ForestShadow
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Hi guys this has been bugging me for so long now so I thought Id ask , questions in red!

So the new ocr biology textbook says

Image


(1) to form a nerve impulse:

-deformation of membrane occurs
-sodium ion channels widen
most places say sodium ion channels open instead, whos right?
-sodium ions diffuse into neurone
-membrane is depolarised
-generator potential formed
-in turn generator potential creates AP (action potential) that passes along sensory neurone

dont generator potentials need to surpass threshold potential first to create ap?

so not every deformation causes an AP if it doesnt surpass threshold?

also what happens with v-gated sodium and potassium channels in nerve impulse formation, are they always shut?

also does the membrane not need to be repolarised like in formation of AP?

I have read about formation of AP:

(2) to form an action potential:

-energy of stimulus causes v-gated sodium channels to open
-membrane more permeable to sodium ions
-sodium ions diffuse into axon
-positive feedback, more sodium ion channels open

so I know APs are a result of nerve impulses formation but I dont see why there are so many gaps in nerve impulse formation, is there no repolarisation, hyperpolarisation etc in (1), the stages arent simultaneous time wise are they? :holmes:

thanks for any help!!
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rosemondtan
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omd some of these questions were exactly the doubts I had not long ago! Yass telepathy

wrt to the widening vs opening, in my spec (AQA) it says open, but in theory I think it widens and opens. This parallels with the idea of the effect of insulin on the target cells in the muscle and liver - it both increases the permeability of glucose channels AND increases the number of glucose channels there are! So both opening and widening could occur. (but I'm not sure, anyone feel free to correct me on this)

Yes, if the threshold isn't crossed then there will be no action potentials! If the threshold is crossed (-50mV usually) then the ap will be the same size no matter what (all-or-nothing principle)

Yep!

Voltage gated are open when the threshold value is crossed - that allows the massive influx of Na+ ions to cause the depolarisation and thus the action potential. Once the maximum depolarisation is reached (+30mV usually), the sodium ion channels close and the v-gated potassium ion channels open to allow for repolarisation to occur. Then, the voltage-gated potassium ion channels close slowly and the fact that it closes slowly means that some K+ ions may leak out and this is where hyperpolarisation occurs. The membrane potential is then restored by the action of the sodium/potassium pumps and the permanently open K+ channels (is this what you're asking?)

There is repolarisation and hyperpolarisation! It will take place after the Na+ ions diffuse to the adjacent part of the membrane and stimulates an action potential there so the previous part of the membrane will undergo repolarisation. This period also takes into account the refractory period as well! So it ensures that the voltage gated Na+ channels are closed and you can't have another action potential right after the first one to ensure the action potentials are discrete and the information does not overload the brain. What do you mean when you say the "stages aren't simultaneous time-wise"?

I'm still in the midst of studying as well, but here are my 2 cents worth!
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ForestShadow
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(Original post by rosemondtan)
omd some of these questions were exactly the doubts I had not long ago! Yass telepathy

wrt to the widening vs opening, in my spec (AQA) it says open, but in theory I think it widens and opens. This parallels with the idea of the effect of insulin on the target cells in the muscle and liver - it both increases the permeability of glucose channels AND increases the number of glucose channels there are! So both opening and widening could occur. (but I'm not sure, anyone feel free to correct me on this)

Yes, if the threshold isn't crossed then there will be no action potentials! If the threshold is crossed (-50mV usually) then the ap will be the same size no matter what (all-or-nothing principle)

Yep!

Voltage gated are open when the threshold value is crossed - that allows the massive influx of Na+ ions to cause the depolarisation and thus the action potential. Once the maximum depolarisation is reached (+30mV usually), the sodium ion channels close and the v-gated potassium ion channels open to allow for repolarisation to occur. Then, the voltage-gated potassium ion channels close slowly and the fact that it closes slowly means that some K+ ions may leak out and this is where hyperpolarisation occurs. The membrane potential is then restored by the action of the sodium/potassium pumps and the permanently open K+ channels (is this what you're asking?)

There is repolarisation and hyperpolarisation! It will take place after the Na+ ions diffuse to the adjacent part of the membrane and stimulates an action potential there so the previous part of the membrane will undergo repolarisation. This period also takes into account the refractory period as well! So it ensures that the voltage gated Na+ channels are closed and you can't have another action potential right after the first one to ensure the action potentials are discrete and the information does not overload the brain. What do you mean when you say the "stages aren't simultaneous time-wise"?

I'm still in the midst of studying as well, but here are my 2 cents worth!
oh my so much detail thank you for all that information

haha telepathy maybe, the whole ion side with chemistry-ish stuff constantly confuses me, same with the stuff from photolysis and things lmao, I can handle pure biology but voltages and ions are outta my league :rofl:

ah good to know they open and widen then and that example is good evidence of that :yep:

yeah I did read up on the hyper polarisation and re polarisation again, thanks for explaining it too

my question was worded badly haha, what I mean is

what is the difference between a nerve impulse and an action potential :dontknow:

they have different paragraphs in my textbook but arent they the same thing so both have depolarisation, repolarisation and hyper polarisation stages?

Is there a nerve impulse even if it doesn't reach threshold potential?

