Saturday, April 25, 2009

Fun with nerve endings

It's called Paradoxical Hotness.

You have several specialized nerve endings. The neurons that sense temperature are just beneath the skin. You have one type that senses warmth and another that fires when it senses cold. Oddly, we don't have receptors for hotness. That's where the fun comes in. I mean, if you ever get bored enough. Or if you have a little brother you want to bully.

The way hotness works is BOTH the warm and cold sensors fire. ("Fire" means they send a message to the brain. The brain accepts messages from nerves as true.) For example, if you jam your hand into, say, a bacon slicing machine or an electric toaster, pain neurons fire. The brain believes you and tells your vocal chords to start screaming. Or wherever screaming comes from. The point is, the brain believes the messages the nerves sent it. And that is a good thing, by the way.

But there are no specialized neurons dedicated to feeling hotness. Fancy that. And God's little attempt at nerve economy can be the source of entertainment, if you like. Here's how:

First, let me remind you (since it has been two or three paragraphs ago since I mentioned it) that the body senses hotness because something hot triggers BOTH nerve receptors - warm and cold. If you hold your hand under very hot water, you will jerk it away quickly because the hot water has triggered both the warm and cold nerve cells near the surface of the skin. Are you with me?

Do this experiment. Run two small copper tubes side by side. Have cold water running through one tube and warm water (not hot water) running through the other tube. Now simply reach out and grasp both tubes in your hand. Simple, right? Har!

Even though your logic tells you it isn't hot (because it isn't really hot) you still can't hold onto the tubes. You simply must let go because you feel searing hotness. This is such a marvelous discovery. Or at least it is to little boys.

So, what you do is, you get a victim (or you try it on yourself because you know your superior reasoning skills will prevail over your brain's reflexive reactions) and you let the person feel the pleasantly warm water coming out of one tube; then you prove the other water is cold. Neither is hot.

If you ARE able clench your fist around them both for more than a second or two, I guarantee you will feel the pain of extreme hotness. But DO try it sometime.

Perhaps you have discovered other ways to amuse yourself with your body. If so, please share.


  1. No, sorry, this doesn't work, or it's a very peculiarly American phenomenon. Or, more likely perhaps, is it a ruse to get people (me) crawling around trying to find pipes where hot and cold run alongside? For the amusement of the masses?

    Re: your last paragraph, I always share.

  2. Would this work if you put one foot in a bowl of warm water, and one in a bowl of cold? Please try it and report back, for the sake of Clarity (who is she, by the way?).

  3. Try swinging your right foot in a clockwise circle and trace the letter L in the air. Hahahahaha Watch your foot.

  4. I don't know if this would work or if it's reflective of actual neurology. My neurology book (seriously, I have one) says we're not quite sure how thermoreceptors work and Wikipedia says that there's speculation that cool neurons may be a collection of thermally sensitive neurons.

    I don't know and won't pretend I do. However, I DO know that we are much more careful, when evaluating EVA surface temperatures (in space thermal extremes often run from -375 to +375 degrees), with cold than with hot temperatures, given that experience shows the crewmember will jerk back from a high temperature before it can damage the suit, but detecting a cold temperature surface is less exact. Frostbite is a serious concern and the crew often puts their glove heaters on preemptively. No joke.

  5. @A. - Well, you can't put one in one hand and one in the other. They must be close enough together where they will trigger receptors in the same close zone.

    @Sheila - Oh, Sheila! If you put one foot in cold water and one foot in warm water your eyes will cross! Must be like what I described. You must not freelance here.

    I do recall in the military that if you placed a sleeping guy's hand in a container of warm water you could sometimes make him pee. I am not sure if that is related. I must ask Soubriquet, a it strikes me as a different area of science. :)

    Perhaps Coronet Windsor would know. Or whatever the delightfully spunky chap's rank is now.

    @Ettarose - Is swinging your foot REALLY the only thing you can think of to derive pleasure from nerve endings? Sigh. I will try it. Right hand or left hand?

    @Stephanie - Yes, it is serious. Copied it out of a college textbook. "Essentials of Psychology" third edition. ::wrinkles forehead and bites lower lip:: No, I am not sure why Psychologists would even need such information to practice psychology. No, I don't know what such a book is doing on my bookshelf. It still has the price sticker: "University Book Store $88.50". At that price I am sure I ripped it off rather than bought it. I assume UNM since I used to live in Albuquerque. Many other cool stuff in the book though, such as the different types of memory and how much one should charge a depressed person for therapy sessions. (I assume if they are suicidal you must hit it hard at first and charge them double or even triple. Otherwise you won't get paid at all, will you?) Ummmm... what was that again about frostbite?

