- [Narrator] You know, stubbing your toe hurts.
It's right up there with paper cuts and chapped lips,
annoying minor injuries that hurt way more
than they have any right to.
But it turns out there's a good reason
why stubbing your toe hurts so much.
When you stub your toe,
you're slamming it with a force
equal to two to three times your body weight.
That's about the same force as a karate punch.
And since your toe has a tiny surface area,
that force can't be spread out,
so the pain stays concentrated at the point of impact.
It's the same reason it hurts so much more
to step on the tiny, pointy end of a thumbtack
than the wider, blunt end.
But you don't just feel the immediate shock
like when you step on a thumbtack.
There's that aching throb that comes after.
That's because when you stub your toe,
you're actually hitting a bundle of special nerve endings
called nociceptors.
They all fire at once, blaring a danger signal.
But some signals travel faster than others.
The faster A-delta nociceptors
fire the first wave of signal,
which races at 20 meters per second
of thousands of densely bundled nerve fibers,
and ultimately to your brain.
That causes the sharp, sudden pain you feel
at the moment of impact.
But some nerve fibers called C nociceceptors
send a slower signal at only 2 meters per second.
So after a moment's delay,
the second wave of pain signals reach your brain.
That's the dull throbbing that lingers on.
You can find nociceptors all over your body
from your eyes to your bladder.
But they're concentrated at the highest densities
in parts of your body that you use
to explore your environment,
like your fingertips and your lips.
That's why accidents like paper cuts and chapped lips
can also hurt more than they seem like they should.
Now, your toe isn't packed with as many nociceptors
as your fingertips,
but since there's not much in the way of padding
to cushion the blow,
it's easy to set those unprotected nociceptors off.
And that's no coincidence.
Researchers suspect the pain that we feel from mishaps
like a stubbed toe
might have even saved our ancestors' lives.
Back before antibiotics,
even the tiniest cut could mean a deadly infection,
and feet, which were constantly in contact
with dirty, bacteria-infested surfaces,
were particularly vulnerable.
So the people who had extra-sensitive feet
might have been more careful about where they stepped.
As a result, they'd be less likely to get infections
and would live to pass on their genes.
So the next time that you collapse on the floor
cradling your aching toe,
you can thank your great-great-great-great-great-great-
great-great-great-great-great-grandpa
for the privilege.