Selective stimulation of retina ganglion cells is a great challenge for the next generation of inner eye prostheses. One strategy to stimulate only certain target cells, is the utilization of a specific stimulation window, a lower and upper limit for stimulus strength to force an action potential. Stimulation strengths above the given upper limit are causing a block of excitation. Such a stimulus window is not only defined by physiological and geometrical properties of the neuronal cell, but also depends on the geometry and location of the electrode itself. There are two hypotheses for the block of excitation: the Anodal Surround Block and the Stimulation Upper Threshold. However, there is a controversy about the physical principles that are causing the block of excitation for higher stimulus amplitudes. The implemented multi compartment model in Neuron and Python supports active membrane mechanisms based on the Hodgkin-Huxley and the Fohlmeister-Miller model.^ ^It allows to simulate intra- and extracellular stimulation of a modelled retinal ganglion cell or parts of it. Besides a highly interactive user interface, also systematic test procedures are supported for analysing results of thousands of model runs with variations in geometrical or biophysical properties. Based on the model, different analyses were performed. First, the direct effects of an electric field on a neuron during extracellular stimulation were investigated. For a spherical soma, a nearly equipotential state of the intracellular potential was found. Further, we were able to confirm experimental and computational results of another research about the time constant to reach intracellular potential equilibrium of a spherical soma within an electric field. Then, the stimulation window for extracellular stimulation for a spherical soma was investigated in detail.^ We could find a correlation between the diameter of a spherical structure and the electrode distance which together define the stimulation window. Further, we were able to mathematically formulate the relationship between stimulation windows determined for different diameters of the spherical soma. Also, we analysed the Na+ current reversal and the total ionic Na+ current flux during the stimulation and its consequences for action potential generation. We found a significant large zone within the stimulation window where a Na+ current reversal happened during stimulation. Further, according to our model results, the relative portion of a Na+ current reversal zone within the respective stimulation window seems to be constant for all stimulation amplitudes. Additionally, we found some stimulation configurations which initiated an action potential in spite a net Na+ ion outflux occurred during the stimulation because of a Na+ current reversal.^ Finally, different electrode positions were tested on a retinal ganglion cell (without dendrites) and evaluated regarding blocking phenomena. For certain electrode geometries which influenced the retinal ganglion cell at different sections with comparable stimulation strengths simultaneously, we were able to reproduce total or partial blocking of the neuron. However, we were not able to distinguish in detail on which blocking phenomena (Anodal Surround Block, Stimulation Upper Threshold, or a combination of both) the determined blocking zones are based on. Out of a computational point of view, at the moment there are still many uncertainties regarding the consequences of the Na+ current reversal on the generation or blocking of action potentials. Therefore, an exact classification was not possible yet.^ The results of this thesis shall give some insight views on blocking phenomena helping to understand the mechanisms when applying extracellular stimulation to a neuronal cell with a spherical soma.