IUBio

minature inhibitor postsynaptic currents

r norman rsn_ at _comcast.net
Thu Sep 16 21:28:56 EST 2004


On Fri, 17 Sep 2004 01:38:13 GMT, BilZ0r
<BilZ0r at TAKETHISOUThotmail.com> wrote:

>r norman <rsn_ at _comcast.net> wrote in 
>news:44bkk0dri5sa7othkk641e3eldm1md6b8l at 4ax.com:
>
>>>Oh... I thought spontaneous potentials were the result of sponateous 
>>>firing of a neuron, as against evoked firing.
>> 
>> No, it is the spontaneous release of a vesicle, as against release
>> evoked by presynaptic depolarization and consequent Ca++ events.
>
>Then what do you call potentials induced by spontaneously firing neurons?

Action potentials?

The issue here is synaptic events.  Once an action potential is
triggered and travels down the axon, the presynaptic terminal can't
tell whether the AP was "evoked" by some other cell's synaptic input
or an experimenter's stimulus or whether it was "spontaneous".  So if
you are talking about post-synaptic events, which you are when you
talk of psp's or psc's, that distinction doesn't matter.

If you are recording action potentials in axons, then you might be
interested in the difference between spontaneous and evoked
potentials.  But when you use the term "spontaneous potential" you
must carefully provide an antecedent to indicate just what kind of
potential you mean. Spontaneous minis always means vesicle release not
evoked by a presynaptic action potential.

You have to be careful, here.  Many cells function quite nicely
without action potentials at all.  Graded potentials in the
presynaptic terminal modulate transmitter release.  In those cells,
the notion of "spontaneous" release is somewhat questionable.  The
frequency of these release events depends upon, and therefore is in a
sense evoked by, changes in potential.







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