Further reading
Current-Voltage Relations
This game asks you to infer a reversal potential from an I-V curve. The model is intentionally simple, but it captures a central idea in conductance-based membrane modeling:
Imem(V) = g(V)(V - Erev).
What the zero crossing means
If the conductance is positive, the current is zero when V = Erev. The conductance changes the size and shape of the current, but the zero-current crossing is determined by the driving force term V - Erev. That is the main inference task in the game.
Conductance changes the shape
The game uses a sigmoid conductance, g(V) = 0.5(1 + tanh((V - V0)/V1)), sometimes reversed and with a small floor. This makes the red curve easier or harder to read without changing the core relation. In real channels, conductance may depend on voltage, time, ligand binding, channel history, and stochastic channel state.
Limitations of the game model
The game suppresses capacitance, space-clamp effects, multiple ionic species, and current sign-convention details. Those omissions are deliberate: the goal is to isolate the algebraic role of the driving force before adding dynamics.
On-topic resources
- Reversal potential: the membrane voltage at which a current reverses direction.
- Nernst equation: how an equilibrium potential follows from concentration ratios for one permeant ion.
- Membrane potential: broader physiological context for voltage across cell membranes.
- Hodgkin-Huxley model: the classic conductance-based framework in which terms like g(V)(V - E) appear.