biology A2 nerve impulses notes and diagrams

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Notes on generating nerve impulses by Stephanie Maurice
Generating nerve impulses
Receptor cells detect change
Gated Na+
Small change causes few channels opening is the generator potential.
Longer the stimulus the more gates open
If lots of Na+ ions enter the cell the potential difference changes
Initiates an action potential
Graph notes
1. Membrane begins polarised (60mV) the resting state.
2. Na+ channels open and some Na+ ions diffuse into the cell.
3. Membrane depolarises become less negative (50mV)
4. Voltage gated Na+ channels open and lots of Na+ ions flood into the cell and the
cell becomes positively charged
5. Potential difference reaches +40mV
6. Na+ ion channels close and K+ channels open.
7. K+ move thought the membrane potential difference becomes negatively charged
8. Potential difference overshoots slightly because they are hyperpolarised.
9. The original potential difference is restored so that the resting state is restored
Quick notes
Gated channels only open when many molecules have already diffused (diffusion
gradient changes.
Polarised positive outside
Depolarised positive inside
Flicks law ­ the higher the concentration inside the faster the diffusion time (effect of


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