Patch Clamp

When many channels are activated, channel opening is a stochastic process and the total current recorded is the sum of the currents flowing through the individual channels. Once a channel opens there is a very high probability that it will go into the inactivateable state.
‘ v’ applied step voltage, ‘I’ individual channel currents and below summated currents. The membrane currents recorded by Hodgkin & Huxley can be seen to form when many channels are activated. The current recorded at a single node of Ranvier represents the contribution of many thousands of ion channels.

The probability that a channel is in the active, conducting state is a function of the transmembrane potential. When step changes in the membrane potential are applied and peak sodium currents are measured and plotted as a function of the magnitude of the step change in membrane potential, the curve shown in blue is recorded when the ion channels in the test patch of membrane were in the inactive/activateable state .
When an intermediate potential is applied, only a fraction of the channels are opened, yellow line, too few to achieve threshold for generating an action potential. If these channels are given time to become inactivateable, and, a second stimulus pulse applied at value that is capable of activating all activatable channels (and before the inactivatable channels have recovered), only those activateable channels are activated leaving the patch unable to develop sufficient depolarization to initiate a propagated action potential.