Due to the very small electrical fields produced by neurons, mathematical models are often used in order to test a number of manipulations. Cable theory is one of the most important mathematical equations in neuroscience. It calculates electric current using capacitance and resistance as variables and has been the main basis for many predictions about ephaptic coupling in neurons. However, many authors have worked to create more refined models in order to more accurately represent the environments of the nervous system. For example, many authors have proposed models for cardiac tissue that includes additional variables that account for the unique structure and geometry of cardiac cells  varying scales of size, or three-dimensional electrodiffusion.