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    I'm also confused about how the nerve impulse is propagated along the neuron.

    I understand about ions moving in and out blah blah, but what about the actual electrical impulse. How is it moved along the axon?

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    (Original post by Doughboy)
    I'm also confused about how the nerve impulse is propagated along the neuron.

    I understand about ions moving in and out blah blah, but what about the actual electrical impulse. How is it moved along the axon?

    The axon starts out having negative inside and positive outside.
    When an impulse arives at a certain point it causes ions to go in(out) changing the distribution of charge. It now becomes positive inside and negative outside..
    The section next to this little section which has switched will now also do the same since there is now a potential difference between the outside (and inside) of the first part and the outside (and inside of the second):
    Like this:

    1

    + + + + + + + + + + + + + + + +
    - - - - - - - - - - - - - - - - - - -
    - - - - - - - - - - - - - - - - - - -
    + + + + + + + + + + + + + + + +

    2

    potential difference between these two sections
    [..]
    - + + + + + + + + + + + + + + +
    + - - - - - - - - - - - - - - - - -
    + - - - - - - - - - - - - - - - - -
    - + + + + + + + + + + + + + + +
    [..]

    3
    potential difference between these two sections
    ...[..]
    + - + + + + + + + + + + + + + + +
    - + - - - - - - - - - - - - - - - - -
    - + - - - - - - - - - - - - - - - - -
    + - + + + + + + + + + + + + + + +
    ...[..]


    A potential difference creates a current and passes along the impulse.


    WORST EXPLANATION EVER BTW
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    The ions themselves are charge carriers. They carry the electrical impulse along as HyperNova has illustrated (surprisingly well!).

    With myelin they (the ions) don't have to move the whole way along, depolarisation only has to occur at nodes between the Schwan cells, because the electrical impulse can 'jump' node-to-node which is much quicker transmission.

    I'm not learning it in too much detail. I might come to regret that.
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    An action potential is when the potential difference has changed from negative to positive, which creates a small current.
    This is just enough to cause polarisation in the adjacent region, which then depolarises etc..
    It's described in the book as a domino effect, which is a good analogy.
    Really short explanation, but thats all thats required anyway..


    Just finished half of my topic 8 mind map.. Including rather awful drawings of neurones lol.
    Will be up tomorrow hopefully guys
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    (Original post by HyperNova)
    GUISE

    I'm really confused.. need advice.

    For neurons it talks about there being a depolarisation causing an action potential..

    But with the rods and rhodopsin it talks about a hyperpolarisation causing a generation potential and then an action potential..

    Can someone explain the differences bettween these polarisations and why they are different.. (I'm sure one is to do with positive charge (hyper) and one negative (depolar) but still not sure..)

    Thanks
    I think you understand the charges, the key thing is that the neurotransmitter released from the rod cell is inhibitory to the bipolar neurone. So an action potential would actually inhibit the bipolar neurone, and hyperpolarisation (when its light) will prevent the release of the inhibitory neurotransmitter and so allow an action potential in the bipolar neurone
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    (Original post by HyperNova)
    GUISE

    I'm really confused.. need advice.

    For neurons it talks about there being a depolarisation causing an action potential..

    But with the rods and rhodopsin it talks about a hyperpolarisation causing a generation potential and then an action potential..

    Can someone explain the differences bettween these polarisations and why they are different.. (I'm sure one is to do with positive charge (hyper) and one negative (depolar) but still not sure..

    Thanks
    Right, here I go...

    In a neurone, depolarisation is when the inside of the neurone becomes less negative (because the membrane becomes more permeable to sodium ions). This allows an action potential to be generated/ nerve impulses to be transmitted.

    On a rod cell (photoreceptor) the membrane is slightly depolarised because sodium ions are actively transported out and can diffuse back in through sodium ion channels. This allows the release of inhibitory neurotransmitters which inhibit the bipolar neurone so an action potential cannot be generated in the bipolar neurone so no information is sent to the brain. Rhodopsin is the light sensitive pigment.

