Very simply Action potential past paper question
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Are the first 2 m
arking points describing what's in the textbook picture ?![Name: Screenshot (38).png
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Last edited by Leah.J; 1 year ago
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#2
(Original post by Leah.J)
Are the first 2 m
arking points describing what's in the textbook picture ?![Name: Screenshot (38).png
Views: 127
Size: 36.4 KB]()
Are the first 2 m
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(Original post by Jpw1097)
The textbook image shows all of the points set out in the mark scheme. In an action potential, sodium ions move into the axon, depolarising the adjacent membrane which causes voltage-gated sodium channels to open and sodium moves into the axon, and then this depolarises the adjacent membrane and so on. This cycle repeats, allowing the action potential to propagate along the entire axon. It looks as though this is for an unmyelinated axon, in a myelinated axon the process is essentially the same however there are much larger gaps between voltage-gated sodium channels (at the nodes of Ranvier, at gaps between the myelin sheath) - this is known as saltatory conduction and explains why action potentials are transmitted much more quickly in a myelinated axon.
The textbook image shows all of the points set out in the mark scheme. In an action potential, sodium ions move into the axon, depolarising the adjacent membrane which causes voltage-gated sodium channels to open and sodium moves into the axon, and then this depolarises the adjacent membrane and so on. This cycle repeats, allowing the action potential to propagate along the entire axon. It looks as though this is for an unmyelinated axon, in a myelinated axon the process is essentially the same however there are much larger gaps between voltage-gated sodium channels (at the nodes of Ranvier, at gaps between the myelin sheath) - this is known as saltatory conduction and explains why action potentials are transmitted much more quickly in a myelinated axon.
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Can you help me in part d ?
I could almost swear my book and my teacher said during that time the K ion channels close and the pump acts to restore the resting potential
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#4
(Original post by Leah.J)
so the answer is for an unmyelinated nerve fibre ? I'm finding it a little difficult to understand what you mean by adjacent membrane. To me it looks like 1 membrane only.
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Can you help me in part d ?
I could almost swear my book and my teacher said during that time the K ion channels close and the pump acts to restore the resting potential
so the answer is for an unmyelinated nerve fibre ? I'm finding it a little difficult to understand what you mean by adjacent membrane. To me it looks like 1 membrane only.
Also
Can you help me in part d ?
I could almost swear my book and my teacher said during that time the K ion channels close and the pump acts to restore the resting potential
Yes that's right for part (d), voltage-gated potassium channels close and the sodium-potassium pump restores the resting membrane potential.
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(Original post by Jpw1097)
Yes, it's the same membrane, but the adjacent part of the membrane. No the principles are the same for both myelinated and unmyelinated nerve fibres - in a myelinated nerve fibre, the sodium channels are located at the nodes of Ranvier.
Yes that's right for part (d), voltage-gated potassium channels close and the sodium-potassium pump restores the resting membrane potential.
Yes, it's the same membrane, but the adjacent part of the membrane. No the principles are the same for both myelinated and unmyelinated nerve fibres - in a myelinated nerve fibre, the sodium channels are located at the nodes of Ranvier.
Yes that's right for part (d), voltage-gated potassium channels close and the sodium-potassium pump restores the resting membrane potential.
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#6
(Original post by Leah.J)
But it says that the membrane remains permeable in the mark scheme, and that the potassium ions move into the axon because of the charge difference, so I'm guessing they mean by diffusion
But it says that the membrane remains permeable in the mark scheme, and that the potassium ions move into the axon because of the charge difference, so I'm guessing they mean by diffusion
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(Original post by Jpw1097)
Do you know the sequence of events that happen during an action potential? If not, I would suggest having a look.
Do you know the sequence of events that happen during an action potential? If not, I would suggest having a look.
An electrical impulse reaches the neurone and causes Na ion channels to open resulting in an influx of Na ions which depolarise the neurone. If this depolarisation is above a threshold value, voltage gated Na ion channels will open and sodium ions will diffuse into the axon depolarising the adjacent part of the membrane then that causes Na ion channels in that part to open and so on and so on.
Then the neurone or axon needs to get repolarised so the K ion channels open and the Na ion channels close, K ions diffuse outside the axon repolarising the neurone. When the resting potential is reached, K ion channels close but take time to do so resulting in hyperpolarisation, to restore the resting potential, the K+ channel proteins close and the Na K pump K+ ions inside.
That's all I know on action potential
Is there anything missing or incorrect ?
This is from the examiner reports
and I'm ... I don't know I'm done with life and with edexcel and I'm just confused
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#8
Leah.J
Your questions are great. Jpw1097 your answers are greater
Your questions are great. Jpw1097 your answers are greater
(Original post by Leah.J)
I swear I do. Or at least I think I do ?
An electrical impulse reaches the neurone and causes Na ion channels to open resulting in an influx of Na ions which depolarise the neurone. If this depolarisation is above a threshold value, voltage gated Na ion channels will open and sodium ions will diffuse into the axon depolarising the adjacent part of the membrane then that causes Na ion channels in that part to open and so on and so on.
Then the neurone or axon needs to get repolarised so the K ion channels open and the Na ion channels close, K ions diffuse outside the axon repolarising the neurone. When the resting potential is reached, K ion channels close but take time to do so resulting in hyperpolarisation, to restore the resting potential, the K+ channel proteins close and the Na K pump K+ ions inside.
That's all I know on action potential
Is there anything missing or incorrect ?
This is from the examiner reports![Name: Screenshot (62).png
Views: 86
Size: 68.4 KB]()
and I'm ... I don't know I'm done with life and with edexcel and I'm just confused
I swear I do. Or at least I think I do ?
