Gravitation was the first force to be discovered among the fundamental forces of nature. Electricity and magnetism only came to be understood later, around the 1600s. But electric and magnetic forces shape natural events and play a major role, perhaps the most significant role for living things and for technology. The nervous system in the human body operates with electric currents and the oxygen exchange in blood takes place with electric potential differences. Light bulbs, radios, televisions and other appliances facilitate domestic life; electric motors and electronic components in technology are included in the structure of all kinds of instruments and machinery.