Hello everyone:
I'm now trying to model some optogenetic experiments. But I'm struggling with propagation of the potential. The modeling requires relatively precise description of the spatiotemporal dynamics of electric potentials. Here is an example question: consider a spherical soma, if I inject current into one point of it, how potential of each patch in this spheres changes in time?
On the internet it's almost exclusively cable theory that provides underlying modeling. Although it is absolutely suitable for most of the events in neurons, it may not be enough precise for ultra-fast source of current that changes in space within micro-second level. I would say before the iso-potential status is reached the source of current has left so old integration process ceased and new integration process occurs in another place. So a more precise model is required here.
I'm not a mathematically or physically intelligent guy so maybe some considerations are wrong. But any suggestion will help! Thank you in advance!
Best
Yao
Hi William:
Thank you for the answer. But I need exact calculation.
Say, the soma is 10um in diameter and is perfectly a sphere. If I inject current continuously into one point like 0.1*0.1um patch of membrane when will the membrane be iso-potential? The charge travelling in intracellular medium I believe is moving so fast, but the membrane time constant which includes charging and conducting property of the membrane is ~ms level. So it will take ~ms level to escape from transient status.
Another possibility is that although all patches of membrane is not in steady state, but all patches are synchronized to be not in steady state.
However, NEURON treats compartment as cylinder so I have no access to single patch of membrane. That means if I want to use NEURON I have to make sure that at least every cylinder is iso-potential respectively. Is that true in reality?
Thank you!
Hi William:
I think I'm getting your point. But what do you mean by 'voltage propagates in the compartment'? When we say voltage, I think we are referring to the voltage drop of between the cell membrane, with bath electrode as the reference point.
So if a voltage propagates from position A to position B, when we say position B has this voltage, I think we are saying that it has been charged. From your statement 'That is why you can treat it as isopotential.' I think you are talking that the patches are not yet charged completely and will be synchronously charged with negligible phase shift , which is the point that you try to prove in the third paragraph, right?
I'm sorry that I cannot grasp what you said in this moment due to my incapability in electronic circuit analysis, but please advise once again. Thank you!
See the reference below.
Comprehensive Morpho-Electrotonic Analysis Shows 2 Distinct Classes of L2 and L3 Pyramidal Neurons in Human Temporal Cortex.
Deitcher Y, Eyal G, Kanari L, Verhoog MB, Atenekeng Kahou GA, Mansvelder HD, de Kock CPJ, Segev I.
Cereb Cortex. 2017 Nov 1;27(11):5398-5414.
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