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Interpreting Oscilloscope Traces: Skills (HL) (HL IB Biology)

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Interpreting Oscilloscope Traces

  • 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

Oscilloscope Trace Graph

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

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

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.