Nerves bundled?

Richard Norman rsnorman at mediaone.net
Sun Sep 3 21:43:27 EST 2000


This depends to some extent on what you mean by nerve "signal".

Individual neurons carry information down individual axons, although
the axon can branch in a complex pattern.  Axons in the peripheral
system are bundled into nerves, like the multiple wires in a telephone
cable.  However, the separate nerve fibers seem to function without
any significant interaction, even if they are quite close together.

The myelin that wraps single axons of vertebrate axons is more than
an insulator, it dramatically alters the speed of conduction.  One
oligodendrocyte in the CNS can wrap an average of some 15 different
axons, while the Schwann cells in the periphery only wrap single axons.
However, I have never seen any suggestion that the group of cells
surrounded by a single oligodendrocyte are functionally related in any
way except to the extent that neighboring cells are likely to have similar
function.  The myelin "interconnection" has no functional significance.

All the above indicates that the neurons are distinct individuals, each
with a different signal.  However, in a broader sense, there is usually
a population of neurons that serves any particular function especially
in the vertebrate animals  A group of several to several hundred
or more cells all participate in the same general function and each
carries a slightly different aspect of the information.  In that sense,
the nerve signal is really carried by the population of cells.  For example
intensity of a signal can be carried by the frequency of firing of an
individual cell or by the total number of cells in the population that
are active.  Look up the terms "labeled line" and "across fiber" coding
in any good neurophysiology text to see more complex examples of
how a population of cells can transmit information.


"Bill Browning" <bbrownin at nospambellatlantic.net> wrote in message
news:wxDs5.6759$rG4.187083 at typhoon1.ba-dsg.net...
>      As I understand it, a nerve signal is carried by multiple nerve
fibers,
> not just by a single axon.  Is the myelin sheath around single axons; or
is
> it around groups of fibers which carry the same signal?
>      I visualize a nerve structure like a stranded electrical wire inside
an
> insulating jacket.
> Bill B.
>
>







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