Ow! A paper cut!

紙で切ると 傷は小さいのに

Paper cuts are usually small and shallow injuries.

なぜ痛いのか

So why do they hurt so much?

解剖学と紙の構造から

A close look at the anatomy of our skin and the structure of paper reveals a few explanations.

少し説明しましょう

We usually get paper cuts on our hands and fingers, where our skin is packed with neurons.

紙でよく切るのは指ですね

Some of these neurons, called nociceptors, detect potential harm.

神経の集まる所です

These cells respond to high temperatures,

神経は有害なものを検出します

harsh chemicals

例えば 熱や

and any pressure that threatens to break the skin.

化学物質

Nociceptors trigger a cascade of electrical and chemical signals

破れるような強い圧力です

that eventually reach the brain, informing it about injury.

神経が電気信号を発信すると

In turn, our brain makes us aware of injury with the experience of pain.

脳に届き けがを知らせます

Also, a paper cut is not quite as clean as it looks.

私たちはそうしてけがに気付きます

A paper's edge may seem perfectly smooth,

また 紙は見た目より攻撃的です

but on a microscopic level, it's actually pretty jagged.

滑らかそうに見えますが

A thin piece of paper cuts through skin more like a saw than a knife,

実際にはギザギザしており

ripping apart our cells.

指を切るような薄い紙は

And paper leaves behind chemical-coated particles, irritating the wound.

ナイフというよりノコギリです

Another thing, since paper cuts are generally shallow,

少し残される物質も痛みの元です

they don't bleed or clot very much.

また 紙の傷は浅いため

That means damaged tissues and neurons remain exposed.

すぐには閉じません

Every time we use our hands, the wound flexes open, disturbing these neurons.

神経が露出したままになり

Finally, we should also consider the psychology of a paper cut.

手を動かす度に

We probably pay more attention to a paper cut because it's on a body part we use so often.

刺激されることになります

It's also surprising and kind of upsetting to be injured by something as seemingly benign as paper.

心理的側面もあるでしょう

For Scientific American's Instant Egghead, I'm Ferris Jabr.

よく使う場所なので