Action potential

Question 1

Describe the six stages of the action potential

Answer 1

1) Neurone is at a resting potential of -70mV and is not transmitting an impulse
- Some potassium ion channels are open
- Sodium voltage-ion channels are closed

2) The energy of the stimulus triggers some sodium voltage-gated ion channels to open, making the membrane more permeable to sodium ions.
- Sodium ions therefore diffuse down into the axon down their electrochemical gradient, making the inside of the neurone less negative

3) The depolarisation causes more sodium channels to open
-Positive feedback
(Depolarisation)

4) When the potential difference reaches +40mV, the voltage-gated sodium ion channels close and the voltage-gated potassium ion channels open
- Sodium ions can no longer enter the axon
- The membrane is now more permeable to potassium ions

5) Potassium ions diffuse out of the membrane down their electrochemical gradient
-This reduces the charge, resulting in the inside of the axon becoming more negative than the outside
(Repolarisation)

6) Initially, lots of potassium ions diffuse out of the membrane which makes the inside of the axon more negative than it’s normal resting state.
(Hyperpolarisation)
-Voltage-gated potassium channels now close
-The sodium-potassium pump causes sodium ions to move outside of the cell and potassium ions now move into the in.
-The axon returns to its resting potential
(Repolarised)