h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Not the concept of pain, the actual physical mechanism of tranferring the "This really isn't clever" warning from the bit being damaged into the brain, and then on to your awareness?

waits for SExpert to arrive, but as I understand it there is a constant 'all is well' signal travelling along the nerves, and when that signal gets interrupted then you feel pain. Obviously a lot more complicated than that, with degrees of pain and interruption.

I've not come across that before, Ictoan, but it may well be true!

There are also specific pain fibres that carry signals to the spinal cord, and then to the brain. The signals start out at individual receptors, of which there are numerous types: mechanical receptors detect when they are bent or stretched; receptors that are triggered by heat or cold; receptors that detect noxious chemicals (such as a wasp sting) etc. When any of these sensors is triggered, a signal travels to the brain where it is interpreted as 'pain'. There are also short-cuts in the spinal cord ('spinal reflexes'), so that you can react to pain without having to think about it. If you put your hand in boiling water, for example, you'll usually have removed the hand before you actually feel the pain.

that last point is very true. I've never thought about it before, always assumed it was some form of 'cut off' that stopped you feeling the pain straight away, or some sort of overload. But yes, you do react and then have the small dread wait before the pain kicks in.

I only wish our bodies were better made to be able to release the inbuilt pain killers we have consciously, since the automatic process seems to be a bit cr*p really.

And there's also all the freaky stuff the brain does, memory of pain and so forth, hence phantom limb experiences.

There is also a syndrom that in the event of traumatic injury allows the body to keep functioning for a time, possibly until a place of safety is reached or help summoned, but afterwards all memory of the incident is lost. I know of a recent tragic car accident were one of the injured crawled a considerable distance, having sustained horrific injury, but afterwards only remembered getting into the car.

Or possibly not. The point of pain is to indicate injury and hence ensure that we can act against the injury.

If a person continues to put stress on an injuried part of their body this could cause irrepairable damage the pain e.g. a twisted ankle or pulled back muscle.

It is quite possible that evolution did come up with in built-pain relief as you say at some point but I would say that the animals with that ability died out due to not allowing their bodies to recover properly during life and finally died out.

Oh I know there is a reason, someone I knew at school had something whereby they had very little sense of pain in their knees (possibly legs) so had to be very careful they didn;t injure them. Had no end of problems.

But on the other hand, if I cut myself, does it really need to go on hurting for that long? I know I did, I stuck a plaster on it. Sorted. Now stop hurting!

Yeah, but think about it Ictoan, it has to keep hurting until it's healed, otherwise you'll forgot about it and won't take care to protect it. Then you'd end up damaging it again.

In that case why bother with having any pain reducing agents in the body? I'd sooner have them under my control than randomly working/not working with seemingly no reason.

A diabetic foot would be a case of this. Because of the poor sensation/feedback you will unfortunatly get cases where the pt has, for example, trod an a nail but never realised this untill they've done a visual inspection. By which point there foot could be ulcerated.

Now phantom limb sensation/pain is something quite different. Like was said previously the brain has a neural map of the body already registered. When someone has an amputation this map takes time to alter. Hence you find a lot of amputees who get out of bed after their operation and unwittingly go to stand on a limb which isn't there!

They think now that the area of brain which was responsible for the amputated limb actualy gets invaded by surrounding areas. Which can throw up interesting little issues like,

"every time I touch my nose I get a sensation from my foot."

The foot in question being no longer there. Some amputees report that they feel the phantom limb starts to shrink move proximaly into the body.

Unfortunatly every amputee exsperiences it differenty. So the've never been able to definativly say what happens.

Ah, yes, but I was thinking from the point of view of pain in the phantom limb. This can either be remembered pain, especially likely in cases where the limb was lost due to some trauma (say industrial accident or bike crash) and the brain replays the last sensation from the limb since it isn;t getting any information from it.

What about endomorphines?

As I understand it the trauma of serious injury, ie loss of a limb, generates morphine type chemicals which allow a person to save themselves or to move from danger in spite of a huge loss of blood, and to remain conscious.

Without this mechanism, nountain rescue would presumably find many more corpses than survivors of mountain disasters.

Pain is also heavily dependent on circumstances and context.

Minor injuries, such as a twisted ankle are sometimes much more incapacitating than more serious injury or illness.

Cancer often only really hurts when it has gone past the point of no return.

Grading pain often depends on the affected area, rather than the severity of the injury.

Generally the more load bearing the area, ie lower leg or foot, the more distressing the pain.

Women, I think are generally more tollerant of pain due to childbearing, and also often more tollerant of the sight of blood than men.

Most men are quite wimpish when it come to pain and discomfort.

Pain is also very good at heightening our senses to the point that there is a crossover.

Chilli powder and the pain of hot spice is quite a thrill to the hardened curry eater.

I think here that the endomorphine buzz in the aftermath of the pain stimulus is a turn on for some people.

Why else would anyone wish to be spanked before sex?

"every time I touch my nose I get a sensation from my foot."
The foot are is usually closer to the groin area which results in the even stranger experience of people getting feelings of sexual arousal in their phantom foot!

I've never had a patient report that back to me! Perhaps it's something they don't want to tell me.

To be honest though in ten years dealing with amputees the only ones who have felt their brain replaying the last sensation have been traumatic upper limb amputees. Three or four who had trans-radial slicing injuries say that their hand is making a 'clenched fist' as it was at the time of their accident.

I'm sure there's an h2g2 entry about alleviating that problem by placing a mirror on a table in front of you, putting the remaining arm on a table so the mirror reflection appears where the missing hand would be, and slowing unclenching the real hand.

Unfortunatly mirror boxes don't work for everyone, although I did read a journal last year about using one on a hip disarticulation patient in Ireland which was very successful.

Interesting! I guess it goes to show, yet again, that the brain is a very complicated thing, and so are we, and there's almost as many experiences of this as there are people.

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Isn't this similar to leprocy? No sensation so no signal of an injured area of the body. Then it gets infected etc, etc, tissue dies...

Alex.