Name: 【TED-Ed】Why do we itch? - Emma Bryce
Uploaded: 2017-05-10T13:54:15.000Z
Duration: 4 min 44 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

You're standing at  the ready inside the goal.

When suddenly, you feel an intense itch on the back of your head.

We've all experienced the annoyance of an inconvenient itch,

but have you ever pondered why we itch in the first place?

The average person experiences dozens of individual itches each day.

They can be triggered by all sorts of things,

And then there are the mysterious ones that pop up for no reason at all,

You're scratching your head right now, aren't you?

Anyhow, let's take one of the most common sources: bug bites.

it releases a compound into your body called an anticoagulant

That compound, which we're mildly allergic to,

a chemical that makes our capillaries swell.

which helpfully accelerates the body's immune response

and it's the same reason pollen can make your eyes puff up.

Histamine also activates the nerves involved in itching,

But the itchy sensation itself isn't yet fully understood.

comes from studying the mechanics of itching in mice.

Researchers have discovered that itch signals in their skin

are transmitted via a subclass of the nerves that are associated with pain.

These dedicated nerves produce a molecule called natriuretic polypetide B,

which triggers a signal that's carried up the spinal cord to the brain,

When we scratch, the action of our fingernails on the skin

causes a low level pain signal that overrides the itching sensation.

It's almost like a distraction, which creates the sensation of relief.

But is there actually an evolutionary purpose to the itch,

The leading theory is that our skin has evolved to be acutely aware of touch

so that we're equipped to deal with risks from the outside world.

Our automatic scratching response would dislodge anything harmful

This might explain why we don't feel itching inside our bodies,

which is safe from these external threats,

though imagine how maddening that would be.

In some people, glitches in the pathways responsible for all of this

can cause excessive itching that can actually harm their health.

One extreme example is a psychological condition called delusory parasitosis

where people believe their bodies are infested with mites or fleas

Another phenomenon called phantom itching

can occur in patients who've had amputations.

Because this injury has so severely damaged the nervous system,

it confuses the body's normal nerve signaling

and creates sensations in limbs that are no longer there.

Doctors are now finding ways to treat these itching anomalies.

In amputees, mirrors are used to reflect the remaining limb,

That creates an illusion that tricks the brain

into thinking the imaginary  itch has been satisfied.

Researchers are also searching for the genes involved in itching

and developing treatments to try and block the pathway of an itch

If having an unscratchable itch feels like your own personal hell,

The Italian poet wrote about a section of hell

where people were punished by being left in pits to itch for all eternity.

Subtitles ListPlay Video

【TED-Ed】Why do we itch? - Emma Bryce

intense

perceive

distraction

phenomenon