The greatest advance in my field was the invention, by Sakmann and Neher in 1976, of a method (the patch clamp) that made it possible to observe the opening and shutting of single ion channel molecules. These are protein molecules which span the insulating membrane that surrounds cells. The opening of a pore through the molecule allows an electric current (carried by ions) to flow through the membrane. Such currents are the basis of the nerve impulse and synaptic transmission, among other things.
The size of the current through one ion channel while it is open is about 5 pA (5 millionths of a millionth of an ampere). Single molecules always behave randomly, but development of the relevant stochastic theory has allowed interpretation of the measurements in terms of mechanisms for the operation of the channel and the means by which neurotransmitters cause it to open.
David Colquhoun is research professor of pharmacology at University College London, editor of the Improbable Science Page and pioneer in the understanding of ion channels.