Ionic Basis of Action Potentials

Question 1

What are the mV of resting membrane potential?

Answer 1

-70

Question 2

What are mV of threshold?

Answer 2

-55

Question 3

What happens once cell reaches threshold?

Answer 3

cell will rapidly de polarize and reach around 30 to 40 mV
then very quickly re polarize
then hyperpolarize before gradually returning to resting membrane potential

Question 4

Describe how cell depolarizes and repolarizes?

Answer 4

cell at resting membrane potential of 70mV
leaky potassium channels continually allow potassium ions to leak out of cell down conc gradient
Once cell reaches threshold (-55mV) , voltage gated sodium channels will open
Sodium ions flood into cell
Will very quickly depolarize cell
Pull cell towards sodium equilibrium position of about +60 mV
Cell will quickly repolarize due to voltage gated sodium channels closing and voltage gated potassium channels opening
Potassium ions leak out of cell down conc gradient and draw the cell towards equilibrium potential for potassium of -90mV
Then voltage gated potassium channels will close and resting membrane potential will return

Question 5

What is the absolute refractory period?

Answer 5

When action potential is triggered and all sodium channels open, excitability drops to zero and you can’t physically open any more channels to generate another action potential

Question 6

What is relative refractory period?

Answer 6

Excitability increasing. Ball of sodium channel ready for another action potential

Question 7

Properties of action potentials?

Answer 7

-have a threshold
-self propagating
-all or nothing (can’t physically open anymore voltage gated sodium channels to get bigger strength action potential)
-have a refractory period
-travel slowly

Question 8

How do we get increased firing rate of action potentials?

Answer 8

for the strength of superthreshold stimuli to increase

Question 9

How are action potentials self propagating?

Answer 9

when membrane potential high enough for action potential (-55)

first set of voltage gated channels open and allows sodium ions to flow into cell - this bit of membrane depolarises (+40)

Depolarisation doesn’t spread far across membrane however spreads far enough that next set of voltage gated sodium channels open

and so on and so on