[Neuroscience] Re: Differential Attenutation of EPSPs in Voltage Clamp vs Current Clamp

r norman via neur-sci%40net.bio.net (by r_s_norman from comcast.net)
Fri Aug 7 22:28:31 EST 2009

A voltage clamp always acts like a low resistance at that point on the
cell.  It is just that when the synapse is far away, it doesn't "see"
the clamp very much so the longitudinal flow of currents down the
dendrite are not much affected.  However when the synapse is very
close, then a major portion of synaptic current is shunted through the
clamp and the pattern of longitudinal current is seriously altered.

On Fri, 7 Aug 2009 16:22:30 -0700 (PDT), "Bill.Connelly"
<connelly.bill from gmail.com> wrote:

>Oh, so when the current is generated far away, the voltage clamp kind
>of acts like a lot of open channels, i.e that end of the cable appears
>to have low resistance?
>On Aug 8, 1:33 am, r norman <r_s_nor... from comcast.net> wrote:
>> With voltage clamp, there is essentially a "short circuit" across the
>> cable at the point of the clamp.  This causes a rather drastic
>> alteration in the pattern of current flow pattern when the clamp is
>> close to the synapse.  However when the clamp is farther down the
>> cable, the current flow near the synapse is virtually unchanged.  As a
>> result, when the clamp is near the synapse it "steals" pretty much all
>> the current, far more than would pass that way unclamped.  When the
>> clamp is far from the synapse, it only gets what current would
>> normally end up passing that far anyway.  Hence an apparent "faster
>> decay with distance" in voltage clamp than unclamped.

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