How strong is the electric field across a resting membrane, and how does it compare with the field that makes air spark? · Lobeworks/17

About 14 million volts per metre: E=V/d≈0.07 V/5 nm=1.4×107E = V/d \approx 0.07\ \text{V} / 5\ \text{nm} = 1.4\times10^{7}E=V/d≈0.07 V/5 nm=1.4×107 V/m.

How strong is the electric field across a resting membrane, and how does it compare with the field that makes air spark?

About 14 million volts per metre: E=V/d≈0.07 V/5 nm=1.4×107E = V/d \approx 0.07\ \text{V} / 5\ \text{nm} = 1.4\times10^{7}E=V/d≈0.07 V/5 nm=1.4×107 V/m. Air breaks down into a spark at about 3 MV/m, so the resting membrane holds some five times that field, and only because it is so thin and so good an insulator. Mica, one of the best solid insulators, holds about 200 MV/m before it fails.