Excitatory and inhibitory post synaptic potentials. An illustration of the action potentials and post synaptic potentials measured at different locations at the neuron. On the left a neuron is displayed and three probes are drawn at the location where the potential is measured. The above picture on the right shows the incoming exitatory action potentials measured at the probe at the top, at the probe in the middle the incoming inhibitory action potential is measured and shown. The neuron processes the incoming potentials: the excitatory action potentials are transformed into excitatory post synaptic potentials, the inhibitory action potentials are transformed into inhibitory post synaptic potentials. When two excitatory post synaptic potentials occur in a small time frame, the neuron fires. This is shown at the bottom figure. The dotted line shows the EPSP, in case there was no second excitatory action potential following. From .