In an experiment, a student measures the resting potential of a neurone as −70 mV and the peak action potential as +40 mV. What is the total change in membrane potential during depolarisation?

The total change in membrane potential during depolarisation is calculated as the difference between the peak action potential and the resting potential: $+40\text{ mV} - (-70\text{ mV}) = +110\text{ mV}$. Common errors include subtracting only the magnitudes (70 − 40 = 30 mV) or using only one of the values. The correct answer accounts for the sign change across the full range of depolarisation.