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    (Original post by super121)
    Can someone please explain to me the process of the propagation of a nerve impulse along an axon? I understand it, but just not sure how to explain it with key words like hyperpolarised and repolarisation.

    Thanks
    You mean the whole process of from when an action potential arrives?
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    (Original post by super121)
    Can someone please explain to me the process of the propagation of a nerve impulse along an axon? I understand it, but just not sure how to explain it with key words like hyperpolarised and repolarisation.

    Thanks
    1. Stimulus: when a stimulus is provided, the neurone cell membrane becomes excited. This causes the sodium ion channels to open. The membrane is now more permeable to sodium, hence sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This results in the inside of the neurone cell membrane being less negative
    2. Depolarisation: this is once the pd reaches the threshold level (-55mV), and so more sodium ion channels open, and as a result more sodium ions diffuse into the neurone
    3. Repolarisation: once potential difference reaches +30mV the sodium ion channels close, and potassium ion channels open. Now the membrane is more permeable to potassium ions. And hence potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This is when the membrane begins to get back to its resting potential
    4. Hyperpolarisation: potassium ion channels are a bit slow to close, this results in a slight "overshoot" - this is when too many potassium ions diffuse out of the neurone. This makes the potential difference become too negative (less than -70mV)
    5. Resting potential: ion channels are reset. Sodium-potassium pump returns the membrane to resting potential and maintains it until another stimulus is given


    Sorry it's long, but it includes everything!
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    (Original post by nukethemaly)
    You mean the whole process of from when an action potential arrives?
    I understand the stuff on synapses up to where the membrane depolarises and initiates an action potential, but then it's the stuff on axons that confuses me.
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    (Original post by nukethemaly)
    1. Stimulus: when a stimulus is provided, the neurone cell membrane becomes excited. This causes the sodium ion channels to open. The membrane is now more permeable to sodium, hence sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This results in the inside of the neurone cell membrane being less negative
    2. Depolarisation: this is once the pd reaches the threshold level (-55mV), and so more sodium ion channels open, and as a result more sodium ions diffuse into the neurone
    3. Repolarisation: once potential difference reaches +30mV the sodium ion channels close, and potassium ion channels open. Now the membrane is more permeable to potassium ions. And hence potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This is when the membrane begins to get back to its resting potential
    4. Hyperpolarisation: potassium ion channels are a bit slow to close, this results in a slight "overshoot" - this is when too many potassium ions diffuse out of the neurone. This makes the potential difference become too negative (less than -70mV)
    5. Resting potential: ion channels are reset. Sodium-potassium pump returns the membrane to resting potential and maintains it until another stimulus is given


    Sorry it's long, but it includes everything!
    Thanks!
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    (Original post by super121)
    Can someone please explain to me the process of the propagation of a nerve impulse along an axon? I understand it, but just not sure how to explain it with key words like hyperpolarised and repolarisation.

    Thanks

    (Original post by nukethemaly)
    1. Stimulus: when a stimulus is provided, the neurone cell membrane becomes excited. This causes the sodium ion channels to open. The membrane is now more permeable to sodium, hence sodium ions diffuse into the neurone down the sodium ion electrochemical gradient. This results in the inside of the neurone cell membrane being less negative
    2. Depolarisation: this is once the pd reaches the threshold level (-55mV), and so more sodium ion channels open, and as a result more sodium ions diffuse into the neurone
    3. Repolarisation: once potential difference reaches +30mV the sodium ion channels close, and potassium ion channels open. Now the membrane is more permeable to potassium ions. And hence potassium ions diffuse out of the neurone down the potassium ion concentration gradient. This is when the membrane begins to get back to its resting potential
    4. Hyperpolarisation: potassium ion channels are a bit slow to close, this results in a slight "overshoot" - this is when too many potassium ions diffuse out of the neurone. This makes the potential difference become too negative (less than -70mV)
    5. Resting potential: ion channels are reset. Sodium-potassium pump returns the membrane to resting potential and maintains it until another stimulus is given


    Sorry it's long, but it includes everything!
    Just to add to the above, depolarisation/repolarisation are a result of positive feedback. For example, during depolarisation, the more sodium ions that flow into the axon, the more positive the axon becomes which triggers the opening of more Na+ channels.

