In some instances neuropathies can be diagnosed through a conduction velocity test. However, not all neuropathies can be classified using this method.Gaining an understanding of how the stimulus level varies for different fiber sizes at different fiber depths within a conductive medium will provide useful information for simulation studies.Following a two-step approach using COMSOL and MATLAB, a simulation was implemented to investigate the stimulus necessary to activate different sized fibers at different depths. In this two-step approach, COMSOL was used to describe the voltage profile that would be present within a conductive medium after a stimulus was applied. This voltage profile could then be analyzed using a program written in MATLAB to determine if the applied stimulus was sufficient to activate a given fiber. The analysis was performed using a stimulus method using a constant DC source. Two finite element models were also used, one using a homogeneous medium and the other inhomogeneous.A three dimensional plot was created to describe the effect of both the depth and diameter of a fiber on the required stimulus for fiber activation. From this plot, an equation was fit to the data to represent the activation function of a nerve fiber at various diameters and depths.v CHAPTER 1 -IntroductionThe biomedical field has changed tremendously throughout the past 20 years. Complicated electrical and mechanical systems are now being implemented into medical devices, which are advancing the field at an extremely high rate. Some of the most significant changes can be seen in the area of neurology and integrating medical devices with the neurological systems of the body. Companies are creating a division to investigate medical devices that address the subject of neuromodulation and neurostimulation.Understanding the intricacies of the nervous system is very important in developing a device that neuromodulates or neurostimulates correctly. One such example can be seen in devices that target people with chronic back pain.Neurostimulation devices are currently being designed to stimulate specific nerve fiber bundles in an attempt to mask the chronic pain signal. During this stimulation a large group of nerve fibers are usually stimulated because current technology is not capable of controlling the stimulation of individual fibers.Although this lack of ability to control the stimulation of individual fibers has not hindered these devices from treating their patients, more knowledge of how different fibers are stimulated could offer great benefits to the future of these devices. Neuroprosthetics is one application that would greatly benefit from differentiating the stimulus required to activate various fiber types. Characterizing how individual fibers respond to a given stimulus would allow much finer control of the nerves being targeted in the neuroprosthetic device and could lead to a much more accurate human-computer interface in these devices. 2Understanding how different nerve fibers respond to a given stimulus is...