Random thought of the day

Our skin doesn’t sense temperature directly. It only senses the difference between the temperature of the skin and the object being touched. I wonder if this means the sensors are actually measure heat/energy flow.

Technologically heat flow sensors are more difficult to build than temperature sensors. I wonder why evolution ended up with heat flow sensors rather than temperature. Was there an evolutionary advantage to this or is it more biologically difficult?

9 thoughts on “Random thought of the day

  1. I’ve always thought it was a rate of heat transfer thing: A 50 degree chuck of plastic will not feel as cold as a 50 degree chunk of copper. Of course the rate of heat transfer also depends on delta T as well, so I guess in a sense it measures both.

  2. Remember evolution is not about optimal solutions. It is about solutions that work good enough for right now. Thing of it as a variation on extreme programing were you only solve the problem you have right now.

  3. LC Scotty,

    Of course it’s transfer rate.

    On the plastic v. copper keep in mind that as soon as you touch the object the contact point of the object is going to change temperature in the direction of your skin. Hence the surface of the plastic may well be closer to the temperature of your skin an instant after being touched because it doesn’t conduct the heat very well. In other words it reaches equilibrium very quickly with the surface much closer to your skin temperature than does the copper.

  4. I’d imagine that biologically heat-transfer rates are much easier than temperature simply because skin is never at a constant temperature, so we can only judge relative temperatures, and since when you pick up a cold or a hot item it alters the temperature of your skin, and your body takes steps to maintain constant temperature, so I’d imagine a simple thermometer would be very difficult with a system like that.

  5. A true thermal sensor requires some sort of rational basis, some sort of scale or zero to measure values against. Here the data is collected at the sensor.

    However our nerves work on protein manipulation. This “hotter or colder” type of sensor is easier to manufacture from a biological standpoint as you can do it easily with protein folding at different temperatures to influence the permeability of cell membranes to ion flow. Because it is the flow of ions across the membrane that “fire” a nerve. So you have an analog sensor sending a “digital” signal. Enough digital signals and the brain will translate that into an analog thought or sensation.

    But from a biological standpoint heat transfer is more important than absolute temperature. Too much heat to quickly and you cook, too little heat too quickly and you freeze. Some animals have developed heat dump cycles like that camel, and others like humans simply spend a lot of energy on homeostasis.

    It is an interesting subject.

  6. Interestingly enough, your skin doesn’t feel anything. The nerves do all the feeling.
    Also, your nerves can’t tell the difference between hot and cold–both are sensations of pain, to the nerve. The rest of your senses tell the brain whether what you are feeling is hot or cold and to respond appropriately.

    I have a somewhat thorough understanding of the intracacies of nerves, damaged nerves, and nerve pain.

  7. “…from a biological standpoint heat transfer is more important than absolute temperature.”

    Exactly. For the environment that is true, and the nerfves in our skin sense the environment. It’s most important for animals to sense what is warming them up or cooling them down. That is to say it answers the question; what are the effects on me from my environment, realitive to my needs? You may feel comfortable in freezing temperatures if you’ve been working really hard, for example, because at that moment you need to off-load some extra heat. Sensing absolute temperature, and desiring 72F after a hard workout would be counter productive to that need.

    Absolute temperature is in fact sensed by other means, as we maintain body core temp. It all fits together rather nicely. The body “wants” to either take in heat or reject heat, so as to maintain core temp, and the skin nerves enable us to find opportunities to do either one as needed.

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