Electromyography (redirected from Electrodiagnostic)

electromyography

Process of graphically recording the electrical activity of muscle, which normally generates an electric current only when contracting or when its nerve is stimulated. Electrical impulses are shown as wavelike tracings on a cathode-ray oscilloscope and recorded as an electromyogram (EMG), usually along with audible signals. The EMG can show whether muscle weakness or wasting is due to nerve impairment (as in amyotrophic lateral sclerosis and poliomyelitis) or muscle impairment or disease (myopathy).

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Electromyography

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