Electrical Properties Of Cell Membranes Flashcards
What is the resting potential of a typical cell?
-70mV
What ions principally determine resting membrane potential?
Na+
K+
What is the equilibrium potential?
Membrane potential that prevents movement of a given ion down its concentration gradient
If you make the intracellular membrane potential very negative, which ion’s net movement will change and how?
K+
Stops leaving
If you make the intracellular membrane potential very positive, which ion’s net movement will change and how?
Na+
Stops entering
For physiological concentrations, what is the equilibrium potential of K+?
-90mV
For physiological concentrations, what is the equilibrium potential of Na+?
+50mV
What is the Nernst equation?
E = RT/zF . ln [concentration gradient]
What is the Nernst equation at physiological concentrations for monovalent ions?
58 log [concentration gradient]
How do you calculate the concentration gradient of a positive ion?
[ion outside]/[ion inside]
How do you calculate the concentration gradient of a negative ion?
[ion inside]/[ion outside]
Why is resting membrane potential so much closer to E(K) than E(Na)?
Membrane is 50x more permeable time K+ than Na+ (more open K+ channels open at rest)
What is the net flow of ions at constant membrane potential?
0
If a membrane becomes permeable to an ion, what will happen?
The ion will move down its concentration gradient
Drive the membrane potential to its own equilibrium potential
How do you calculate the driving force on an ion (across a membrane)?
Driving force = Vm - E(eq)
Vm - membrane potential
E(eq) - equilibrium potential for that ion
What is the driving force on K+ ions at rest?
(Driving force = -70 - (-90) = +20mV)
+20mV forcing K+ out
What is the driving force on Na+ ions at rest?
(Driving force = -70 - (+50) = -120mV)
-120mV forcing Na+ in
Why is the resting membrane potential closer to E(K) when the driving force on Na+ is so much greater?
Membrane is much more permeable (50x) to K+ than Na+
Less force required to force the same number of K+ out than Na+ in
What is permeability?
Ease with which an ion can cross the membrane (no. of open channels)
What is conductance?
What actually gets across the membrane in terms of current/flow of ions
How would a lower concentration gradient affect an ion’s conductance?
Lower driving force
Lower conductance (altered E(K))
How would a decreased permeability affect an ion’s conductance?
Decreased conductance
What is the Goldman Hodgkin Katz equation?
Vm = 58 log { (PK.[K+ outside] + PNa.[Na+ outside]) / (PK.[K+ inside] + PNa.[Na+ inside]) }
Why is the Goldman Hodgkin Katz better than the Nernst equation?
Considers relative permeabilities of each ion
What triggers an action potential?
Depolarisation to threshold (suprathreshold depolarisation)
Why does the membrane potential become more positive during an action potential?
Voltage-gated Na+ channels open
Na+ moves into cell down concentration gradient
Pushes membrane potential to E(Na)
What is the absolute refractory period?
From peak depolarisation to hyperpolarisation
What is the relationship between conductance and resistance?
Conductance = reciprocal of resistance
How long does an action potential take?
~4ms
How does the action potential line relate to the Na+ conductance line on a conductance/time graph?
Action potential line is always above Na+ conductance (for duration of the Na+ movement)
How does the action potential line relate to the K+ conductance line on a conductance/time graph?
Peak of K+ conductance is midway up the repolarisation slope of the action potential
Which direction does current move?
Positive to negative
