Why do our “pain” receptors work so much more slowly than our “touch” receptors? When I touch something with any part of my body, there’s no perceived delay in the time the sensory data reach my brain. But when I stub my toe, there’s an oh-God-this-is-gonna-hurt-like-hell-real-soon, followed by the actual pain.
Why is this, and from an evolutionary point of view, does it serve any purpose?
Well this is my first offical post ever, but anyways, in refernce to your question I believe it has something to do with when you touch something and you realize its gonna hurt (ie something hot) your reflex is to pull away, so if you can feel that you’re touching it before you are seriously burned then you can get away with less injury.
As the previous poster implied, there is a difference between the time your brain receives an unconcious impulse, which it may react to instantly, and the time you become consciously aware of the impulse.
Also, I would think that you’d be aware of the fact of contact with another object (which requires only the slightest pressure or temperature or even voltage differential) before you became aware that it was too hot or cold (which requires longer just for heating/cooling to take place. IE, it takes a while before damage begins to occur to the body, and touch happens faster.
Pain doesn’t go to the brain first like touch. It goes directly to a muscle reflex to protect you. If you grab a hot pan the touch signal and the pain signal will go to your spinal cord. The touch will go to your brain while the pain is directed to a muscles reflex to drop the pan. After you drop the pan the pain registers in the brain to remind you not to do it again.
Nerve impulses travel at different speeds. Some nerve fibers conduct impulses very quickly and some relatively slowly, all depending upon the degree of myelination along the nerve fibers.
There is distinct (survival) advantage to having touch signals travel quickly, e.g., swatting insects or otherwise escaping harm. And besides, it’s good not be distracted with pain when you may be running for your life, or swinging your club (accurately) at that sabre-tooth tiger who thinks you are lunch.
Pain, isn’t usually transient. Pain can afford to be much slower, because it’s going to stick around a while. And presumably, if you’ve managed to escape your latest brush with death, you’ve got time to deal with the pain.
The first kind are identical to fine touch receptors and travel in the same segment of the spinal cord as them (the dorsal columns). This is the “pinprick” type receptors – sharp pain which we can feel quite quickly and respond to (by fast spinal reflexes). It is carried by the same, fast, myelinated A neurons as light touch. It also goes to the same part of our brain as normal touch (the precentral gyrus).
The other kind of pain is more like chronic, aggravating, wearing pain. It is carried by much slower C fibers which are unmyelinated. It travels in another part of the spinal cord, the ventrolateral system. It actually goes directly into the cingulate gyrus, the part of our brain responsible for emotion. This is a much harder pain to deal with, especially chronically.