    When the rod cell is exposed to light however, rhodopsin breaks down into retinal and opsin. Opsin binds to the rod cell membrane and this closes sodium ion channels. Since sodium ions are actively transported out, they build up on the outside of the rod cell, so the inside is more negative (hyperpolarised). This stops the release of inhibitory neurotransmitters, meaning the bipolar neurone can now be depolarised so action potentials can be generated and information can be transmitted to the brain along the optic nerve.

    Basically, depolarisation is what causes an action potential. In rod cell, when it is slightly depolarised, action potentials occur which allow the release of inhibitory neurotransmitters. However, when it's hyperpolarised, no neurotransmitters are released because no action potentials are generated in the rod cell (I think).

    It's a lot to get your head around, but honestly it's easy once you get it. Do you have a SNAB book?
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    (Original post by markioe)
    I got to know, i asked and they told me, obviously this was the pre-standardisation mark (like without grade boundaries)
    did your teacher mark yours and send it off for moderation, because my teacher sent them straight off to the examiner to be marked.
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    how much revision has everyone done on this paper so far? i started this afternoon... although i was last min in jan n got 75% still :/ im kinda gettin worried though, is anyone in same position as me?
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    (Original post by skotch)
    If you work through the questions I posted up and the other resources on here, you should be alright for the article.
    Thank yuuu =]
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    (Original post by Presidential)
    did your teacher mark yours and send it off for moderation, because my teacher sent them straight off to the examiner to be marked.
    yeah they marked them and sent 3 of them off or so for moderation. I think they marked us bloooody hard though, so hoping to be bought up a) by moderation
    b) by gradeboundaries


    What did you lot think of the BIO unit 4?
    and what % did u get last year overall
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    AHA! Inhibitory Rod cells!

    Thank you so much X-KiwiTheIncapable- X and jimber!
    =]
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    (Original post by skirt)
    how much revision has everyone done on this paper so far? i started this afternoon... although i was last min in jan n got 75% still :/ im kinda gettin worried though, is anyone in same position as me?
    June is the first time this exam is being offered though.... :confused:
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    Guys, I;ll upload the 3rd set of questions for the pre-release tomorrow as my computer keeps switching itself off and I cba with it now.
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    UGH.. I'm learning so many new things so late due to crap teacher that I'm afraid I'm either not going to remember anything or the things that I learn in detail will not even come up in exam!

    I miss good ol' AS biology.. times were simpler..

    I got 89% overall for my Biology AS.. got above 90% for unit 1 I think..

    Got C for January unit 4 and retook and hoping for above 80% which I think should be attainable due to it going pretty..
    Apparently I got a B for unit 6 but that could change depending on the markers..

    Need that wonderful A...
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    was there a specimen paper for this exam?
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    (Original post by skotch)
    June is the first time this exam is being offered though.... :confused:
    lol sorry i meant the one i did in jan was very last min revision, topic 4 was it? forensics and plant stuff lol
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    I hate that I have to study Unit 5 AND deal with that annoying article. In addition, Physics and Chemistry are in between it all. Jeez.
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    hey guys wht book do you use which covers everything the best?? i have the large green edexcel textbook and the green cgp revision guide specific to edexcel...would you say revising the spec from those 2 books is sufficient???
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    CGP!!!

    I am getting a panic attack now... will I finish in time?!

    I might have to delay Physics and Chem revision cause of this. AAAAAAAAAAAAA
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    The green student book says,
    Deoxyhaemoglobin absorbs the radiowave signal and later re-emits it, while oxyhaemoglobin does not. When an area of the brain is active, the blood flow to that area increases and more oxyhaemoglobin is delivered to supply the active cells with the oxygen they need from aerobic respiration. Less of the signal is absorbed as a result.
    But, isn't amount of deoxyhaemoglobin increases when oxyhaemoglobin is more...and so shouldn't more of the signal be absorbed when the brain is active?
    I havent got my answer and think it felt too back in the thread..and so posted it again!.......someone please help!
 
 
 
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