Or does nerve impulse = action potential

or do they happen together, idk how the 2 things are related or not lmao :holmes:
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ForestShadow
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(Original post by rosemondtan)
omd some of these questions were exactly the doubts I had not long ago! Yass telepathy

wrt to the widening vs opening, in my spec (AQA) it says open, but in theory I think it widens and opens. This parallels with the idea of the effect of insulin on the target cells in the muscle and liver - it both increases the permeability of glucose channels AND increases the number of glucose channels there are! So both opening and widening could occur. (but I'm not sure, anyone feel free to correct me on this)

Yes, if the threshold isn't crossed then there will be no action potentials! If the threshold is crossed (-50mV usually) then the ap will be the same size no matter what (all-or-nothing principle)

Yep!

Voltage gated are open when the threshold value is crossed - that allows the massive influx of Na+ ions to cause the depolarisation and thus the action potential. Once the maximum depolarisation is reached (+30mV usually), the sodium ion channels close and the v-gated potassium ion channels open to allow for repolarisation to occur. Then, the voltage-gated potassium ion channels close slowly and the fact that it closes slowly means that some K+ ions may leak out and this is where hyperpolarisation occurs. The membrane potential is then restored by the action of the sodium/potassium pumps and the permanently open K+ channels (is this what you're asking?)

There is repolarisation and hyperpolarisation! It will take place after the Na+ ions diffuse to the adjacent part of the membrane and stimulates an action potential there so the previous part of the membrane will undergo repolarisation. This period also takes into account the refractory period as well! So it ensures that the voltage gated Na+ channels are closed and you can't have another action potential right after the first one to ensure the action potentials are discrete and the information does not overload the brain. What do you mean when you say the "stages aren't simultaneous time-wise"?

I'm still in the midst of studying as well, but here are my 2 cents worth!
found some other detail if you want to know

An action potential is the change in voltage across a cell membrane as a nerve impulse is transmitted. So basically as a nerve impulse is transmitted the voltage will change....and this change is called the action potential.

Whereas nerve impulses are messages which are sent to the brain or muscles. These nerve impulses can be imagines like messages which are sent to the brain and muscles.

So as u can see nerve impulses are messages and an action potential is just a change in voltage when these impulses are sent.
(https://www.thestudentroom.co.uk/sho....php?t=2185147)

Action potential ia a brief (about one-thousandth of a second) reversal of electric polarization of the membrane of a nerve or muscle cell. Stimulation of the cell by certain chemicals or by sensory receptor cells causes depolarization of the membrane.


https://answers.yahoo.com/question/i...3040030AAxye3d


the main points seem to be

A nerve impulse is the movement of an action potential along the nerve fibre as a wave of sequential depolarizations.

therefore nerve impulses do not have hyperpolarisation but should have re polarisation I guess? :holmes:

and all APs cause a nerve impulse I guess :holmes:

still some questions lol :rofl:
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Reality Check
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(Original post by ForestShadow)
the main points seem to be

A nerve impulse is the movement of an action potential along the nerve fibre as a wave of sequential depolarizations.

therefore nerve impulses do not have hyperpolarisation but should have re polarisation I guess? :holmes:

and all APs cause a nerve impulse I guess :holmes:

still some questions lol :rofl:
Remember that the majority of nerves are myelinated, which means the AP doesn't travel down the nerve fibre as a 'wave', but more the AP 'jumps' from node to node vastly speeding up the speed of conduction. This is saltatory conduction (saltatory L = jump)
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rosemondtan
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(Original post by ForestShadow)
found some other detail if you want to know

An action potential is the change in voltage across a cell membrane as a nerve impulse is transmitted. So basically as a nerve impulse is transmitted the voltage will change....and this change is called the action potential.

Whereas nerve impulses are messages which are sent to the brain or muscles. These nerve impulses can be imagines like messages which are sent to the brain and muscles.

So as u can see nerve impulses are messages and an action potential is just a change in voltage when these impulses are sent.
(https://www.thestudentroom.co.uk/sho....php?t=2185147)

Action potential ia a brief (about one-thousandth of a second) reversal of electric polarization of the membrane of a nerve or muscle cell. Stimulation of the cell by certain chemicals or by sensory receptor cells causes depolarization of the membrane.


https://answers.yahoo.com/question/i...3040030AAxye3d


the main points seem to be

A nerve impulse is the movement of an action potential along the nerve fibre as a wave of sequential depolarizations.

therefore nerve impulses do not have hyperpolarisation but should have re polarisation I guess? :holmes:

and all APs cause a nerve impulse I guess :holmes:

still some questions lol :rofl:
Just had my econ paper today!! Sorry for the very late reply but THANK YOU and I'm going to start studying bio now so give me a sec I gotta read those questions again ha
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ForestShadow
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(Original post by Reality Check)
Remember that the majority of nerves are myelinated, which means the AP doesn't travel down the nerve fibre as a 'wave', but more the AP 'jumps' from node to node vastly speeding up the speed of conduction. This is saltatory conduction (saltatory L = jump)
ah thanks thats a very good point but the main thing I was trying to figure out was if:

nerve impulses do not have hyperpolarisation but should have re polarisation ? Image

(Original post by rosemondtan)
Just had my econ paper today!! Sorry for the very late reply but THANK YOU and I'm going to start studying bio now so give me a sec I gotta read those questions again ha
Ah dont sweat it and I hope the econ went well yesterday

take your time, my questions are a muddle :dontknow: :rofl:
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