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Minor capacitive current during IClamp simulation
Posted: Fri Aug 18, 2017 6:38 am
by vogdb
Simple soma-only that does not have any current mechanism except the capacitive one.
Code: Select all
create soma
access soma
objref stim
soma stim = new IClamp(0.5)
stim.amp = 1
stim.del = 50
stim.dur = 200
tstop = 300
During the injection the capacitive current is constant and equals a minor value 6.3e-04 micro A (IClamp is 1 micro A). My question is why? Shouldn't the current stop as soon as the capacitor is charged fully?
Re: Minor capacitive current during IClamp simulation
Posted: Fri Aug 18, 2017 5:10 pm
by ted
I don't see the problem.
When the IClamp generates no current, soma.i_cap(0.5) is 0.
When the IClamp generates a nonzero current, soma.i_cap(0.5) is nonzero.
In both cases, the value of soma.i_cap(0.5) is what Kirchhoff's current law predicts that it must be.
By the way, keep in mind that IClamp.i is in nA, but i_cap is in units of mA/cm2 because it is the density of capacitive current over the soma's PI*diam*L surface area.
soma print area(0.5)
will report the value in square microns, and 1e8 square microns equals 1 square cm.
Re: Minor capacitive current during IClamp simulation
Posted: Mon Aug 21, 2017 5:59 am
by vogdb
Sorry for the late response. I forgot to turn on notifications.
ted wrote:I don't see the problem.
When the IClamp generates a nonzero current, soma.i_cap(0.5) is nonzero.
In both cases, the value of soma.i_cap(0.5) is what Kirchhoff's current law predicts that it must be.
I agree totally but I don't understand still a single detail. Shouldn't be the plot of
i_cap be the same as in the case when
i_pas is used?
Am I correct that in the case when there are no mechanisms in
soma the circuit can be represented as a capacitor, an injected current and no battery
I'm missing something very important and fundamental.
Re: Minor capacitive current during IClamp simulation
Posted: Mon Aug 21, 2017 10:20 am
by ted
Code: Select all
. Icl Im
. +---current clamp->-+->-membrane---+
. | |
. --- ---
. - -
Im = Icl
c*dv/dt + g_pas*(v-e_pas) = Icl
If g_pas == 0
c*dv/dt = Icl