2 Answer ALL questions. Write your answers in the spaces provided. 1 Nerve impulses are transmitted along neurones. (a) (i) In the time period between two nerve impulses, the potential difference across the membrane is –70 mV. State the term given to this potential difference. (1) .................................................................................................................................................................................................................................................................................... (ii) When the neurone is stimulated, an action potential may occur in the axon, due to the change in permeability of the membrane to ions. The graph shows an action potential. 2.5 2.0 1.5 1.0 0.5 +50 +30 +10 –10 –30 –50 –70 –90 Time / ms Membrane potential / mV Describe what happens in the axon membrane to cause the change in potential difference between 0.55 ms and 0.80 ms. 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Turn over 3 (b) Scientists investigated the effect of stimulating an axon with different voltages and measured the response. The table shows the results of this investigation. Stimulus voltage / mV Response 25 No action potential 35 No action potential 45 No action potential 55 Action potential 65 Action potential 75 Action potential Analyse the data to describe the conclusions which can be drawn. 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(Total for Question 1 = 7 marks)