• It is possible to?measure membrane potentials?in neurones by placing electrodes on each side of the membrane
  • A membrane potential is the?difference in charge?between one side of a membrane and the other, sometimes described as the potential difference, or the voltage
• The membrane potential can then be?visually represented?and?displayed?using an?oscilloscope
• An oscilloscope is a type of?electronic test instrument?that?graphically displays varying signal voltages
• The display produced is?like a graph?with?time?in milliseconds on the?x-axis?and the membrane?potential?in millivolts on the?y-axis

How to analyse oscilloscope traces showing resting potentials and action potentials

• If there is a?resting potential, a?straight, horizontal line?should be shown on the display screen of the oscilloscope at a level of?-70 mV
• If an?action potential?occurs a?spike,?rising up to a maximum voltage of?between +30 and +40 mV,?should be shown on the display
  • The?rising phase?of the spike shows?depolarisation
  • The?falling phase?of the spike shows?repolarisation
• Often not shown on an action potential graph is the gradual rise in membrane potential just before the membrane rapidly depolarises
  • Before threshold potential is reached, only a small number of sodium channels in the membrane are open, so the membrane depolarises slowly, but when the threshold is reached many more sodium channels open
• Instead of repolarisation causing the membrane potential to return?immediately?to the normal resting potential of -70 mv, the trace often shows a?short period?of?hyperpolarisation
  • This is when the membrane potential briefly becomes?more negative?than resting potential

An example of an oscilloscope trace showing resting potential and an action potential