    PS- you don't HAVE to know. I just told you. :) :) You are such a skeptic.... Sigh.

  6. Sounds a fun thing to try out on someone! I will try and report back sometime to make sure it is not just an American thing, ha ha

  7. "Well, you can't put one in one hand and one in the other. They must be close enough together where they will trigger receptors in the same close zone."How close is close? Have you actually tried this? I did have both in one hand. I was crawling under a sink at the time (the things I do for you!). Now I admit that our pipes don't run in a double helix - is that a requirement? I'm not sure how popular I will be if I demand some re-plumbing in order to try out this experiment.

  8. @Frostygirl - Let me know... :)

    @A. - Maybe the psychology was to see if they could get anyone to try this. I am having my doubts now, because I know you always tell the truth.

    On the other hand, if may not work in France. I don't know why. Many things don't work in france. Perhaps the water is too lukewarm. Please report back if you meet with success. But I am starting to things we should all move on. :(

  9. Hey, I took you on faith with Madison and was mocked for my trust. Now, you pay the consequences.

    I don't believe if can happen, but then I also have read that water always turns a particular direction in a drain - except it doesn't.

    I'm actually a professional skeptic. My job is often to listen to what experts assert and find out what's wrong with it.

  10. "I don't believe if can happen,the then" should have been "I don't doubt this experiment has had the results you cite since you tell me your serious, but WHY, I can't say I'm convinced."

  11. Having made my living for some time as a plumber and heating engineer, I have often spent time with a hand wrapped around two parallel pipes, one carrying cold incoming water from the main, and the other carrying that same water after it has passed through a heat exchanger above very fierce gas flames.
    I have never had the experience you describe. part of the hand feels cold, the other feels cold turning to warm, and holds on until hot is achieved. I have accurate electronic measuring devices, but the mark-one hand is the best device so far.
    Maybe the spiral is vital?
    No. The more I think about it, the more sure I am that for me, at least, that theory is bogus.
    As for the water in a drain.... Maybe in a perfectly hemispherical bowl, in a perfectly still room, with no air movement, no convection currents, water left to stand for several hours, yes, maybe it works. In the real world there are so many random influences that serve to mess up the experiment, and it is interesting to watch how a spiralling drain can reverse direction. And not predictably.

    Question for the rocket scientist: I knew a man who claimed his engineering company had made some socket-wrenches (see, I'm talking american, not english there!) for EVA use on the space shuttle. He told me they had to be gold plated in order not to weld or seize to the workpiece in the vacuum of space. Was he telling the truth?
    About the goldplate and the reasons... mid 1990s this was.

    Max: Some years ago I had a book called "The Physiological Basis of Personality" I can't recall the author, but it was a fascinating read, I lent it to a 'friend', it never came back. However, if you were to find a book of that name, I'd recommend it highly.

  12. You're exactly correct on the water draining, but I couldn't convince my husband that, though I had witnessed it (we'd tested the theory in college), water could go different directions. He'd seen it on TV! (I really do not miss the man)

    As for your question sobriquet, your friend was wrong. There is gold on the sun visor because it's such a good reflector for a wide spectrum of light, but not any of the tools (they are generally reworked Snap-On tools, often with holes cut into the handles to make them lighter, with special tether points added or made to be pressurized-glove friendly). I have never seen one gold plated (the socket wrenches I have seen are clear anodized - they look like metallic silver). Gold would not wear well.

    Now, EVA handholds ARE anodized yellow or gold so they can be differentiated from handholds that are not rated for human mass and loading (which are generally white or silver - you can tether a load to them but not a crewmember). However, they are not gold plated.

    In fact, most metal surfaces are anodized, alodined or painted to (a) protect against corrosion (which isn't an issue for gold) and (b) reduce overheating in the massive thermal extremes, where a gold or other bare metal surface would be BAD.

    I'm going to have to steal this comment for Thursday's Thieving.

    Soubriquet, feel free to ask any other rocket sciency questions at Ask Me Anything. That's why I have it.

  13. Max, I apologise for the questioning digression on your blog, I'll try not to do that, it's naughty.
    But I must say thank you for the answer. The guy in question did manufacture for snap-on, so maybe part of his story was true. Maybe he said anodised? but I'm pretty sure he said gold-plated, and that it was to do with either seizing to, or not contaminating stainless steel...
    Anyway, thanks to Max's blog, I know a few more random things than I did yesterday. Which is good.

  14. Where were you when I was doing science experiments with the kids? We would have definitely received a blue ribbon for this one.



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