## Specifying a finite volume of Extracellular fluid

Anything that doesn't fit elsewhere.

### Specifying a finite volume of Extracellular fluid

Hi all

I am very new to Neuron, so apologies if I am asking a stupid question.

Does anyone know of a way to specify a finite volume of extracellular fluid?

Thanks

Rob
physrob

Posts: 2
Joined: Mon Jan 16, 2012 4:54 am

### Re: Specifying a finite volume of Extracellular fluid

You want a model of ion accumulation in extracellular space. Doable with NMODL, for example see the implementation of Frankenhaeuser-Hodgkin space in chapter 9 of The NEURON Book. For your convenience, I reproduce kext.mod here
Code: Select all
`: Extracellular potassium ion accumulation: fhspace and kxfer are from Frankenhaeuser & HodgkinNEURON {  SUFFIX kext  USEION k READ ik WRITE ko  GLOBAL kbath  RANGE fhspace, txfer}UNITS {  (mV) = (millivolt)  (mA) = (milliamp)  FARADAY = (faraday) (coulombs)  (molar) = (1/liter)  (mM) = (millimolar)}PARAMETER {  kbath = 2.5 (mM)  : Frankenhaeuser-Hodgkin space parameters  fhspace = 300 (angstrom) : thickness  txfer = 50 (ms) : fhspace <-> bath transfer time}ASSIGNED {  ik (mA/cm2)}STATE {  ko (mM)}BREAKPOINT {  SOLVE state METHOD derivimplicit}DERIVATIVE state {  ko' = (1e8)*ik/(fhspace*FARADAY) + (kbath - ko)/txfer}`

An aside: astute readers may notice that the METHOD is now derivimplicit rather than cnexp. derivimplicit is appropriate for ion accumulation mechanisms specified by ODEs and will work regardless of the equilibration time constant.
ted

Posts: 3618
Joined: Wed May 18, 2005 4:50 pm
Location: Yale University School of Medicine

### Re: Specifying a finite volume of Extracellular fluid

Thanks Ted

I will have a good look at the relevant sections in the NEURON book.

Rob
physrob

Posts: 2
Joined: Mon Jan 16, 2012 4:54 am