The Basic Electrical Circuit

Understanding the electrophysiology of the oocyte involves a basic understanding of electrical circuits. By basic, I mean really simple, so don't get scared yet.

A simple circuit:

Electrical circuits involve 3 basic components:

is the force created by the separation of charges. Kind of like when two opposite poles of a magnet are put close together, but are separated by a short distance. A force tries to pull them together. When there are more negative charges on the inside of the membrane of a cell, there is a force driving positive charges inward to neutralize them. The unit of voltage is the volt and it is represented by the symbol V. Voltage is also called "potential" or "potential difference".

is a measure of how hard it is for charges to move in the system. In a cell, the lipid portion of the membrane is impermiable to ions, so the resistance to current across the membrane is determined by the opening and closing of ion channels. When the channels open, the resistance decreases. When they close, resistance increases (because ions can't move through the membrane). The units of resistance are ohms and it is represented by the symbol R. (Note - When talking about channels, "conductance" is usually used instead of resistance. Conductance is the inverse of resistance (1/R), or how easy it is to pass charges. Its units are seimans [S].)

is the movment of charges. In an electrical circuit, electrons move from the negative pole to the positive pole (although electrical current is defined as the movement of positive charges, so current is said to go from the positive pole to negative pole - go figure). In cells, current is when ions move through the membrane (usually Na+, K+, Ca2+, or Cl-).


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