L6 Flashcards
what is the membrane potential of a cell
it is the combination of all the equilibrium potentials of the ions that the membrane is permeable to
what does the Nernst potential tell us
it is what tell us what the driving force will be in order for equilibrium to occur
what does the Nernst equation calculate
the diffusion potential for an ion
ie if diffusion can occur freely what will the membrane potential would be when the electrical and chemical gradients are equal and opposite
how many more times more permeable is the membrane for K+ compeered to Na
10,000 x
when an action potential is fired the membrane potential never reaches the equilibrium potential for K+ or Na+. why is this
because then there would be no movement of that ion.
They just get close to it
what is the Nernst equation for cation and anions
Outside over inside UNLESS it is a -ively charged ion then it is inside over outside
what happens to the electrical potential is the chemical potential is balanced
is there is no chemical graident then there is no need for an electrical gradient to oppose it
therefore the ion is at equilibrium (E = 0)
the equilibrium potential for Cl- is the same as the membrane potential. why is this
This happens because Na and K keep the MP the same is Ecl.
This means that there is no net movement of Cl
This happens because the cell wants to strictly regulate the intracellular conc of Cl-
what determines the intracellular conc of Cl-
The membrane potential (Vm) and the extracellular concentration of Cl- determines the intracellular concentration of Cl-
what does driving force =
driving force = membrane potential - equilibrium potential (for that ion)
-ive driving force = influx
+ive driving force = efflux
what does the movement of ions determine
The movement of ions determines osmolarity, pH and volume
is the cell at equilibrium when it is at RMP
the cell membrane is in a steady state NOT equilibrium
if it was at equilibrium then the cell would have no energy as the ions would all have to be at their equilibrium and be balanced on either side of the membrane
what maintains the membranes steady state
Na/K ATPase
why does the membrane potential sit closer to K+ equilibrium potential than it does for Na
because the membrane is more permeable to K
what happens in secretory cells (in terms of Cl-)
in secretory epithelia you want there to be more Cl- inside the cell (more than 5mmol)
NKCC brings 2Cl, Na and K into the cell
Na/K ATPase pumps 3Na out and 2K in the cell. the rest of the K leaves through a K+ leak channel
There is a driving force for cl to leave the cell and you increase this by adding channels into the apical membrane
this makes the lumen -inely charged. Na from the blood travels into the lumen (+ follows - charge). then water follows salt into the lumen
