process in which the endometrium of the uterus is shed from the body during the first several days of the menstrual cycle; also called monthly period or menses one of twelve teeth with cusps in the ba...process in which the endometrium of the uterus is shed from the body during the first several days of the menstrual cycle; also called monthly period or menses one of twelve teeth with cusps in the back of the mouth behind the premolars that are used for crushing and grinding food increase in the tension or decrease in the length of a muscle that occurs when muscle fibers receive a nervous stimulus