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Author Topic: Related points?  (Read 3763 times)

Offline neilep

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Related points?
« on: 06/09/2004 19:47:29 »
Sorry...can't think of a good enuff title for this question but can you please me why that when I scratch an itch, I often get a reaction/sensation elsewehere in my body ?....why is this and why are they connected this way ?...is this related to the science of accupressure/puncture ?

Your touchy feely pressure pointy anaswers will be most welcomed...ta

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Offline chris

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Re: Related points?
« Reply #1 on: 07/09/2004 15:57:13 »
Right, this is a very good question, and I too have had this experience. There is a region of my flank that is 'repeated' in the equivalent position on my arm, so if I pinch my side I simultaneously elicit pain in my elbow.

This can be explained by a bit of cross-wiring in the nervous system. It's like plugging your telephone into someone else's line - when their phone rings, so does your's, even though the phone call isn't for you.

Nerve endings from the skin run up to the spinal cord where they connect up with a second nerve cell which relays up to the brain the information arriving in the first nerve fibre from the skin.

These inputs to the spinal cord from the skin form a representation of the surface of the body within the cord, but the odd nerve fibre can go a bit off course and connect to the wrong place, or to both the right place and the wrong place. Often this involves the limbs and the adjacent part of the trunk because of the way the body develops as an embryo.

You started off as a flat sheet of cells that rolled up sideways to form a tube; one end formed your head, the other your 'tail'. From the sides of this tube, at the top and bottom, the limb buds sprouted, and went on to grow into arms and legs. As they grew they took with them the nerve supply from that part of the trunk from which they originated.

Occasionally some of the nerve fibres supplying the limb also branch into the trunk, so stimulating the nerve on the trunk makes you 'think' the pain is coming from the arm.

The phenomenon is termed 'referred pain' - because the sensation is quite literally referred from one body part to another - and is a similar phenomenon, in some ways, to synaesthesia where mis-connections in the brain enable people to feel smells, taste shapes and hear colours, among other things.

Where is your referred sensation, if I dare ask ?

Chris

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Offline neilep

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Re: Related points?
« Reply #2 on: 07/09/2004 19:49:21 »
Thanks Chris....erhmm !!!...I purposely did not say where the ' referred pain ' manifests itself because I was a bit embarrassed, but, seeing as this is between you and I only..I know I can rely on your confidence[:I];)...err...it's when I scratch my BOLLOCKS !! Specifically at the base underneath[:I]..the referred pain manifests itself behind my right ear !!..it can ruin a perfectly good scratching session !!:)

Phew, glad I could divulge that to you Chris...I know my secret is safe.[:I]


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Offline roberth

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Re: Related points?
« Reply #3 on: 08/09/2004 00:23:51 »
So, now your secret is out, does it work in reverse? While it may ruin a good scratch, someone nibbling your ear must be fun !!
 

Offline tweener

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Re: Related points?
« Reply #4 on: 08/09/2004 03:08:32 »
I don't have anything as funny as Neil, but this weekend I got stung by a wasp on the lower part of my shoulder blade and felt the sting on the side of my neck also.  Two for the price of one.  Fortunately the sting was the only injury as I bailed off the ladder from about 14 feet up.

Also, isn't "referred pain" the reason that a heart attack often makes a pain in the left arm?  I also remember that when my wife's gallbladder was attacking it made her right shoulder hurt and the doc said that was typical and was referred pain.

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John - The Eternal Pessimist.
 

Offline neilep

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Re: Related points?
« Reply #5 on: 08/09/2004 10:35:52 »
....sorry Roberth for not replying sooner, spent the whole night scratching my ear !!....

John, yes I've heard that too about the left arm/heart attack thing... and I do hope nasty wasp got his comeuppance !!

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Offline chris

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Re: Related points?
« Reply #6 on: 08/09/2004 13:03:52 »
Absolutely right - pain from the heart - usually provoked by ischaemia (insufficient blood flow which starves the heart muscle of oxygen) - is felt all over the chest, down the arms (most usually the left) and up into the neck and left jaw. Sometimes patients will complain only of an arm ache which is why heart attacks and angina can be difficult for people to recognise.

Pain originating in the gallbladder (which dangles below the liver and stores bile to aid in fat digestion) is also felt in the right shoulder blade because the nerves supplying the gall bladder run with the phrenic nerve (to the diphragm) which originates from the neck. Pain is therefore referred to the part of the body supplied by that region of the neck - the so-called C4 dermatome.

Another common situation in which patients experience referred pain is ureteric colic - when a kidney stone (calculus) leaves the kidney and starts to ream its way down a ureter towards the bladder. This is reputedly one of the worst pains an individual can experience (women may disagree on this one) and sufferers classically report that the pain radiates "from the loin to the groin" - often to the tip of the penis or into the labia.

The reason for this comes down to embryology again. The kidney initially forms in the foetus deep down in the pelvis and, as the baby develops, it migrates upwards, taking its local nerve supply (from the groin) with it. So when the kidney or the ureter (the tube connecting the kidney to the bladder) are irritated or become inflammed the pain is 'referred' to the groin.

The feature that unites these examples is that each of the organs concerned are 'viscera' and typically pain from viscera is poorly localised. Whilst it is extremely useful to be able to pinpoint where on the body surface a stimulus has arisen (so you can put your hand in your pocket and select 50p from a collection of coins, for example) the same degree of accuracy in localising pain is not required for deep viscera because it confers no day to day advantage. It would also be extremely costly, biologically, to build a representation of the internal organs in the same way that the brain maps the external body surface and limb position.

Chris

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Re: Related points?
« Reply #6 on: 08/09/2004 13:03:52 »

 

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