Q: dendrites/gates

r norman rsn_ at _comcast.net
Sun Mar 20 09:05:03 EST 2005


On 20 Mar 2005 05:21:19 -0800, mimo_545 at hotmail.com wrote:

>
>r norman wrote:
>> On Sat, 19 Mar 2005 10:49:09 -0500, "Rick Craik"
>> <rick@@icebergideas..com> wrote:
>
>I found this
>
>http://www.sfn.org/content/Publications/BrainBackgrounders/communication.htm
>
>I think the studies which suggest that synapses are working like
>keys and locks, with positive/negative charged neurostransmitters
>makes sense for me to put an idea or two together.The only problem
>being that there should be an 'earth' shouldn't there?, wouldn't
>a neuron burn out if the charges are sent back?, (maybe a break
>in the myelin insulation attracts connections from other cells along
>the dendrite? I'm trying to assimilate the post) 
>

The whole subject is really rather complex.  It seems like you really
don't have enough background on cell structures and functions to put
things together properly -- I suggest that you get a good college
level intro biology book and read the several chapters that most have
on the nervous system and how it works.

You are mixing together several very different concepts.  First, at
the synapse the chemical transmitters do fit into the synaptic
receptors in a "lock and key" fashion.  This is exactly parallel to
the way that enzymes work -- the substrate chemical fits into the
enzyme active site using the same "lock and key" fit.

A completely different concept is that of the positive and negative
ions flowing across the cell membrane to produce electrical
potentials.  As described in the web site, positive charges entering
the cell makes it more "excitable", more active. Positive charges
leaving the cell or negative charges entering inhibit the cell, making
it less active.  All electrical currents must flow in closed loops --
that is a law of physics.  So there must be a "return path" for every
ion flow.  When positive charges flow across a membrane into a cell,
exciting it, there is also a flow of current down the inside of the
cell, out the membrane at a different location, and then down the
outside of the cell back to the starting point. These current loops
are easily detected -- the currents flowing in the salt solution
outside the cell produces small electrical potentials that are the
basis for extracellular monitoring of nerve activity.

A third completely different concept is that of the interruptions of
the myelin coat of vertebrate axons by the Nodes of Ranvier.  Not all
animals have myelin -- only vertebrates do.  Not all cells have myelin
-- there are many unmyelinated axons.  And the myelin only occurs on
the axon.  It works to a great extent by controlling the path of those
current loops.   The myelin is an insulator so current can only enter
or leave the cell at a node.  Since the nodes are spaced rather far
apart, one effect of myelin is to force the current loops to travel a
long distance down the cell before turning back.  This makes the
action potential travel much more quickly than it would in an
unmyelinated axon.  However the myelin is not located along the
dendrite, as you suggest, and it has nothing whatsoever to do with the
synaptic connections between cells.





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