Definition
Electromyography (EMG, electromyography) is a clinical examination method with the help of which the electrical activity of individual or several muscle fibers can be objectively recorded simultaneously. This may be necessary in order to identify and more precisely limit damage in the muscular area.
Measurement procedure
In electromyography, the electrical activity of the muscle fibers can be dissipated either by a superficial electrode attached to the skin or by a needle electrode directly on the muscle. Two different types of needle electrodes are used. The monopolar electrode of electromyography serves as a measuring electrode, while an electrode glued to the skin serves as a reference electrode. With the concentric electrode, a fine wire is placed in the needle as the measuring electrode, while the needle sheath serves directly as the reference electrode. In both methods of electromyography (EMG), the voltage difference between the measuring and reference electrode is used for clinical evaluation.
Anatomical basics
A muscle is made up of many individual motor units, which can consist of a few to many muscle fibers, depending on the muscle type. Each of these motor units is controlled by a single nerve (anterior horn cell with axon). The more motor units a muscle has, the finer movements are possible, since many different motor units can be individually controlled by different nerves.
When a nerve (anterior horn cell) is controlled by the brain, all muscles belonging to this motor unit are discharged (depolarized) and contract, i.e. the muscle moves (contraction). The electrical activity that results from this movement is called the action potential of a motor unit (MUAP), since the electrical potentials of many individual muscle fibers are superimposed and recorded together. You can read more about the exact transmission of excitation to the muscles under “Motor End Plate”.
Risks of electromyography
Electromyography (EMG) is an invasive diagnostic method that is very widespread and rarely leads to complications such as bleeding, infection and injury to the nerve itself.
