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What is a potential difference?
- A charge separation across a cell membrane - a difference (delta) in volts (V). Measured in mV
- Outside is more positive
- Inside is more negative
- Calculated for one ion species by the Nernst equation.
How does charge separation arise?
Transmembrane concentration differences and the presence of leak ion channels
What is conductance?
- Conductance (Gion) = measure of the ease with which an ion can cross a unit area of 1cm2 of membrane
- =Po n gamma
- Po is the probability the channel is open
- n is the number of channels
- gamma is the number of ions per second that a chanel can conduct
If Po = 1, then channels are open all the time and are therefore "leak" channels
How do we calculate the resting membrane potential?
- The Goldman Equation
- This takes into account the conductance of the K, Na and Cl and their equilibrium potential, sums it and this = Vm (AKA RMP)