white surface of the brain

Kalman Rubinson kr4 at nyu.edu
Thu Sep 6 12:53:02 EST 2001


On Thu, 06 Sep 2001 17:41:43 GMT, remove_this!helbrecht at gmx.net
(Wolfram Sieber) wrote:

>This is a quote from comp.ai.philosophy, from 3 Sept 2001:
where, apparently, few know anything about neuroscience.
>
>CyberLegend:
>> > > Human brains have the common thing of having a layer of
>> > > signal-carier neurons around it, that can carry the signal from one
>> > > circut to another

Sure but, since neurons make up the circuits, this has little useful
meaning.

>Wolfram:
>> > Well my understanding of brains i not wide enough to follow. Does
>> > the above mean that there are neurons working like
>> > "transcontnental" pipelines for signals? Dragging signals here and
>> > dropping them over there? (Are these "pipelines" fixed in place or
>> > are they just hiking around? [Well, this is a bit off topic here.
>> > Should i better ask in a neuroscience group?])

Yes.  There are long pathways which have been described as conveying
information from one circuit region to another (e.g., from the spinal
cord to the brainstem or thalamus) but these pathways are the axons of
neurons and, therefore, are not completely separable from those
circuits.

>CyberLegend:
>> [Don't worry about it, it's a common subject around here. =]
>> These signal-cariers are the whiter layer, surely you've heard of them
>> before. Yes, they do what you described, in fact they're perfect for the
>> job, because they transist signals about 3 times faster than normal

Really?  First, there is a SUBcortical stratum of white matter that
interconnects regions of grey matter.  Second, these are, still (as
above), the axons of cortical neurons, Third, what evidence is there
that they conduct faster?

>Here i heard about that.
>> (gray) neurons. I don't know if they are mobile, I'd say they are fixed,
>> what I do know is that they can grow, causing more contacts and thus
>> more room for meaning transfer (as I define meaning in the brain).

Grey matter is grey because, due to the dense packing of neuronal cell
bodies, the density of myelinated axons is low.  When that density is
high, i.e., in white matter, the material reflects light better.
Neurons make up a substantial portion of both with most of the cell
bodies in the grey and most of their axon lengths in the white.  There
are, of course, intermediary densities.

Kal




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