The Etectromyogram Is the Clinical Measurement of the Electrical Behavior Within a Skeletal Muscle

As an action potential spreads along a muscle fiber, a small portion of the electrical current generated spreads away from the fiber, even to the overlying skin. Electrodes placed on the skin or inserted into the muscle belly can record a summated electrical potential when the muscle contracts. Such a meas­urement, when displayed on an oscilloscope or computer screen, is called an electromyogram (EMG) and is for skeletal muscle what the electrocardiogram (ECG) is for cardiac muscle. The EMG, often used in conjunction with nerve conduction analysis, helps to determine whether weakness or paralysis is caused by disease in the skeletal muscle, neuromuscular junction, motor neuron, or CNS.