IB Biology SL

Revision Notes

6.5.4 Skill: Neurones & Synapses

Analysis of Oscilloscope Traces

  • It is possible to measure membrane potentials in neurones by placing electrodes on each side of the membrane
  • 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 narrow 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 depolaristation
    • The falling phase of the spike shows repolarisation
  • The trace produced on the oscilloscope display may also show the membrane potential rising (just before depolarisation) until the threshold potential is reached and an action potential is initiated
  • Instead of repolarisation causing the membrane potential to return to the normal resting potential of -70 mv immediately, there may actually be a short period of hyperpolarisation shown on the oscilloscope display
    • This is when the membrane potential briefly becomes more negative than the normal resting potential

Action potential graph, downloadable AS & A Level Biology revision notes

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

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