"Wolfram Sieber" <remove_this!helbrecht at gmx.net>:
> Is there any experience, how a neuron A connected only to a neuron
> B find its way to a neuron C more far away?
>> Assumed A "wants" to "connect" a dentrite to C? How would A find
> C? Or, more simple: Assumed A just "connected" to C, how did it
> find its way to C? Are there any signs showing up "follow this way
> to go to C, follow that way to meet D" or do they just grow along
> any existing neuron's extension?
There are whole books about this topic, development of the nervous
system. In short, the "growth cone" surveys its immediate environment
which might contain attractive and repulsive factors, and chooses its
pathway accordingly. The target also contains factors that tell it to stop
and make synapses. The receptors on the growth cones can also
switch from one type to another along the path, so that it depends on
one factor earlier and then on another factor later. Also, many factors
act redundantly to specify the pathways, so a single mutation often
have very mild effects.
In the case of the spinal cord you have nerves sending out from all
segments to reach the limbs, and those segments without a limb as
taget will have the neurons die from programmed cell death.
I dont know much about the details for the cerebral cortex and am
trying to figure out. The mechanisms are probably similar.