Inhibitory vs Excititory spike

nettron2000 at nettron2000 at
Sat May 1 10:52:36 EST 2004

r norman <rsn_ at> wrote in message news:<r6s590hs7k98kfc34dlb15etoo0r2o2gdc at>...
> On 30 Apr 2004 17:17:02 -0700, nettron2000 at wrote:
> >would someone please explain the difference ? What im confused about
> >is how both excititory and inhibitory spikes can occur in a spike
> >train on an axon.How is this possible ? or is it ?
> > I was under the impression that all action potentials were pretty
> >much the same, according to the liturature.But then i read about
> >IPSP's and EPSP's or is this something completely different ?
> Yes, EPSPs and IPSPs are something completely different.
> The spikes are action potentials running down an axon.  When the
> action potential gets to the end, at the axon terminals, it causes the
> release of synaptic transmitter from the presynaptic side of the
> synapse.  Then, when the synaptic transmitter hits the membrane on the
> postsynaptic side, it binds to membrane receptors and causes ion
> channels to open.  Ions flow through the channels causing currents
> (postsynaptic current, or PSC) which changes the voltage (potential)
> on the postsynaptic cell, the postsynaptic potentials.  These can be
> excitatory or inhibitory.
> So the EPSP and IPSP is in a different cell and many steps removed
> from the spikes.  However, someone might take a shortcut in explaining
> what is happening and speak of an action potential in a presynaptic
> cell that has an inhibitory synapse (and hence produces an IPSP) as an
> inhibitory spike, or an action potential in a presynaptic cell that
> forms an excitatory synapse as an excitatory spike.  But this would
> have to be determined by context. There is no inherent excitatoriness
> or inhibitoriness about an action potential.
> Note: things are a lot more complicated than what I described in the
> earlier paragraph.  There are cells that work without action
> potentials and there are synapses on presynaptic terminals and
> reciprocal synapses and metabotrophic receptors that produce far more
> complex responses than postsynaptic potentials and all.  But that is
> enough for a start.

Thanks r norman for your very informative reply.Just to clarify one
specific detail; when you mentioned " a different cell and many
steps removed from the spikes.", did you mean to say in a different
PART of the cell that the spikes are impinging on ?

Thanks again, much appriciated.

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