Neurone cell membranes become depolarised when they’re stimulated.
A stimulus triggers other ion channels, called sodium ion channels, to open. If the stimulus is big enough, it will trigger a rapid change in potential difference. The sequences of events that then happen are known as an action potential and works as follows:
1. Stimulus – this excites the neurone cell membrane, causing sodium ion channels to open. The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This makes the inside of the neurone less negative.
2. Depolarisation – if the potential difference reaches threshold (around -55mV), more sodium ion channels open. More…