Does anyone know?
Could you please provide a cite as well?
WHACK** now, let me know when it hurts. 
Guess it depends on what kind of pain or where the injury occurs.
Having been hit in the nuts I’m not sure if the pain is worse or the 5 seconds waiting for it is. Ok…the pain IS worse but I hope you see my point.
I’d also imagine many factors relate to this. Does burning register at a different speed that say stabbing? Does getting stabbed in the ass register at a different speed than getting stabbed in the finger? Does being aware that you are about to receive an injury differ in the realization time from getting blindsided?
In short, and this is a WAG, I think the question as stated is too broad to get a meaningful answer. Perhaps something like, “How fast do nerves transmit impulses?” Of course, that doesn’t account for ‘processing time’ for your brain but maybe that’ll be closer to what you are looking for.
Just say I get stabbed in the arm… how long does it take for my nerves to pulse a message to my brain and then back to my arm to register the pain?
How fast does the pulse travel?
The pulse would travel at the intrinsic rate of nervous conduction. There would be a reflex component that involves a simple arc to the nearest ganglion and back to the motor nerve, prompting a withdrawal action.
The pain is registered with transmission to the pain centre in the brain, which, if my memory is correct, is in the hypothalamus.
There’s a telegram for you sir,
Better read it on the spot.
It says your hand is near a stove
That’s very, very hot.
The results can be quite painful,
And there’s no time to think,
Quick! Pull that hand away, and get it to the sink’
There’s a telegraph line,
You got yours and I got mine.
It’s called the nervous system,
And everybody understands
Those telegram commands
And you know that everybody better listen!
Cite: “Telegraph Line,” Schoolhouse Rock
Didn’t like my smartass answer :).
Ok…here’s what I found after an admittedly brief search for an answer.
I have no idea what a “myelinated” axon is but the link mentions that myelination does not complete till around age 12 and that Multiple Sclerosis destroys myelin leading to motor difficulties.
I also have no idea how reliable the info in that link is but there you have it for what it’s worth.
Sorry I don’t have a better cite but I heard a bit on NPR Science Friday a few weeks ago on this topic. One of the researchers said that the impulse for pain is significantly slower than ordinary sensations even thought it seemed to make no sense from an evolutionary standpoint.
Myelin is a protein sheath that insulates the nerve tissue and speeds up the signal. Myelinated nerves are usually major nerve bundles or tissues, whereas non-myelinated nerves consist of most of the lesser nerves in your body. IIRC, non-myelinated nerves transmit at approx. 1/2 to 1/4th the speed of myelinated nerves.
–Tim
Madhatter, the pulse needs only to travel to your brain to register as pain, not back down to your arm. The pulse back to your arm is only to recoil from the pain.
Also, IIRC, nerves that sense pressure fire more quickly than nerves that sense heat. Once the impulses get started, one would think that they travel at the same speed, but the lag time in the first sensation might make a difference. For example, if I branded your left arm and hit your right arm, in the same place, with a hammer, your right arm would hurt first. I have no idea if this lag time is significant or not.
There is also a distinct difference between the time it takes your nervous system to detect and react to a stimulus and the time you become consciously aware of the stimulus.
Reflex-type reactions (jerking your hand away from something that causes pain) will happen long before you are consciously aware of them, on a time scale consistent with the numbers given above for signal propagation speed.
Non-reflex reactions that require you to actively send messages (like the old dropping-the-ruler-between-the-fingers-and-trying-to-catch-it game) happen much, much slower because of the cognition required.
Also, you may remember both events as having been cognitive even if they were not (IOW, you may remember the jerking-away-the-hand event as having been a cognitive choice, even though it was not.)
My information comes from many sources, having read a lot about this. One small book that comes to mind is “The Mind’s Past” by Michael S. Gazzaniga (sp?). IIRC, he reviews some of the actual experiments that were done to verify what I’m claiming here. Also it’s written for the non-technical person, so it’s not too hard to follow.
Slight hijack here, but that trick where you catch a dollar bill dropped between your fingers really is possible: I’ve done it. The trick is to not look directly at the bill, but at something else. Apparently, response times are faster for periphreal vision (less data to process, perhaps?).
I’m sorry, you can’t register pain, because it’s already been registered…
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