Despite the complex nonlinear equations ruling the membrane potential its behavior must be understood when dealing with neuronal structures. For that reason, models taking into account the main characteristics of responses of the membrane potential to stimuli have been developed. How such models have been established is the main concern of this work. The additive and shunting models of cells are particularly considered and their related differential equations are illustrated by using simple equivalent electrical circuits. Then, on the basis of these models, the lateral inhibitory and the winner-take-all neuronal structures are studied.