Relation between Ra and a neck resistance.
Posted: Mon Mar 24, 2014 9:08 am
Hello,
I have a question about the cytoplasmic resistance Ra defined in NEURON:
In my model (about dendritic spines), I want to express the neck resistance (Ohm, not Ohm.cm) as explicitly as possible. The relation between Rneck and Ra is the following:
Rneck = (Ra*nech_Length)/(pi*(neck_Diameter)^2)
My problem is that when I enter this formula and set Rneck as a variable, varing its value on the GUI just doesn't change anything. As if it wasn't linked to anything regarding the spine. Howerver, Ra (which I conserved in the model) does affect the voltages in the spine when I vary it.
Here are the formulae where I cahnged Ra to Rneck:
forall { // this block is set in the cell definition (topology, geometry and conductances)(independante hoc.file)
insert pas
g_pas = 1/RmSpec // mho/cm2 conductance
e_pas = -70 // mV reversal potential (will be modified by seting Vrest)
Ra = RaSpec
for i = 0, 3 { // because I work with 4 spines
neck {
Rneck = (RaSpec*NECK_LENGTH)/(pi*(NECK_DIAM)^2)
Rn = Rneck
}
}
Then, in the simulation hoc.file I set this:
strdef space_constant_axon, space_constant_dendrite
proc ch_space_constant() {
forall{
Ra = RaSpec
g_pas = 1/RmSpec
}
for i = 0, 3 {
neck {
Rn = Rneck
}
}
lamda_ax = sqrt((RmSpec * axon.diam * 0.0001)/(4 * axon.Ra)) * 10000 // µm
lamda_dend = sqrt((RmSpec * dend.diam * 0.0001)/(4 * dend.Ra)) * 10000 // µm
sprint(space_constant_axon, "axon space constant %.0f um", lamda_ax)
sprint(space_constant_dendrite, "dendrite space constant %.0f um", lamda_dend)
}
What I am expecting is to see the amplitude of EPSPs in the dendrite decrease (and increase in the spine head) when I increase the neck resistance. But it doesn't work (no change at all) and I don't really se what's wrong.
Could you advice, please.
Thanks in advance.
I have a question about the cytoplasmic resistance Ra defined in NEURON:
In my model (about dendritic spines), I want to express the neck resistance (Ohm, not Ohm.cm) as explicitly as possible. The relation between Rneck and Ra is the following:
Rneck = (Ra*nech_Length)/(pi*(neck_Diameter)^2)
My problem is that when I enter this formula and set Rneck as a variable, varing its value on the GUI just doesn't change anything. As if it wasn't linked to anything regarding the spine. Howerver, Ra (which I conserved in the model) does affect the voltages in the spine when I vary it.
Here are the formulae where I cahnged Ra to Rneck:
forall { // this block is set in the cell definition (topology, geometry and conductances)(independante hoc.file)
insert pas
g_pas = 1/RmSpec // mho/cm2 conductance
e_pas = -70 // mV reversal potential (will be modified by seting Vrest)
Ra = RaSpec
for i = 0, 3 { // because I work with 4 spines
neck {
Rneck = (RaSpec*NECK_LENGTH)/(pi*(NECK_DIAM)^2)
Rn = Rneck
}
}
Then, in the simulation hoc.file I set this:
strdef space_constant_axon, space_constant_dendrite
proc ch_space_constant() {
forall{
Ra = RaSpec
g_pas = 1/RmSpec
}
for i = 0, 3 {
neck {
Rn = Rneck
}
}
lamda_ax = sqrt((RmSpec * axon.diam * 0.0001)/(4 * axon.Ra)) * 10000 // µm
lamda_dend = sqrt((RmSpec * dend.diam * 0.0001)/(4 * dend.Ra)) * 10000 // µm
sprint(space_constant_axon, "axon space constant %.0f um", lamda_ax)
sprint(space_constant_dendrite, "dendrite space constant %.0f um", lamda_dend)
}
What I am expecting is to see the amplitude of EPSPs in the dendrite decrease (and increase in the spine head) when I increase the neck resistance. But it doesn't work (no change at all) and I don't really se what's wrong.
Could you advice, please.
Thanks in advance.