Difference between revisions of "5° Klinischer Fall: Spontane elektromyographische Aktivität"

File:Distonic 1.jpg|'''Figure 1C:''' Analysis of the morphology of the masseter motor unit (MUs)  

File:Distonic 4.jpg|'''Figure 1D:''' Calculation of the discharge parameters of the MUs

In one subject, the insertion activity appears as high-frequency positive and negative spikes in a single group and are typically a representation of muscle fiber damage or mechanical stimulation due to needle penetration into the muscle. In our patient this activity occurred with a duration of 80 mS and was referable to a normal picture. Also note the phenomenon of plaque activity. If a needle electrode is held stationary at one point in the muscle, normal muscles at rest show absolutely no electrical activity except in the region of the neuromuscular endplate. These consist of two components: low amplitude (on the order of 10-50 μV) and low duration (1-2 msec) which to the loudspeaker EMG resemble the sound of sea shells on the ear. In our case (fig.1A) the total absence of plaque activity in the right masseter can be explained by the recording performed with surface electrodes which partially reduce the energy of the signal but the activity recorded on the left masseter, again with surface, has a width of<math>\approxeq100\mu V</math> . For the same reasoning, this activity should not be considered as plate activity since, as can be seen in fig. 1B, recording of the left masseter performed with a coaxial electrode, the amplitude is <math>\approxeq 400\mu V</math>. Sometimes plaque potential spikes are indistinguishable in waveform from fibrillation potentials which also show initial negativity when recorded near the plaque. Another curious element is the similarity of the discharge model between the discharges of the neuromuscular spindles and of the plate potentials, so much so that some authors<ref>{{cita libro  

  }}</ref> hypothesized that these potentials could originate from the intrafusal muscle fibers. The discussion and the electrophysiological meaning to be given to the electrical activity observable in fig. 1B.

In the first 2 weeks after denervation, the sensitivity of a muscle fiber to acetylcholine (ACh) increases up to 100-fold. This phenomenon known as “denervation hypersensitivity” may explain the spontaneous firing of denervated muscle fibers in response to minute ACh quanta.<ref>{{cita libro  

  }}</ref> The fact that the infusion of curare blocks the receptors of the neuromuscular plate but does not abolish the spontaneous discharge, that the denervation of the frog muscle can lead to an increased sensitivity to ACh but not generate spontaneous activity. <ref>{{cita libro  

  }}</ref>. These studies have suggested an alternative hypothesis that of slow changes in membrane potentials of metabolic origin which can periodically reach a critical level and evoke propagated spikes.<ref>{{cita libro