Resting membrane potential Flashcards
What is the resting membrane potential?
The potential difference (mv) between the inside and outside of a cell at rest
What is the value of the resting membrane potential?
-30mv and -90mv always polarised
What is the average RMP for a neurone?
~-70mv
What is the average RMP for a skeletal muscle cell?
~-90mv
What ion are cells most permeable to at rest?
Potassium
What leads to potassium loss from a cell?
High concentration gradient within the cell, diffusion of K+ out down conc grad.
What pulls potassium into the cell?
Loss of +ve charge from cell as K+ moves down its concentration gradient creates and electrical pull into the cell
If membrane just permeable to potassium at what point is there no net flux?
Flux driven by chemical gradient = flux driven by electrical gradient
-90mv
What is equilibrium potential for potassium?
-90mV
What is equilibrium potential?
Potential at which flux driven by chemical = flux driven by electrical gradient
What is ENa?
+58mV
Why is Em closer to Ek?
Cell at rest more permeable to potassium
What is meant by the Nernst equation?
Gives the ion equilibrium potential
What are components of Nernst equation?
Gas constant Temp Farradays constant Valency Concentration of ion in and out of the cell
What does Na+K+ Pump do?
Uses ATP hydrolysis to pump 3NA+ out and 2 K+ in
Why is Na+K+ important?
Ion gradient created allows ion movement to establish membrane potential
What is the downfall of Nernst in estimating a cells Em?
Does not take into consideration concentrations and permeability of other ions
What equation is better at estimating Em than Nernst?
Goldmann-Hodgkin-Catz
Describe kinetics relationship between Na+ concentration and Na+ efflux from pump
Sigmoidal
What is the effect of increased extracellular K+?
Reduces outward gradient so Em less negative and membrane repolarised
What is effect of more external Na+ on Em?
Increased diffusion into cell depolarisation
What is the effect of increased Cl- extracellularly on Em?
Concentration gradient to drive Cl- into cell so hyperpolarise membrane
What is meant by the valence of an ion (Z) in Nernst?
Ion charge
Cl-= -1
Na+=+1
When and ion is in steady state what can be said about ratio of +ve to -ve ions on inside and outside of cell?
Equal numbers
Raising the extracellular K+ concentration bathing a nerve cell would
Make Ek less negative (more positive)
Reducing the extracellular concentration of Na+ ions would
Make ENa more negative (less positive)
A doubling of the intracellular Na+ ion concentration will
Stimulate membrane ion transport by Na+/K+ ATPase proteins
A change of extracellular K+ ion concentration to 2.0 mM will
Decrease membrane ion transport by Na+/K+ ATPase proteins.
