L10 - resting and action potential Flashcards
define equilibrium potential for an ion
the membrane voltage that a cell needs to be at to prevent movement of that ion down its concentration gradient
what does E stand for? eg Ek or Ena
equilibrium potential (of potassium or sodium)
what will stop K+ from leaving cell
if the inside is very negative
what will stop Na+ entering cell
if inside is very positive
value of Ek
value of Ena
-90mV
+50mV
what is Vm
resting membrane potential
why is the Vm closer to Ek than Ena
because the membrane is about 50x more permeable to K
what happens to Vm when a membrane becomes more permeable to an ion?
the ion drives Vm towards its equilibrium potential (by moving down conc gradient)
what is the equation for driving force of an ion?
Vm - Eeq
resting mem potential - equilibrium potential of ion
what is driving force of:
K
Na
what does this mean?
K = +20mV forcing K+ out of cell Na = -120mV forcing Na into cell
at rest,
there is a force of +20mV trying to push K out
and
a force of -120mV trying to push Na in
what does the Goldman Hodgkin Katz equation do
considers relative permeabilities of ions to calculate Vm
what is the Goldman Hodgkin Katz equation
Vm = 58mV x log ( Pk [K+out] / Pk [K+ in] + Pk[Na out] / Pk[Na in] )
why is driving force on sodium greater than on K
because it is less permeable to Na
how is an action potential generated
- depolarisation causes Vm increase towards Ena (gets more positive)
- when threshold is reached Na+ channels open causing an Na influx making inside more positive (+ve feedback)
- peak
- Na channels snap shut
describe repolarisation
- depolarisation causes slow opening of K+ channels
- K+ efflux out
- Vm goes back towards Ek
