What lowers the potential of neurons?

Richard Norman rsnorman at mediaone.net
Sun Dec 2 16:58:49 EST 2001


On 2 Dec 2001 20:23:06 GMT, dag.stenberg at nospam.helsinki.fi wrote:

>Christian Wilms <cwilms at stud.uni-frankfurt.de> wrote:
>> If a so called "post-synaptic potential" is negative (inhibitory) or
>> positive (excitatory) depends alone on the neuron, which recieves the
>> signal (the so called "post-synaptic cell). The cell-membrane of this
>> neuron contains ion-channels which function as receptors. If these are
>> permeable for positively charged ions (Na+, K+, Ca2+), the potential
>> will be excitatory, if they are negative (Cl-), the potential will be
>> inhibitory. ....
>> The direction an ion will move, when a channel permitting it to permeate
>> is opened depends on the orientation of the driving force for this ion.
>
>While your description is correct in most aspects, it does contain the
>inaccuracies that
>1) increasing the permeability for K+ will cause inhibition, and
>decreasing it excitation, because the driving force for K+ is normally
>such that it will flee from the cell, thus hyperpolarizing = inhibiting
>the cell
>2) increasing the permeability for Cl- will always cause inhibition, but
>this can occur without any change in membrane potential (because of
>"short-circuiting")
>
>Dag Stenberg

And even more confusing -- if the membrane potential happens to be
more negative than ECl, the equilibrium or Nernst potential) for
chloride, then a synapse that increases the permeability for Cl will
actually cause a depolarization that looks like an EPSP.  In reality
that synapse will still be inhibitory.  A synapse is inhibitory if its
reversal potential is below threshold.

And don't even think about a synapse that actually DEcreases ion
permeabilities! 




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