d_lambda rule

[Meena]

Hi,

I have some questions regarding how nseg is determined in NEURON to achieve the best possible accuracy. Some of my questions maybe be basic, but please bear with me.

I know from reading the textbook that the d_lambda rule can be used to determine the optimal nseg number. (Page 122).

The first few lines in the d_lambda rule section in the NEURON textbook(Pg 122) go as follows:

“The d_lambda rule predicates the spatial grid on the AC length constant (lambda_f) computed at a frequency f that is high enough for transmembrane current to be primarily capacitive, yet still within the range of frequencies relevant to neuronal function.

i) Why does the transmembrane current need to be primarily
capacitive? How does this relate to setting up the nseg value?

ii) When we say, “within the range of frequencies relevant to
neuronal functionâ€

[ted]

i) Why does the transmembrane current need to be primarily
capacitive? How does this relate to setting up the nseg value?

One wants a spatial grid that is sufficiently fine to give good accuracy regardless of how
densely populated the membrane is with ion channels, or how open or closed those
channels might be. To ensure this, choose a frequency that is well above 1/2*PI*tau_m

ii) When we say, “within the range of frequencies relevant to
neuronal functionâ€