Action potential

Question 1

What is depolarisation?

Answer 1

the energy of the stimulus temporarily reverses the charg eon the axon membrane

as a result the PD across the membrane rapidly changes and becomes postively charged at approximately +40mV

this is known a depolarisation

Question 2

What happens as the impulse passes?

Answer 2

repolarisation then occurs

a chanmge in potential difference from positve to negative

the neurone then reutrns to its resting potential

Question 3

When does an action potential occur?

Answer 3

when protein channels in the axon membrane change shape as a result of the change of voltage across its membrane

the change in protein shape results in the channel opening or closing, these channels are known as voltage-gated ion channels

Question 4

What channels are open/closed when the neurone has resting potential?

Answer 4

some potassium ion channels are open (mainly those that are not voltage-gated)

but sodium voltage-gated ion channels are closed

Question 5

What happens to the channels as the strimuls occurs?

Answer 5

some sodium voltage-gated ion channels. making the membrane more permeable to sodium ions

sodium ion therefore diffuse into the axon down their electrochemical gradient

this majes the neurone less negative

Question 6

What does the change in charge cause?

Answer 6

causes more sodium ion channels to open, allowing more sodium ions to diffuse into the axon

this is an example of positive feedback

Question 7

What happens as the PD reaches +40mV?

Answer 7

the voltage-gated sodium ions channels close and the voltage-gated potassium ion channels open

sodium ions can no longer enter the axon, but the membrane is now more permeable to potassium ions

Question 8

How does repolarisation occur?

Answer 8

potassium ions diffuse out of the axon down their electrochemical gradient

this recudes the charge, resulting in the inside of the axon becoming more negative than the outside

Question 9

How does hyperpolarisation occur?

Answer 9

initially, lots of potassium ions diffuse out of the axon, resulting in the inside of the axon becoming more negative (relative to the outside) than its normal resting state

the voltage-gated potassium channels now close

Question 10

How is hyperpolarisation corrected?

Answer 10

the sodium-potassium pump causes sodium ions to move out of the cell, and potassium ions to move in

the axon returns to its resting potential