[long, off topic info] decussation problem

miandan at geocities.com miandan at geocities.com
Fri Nov 1 20:44:29 EST 1996


> I'm telling you, it does. How it's so is disclosed following
> hemisection of the brain stem at the level of the medula. Pain &
> temperature sensation are lost on the same side of the face and on
> the opposite side of the body. This occurs because the ipsilateral
> spinal trigeminal tract, and the contralateral spinothalamic tract
> are severed.

OK.  You cut a fiber tract, and get a loss of the corresponding
sensation.  So what?

> The correlation with necessary movement is that while the head
> must "move away from" environmental sources of noxious stimulation
> to the face (to avoid further tissue damage), it's useful for the
> head to orient toward environmental sources of noxious stimulation
> to the body (so that the powerful visual and auditory systems
> enter into the determination of avoidance behavior).

Let's imagine the behavior you describe is meaningful.  I just
do not understand what is the role of decussation in it.
A brain without decussation can control the same behavior as well.
 
> The correlation with the neuroanatomy

Correlation of what with neuroanatomy?

> is that both the
> spinaltrigeminal & spinothalamic tracts project collaterals to
> reticular nuclei which project ipsilaterally to the cerebellum.
> The activation that follows this route conveys pain's "mountain".
> The outputs of the cerebellum are entirely-inhibitory, so they
> take the "mountain" and transform it into a "valley", and project
> this "valley" back to the effectors via the deep cerebellar
> nuclei.

The output of the cerebellar nuclei is excitatory, by the way.
 
> Now, this could be accomplished without the great decussations,
> but the result would be significantly less-powerful because fiber
> lengths would be increased, and therefore activation latencies,
> and therefore, survival propensity would be decreased relative to
> organisms having the crossed neural topology.

Fiber lengths?  That's interesting.  Can you estimate the yield
you are talking about in ms?  So, you think that only the
animals with short fibers are good?  How about basketball players?

> This pain-avoidance architecture permeates the CNS at all levels.

A drawing might be helpful here.
 
> It's necessary to use the "topologically-distributed" modifier in
>  order to address the twists, turns, and crossings of the fiber
> pathways.

OK

> "Topographical" does not connote such.

???

> Decussation
> constitutes the structural order that aligns the neural
> "neighborhoods", preserving their topographical correlations,

Again, a drawing might help.

> so
> that the necessary inversion of inputs and outputs (the
> "mountain"-"valley" transformation) will occur.

This may become clear when you show a drawing.

> The minimization

Minimization of what ????????????????

> occurs because the reticular excitation breeds cerebellar

I do not see any logical connection here.

> inhibition. (Using the "ratio" is just a compact way of saying
> excitation is minimized and inhibition is maximized.)

Well, that's a too compact way.  Sometimes you need to write
less compactly.

> I'm sorry, it has everything to do with decussation. Decussation
> is =required= if neighborhood relationships are to be perserved
> while fiber lengths, and hence activation latencies, are
> minimized.

But you agree that you did not say that in you previous message?

> but, as is explained above, a crossed will outperform an
> otherwise-equivalent non-crossed system.

You still have to convince me in that.

> The correlation between decussation and what's described by the
> 2nd Law of Thermodynamics (WDB2T) is huge, but consider only the
> shortening of fiber lengths that decussation makes possible. Not
> only does this shorten activation latencies, it also
> lowers energy consumption, thus increasing the efficiency of the
> system's performance.

May be.

The bottom line is the following.  Your writing became somewhat
more clear.  Please post a drawing and clearly explain what
benefits decussation gives.



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