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neuron connections

AngleWyrm no_spam_anglewyrm at hotmail.com
Thu Dec 2 02:57:32 EST 2004

"Matthew Kirkcaldie" <m.kirkcaldie at removethis.unsw.edu.au> wrote in message
news:m.kirkcaldie-7151BA.18171102122004 at tomahawk.comms.unsw.edu.au...
> In article <f%xrd.429771$wV.213471 at attbi_s54>,
>  "AngleWyrm" <no_spam_anglewyrm at hotmail.com> wrote:
> Yes, nearly all neurons have a part which receives signals (dendrites),
> which then decide whether they will fire or not.  If the cell does fire
> it sends a signal down its axon, a long tube which may be super-short
> and contact the neighbouring neuron, or may extend all the way down the
> spinal cord and make contact with a motor neuron in the lower back.
> Some neurons have sensors down in the feet, and generate signals which
> travel all the way to the neck.  All of this transmission is one-way.
> There's not really a map of what goes to where: in the brain, everything
> connects to everything using one set of cells to go forward, and another
> to come back.  In the body, sensory fibres send signals in toward the
> spinal cord or the brainstem, and motor fibres come from those same
> places to make contact with muscles or glands.
> There's a lifetime to be spent figuring it all out!  Anything in
> particular you're interested in?

Yes, with respect to neural nets and artificial intelligence. I have seen
many such networks, and they involve a set of input neurons, which pass
signals to one or more layers, and then on to an output set. What I'm
wondering is if this directedness between neuron layers is an accurate
model. I have seen pictures of neurons, which look like a complex root
structure of inputs, and it gets me wondering.

If axons can be long (as in longer than just adjacent neurons), do some of
these axons feed signals to neurons that--either directly or indirectly
through other neurons--supply inputs to that very neuron? More technically,
is it correct to consider the brain as containing cyclic directed graphs?

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