See how the equation form of Ohm's law relates to a simple circuit. Adjust the voltage and resistance, and see the current change according to Ohm's law. The sizes of the symbols in the equation change to match the circuit diagram.
The University of Arizona College of Medicine has a nice description of the Nernst equation. The Nernst equation (named after its originator, the German Chemist and Nobel laureate, Walther Nernst), provides a quantitative measure of the equality that exists between chemical and electrical gradients and is the starting point for understanding the basis of the "membrane potential."
The Goldman-Hodgkin-Katz equation (named in honor of American David Goldman and the British Nobel laureates Sir Alan Hodgkin and Sir Bernard Katz; frequently simply referred to as "the Goldman equation" calculates an estimated membrane potential that reflects the relative contributions of the chemical concentration gradients and relative membrane permeability for K+, Na+ and Cl-.
Understanding of the concepts associated with the simulator requires familiarity with the parameters involved in Nernst/Goldman calculations. Following is a brief discussion of these parameters as they pertain to the simulator's use.
Ion ConcentrationsFor each ion (i.e., K+, Na+ and Cl-) a ?slider? is provided to adjust one of three parameters. Two of these sliders control the intracellular and extracellular concentrations of the ion in question, and these can be varied between values of 1 mM and 600 mM. All slider values can be adjusted by double clicking on the value reported in the slider box and typing in the desired value. The default values are: for K+, 10 mM out and 100 mM in; for Na+, 100 mM out and 10 mM in; and for Cl-, 100 mM out and 10 mM.