Hemispheric control....

MS marshmallow5 at yahoo.com
Wed Jan 24 10:43:40 EST 2001


I hadn't heard the chordate/invertebrate theories before. Sound interesting.
Thanks. :)


Marcello


Richard Norman <rsnorman at mediaone.net> wrote in message
news:KABb6.44371$ft6.990132 at typhoon.mw.mediaone.net...
> Thanks for the reference.  I certainly didn't mean to imply that you
> actually held to this idea (that the retinal image reversal is related
> to the contralateral control in vertebrates).  You did clearly indicate
> that you had seen it proposed and that was the "best" yet.
>
> The real problem is that there really is no explanation for the
> contralateral
> connections, so anything, no matter how far fetched, seems better than
> nothing.
>
> Frankly, I like the old idea based on the fact that many invertebrates
> (the protostomes, like arthropods, annelids)  have ventral longitudinal
> nerve cords while the chordates (like vertebrates and us) have dorsal
> longitudinal nerve cords.  The idea is that the connection between the
> brain and the longitudinal cord rotated 180 degrees sometime in evolution,
> the chordate body developed "upside down" and that switched left and
> right as well as dorsal and ventral.  The notion that the hearts of those
> invertebrates are dorsal while ours is ventral might be related.  Of
> course this can't be true.  There are also major developmental
> differences in these two groups of organisms.  The last common
> ancestor must have been something more along the lines of a flatworm
> or possibly a roundworm with multiple nerve cords.   But the hypotheses
> enjoyed some success early in the 1900's.
>
> I like to use this as an example of the principle that, no matter how
> weird an idea you can come up with, you can find somewhere in
> biology an organism that tops it.  And, also, that evolution does
> not drive organisms to "perfection".  We are only "good enough
> to beat anything else".
>
>
> "MS" <marshmallow5 at yahoo.com> wrote in message
> news:8Xrb6.4162$mo2.473354 at news1.news.adelphia.net...
> > I found it:
> >
> > Why are vertebrate nervous systems crossed?
> > Capozzoli NJ
> > Med Hypotheses 1995 Nov 45:5 471-5
> >
> > Abstract
> > Contralateral central nervous control may be an evolutionary consequence
> of
> > dependence on the image-forming eye, especially in large organisms. As a
> > result of the topological transformation of the visual stimulus in the
> > pupillary eye, the external environmental hemispace impinges directly
upon
> > the contralateral internal organismal hemispace. Selective pressure
leads
> to
> > the development of central connections capable of the most rapid and
> precise
> > functional association of the internal milieu with the organism's
> > environment. The consequence is contralateral central sensorimotor
> control.
> > Previous hypotheses are discussed, including those based on
bilaterality,
> > binocularity the optic chiasm and avoidance behaviors.
> >
> >
>
>







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