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### What is the unit of xraxial in the Extracellular mechanism?

Posted: **Wed Jun 21, 2017 5:36 am**

by **Krollibrius**

Hi,

May be a dumb question. What is the unit of the axial resistance (xraxial) in the Extracellular mechanism?

The documentation (

http://www.neuron.yale.edu/neuron/stati ... racellular) mentions MOhms/cm. The way I understand this is megohms/cm = 10^6 ohms/cm. But I keep seeing huge numbers for xraxial (e.g. 6615 at the nodes of Ranvier of the model I'm working with), so that looks weird to me...

Can you help?

### Re: What is the unit of xraxial in the Extracellular mechani

Posted: **Fri Jun 23, 2017 12:28 am**

by **ted**

Krollibrius wrote:What is the unit of the axial resistance (xraxial) in the Extracellular mechanism?

The documentation in the Programmer's Reference is correct. xraxial[0] and xraxial[1] are the extracellular longitudinal resistances in layers 0 and 1 of the extracellular mechanism, in units of megohms/cm. The corresponding extracellular resistances between adjacent nodes along a section equals the product of xraxial[0] or [1] and the distance between the nodes, taking conversion from um to cm into account as necessary. Section diameter has no effect on these values.

But I keep seeing huge numbers for xraxial (e.g. 6615 at the nodes of Ranvier of the model I'm working with), so that looks weird to me

If you developed the model in question, you're responsible for the values of its parameters, so why did you choose those values? If you didn't, then someone else did, and you need to find out why they chose those values. Read the paper in which they describe the model to see what their basis for that values is. If it remains obscure, ask them.

### Re: What is the unit of xraxial in the Extracellular mechani

Posted: **Sat Jun 24, 2017 1:22 pm**

by **Krollibrius**

Thanks a lot Ted!

Indeed, I'm using someone's else model, so I'll investigate. I thought at first that the problem came from my understanding of the units.