Tremor is a continuous rhythmic movement consisting of regular oscillations of the affected body part, usually entrained by alternating contractions of reciprocally innervated muscles or muscle groups. Tremor is the most common abnormal involuntary movement and as a pathological symptom of various movement disorders, tremor reflects impairment of the basal ganglia system, but may be also due to pathological involvement of the cerebellum, brainstem, spinal cord or of peripheral nerves.