up-to-date values for dendrite model

holmes at cneuro.zool.ohiou.edu holmes at cneuro.zool.ohiou.edu
Mon Sep 20 07:23:01 EST 1999


Perhaps the best review of the issues you are concerned with is:
 Rall et al.  Physiological Reviews 74(4,Suppl):S159-S186, 1992. 

Typical ranges for Rm, Cm, and Ri (also called Ra) are:
  Rm 5-100 k-ohms-cm2
  Cm 0.6-1.2 microF/cm2
  Ri 50-400 ohm-cm

Typical values used in models are:
  Rm 20-40 k-ohms-cm2
  Cm  1.0 microF/cm2  (Cole's number from long ago)
  Ri  100-200 ohm-cm

Sharp electrode recordings tend to introduce an artificial soma
shunt.  Patch electrode recordings tend to change the intracellular
medium.  Perhaps the best estimates come from perforated patch 
recordings.

(Sometimes larger Cm values and smaller Rm values are used in 
models to make up for not explicitly including dendritic spines
and their large--in total--contribution to membrane area.  See
the Rall reference for more details).

These days we realize that dendrites are not passive cables, so 
although passive cable theory is a good starting point for 
understanding PSP shape and spatial summation, we also have to 
consider the effects of voltage-conductances in dendrites.

--Bill Holmes
  holmes at ohiou.edu

Seguier (Renaud.Seguier at supelec.fr) wrote:
> Hy,

> I'm searching for latest value about the membrane time constant,
> membrane capacitance and membrane resistance. I
> heard that those values change in 90th with patch clamp technique.
> My problem is to know if we are sure that spatial sommation exist in the
> dendrite.
> Are the shapes of the PSP very different one from an other ?
> Are those differences coming from different location of synapses on the
> dendritic tree ? But if Rm is very high : the
> neurone
> is very compact so the shape of a PSP just on the location of the
> synapse is the same as the shape of this PSP on the
> soma.
> Maybe the neurone is effectively very compact, but the shape of
> different PSP can also be different because of the
> synapses can create different shape of PSP ?

> Sorry for those very innocent questions, but Thanks a Lot for the hoped
> replied !

> PS. Sorry for my very very very poor English ...





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