IUBio

grey vs white brains' surface

Richard Norman rsnorman at mediaone.net
Sat Oct 6 17:36:47 EST 2001


On Sat, 06 Oct 2001 18:36:49 GMT, REMOVE_CAPShelbrecht at gmx.net
(Wolfram Sieber) wrote:

>Hello group,
>
>(I had to move, so i was a while away. Now i am back. :)
>
>During further thinking on the job of a neuron, i came to the
>question, if grey and white components of brain exist on any kind
>of brain. That means: as well on a human brain as on a
>Drosophila's "brain".
>
>Do you know of any animal with brains not divided into these two?

As others have mentioned, white matter is white because of myelin.
Since myelin is only found in vertebrate animals, the distinction of
white vs grey makes no sense for other types of animal.

However, the real distinction is between areas largely composed
of cell bodies, dendrites, and synapses (the grey matter) and areas
largely composed of axons of projection neurons carrying information
over a relatively large distance.  That distinction is certainly found
in virtually all animals.  The 'higher" invertebrates (annelids,
arthropods, and molluscs) have central nervous systems containing a
collection of ganglia joined by connectives,  Within each ganglion is
an area called "neuroipl" which consists of the dendrites and
synapses. (The cell bodies tend to be off to the side).  Certainly
this area corresponds with "grey" matter.  Tere are longitudinal
connectives and transverse commisures containing bundles of axons
interconnecting regions.  Certainly these correspond to "white"
matter.  The brains of these animals are greatly enlarged clumps of
usually multiple segmental ganglia merged together.  But, then, that
is exactly the same description as the vertebrate and mammalian brain,
a greatly enlarged and expanded portion of the anterior segmental
spinal cord.




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