### Classical Cable Theory

Posted:

**Wed Oct 03, 2007 6:12 pm**Hi!

I was just looking at the paper:

http://www.neuron.yale.edu/neuron/paper ... psfin.html

I have a question on defining electrotonic distance in the classical cable theory and in NEURON.

1. When we say electrotonic distance do we mean the distance at which

the voltage has reduced to 1/e of its initial value?

But I thought thats the definition of space constant?

Also, when we say a dendrite has electrotonic distance of 1.5, do we mean that the length of the dendrite is 1.5*lambda??

So, then ideally for no attenuation at all we want a dendrite to have electrotonic distance of "0" or numbers very close to zero??

2. In the classical cable theory, voltage decay along an infinite cylindrical

cable can be defined as V(x)=V0*e^-(x/lambda)

Then, it follows that x/lambda = ln(V0/V(x))???

Okay this maybe an extremely basic question, but why in a infinitely long cable does the electrotonic distance X become x/lambda???

I mean I understand that if a cable is infinitely long, then the signal will

never reach the end. And since it can never reach the end, whatever

at the end will not affect it?

But how does X equal to x/lambda?

I really do appreciate all your time and efforts.

Thanks,

Meena

I was just looking at the paper:

http://www.neuron.yale.edu/neuron/paper ... psfin.html

I have a question on defining electrotonic distance in the classical cable theory and in NEURON.

1. When we say electrotonic distance do we mean the distance at which

the voltage has reduced to 1/e of its initial value?

But I thought thats the definition of space constant?

Also, when we say a dendrite has electrotonic distance of 1.5, do we mean that the length of the dendrite is 1.5*lambda??

So, then ideally for no attenuation at all we want a dendrite to have electrotonic distance of "0" or numbers very close to zero??

2. In the classical cable theory, voltage decay along an infinite cylindrical

cable can be defined as V(x)=V0*e^-(x/lambda)

Then, it follows that x/lambda = ln(V0/V(x))???

Okay this maybe an extremely basic question, but why in a infinitely long cable does the electrotonic distance X become x/lambda???

I mean I understand that if a cable is infinitely long, then the signal will

never reach the end. And since it can never reach the end, whatever

at the end will not affect it?

But how does X equal to x/lambda?

I really do appreciate all your time and efforts.

Thanks,

Meena