Surface Electrodes: These are used to measure Potentials from the surface of skin and to sense potentials from heart, brain and nerve.
Internal electrodes: These are used to measure the bioelectric potentials of highly localized extra cellular regions in brain or Potentials from a specific group of muscles.
Micro electrodes: These are used to measure the bioelectric potentials near or within a single cell. These are also called as intracellular electrodes.