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The detection and recording of electrical activity generated by muscle fibers. The basic elements of motor control in the body are the motor units which comprise motor neurons in the brainstem or spinal cord, their axons, and from ten to several hundred muscle fibers supplied by each motor neuron. Motor units vary in the size and properties of their motoneurons, the sizes and conduction velocities of their axons, the morphology of their nerve muscle junctions, and the structure and physiological properties of the muscle fibers supplied by each motor neuron.
Impulses originating in single motoneurons in response to various command signals from the central nervous system conduct to the periphery of the unit, normally causing all the muscle fibers in the unit to discharge. The electrical activity generated by the more or less synchronous discharges of all the muscle fibers in the unit may be detected by recording electrodes on the skin surface or by needles inserted into the muscle. Such potentials reflect the electrical activity generated by the whole motor unit.
Diseases affecting motor neurons are sometimes accompanied by spontaneous discharges of the axons. Additionally, degeneration of motor axons may leave some muscle fibers deprived of their normal innervation, some of which spontaneously fire. Such single muscle-fiber discharges are called fibrillations and are readily detected for diagnostic purposes by needle electrodes inserted into the muscle.
Electromyography may also be used to study primary muscle diseases such as the muscular dystrophies, and a wide variety of other metabolic inflammatory and congenital myopathies affecting the muscle fibers rather than motor neurons or their axons. See Biopotentials and ionic currents
a method of investigating the bioelectric potentials that arise in the skeletal muscles of animals and humans after the excitation of muscle fibers. The method was first applied to humans in 1907 by the German scientist H. Pieper.
Because the amplitude of oscillations of muscle potential usually does not exceed several millivolts and their duration does not exceed 20–25 microseconds, electromyography is performed with an amplifier and quick-response recorder. The curve recorded on photographic paper or film is called an electromyogram (EMG). There are three principal methods. The first involves the insertion into a muscle of needle electrodes that, owing to the small deriving surface, detect the oscillations of potential arising in individual muscle fibers or group of fibers innervated by a single motoneuron. As a result, it is possible to investigate the structure and function of motor units. The second method uses cutaneous electrodes that lead off from the summary EMG, which results from interference with the oscillations of potential of many motor units in the region of derivation; such an EMG reflects excitation of a muscle as a whole. The third method of electromyography is the recording of oscillations of potential that arise in a muscle after artificial stimulation of a nerve or sense organ; this technique is used to investigate myoneural transmission, motor reflexes, and speed of passage of excitation along a nerve.
Electromyography is used to determine the condition and activity of the muscles and nerve centers participating in movement. It is used in physiology to study the motor functions of animals and, especially, humans. It is also used in applied sciences, for example, work and sports physiology and engineering psychology (for example, to study fatigue and the development of motor skills).
R. S. PERSON
Electromyography is widely used in neuropathology and some other branches of medicine to diagnose several neurological and muscular diseases. It is also used in orthopedics and prosthetics to evaluate the condition of the motor apparatus after restoration of impaired motor function.
REFERENCESPerson, R. S. Elektromiografiia v issledovaniiakh cheloveka. Moscow, 1969.
Iusevich, Iu. S. Ocherki po klinicheskoi elektromiografii. Moscow, 1972.
Baikushev, St., Z. Kh. Manovich, and V. P. Novikova. Slimuliatsionnaia elektromiografiia i elektroneirografiia v klinike nervnykh boleznei. Moscow, 1974.
Cohen, H., and J. Brumlik. Rukovodstvo po elektromiografii i elektrodiagnostike. Moscow, 1975. (Translated from English.)