Why does a poke sometimes sting right away, and sometimes ache a beat later?

Stub your toe and you feel a sharp jolt — then, a moment later, a dull throbbing ache rolls in. Same toe, two feelings, two different times. The secret is hiding on the nerve wires themselves. Let's go find it.

1What carries the "ouch"

A nerve is a wire — and some wires wear a fatty coat

You only need two ideas. Watch each one:

A nerve carries a tiny zap

A nerve is a long wire from your skin to your brain. When something pokes you, a tiny electric zap travels up the wire to tell your brain "hey — something happened down here!"

Some wires wear a fatty coat

Some nerve wires are wrapped in a fatty sleeve with little bare gaps between the wraps. Other wires are bare the whole way. That fatty coat is the thing to keep your eye on.

2Two kinds of nerve wire

The leaper vs the crawler

Your body has both kinds of wire running side by side. They carry the same kind of zap — but in completely different ways:

Wrapped wire

The leaper

The fatty wrap lets the zap jump from gap to gap — leaping down the whole wire in a flash.

Bare wire

The crawler

No wrap, so the zap can't jump. It has to re-make itself at every tiny step — and that crawls.

3Your turn — fire a zap yourself

Tap the toe and watch the zap LEAP between the gaps

Here's one wrapped wire. Tap the toe (or the button) to send your own zap, and watch how it doesn't slide along smoothly — it jumps from one bare gap to the next, skipping the wrapped parts entirely.

One wrapped nerve — tap the toe to fire

or tap the toe in the picture

4Now strip the wrap and race them

Two nerves, one pinch — which "ouch" reaches the brain first? 🦶

Now there are two wires running up the same leg. Drag the slider to strip the fatty wrap off the bottom one, then pinch the toe and race both zaps to the brain. But guess first.

Guess before you race them

You strip the fatty wrapping off a nerve. Does the "ouch" still reach your brain just as fast?