Muscle tremor refers to the continuous and rhythmic contraction and relaxation of muscles at a frequency of 4-6 times per second. It is a symptom of central nervous system diseases, mainly caused by pathological changes in substantia nigra and substantia nigra striatum pathways. Common diseases include encephalitis, craniocerebral injury, arteriosclerosis, basal ganglia tumor, and poisoning of certain chemicals, such as chronic poisoning of mercury and manganese, which can cause toxic effects of muscle tremor.