How much current is required to stimulate a neuron?

Extracellular stimulation of neural tissue is done using electrode. Amount of current determines neurons how far from the electrode will be excited. How much current is required to stimulate the neuron in immediate vicinity? Such information is not available on internet.

• "Such information is not available on internet." - wrong, but okay, I understand it's hard to find. The problem with your question is it is ill-defined: what do you mean by immediate vicinity? That term is meaningless. It also doesn't say anything about the rest of the setup: how far apart are the electrodes, how big are they, what part of the neuron is nearby? If you really want to know the minimum current to make a neuron spike, all you need is the input resistance, resting potential, and threshold, but that's for current delivered directly across the membrane. – Bryan Krause May 26 '17 at 22:07
• immediate vicinity means neurons in contact with the electrode. single electrode. how big? why? say 100 micron dia. axon is in contact. – ertyu May 26 '17 at 22:30
• "If you really want to know the minimum current to make a neuron spike, all you need is the input resistance, resting potential, and threshold, but that's for current delivered directly across the membrane. " interesting.please tell me the calculation. rest potential -70mV, threshold -55mV and what is input resistance- resistance of electrode wire? let us say it is 100 Ohms or R if you would like. – ertyu May 26 '17 at 22:33
• Because not all of the current will actually go through the membrane of the cell, especially if the ground is far away or not in the same direction. Input resistance is the input resistance of the cell. If you just want a ballpark estimate for some engineering project, typical extracellular stimulation intensities are in the microamp range, but the current you have to deliver across a membrane to make a cell spike is in the picoamp range, depending on cell type and other conditions. – Bryan Krause May 26 '17 at 22:39
• To calculate for one cell, knowing the input resistance of the cell (not your wire), all you need is Ohm's law, knowing you want to change the voltage by, in your case, 15mV. – Bryan Krause May 26 '17 at 22:40