Rhythmic trembling that occurs because of the involuntary contraction of opposing muscles. It occurs mainly when fear, other emotions or cold are being experienced. Some people always have such a slight tremor. These so-called physiological tremors are normal. Senile tremor in old people is an intensification of this normal tremor. Benign family tremor is an intensified physiological tremor which decreases with the use of alcohol and certain medicines. Other members of the family usually also have such a tremor. Another type of tremor occurs in Parkinson’s disease. When the cerebellum is affected, a tremor arises, particularly when specifically directed movements are made. Tremors also occur in protracted cases of alcoholism, increased hormone production by the thyroid gland, serious liver diseases, and in other cases. Treatment is directed against the cause.