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Publisher Summary This chapter focuses on single-fiber electromyography (SFEMG). An SFEMG electrode has a small recording surface with a diameter of just 25 μm, and therefore it has high input impedance and a minimal shunting effect rather similar to a point-size electrode. When the source—that is, an active muscle fiber, is close to an electrode, the amplitude of its action potential (AP) recorded by an SFEMG electrode is considerably higher than that obtained with a concentric electrode. However, with increasing distance, the AP amplitude recorded with the SFEMG electrode falls with a much steeper gradient. As a result, the SFEMG electrode is highly selective, detecting mostly activity of the closest muscle fibers. SFEMG can serve as a useful research tool in situations where single-muscle fibers, neuromuscular junctions (NMJs), motor axons, or ventral horn cells need to be studied in isolation in humans. The method is relatively robust; it involves minimal discomfort and allows reliable recognition of a motor unit (MU) or its portion selected, thereby allowing prolonged observation. |
