This is a network of three point neurons (PTNRN11). The neurons are connected by synapses that resemble chemical synapses. When a neuron reaches firing threshold, the other neurons are given a synaptic current equal to the number of synapses between the pair, times the unitary synaptic conductance. In the initial settings for this model, neuron 1 is designated as a "pacemaker" neuron, and is given a steady current to depolarize it and cause it to fire.
A feature of this implementation of the model is that it can run continuously. Check "run contin." in the "Display" dialog box. You can change the parameters as it runs to see the effect.