What If You Were 620 Miles Long?

Let's talk about double pain. If your body was 620 mil long, pain could be your alarm clock. You could bite your toe at bedtime and then go to sleep; you wouldn't feel any pain until the signal from your toe reached your brain and woke you up 8 hours later.

That'd be pretty nice and pretty suscal. But about 3 weeks later, your toe would start to hurt again in a completely different way. It would feel really strange, but it's not at all. It's called double pain, and it happens to all of us.

When you stub your toe, almost immediately, you feel a sharp, localized pain. But then, a second or so later, you feel a broader, aching pain. That first pain is caused by signals that travel through your myelinated A-delta fibers. They go quickly, 35 m/second, and their purpose is to quickly change your behavior so you withdraw from danger.

That slower pain is caused by signals that come through your unmyelinated C fibers. Their purpose is to provide a long-lasting pain that encourages you to nurse and rest your injury while it heals.