Modifica di Clinic Electromyography (sezione)

====Definition of Motor Unit (MU)====
The MU is composed of a motor neuron, its axon, and the muscle innervated by the axon.  The motor unit activity can be recorded with various types of electrodes:  - **Single Fiber Electrode (SF-EMG)**: It records only one or a few fibers of the motor unit. It has a diameter of 25 μm, smaller than a normal muscle fiber, which has a diameter of about 40-50 μm. The recording area of an SF-EMG electrode is comparable to a sphere with a spatial distribution of 300 μm. In a normal subject, this electrode simultaneously records 1 or 2 muscle fibers belonging to the same motor unit.<ref name="Sonoo">Sonoo M., Stalberg E.: The ability of MUP parameters to discriminate between normal and neurogenic MUPs in concentric EMG: analysis of the MUP thickness and the proposal for a "size index". Electroencph. Clin. Neurophys. 3:291-303, 1993.</ref>  '''Fig.1'''[[File:Figura 1 copia.jpg|left|thumb|'''Figure 1:''' Types of needle electrodes]]The **Macro-EMG needle electrode** has a very large recording surface: ≅15 mm from a modified EMG electrode cannula. It simultaneously records from the entire motor unit.<ref name="Buchthal">Buchthal F., Pinelli P. et al.: Action potentials parameters in normal human muscle and their physiological determinants. Acta Physiol Scand 22:210-229, 1954.</ref>  The most commonly used electrodes in clinical diagnostics, however, are concentric and monopolar electrodes, which have intermediate characteristics between the two types described above.<ref name="Stalberg1">Stalberg E., Antoni L.: Computer aided EMG analysis. In (Desmedt ed.) Progress in clinical neurophysiology. Karger, Basel vol.10 186-234, 1983.</ref>  The **concentric electrode** has a recording surface of 150 x 580 μm with an area of 0.07 mm², while the **monopolar electrode** is insulated with Teflon except at the terminal portion and has a recording area of 0.5-0.8 mm², thus recording a wider spherical region than the concentric electrode.  In routine recordings, the concentric electrode has significant advantages over the monopolar one, canceling out activity from remote motor units and partially canceling action potentials from distant fibers of the same motor unit. In conclusion, the concentric electrode recording method ensures greater baseline stability.