Hey, first post in this forum! Ive been reading a lot of books related to biology and the more I read the more confusing the subject of electricity in living organisms gets. For example, a lot of books introduce membrane potentials as something that can be measured using two microelectrodes and voltmeter, placing one in the intracellular and one in the extracellular fluid. But how does it really work like that? When I normally think about a voltmeter, I imagine it as ammeter with a component of high resistance and there is a current flow that is converted into a value of voltage, but when the voltage is caused by small separation of ions I dont see how it really works then. I mean, the situation is similar to capacitor, and the plasma membrane works as dielectric, but If I would connect both ends of capacitor with a resistive path current proportional to the voltage created between the plates would flow and it could be measured, but I dont get how it would be done when the charge separation comes from ions not electrons. Even more confusing seems the electric mechanism of defense of some fish, like electric ray. If I imagine that the fish has two points in the body with potential difference between them and current can flow from one to the other. Why would the fish discharge when those two points come in contact with the victim, but not while it flows freely around? I hope I made some sens with this, because english is my second language.