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nerve message transmission. Help please.

Brian Bjørn bbjorn at mdb.ku.dk
Sun Oct 19 06:43:45 EST 1997


Lars Thomsen wrote:

> Brian Bjørn wrote in message <344598C0.875E1A20 at mdb.ku.dk>...
>
> >> If it is electro/chemical what sort of levels.  I assume the greater the
> >> level the greater the reaction?
> >
> >No, not really. Action potentials are all-or-none responses: If a certain
> >treshold level is reached an action potential with a distinct shape
> >(amplitude and duration) is fired. The transmitter release from one single
> >nerve terminal is therefore also an all-or-none response.
>
> A little correction here...
> Gradually changing the frequency of action potential will give a gradual
> release of neurotransmitters. So the neurotransmitter realease is not an
> all-or-none event. Furthermore, the post-synaptic membrane potential is
> strongly modulated (in many systems e.g. by GABA)

I agree on that, but if you look at an axon where there is no change in
modulation and no change in action potential frequency, I still believe that it
makes sense to claim that neurotransmitter release is an all-or-none event. But
of course there will be an increased (frequency of) transmitter release if there
is an increased AP frequency.

> >Yes, there are different electrophysiological ways of assessing nerve and
> >muscle function. The techniques are quite sofisticated and requires a lot
> >more explanation and understanding of the basic principles underlying the
> >function of the motor system.
>
> The principle behind measurements are very simple...just as you can read the
> voltage of a battery with a voltmeter you can read the voltage across a
> neurone (or any other cell). However, to record from a cell you need a small
> electrode (at least if you want to record the cell membrane potential). You
> make the electrode by heating a thin glass tube and pulling it only the tip
> gets very thin...this electrode can then be inserted into a cell (which can
> be done by hand...e.g. dropping the electrode into a big collection of
> cells...like the brain...brrr...)

Sure, but measuring the potential of a single mucle fiber will not give you any
idea of nerve and muscle function at a more macroscopic level. This kind of
assessment would require more sophisticated techniques like electromyography. I
agree that the principles behind the measurements are quite simple, but
considering the level of knowledge of the questioner (no offense) I guess that a
little more basic knowledge on neuromuscular function would be a good idea
before discussing ways of measuring it. Just as basic knowledge of electrical
circuits is a good starting point for understanding measurements of
potentials...

> >> Are the same nerves used to transmit as well as to receive?
> >> (simplex/duplex)?
> >
> > No, not under physiological conditions.
>
> Not motorneurones...(ok..they dont recieve anything from the same target,
> but they do recieve) and many neurones in the peripheral system (e.g. the
> enteric nervous system) has a much more branched morphology that would give
> them the ability to recieve a signal from a cell in the surroundings and
> also act on it...Take for example neurones with P2X receptors innervating
> some kind of cell...the cell gets damanaged and releases some ATP which
> activates the neurone via the P2X receptors...just one example of a target
> that interacts with the post-synaptic cell and the wellknown NO/VIP relation
> betwwen smooth muscle cells and neurones is another..

And I only discussed motor neurons, which do not receive from the muscle fibers.

Thanks for you comments and corrections. I do not disagree with you, just wanted
to explain what I actually ment which maybe not was very clear from my first
posting :-) Hope that you will bear with me.
--
Venlig hilsen


Brian Bjørn
http://www.mdb.ku.dk/bbjorn/
'We all agree that your theory is crazy. The question which divides us is
whether it is crazy enough.' - Niels Bohr





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