A fasciculation /fəˌsɪkjʉˈleɪʃən/ , or muscle twitch, is a small, local, involuntary muscle contraction and relaxation which may be visible under the skin.Deeper areas can be detected by EMG testing, though they can happen in any skeletal muscle in the body.Fasciculations arise as a result of spontaneous depolarization of a lower motor neuron leading to the synchronous contraction of all the skeletal muscle fibers within a single motor unit.An example of normal spontaneous depolarization is the constant contractions of cardiac muscle, causing the heart to beat.eeper areas can be detected by EMG testing, though they can happen in any skeletal muscle in the body. Fasciculations arise as a result of spontaneous depolarization of a lower motor neuron leading to the synchronous contraction of all the skeletal muscle fibers within a single motor unit.