Establishment of an Action Potential

Question 1

What is an action potential?

Answer 1

An action potential is when a stimulus of sufficient size is detected by a receptor in the nervous system and its energy causes temporary reversal changes either side of the specific part of the axon membrane

Question 2

Once an action potential has been established, what occurs?

Answer 2

Once an action potential has been established, the negative charge of -65mV/-70mV inside the membrane becomes a positive charge of around 40mV

Question 3

Once an action potential has been established, what is the region of the axon membrane that undergoes this reaction referred to as?

Answer 3

The region that has the action potential established is described as depolarised

Question 3

Why does depolarisation occur?

Answer 3

Depolarisation occurs because the channels in the axon membrane change shape, hence opening/closing

Question 4

How is an action potential established?

Answer 4

1/ At resting potential some potassium voltage - gated channels are open (permanently) but the sodium voltage - gated channels are closed

2/ Energy from a stimulus causes some sodium voltage gated channels to open therefore sodium ions diffuse into the axon through these channels along their electrochemical gradient

Their positive charge triggers a reversal in the potential difference across the membrane

3/ As sodium ions diffuse into the axon, more sodium channels open, causing an even greater influx of sodium ions by diffusion

4/ Once the action potential of +40mV is established, the voltage gates on the sodium ion channels close and the voltage gates on the potassium ion channels begin to open, depolarisation occurring

5/ With some potassium voltage - gated channels now open, the electrical gradient that was preventing further outward movement of potassium ions is now reversed, which causes more potassium ions channels to open. This causes more potassium ions to diffuse out, beginning the repolarisation of the axon

6/ The outward diffusion of these potassium ions causes a temporary overshoot of the electrical gradient, having the inside of the axon be more negative (relative to the outside) than usual

The closable gates on the potassium ion channels now close and the activities of the sodium - potassium pumps once again cause sodium ions to be pumped out and potassium ions in

7/ The resting potential of -65mV is reestablished and the axon is repolarised