Axial currents between two compartments

Managing anatomically complex model cells with the CellBuilder. Importing morphometric data with NEURON's Import3D tool or Robert Cannon's CVAPP. Where to find detailed morphometric data.
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shyam_u2
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Joined: Sun Feb 20, 2011 7:15 pm

Axial currents between two compartments

Post by shyam_u2 »

Consider we have two sections soma and dend and connect them in the following way: connect dend(0),soma(0).
If I print the axial resistance (ri) at soma(0) and dend(0) it says 1e30. Does it mean that there is no flow of current between these points ?
ted
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Re: Axial currents between two compartments

Post by ted »

shyam_u2 wrote:If I print the axial resistance (ri) at soma(0) and dend(0) it says 1e30.
What does the documentation of ri() say about this?
Does it mean that there is no flow of current between these points ?
What does the documentation of connect suggest? What do you discover by using a model designed to disambiguate this issue?
shyam_u2
Posts: 77
Joined: Sun Feb 20, 2011 7:15 pm

Re: Axial currents between two compartments

Post by shyam_u2 »

The documentation of 'ri' says that it returns the resistance (in megohms) between the center of the segment containing x and its parent segment. First of all, I don't understand how NEURON computes the parent segment of a section. How could the resistance at the point of connect between soma and dend could be infinite (since they are connected) ? I also found that ri at soma(0) is always infinite no matter whether I connect the 0 or 1 end of the dendrite.
ted
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Re: Axial currents between two compartments

Post by ted »

shyam_u2 wrote:I don't understand how NEURON computes the parent segment of a section.
Consider this example:

Code: Select all

oc>create soma, dend
oc>access soma
oc>connect dend(0), soma(1)
oc>topology()

|-|       soma(0-1)
   `|       dend(0-1)
soma is the root of the tree and has no parent section. Furthermore soma's root node is soma(0) and has no parent node, so the following result would not surprise you.

Code: Select all

oc>forall { L = 100 diam = 1 }
oc>forall for (x) print secname(), " ", ri(x)
first instance of x
soma 1e+30 
soma 22.53634 
soma 22.53634 
dend 22.53634 
dend 22.53634 
dend 22.53634
In particular the first
dend 22.53634
is no surprise because you realize that dend(0) refers to the same node as soma(1) and therefore its parent node is soma(0.5).

Now attach a new section to the 0 end of soma.

Code: Select all

oc>create axon
oc>connect axon(0), soma(0)
oc>topology()

|-|       soma(0-1)
   `|       dend(0-1)
 `|       axon(0-1)

	1 
oc>axon { L = 100 diam = 1 }
oc>forall for (x) print secname(), " ", ri(x)
soma 1e+30 
soma 22.53634 
soma 22.53634 
dend 22.53634 
dend 22.53634 
dend 22.53634 
axon 1e+30 
axon 22.53634 
axon 22.53634
axon(0) lies on top of soma(0) so it has the same parent node as soma(0) does--none. That's why
axon print ri(0)
returns 1e+30.
How could the resistance at the point of connect between soma and dend could be infinite
That's not the meaning of the value returned by ri(0) when the currently accessed section is axon.
ri at soma(0) is always infinite no matter whether I connect the 0 or 1 end of the dendrite.
That's as it should be if soma is the root section.
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