Propagation of action potentials

Question 1

Explain how action potentials are propagated

5 stages

Answer 1

1) At resting potential, the concentration of sodium ions outside of the axon membrane is high, relative to the inside
- Concentration of potassium ions is high on the inside of the membrane relative to the outside of the membrane
- Overall concentration of positive ions is higher outside of the membrane than inside of the membrane
- Therefore, the outside of the membrane has a more positive charge than the inside of the membrane

2) A stimulus causes a sudden influx of sodium ions and hence a reversal of charge on the axon membrane
- This is the action potential and the membrane is being polarised

3) The localised electrical circuits established by the influx of sodium ions cause the opening of sodium voltage-gated ion channels further along the membrane
- The resulting influx of sodium ions makes the causes depolarisation
- Behind the wave of depolarisation, sodium ion channels close and potassium ion channels open
- Potassium ions leave the membrane via diffusion down their electrochemical gradient

4) The action potential is propagated in the same way further along the axon.
5) Following repolarisation, the axon membrane returns to it’s resting potential.

Question 2

After the action potential, there is a a period of time where the axon cannot be excited again, what is this period called?

Answer 2

Refractory period

Question 3

What occurs during the refractory period?

Answer 3

Voltage-gated sodium ion channels cannot open, ensuring that the flow of action potentials is unidirectional