Fine, irregular contraction of individual fibers is called:

Fine, irregular contractions of individual fibers is known as fibrillations. This is the classic picture of a lower motor neuron lesion. If the motor nerve regenerates, the fibrillations disappear.  Usually,  the contractions are not visible grossly, and they should not be confused with fasciculations, which are jerky, visible contractions of groups of muscle fibers that occur as a result of pathologic discharge of spinal motor neurons.