An electrical impulse reaches the neurone and causes Na ion channels to open resulting in an influx of Na ions which depolarise the neurone. If this depolarisation is above a threshold value, voltage gated Na ion channels will open and sodium ions will diffuse into the axon depolarising the adjacent part of the membrane then that causes Na ion channels in that part to open and so on and so on.
Then the neurone or axon needs to get repolarised so the K ion channels open and the Na ion channels close, K ions diffuse outside the axon repolarising the neurone. When the resting potential is reached, K ion channels close but take time to do so resulting in hyperpolarisation, to restore the resting potential, the K+ channel proteins close and the Na K pump K+ ions inside.
That's all I know on action potential
Is there anything missing or incorrect ?
This is from the examiner reports
and I'm ... I don't know I'm done with life and with edexcel and I'm just confused
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Report
#9
(Original post by Leah.J)
I swear I do. Or at least I think I do ?
An electrical impulse reaches the neurone and causes Na ion channels to open resulting in an influx of Na ions which depolarise the neurone. If this depolarisation is above a threshold value, voltage gated Na ion channels will open and sodium ions will diffuse into the axon depolarising the adjacent part of the membrane then that causes Na ion channels in that part to open and so on and so on.
Then the neurone or axon needs to get repolarised so the K ion channels open and the Na ion channels close, K ions diffuse outside the axon repolarising the neurone. When the resting potential is reached, K ion channels close but take time to do so resulting in hyperpolarisation, to restore the resting potential, the K+ channel proteins close and the Na K pump K+ ions inside.
That's all I know on action potential
Is there anything missing or incorrect ?
This is from the examiner reports![Name: Screenshot (62).png
Views: 86
Size: 68.4 KB]()
and I'm ... I don't know I'm done with life and with edexcel and I'm just confused
I swear I do. Or at least I think I do ?
An electrical impulse reaches the neurone and causes Na ion channels to open resulting in an influx of Na ions which depolarise the neurone. If this depolarisation is above a threshold value, voltage gated Na ion channels will open and sodium ions will diffuse into the axon depolarising the adjacent part of the membrane then that causes Na ion channels in that part to open and so on and so on.
Then the neurone or axon needs to get repolarised so the K ion channels open and the Na ion channels close, K ions diffuse outside the axon repolarising the neurone. When the resting potential is reached, K ion channels close but take time to do so resulting in hyperpolarisation, to restore the resting potential, the K+ channel proteins close and the Na K pump K+ ions inside.
That's all I know on action potential
Is there anything missing or incorrect ?
This is from the examiner reports
and I'm ... I don't know I'm done with life and with edexcel and I'm just confused
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(Original post by Jpw1097)
That’s fine, I think you have a very good idea about action potentials.
That’s fine, I think you have a very good idea about action potentials.
Did you read the examiner reports ? It says that K Na pumps do not restore the resting potential and that that's a misconception which "obviously" doesn't get credit ... everywhere else on earth, Na K pumps restore resting potential, did I misunderstand part d ? Or do I not know sth about restoring the resting potential ?
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#11
(Original post by Leah.J)
I swear, last thing, just answer part d please.
Did you read the examiner reports ? It says that K Na pumps do not restore the resting potential and that that's a misconception which "obviously" doesn't get credit ... everywhere else on earth, Na K pumps restore resting potential, did I misunderstand part d ? Or do I not know sth about restoring the resting potential ?
I swear, last thing, just answer part d please.
Did you read the examiner reports ? It says that K Na pumps do not restore the resting potential and that that's a misconception which "obviously" doesn't get credit ... everywhere else on earth, Na K pumps restore resting potential, did I misunderstand part d ? Or do I not know sth about restoring the resting potential ?
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#12
(Original post by Leah.J)
I swear, last thing, just answer part d please.
Did you read the examiner reports ? It says that K Na pumps do not restore the resting potential and that that's a misconception which "obviously" doesn't get credit ... everywhere else on earth, Na K pumps restore resting potential, did I misunderstand part d ? Or do I not know sth about restoring the resting potential ?
I swear, last thing, just answer part d please.
Did you read the examiner reports ? It says that K Na pumps do not restore the resting potential and that that's a misconception which "obviously" doesn't get credit ... everywhere else on earth, Na K pumps restore resting potential, did I misunderstand part d ? Or do I not know sth about restoring the resting potential ?
Now consider the factors that determine the rate at which ions will move across the membrane. One of these factors is the electrochemical gradient of a particular ion (the difference in charge and concentration across the membrane) and the other is the permeability of the membrane to the ion.
Imagine a scenario where the membrane is permeable ONLY to potassium ions. Potassium ions would move from inside the cell to the outside via these leak channels via their concentration gradient. As a result, the outside of the cell would become more positive and the inside of the cell would become more negative (as positive ions are leaving the cell) - making the resting membrane potential more negative. Now, the build up of positive charge on the outside of the cell would begin to reduce the rate at which potassium ions are leaving the cell across the membrane as the positive charge outside the cell would repel the positively charged potassium ions. The membrane potential at which there would be no net flow of potassium ions (the equilibrium potential) would be around -84mV.
Now imagine if the membrane were only permeable to sodium ions. Sodium ions would move from the outside to the inside of the cell (down its concentration gradient). This would make the inside of the cell more positive relative to the outside, however, the build up of sodium ions inside the cell would make the membrane potential positive. This would then begin to slow down the movement of sodium ions from the outside to the inside of the cell. The membrane potential at which the chemical and electrical forces (due to the concentration and electrical gradient) would be balanced, and therefore there would be no net flow of sodium ions, would be around +62mV.
However, since the membrane is more permeable to potassium, the resting membrane potential is much closer to the equilibrium potential of potassium (-80mV) rather than sodium (+62mV). It’s quite complicated and I’m not sure if I have explained it very well, but hopefully that gives you an idea of the reason why the resting membrane potential is the value that it is.
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