E. Neher and B. Sakmann were awarded the Nobel Prize for achievements in Physiology or Medicine in 1991. They developed the "patch clamp technique" which enables measurement of ionic currents through channels in the plasma membrane of living cells, and characterized their functional properties. An overview of three types of ion channels is presented: voltage gated channels, ligand gated channels and G-protein gated channels. An attempt was made to correlate their function with the structure of the protein complexes that represent ionic channels. The perforated patch clamp technique is mentioned as an alternative that enables recording of membrane currents without washing out the content of the interior of the cells.