Diagnosis employing equipment that can be used clinically to measure the intrinsic electrical activity of the heart (electrocardiography), the brain (electroencephalography), peripheral nerves (nerve conduction), and skeletal muscles (electromyography). Electrodiagnostic procedures depend upon the difference in electrical potential between the interior and external surfaces of living cells. This potential difference is created by use of cellular metabolic energy to establish and maintain the concentration gradient of ions across the cell membrane. A discharge of the electrical potential (depolarization) by stimulation or injury occurs in a wave proceeding from cell to cell. The ensuing electrical currents are conducted through the tissues to the surface of the body where electrodiagnostic equipment amplifies and records the changes in potential.