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mat mats_trash at hotmail.com
Wed Apr 10 04:20:15 EST 2002

Larry Lart <larry at alphyra.ie> wrote in message news:<a8sm6e$v9t$1 at kermit.esat.net>...
> Is it possible (normal?) that the firing potential of one single neuron 
> to determine the excitation(firing) of another? So, is that a matter of how 
> many synapsis are between two neuron or you need signal from more then just 
> one neuron?
>   And also(becauseI reckon that in nerves that's true) is this dependent to 
> the type of neuron ?

When a neurone synapses onto another, depending on the transmitter
released and the array of receptor expressed at the post-synaptic cell
different things can happen.  In general the input of one synapse will
only be enough to cause a minimal (but important) change in the
membrane potential of the post-synaptic cell.  These are called
post-synpatic potentials and may be inhibitory (IPSP, hyperpolarising)
or excitatory (EPSP, depolarizing).  In the case of a single EPSP it
would rarely be enough to induce an action potential firing in the
second cell.  Whether the post-synaptic cell fires is determined by
the temporal and spatial summation of EPSPs and IPSPs from the
thousands of inputs over the dendrites and cell body (soma).  In the
cortex at least, a particular cell will only have a few syanpses onto
any other particular cell, but each cell has input from thousands
surrounding it.  This is called divergence-convergence and ensures
that no cell has too much influence.

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