From: sbharris@ix.netcom.com (Steve Harris  sbharris@ROMAN9.netcom.com)
Newsgroups: sci.cognitive,sci.med
Subject: Re: Explain this brain paradox.
Date: 27 Sep 2004 17:52:23 -0700
Message-ID: <79cf0a8.0409271652.26bc17df@posting.google.com>

sawal_7432@yahoo.co.uk (Sawal_7432) wrote in message
news:<5cd326f1.0409270852.47c9e631@posting.google.com>...

> >
> > Migraines and headaches appear to originate in inflammation of the
> > covering of the brain. In migraines there is often abnormal blood
> > flows so the pain may be originating in blood vessels but I suspect it
> > still involves the tissues surrounding the brain. As usual the
> > research is controversial but if you read enough neuroscience you get
> > used to that. Certainty is for the ignorant.
>
>   Hi again, thanks for the replies to my original question, i think i
> understand what you said.So i would like to make some further pints to
> clarify what i have been told:
>      1)So, a person using drugs, or someone feeling pain in their
> heads, might feel as if the pain's originating from their brains,but
> in actuality the pain is from an area adjacent to the brain,such as
> the membranes surrounding the brain? Does that mean these tissues can
> feel pain? If so, during the preliminary stages of brain sugery,whilst
> the skin around the head and membranes/tissues around the brain are
> being cut,the patient needs anaesthesia administered to him? And once
> the surgeon reaches the brain there is no need for anaesthesia then?
>   2)For the pain to originate in the areas near the brain,but to be
> actually perceived as if coming from the brain is a little odd.For a
> human,the brain is arguably the most vital organ,and yet a person is
> not even able to sense whether the pain of a headache or the euphoria
> from cocaine is from the brain or from the spinal cord or from the
> tissues surrounding the brain.How is it such an incredibly complex
> organ like the brain can mis-interpret the origin of relatively simple
> sensations?
> Sorry if my questions seem odd, or as if i'm being too fussy, but i
> just don't understand why the brain can't sense the origin of these
> signals.


COMMENT:

As has been explained, it's not so simple as just pain receptors being
present only in tissue "surrounding the brain". The dura mater, which
contains pain fibers, not only surrounds the brain, but in several
places penentrates it deeply. It goes vertically in a double layer
quite deeply between the two halves of the brain (the falx) and also
cuts laterally between occipital brain and cerebellum (tentorium). All
these tissues are enervated and can feel pain.  In addition, the
vessels (both arteries and veins) which lace through every part of the
brain at every depth, are sensitive to pain in dilation, and possibly
also to pain from stretching. So there are pain receptors throughout
the mass of your brain.

All in all, what this means is if you get past the dura, you can poke
a *needle* into the brain without feeling much, so long as you don't
poke big vessels, stretch anything too far, or nail a big deep
infolding of the dura.

BUT, please note that that much is true of just about all of your
internal organs. The brain is here being pretty representative of the
way the rest of you is put together. Generally, your internal organs
are sensitive only to pain from *stretching* their outer capsules, and
once you get past that, are made of substance which has few nerve
fibers, and which doesn't feel a needle or probe being pushed through
it and cutting it cleanly and without any pressure.

So, again, the brain here is acting like any other organ in your body.
If anything, because of the invaginations of the dura and the many
sensitive vessels which penetrate it, the brain is *more* sensitive to
internal damage than are MOST internal organs. So what looks like a
paradox really isn't. The only odd thing, of course, is that by
contrast to other organs, when the brain feels internal pain, the
signals might be taking a rather odd way around, to end up in neurons
not far from where the painful stimulus originated (depending of
course on which part of the brain is being damaged or stretched).

SBH