A level biology refractory period help please

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Mavs04
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My notes say that action potentials are only able to pass from an active to a resting region because they can't be generated in a region that's in refractory period.
I'm probably over complicating this but I'm very confused about how the refractory period links to the axon membrane not being at resting potential. I get that the Na+ voltage gated channels are closed, but aren't they also closed at resting potential? Which part of a graph of membrane p.d against time would the refractory period actually be? Is it just the hyperpolarisation part or does it also include the flat line where the resting potential has been re-established before the next action potential occurs?

If someone could explain this to me I'd be very grateful, thanks!
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BlueChicken
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(Original post by Mavs04)
My notes say that action potentials are only able to pass from an active to a resting region because they can't be generated in a region that's in refractory period.
I'm probably over complicating this but I'm very confused about how the refractory period links to the axon membrane not being at resting potential. I get that the Na+ voltage gated channels are closed, but aren't they also closed at resting potential? Which part of a graph of membrane p.d against time would the refractory period actually be? Is it just the hyperpolarisation part or does it also include the flat line where the resting potential has been re-established before the next action potential occurs?

If someone could explain this to me I'd be very grateful, thanks!
It is the period when the sodium channels close (repolarisation) and then the potassium channels close (hyperpolarisation) - to reset the resting potential. It's typically the part of the graph from the down slope of the big peak below the threshold (the amount of repolarisation that is included can vary from all to none, so I'd see what your spec says) to the point where the graph becomes flat again (all of hyperpolarisation). It does not include the flat line (it is to the flat line, i.e. back to resting potential).

See graph examples: https://www.savemyexams.co.uk/a-leve...actory-period/
http://www.a-levelnotes.co.uk/biolog...-impulses.html
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Jpw1097
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(Original post by Mavs04)
My notes say that action potentials are only able to pass from an active to a resting region because they can't be generated in a region that's in refractory period.
I'm probably over complicating this but I'm very confused about how the refractory period links to the axon membrane not being at resting potential. I get that the Na+ voltage gated channels are closed, but aren't they also closed at resting potential? Which part of a graph of membrane p.d against time would the refractory period actually be? Is it just the hyperpolarisation part or does it also include the flat line where the resting potential has been re-established before the next action potential occurs?

If someone could explain this to me I'd be very grateful, thanks!
The refractory period has two parts: the absolute and relative refractory period. During the absolute refractory period, another action potentials cannot be generated regardless of the strength of the stimulus. During the relative refractory period, action potentials can be generated, however, it requires a greater stimulus.

The absolute refractory period is caused by inactivation of sodium channels after depolarisation - they are closed and locked and will not open until the membrane potential is sufficiently repolarised.

As the membrane repolarises, these inactivated sodium channels begin to reactivate, and are ready to open if the membrane is depolarised again. However, since there are some active sodium channels, another action potential can be fired, though it is more difficult as not all sodium channels are activated. When the membrane is hyperpolarised, all sodium channels are now activated, however, a greater stimulus is required to depolarise the membrane to the threshold potential and fire an action potential, making it more difficult to fire an action potential. These two phenomena are responsible for the relative refractory period.
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BlueChicken
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(Original post by Jpw1097)
The refractory period has two parts: the absolute and relative refractory period. During the absolute refractory period, another action potentials cannot be generated regardless of the strength of the stimulus. During the relative refractory period, action potentials can be generated, however, it requires a greater stimulus.

The absolute refractory period is caused by inactivation of sodium channels after depolarisation - they are closed and locked and will not open until the membrane potential is sufficiently repolarised.

As the membrane repolarises, these inactivated sodium channels begin to reactivate, and are ready to open if the membrane is depolarised again. However, since there are some active sodium channels, another action potential can be fired, though it is more difficult as not all sodium channels are activated. When the membrane is hyperpolarised, all sodium channels are now activated, however, a greater stimulus is required to depolarise the membrane to the threshold potential and fire an action potential, making it more difficult to fire an action potential. These two phenomena are responsible for the relative refractory period.
I don't think this level is of detail is common to UK A-level exam boards - can you specify which specification covers this? Usually, the refractory period (at A-level, they mean the relative RP) is mentioned to get across that action potentials are discrete and one-directional. Thanks.
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Jpw1097
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(Original post by BlueChicken)
I don't think this level is of detail is common to UK A-level exam boards - can you specify which specification covers this? Usually, the refractory period (at A-level, they mean the relative RP) is mentioned to get across that action potentials are discrete and one-directional. Thanks.
I never said it was A level knowledge, but OP seems confused over sodium channels being closed during action potential, and this is a common error, but the refractory period is caused by inactivation of sodium channels, not just that they are closed.
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Mavs04
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(Original post by BlueChicken)
I don't think this level is of detail is common to UK A-level exam boards - can you specify which specification covers this? Usually, the refractory period (at A-level, they mean the relative RP) is mentioned to get across that action potentials are discrete and one-directional. Thanks.
I do AQA and the spec doesn't go into much detail apart from what you mentioned. I don't need to know the other stuff although it's been useful in helping me understand. Ty both for your answers!
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BlueChicken
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(Original post by Jpw1097)
I never said it was A level knowledge, but OP seems confused over sodium channels being closed during action potential, and this is a common error, but the refractory period is caused by inactivation of sodium channels, not just that they are closed.
Apologies, it wasn't a criticism - just so as not to scare the OP! Also, if it is in some A-level syllabi, then that info will be useful for others to know. Thanks.
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