨時準備行動

  • They're the only neuron in the body

    它們是我們身上唯一

  • that gets replaced regularly,

    定時更新的神經元

  • every four to eight weeks.

    每四到八周更新一次

  • Once those neurons are triggered,

    一旦這些神經元被觸發

  • the signal travels through a bundle

    氣味訊號就會經由

  • called the olfactory tract

    一個叫做「嗅覺神經束」

  • to destinations all over your brain,

    傳達到分佈在你整個大腦

  • making stops in the amygdala,

    停留在扁桃腺、

  • the thalamus,

    丘腦、

  • and the neocortex.

    和腦皮質

  • This is different

    這有別於

  • from how sight and sound are processed.

    視覺與聽覺訊號的傳遞

  • Each of those signals goes first

    每個視覺與聽覺訊號

  • to a relay center

    會先停留在一個

  • in the middle of the cerebral hemisphere

    位於大腦半球中央的中繼中心

  • and then out to other regions of the brain.

    然後分送到大腦的其他區域

  • But smell, because it evolved

    但嗅覺呢,因為它的演化

  • before most of your other senses,

    早於你大部分的其他感官

  • takes a direct route

    嗅覺是直接進入

  • to these different regions of the brain,

    腦中不同的區域

  • where it can trigger your fight-or-flight response,

    這些區域是可以觸發戰鬥或逃跑反應、

  • help you recall memories,

    幫助你喚起記憶、

  • or make your mouth water.

    或讓你分泌唾液

  • But even though we've all got

    但即便我們有一樣的生理構造──

  • the same physiological set-up,

    但即便我們有一樣的生理構造──

  • two nostrils and millions of olfactory neurons,

    兩個鼻孔和數百萬的嗅覺神經元

  • not everybody smells the same things.

    卻不是每個人聞到的氣味都一樣

  • One of the most famous examples of this

    其中最著名的一個例子是

  • is the ability to smell so-called "asparagus pee."

    嗅出所謂的「蘆筍尿」的能力

  • For about a quarter of the population,

    大約 1/4 的人們

  • urinating after eating asparagus

    吃了蘆筍後排尿時

  • means smelling a distinct odor.

    會聞到尿液裡的特殊異味

  • The other 75% of us don't notice.

    但其他 3/4 的人卻聞不出來

  • And this isn't the only case

    而這還不是

  • of smells differing from nose to nose.

    每個鼻子聞到的氣味不同的唯一例子

  • For some people,

    對某些人而言

  • the chemical androstenone smells like vanilla;

    化學物質「雄甾酮」聞起來像香草

  • to others, it smells like sweaty urine,

    別人聞起來卻像汗尿味

  • which is unfortunate

    這很可惜

  • because androstenone is commonly found

    因為雄甾酮通常存在像豬肉這樣好吃的東西裡

  • in tasty things like pork.

    因為雄甾酮通常存在像豬肉這樣好吃的東西裡

  • So with the sweaty urine smellers in mind,

    因顧慮到這些會聞到尿汗味的人

  • pork producers will castrate male pigs

    豬肉供應商將公豬去勢

  • to stop them from making androstenone.

    來防止公豬製造雄甾酮

  • The inability to smell a scent

    無法聞到某種氣味

  • is called anosmia,

    稱為嗅覺喪失症

  • and there are about 100 known examples.

    而且已知的例子大概有一百種

  • People with allicin anosmia can't smell garlic.

    有大蒜素嗅覺喪失症的人聞不出大蒜味

  • Those with eugenol anosmia can't smell cloves.

    有丁香酸嗅覺喪失症的人聞不出丁香味

  • And some people can't smell anything

    而有些人則完全聞不出任何氣味

  • at all.

    而有些人則完全聞不出任何氣味

  • This kind of full anosmia

    這種完全嗅覺喪失症

  • could have several causes.

    可能有幾個肇因

  • Some people are born without a sense of smell.

    有些人天生就沒有嗅覺

  • Others lose it after an accident

    有些人是意外傷害後

  • or during an illness.

    或是患病時喪失嗅覺

  • If the olfactory epithelium gets swollen or infected,

    如果嗅覺上皮腫脹或感染

  • it can hamper your sense of smell,

    會對你的嗅覺造成阻礙

  • something you might have experienced

    當你生病時你可能有這樣的經驗

  • when you were sick.

    當你生病時你可能有這樣的經驗

  • And not being able to smell anything

    然而聞不到任何氣味

  • can mess with your other senses, too.

    也會影響你其他的感官

  • Many people who can't smell at all

    許多完全聞不到氣味的人

  • also can't really taste the same way

    嚐到的味道也和我們不盡相同

  • the rest of us do.

    嚐到的味道也和我們不盡相同

  • It turns out that how something tastes

    事實證明,東西嚐起來的味道

  • is closely related to how it smells.

    和聞起來的氣味是息息相關的

  • As you chew your food,

    當你咀嚼食物時

  • air is pushed up your nasal passage,

    夾帶食物氣味的空氣

  • carrying with it the smell of your food.

    被推上你的鼻腔

  • Those scents hit your olfactory epithelium

    那氣味到達你的嗅覺上皮

  • and tell your brain a lot

    告訴你的大腦許多

  • about what you're eating.

    關於你正在進食的東西的訊息

  • Without the ability to smell,

    沒了嗅覺的能力

  • you lose the ability to taste

    你喪失了品嚐任何

  • anything more complicated

    比五味更複雜的味道

  • than the five tastes

    比五味更複雜的味道

  • your taste buds can detect:

    你的味蕾可以分辨

  • sweet,

    甜、

  • salty,

    鹹、

  • bitter,

    苦、

  • sour,

    酸、

  • and savory.

  • So, the next time you smell exhaust fumes,

    所以,下次你聞到排出的煙、

  • salty sea air,

    海的鹹味、

  • or roast chicken,

    或烤雞的香味

  • you'll know exactly how you've done it

    你就知道你到底怎麼辦到的

  • and, perhaps, be a little more thankful that you can.

    也或許,為你可以聞到那些氣味有多一點點的感激

It's the first sense you use when you're born.

嗅覺是你出生時頭一個使用的感官

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B2 中高級 中文 TED-Ed 嗅覺 氣味 聞到 神經元 鼻子

【TED-Ed】嗅覺是怎麼一回事? (How do we smell? - Rose Eveleth)

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    Zenn 發佈於 2014 年 04 月 07 日
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