Hypothalamus: This part of the brain regulates body temperature; when it senses that you're too cold, it triggers shivering.
Thermoregulation: The process by which the body maintains its optimal temperature. Shivering is a part of this system.
Muscle Contractions: These are movements caused by the shortening and lengthening of muscle fibers. In shivering, rapid contractions generate heat to raise body temperature.