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CELL PARAMETERS
The equivalent circuit for each cell compartment looks like this:
Vm
o__________________________________________________________
| | | | | |
| | | | | |
| \ \ \ | |
| --/--> --/--> / / \ ___|___
| Gex \ Ginh \ Rm \ / A \ _______ Cm
| | | | \ | / |
| | | | \ / |
| Eex --- Einh --- Eleak --- | Iinject|
| ------- ------- ------- | |
/ | | | | |
\ |______________|_____________|________|________|
/ Ra
\
|
|
o
Vm represents the membrane potential, or the potential in the interior of a
compartment relative to a point outside the cell. It appears across the
membrane capacitance Cm, and causes a current flow into the next
compartment through the axial resistance Ra when there is a difference in
potential between the two compartments. Iinject is the optional injection
current provided by an electrode inserted into the compartment. Eex and
Einh are the equilibrium potentials for the two types of channels which
are nominally excitatory and inhibitory. If no other channels existed,
Eleak would simply be the resting potential of the compartment.
Conduction through other passive channels causes this parameter to have a
value slightly depolarized from the rest potential, however. All of the
above parameters except Iinject may be set through the Cell Parameters
menus and channel submenus.
Gex and Ginh represent the variable conductances of these two channels.
The channel submenus allow some of the parameters which affect these
conductances to be set.
For soma channels, Gbar (in milli-Siemens) gives the peak magnitude of the
channel conductances.
For dendrite channels, gmax plays a similar role in setting the magnitude
of the conductances. The time behavior of the conductance is determined by
two parameters, tau1 and tau2. In the limit tau1 = tau2 (which is the
default case), a delta-function input to a synapse produces an initial
linear increase in conductance and an exponential decay with time constant
tau1. This is often referred to as the "alpha-function" form. When the
two parameters are different, the time behavior is of the
"dual-exponential" form.
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