Acupuncture originated 5,000 years ago in China. Today it is commonly used throughout the world. Chinese medicine theory holds that the human body contains a network of energy pathways through which vital energy, called "chi" (also spelled "qi"), circulates. These pathways are called "meridians." The meridians contain specific "points" that function like gates, allowing chi to flow through the body. Needles are inserted into these points to regulate the flow of chi. Illness and symptoms are thought caused by problems in the circulation of chi through the meridians.