An interactive simulation of neuronal synaptic potential is presented. The set-up comprises of two synaptic terminals and one postsynaptic membrane from which the intracellular potential is recorded. Certain parameters are interactively changeable by the user. For example, each synaptic terminal may cause changes in the membrane conductance to sodium, potassium, or chloride ions, or some combinations of them. One synaptic terminal may be turned on/off to allow study of the spatio-temporal summation of postsynaptic potentials with adjustable delay. The postsynaptic membrane may also be set at various values in order to study the effects of membrane potentials on the direction and magnitude of postsynaptic potentials. This simulation has been used with some success as an aid for teaching cellular neurophysiology.