    Also, depolarisation only occurs at the nodes of Ranvier. The myelin sheath acts as an electrical insulator conducting electrical currents between the nodes through saltatory conduction which helps speed up action potential propagation.
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    (Original post by super121)
    I understand the stuff on synapses up to where the membrane depolarises and initiates an action potential, but then it's the stuff on axons that confuses me.
    Ah I hope I answered the correct question haha!
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    (Original post by AmirHabeeb)
    Just to add to the above, depolarisation/repolarisation are a result of positive feedback. For example, during depolarisation, the more sodium ions that flow into the axon, the more positive the axon becomes which triggers the opening of more Na+ channels.

    Also, depolarisation only occurs at the nodes of Ranvier. The myelin sheath acts as an electrical insulator conducting electrical currents between the nodes through saltatory conduction which helps speed up action potential propagation.
    We're speaking about a non myelinated neurone.
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    (Original post by nukethemaly)
    Ah I hope I answered the correct question haha!
    Does the axon membrane depolarise to +40mV?
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    (Original post by nukethemaly)
    We're speaking about a non myelinated neurone.
    My bad. It's the same process though as you described above for myelinated neurones apart from the fact that depolarisation can only occur at nodes.
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    (Original post by AmirHabeeb)
    My bad. It's the same process though as you described above for myelinated neurones apart from the fact that depolarisation can only occur at nodes.
    Yep!
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    (Original post by super121)
    Does the axon membrane depolarise to +40mV?
    I checked the official textbook, and yeah it does say +40mV for depolarisation. For some reason the revision guides quote a different value :/
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    Has anyone made a list of topics in relation to the pre-release?

    or A list of questions?
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    (Original post by thelion0)
    Has anyone made a list of topics in relation to the pre-release?

    or A list of questions?
    if you flick through the whole of this thread, you'll find lots.
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    Where do the Schwann cells and nodes of Ranvier stuff come in? Is it something completely different?
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    (Original post by super121)
    Where do the Schwann cells and nodes of Ranvier stuff come in? Is it something completely different?
    Myelinated neurones. Page 208 Edexcel SNAB textbook.
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    (Original post by AmirHabeeb)
    Myelinated neurones. Page 208 Edexcel SNAB textbook.
    So, in myelinated neurones, nodes of Ranvier just speed up the movement of an impulse along the axon, and there's a layer of myelin sheath around the axon which is made up of Schwann cells. If the axon is unmyelinated, the movement of nerve impulses along the axon is slower?
    Also, are nodes of Ranvier in both myelinated and unmyelinated neurones, or just myelinated ones?

    Thanks
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    (Original post by super121)
    So, in myelinated neurones, nodes of Ranvier just speed up the movement of an impulse along the axon, and there's a layer of myelin sheath around the axon which is made up of Schwann cells. If the axon is unmyelinated, the movement of nerve impulses along the axon is slower?
    Also, are nodes of Ranvier in both myelinated and unmyelinated neurones, or just myelinated ones?

    Thanks
    The myelin sheath speeds up the conduction of local currents between the nodes where all the usual steps happen (depolarisation etc.). Yes, movement is slower in unmyelinated axons. There aren't nodes specifically no. There are also degrees of being myelinated. So the more myelinated a sheath is, the faster it will conduct too.
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    (Original post by AmirHabeeb)
    The myelin sheath speeds up the conduction of local currents between the nodes where all the usual steps happen (depolarisation etc.). Yes, movement is slower in unmyelinated axons. There aren't nodes specifically no. There are also degrees of being myelinated. So the more myelinated a sheath is, the faster it will conduct too.
    Thanks, it makes sense now
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    This is the mock (questions and answers) that we did in class for the pre release. Our teachers made the questions and mark schemes
    Attached Files
  1. File Type: docx Pre-release_mock_2013_V2_A.docx (23.2 KB, 841 views)
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    (Original post by cwood166)
    This is the mock (questions and answers) that we did in class for the pre release. Our teachers made the questions and mark schemes

    Hi,

    I am having problem to download this material.Although it seems stupid, but I am stuck. Please help me.
 
 
 
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