Why do you feel it immediately when something touches your feet, but does the pain of stubbing your toe take seconds to register?

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Why do you feel it immediately when something touches your feet, but does the pain of stubbing your toe take seconds to register?

In: Biology

“Pain from delayed injuries is sometimes masked temporarily by adrenaline, especially in traumatic accidents. In these cases, pain often sets in once the adrenaline and endorphins have receded to their normal levels.”

You don’t actually feel pain with your pain receptors. You feel pain with your brain.

What happens is that your pain receptors get a stimulus – you stub your toe. That lights up all your mechanical pain receptors in your toe. They send a “um something happened dude” signal up to your brain.

Your brain receives this message near-instantly. Then, it correlates that information with every other bit of information it has coming in from all the other senses, plus your short- and long-term memories. What can you see? Hear? Smell? What were you just doing? Have you ever experienced a sensation or situation like this before?

Your brain puts all of this together in a fraction of a second and decides that yes, you are in pain. It sends back a “OW THAT HURT” signal.

Now, the turnaround on this is incredibly fast. Like, insanely fast. Be impressed by how quickly your brain can sort through information when it really matters.

But even so, by the time your brain sends a message down to your nerves telling them to explode with pain, a strange survival mechanism has happened. Adrenaline has overloaded your nerves. Adrenaline is a neurotransmitter, so it can make your nerves unable to transmit any more signals by maxing them out. The nerves become numb until the adrenaline dissipates. So although your brain is telling your toe to HURT LOTS, your toe literally can’t until that adrenaline dump wears off.

This probably takes about 3 or 4 seconds because you’re not in a dangerous situation. Adrenaline wears off very quickly. Actual danger or significant injury can delay that pain for an impressively long time because the adrenaline keeps getting replaced.

The reason why this survival mechanism exists is so that we don’t reflexively move our (very sensitive) hands or feet in a life-threatening situation. You can stub your toe scrambling away from a lion and never register it. You can have your fingers badly bruised catching your child as they fall out of a tree and only notice later. It’s so we don’t stop right at the wrong moment.

The other answers address adrenaline, but the likely true explanation is that touch and general stimulus are carried by coated (myelinated,, meaning covered in myelin, a fatty sheath) nerves which carry information quickly, but specialized pain nerves are not insulated(unmyelinated) and carry information slower. So you feel the stub quickly, but the pain from the stub doesn’t arrive at your brain until later.

ELI2: Touch nerves transmit quickly, pain nerves transmit slowly.

You sense the act of stubbing your toe as fast as any other touch, the OUCH builds a little bit later as the internal things that got ‘insulted’ or even injured make that known, the nerves that register touch as located on the skin, your muscles may have nerves but their job is very different. I don’t know what is in tendons and cartlege but you can go for a long time before your body gets around to telling you DUDE, we’re really in a bad way here…..