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    Hi, I don't really understand the structure of rod cells or how they result in an action potential going to the brain.

    I understand that there is a resting potential of -40mV across the rod cell created by the sodium-potassium pump but I don't understand what happens when light hits it. What does hyperpolarisation mean? Also are the sodium and potassium channels separate to the Na-K pump?

    My book says that glutamate prevents a generator potential from being generated but I'm not sure how? I'm also not sure on how a generator potential would be generated in the first place nor what a generator potential even is?!

    What's the difference between generator potentials and action potentials?

    Thank you, sorry for all the questions haha.
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    (Original post by LeaX)
    Hi, I don't really understand the structure of rod cells or how they result in an action potential going to the brain.

    I understand that there is a resting potential of -40mV across the rod cell created by the sodium-potassium pump but I don't understand what happens when light hits it. What does hyperpolarisation mean? Also are the sodium and potassium channels separate to the Na-K pump?

    My book says that glutamate prevents a generator potential from being generated but I'm not sure how? I'm also not sure on how a generator potential would be generated in the first place nor what a generator potential even is?!

    What's the difference between generator potentials and action potentials?

    Thank you, sorry for all the questions haha.
    Hey, I'm not doing your exam board, because you've mentioned different things, however I think I can answer some of your questions and I'm obsessed with being an optician so I've already looked up some eye stuff anyway.

    Basically a rod is a photoreceptor with two segments; inner and outer. The generator potential occurs in the outer segment, where the pigment that absorbs light is located, and the inner segment contains mitochondria and a nucleus etc. numerous rods (3/4) converge to one bipolar neurone, and this then connects to a sensory neurone, which transmits an action potential to the brain.

    I'm not sure how much detail you want so I'll simplify it, and if you want more detail, just ask. The rod changes shape when it absorbs light energy (bleaching), this causes hyperpolarisation of he outer segment (which means the potential difference overshoots slightly so that it is more negative), and therefore there less glutamate is released so the membrane of the bipolar neurone becomes depolarised. This creates a generator potential (a change in potential caused by Na+ ion channels opening), and if this exceeds the threshold potential then it will initiate an action potential in the bipolar neurone, and is transmitted to the brain via the optic nerve.

    The channels and pumps are independent. The normal resting potential is maintained by the Na+/K+ ion pumps, while the voltage-gated Na+ ion channels are closed. The channels only become involved if some of the Na+ ion channels are opened, and sodium ions quickly diffuse in, causing depolarisation. Because they are voltage-gated, the opening of one induces others to be opened as well further along the neurone.

    A generator potential becomes an action potential if it exceeds the threshold potential. It basically refers to initial changes with regards to depolarisation, and then action potentials are the impulses that are transmitted (all the stages of depolarisation, repolarisation, hyperpolarisation an refractory period repeated in a cycle)

    Hope that helped at all


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    (Original post by Rhodopsin94)
    Hey, I'm not doing your exam board, because you've mentioned different things, however I think I can answer some of your questions and I'm obsessed with being an optician so I've already looked up some eye stuff anyway.

    Basically a rod is a photoreceptor with two segments; inner and outer. The generator potential occurs in the outer segment, where the pigment that absorbs light is located, and the inner segment contains mitochondria and a nucleus etc. numerous rods (3/4) converge to one bipolar neurone, and this then connects to a sensory neurone, which transmits an action potential to the brain.

    I'm not sure how much detail you want so I'll simplify it, and if you want more detail, just ask. The rod changes shape when it absorbs light energy (bleaching), this causes hyperpolarisation of he outer segment (which means the potential difference overshoots slightly so that it is more negative), and therefore there less glutamate is released so the membrane of the bipolar neurone becomes depolarised. This creates a generator potential (a change in potential caused by Na+ ion channels opening), and if this exceeds the threshold potential then it will initiate an action potential in the bipolar neurone, and is transmitted to the brain via the optic nerve.

    The channels and pumps are independent. The normal resting potential is maintained by the Na+/K+ ion pumps, while the voltage-gated Na+ ion channels are closed. The channels only become involved if some of the Na+ ion channels are opened, and sodium ions quickly diffuse in, causing depolarisation. Because they are voltage-gated, the opening of one induces others to be opened as well further along the neurone.

    A generator potential becomes an action potential if it exceeds the threshold potential. It basically refers to initial changes with regards to depolarisation, and then action potentials are the impulses that are transmitted (all the stages of depolarisation, repolarisation, hyperpolarisation an refractory period repeated in a cycle)

    Hope that helped at all


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    Ohh I see, thank you so much. Just one tiny thing, so does glutamate close the sodium channels in the bipolar cell?
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    (Original post by LeaX)
    Ohh I see, thank you so much. Just one tiny thing, so does glutamate close the sodium channels in the bipolar cell?
    I think the glutamate acts as an inhibitor normally by blocking the receptors on the bipolar neurone, so an action potential can't be transmitted. Then when glutamate production is suppressed (as discussed above), less is released and therefore less can bind to the receptors of the bipolar cell. This in turn means that the normal neurotransmitter (probably acetylcholine) can bind to the receptors, which cause the sodium ion channels to open, and then the influx of Na+ causes depolarisation and so on. The sodium channels are normally closed, but glutamate just stops them from being opened.


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    (Original post by Rhodopsin94)
    I think the glutamate acts as an inhibitor normally by blocking the receptors on the bipolar neurone, so an action potential can't be transmitted. Then when glutamate production is suppressed (as discussed above), less is released and therefore less can bind to the receptors of the bipolar cell. This in turn means that the normal neurotransmitter (probably acetylcholine) can bind to the receptors, which cause the sodium ion channels to open, and then the influx of Na+ causes depolarisation and so on. The sodium channels are normally closed, but glutamate just stops them from being opened.


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    Thank you so so so much. I finally understand it now.
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    (Original post by Rhodopsin94)
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    Sorry, me once more. Is there a reason that he light stimulus causes Na channels to close in the rod cells whereas a stimulus in other neurones causes the sodium channels to open? Or is it just something I should accept and remember for the exam. Thank you.
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    (Original post by LeaX)
    Sorry, me once more. Is there a reason that he light stimulus causes Na channels to close in the rod cells whereas a stimulus in other neurones causes the sodium channels to open? Or is it just something I should accept and remember for the exam. Thank you.
    I'm not sure, sorry! I think it's the same, except for the fact that numerous neurones are used with rod cells, so each neurone is opposite in action to the next, and the change in action of the first leads to a sort of 'domino effect', so some will have the same response as with other neurones at one point in time, while other neurones will be in a differen state....I think...

    Unless you can find out otherwise, you may be better just accepting it


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    (Original post by Rhodopsin94)
    I'm not sure, sorry! I think it's the same, except for the fact that numerous neurones are used with rod cells, so each neurone is opposite in action to the next, and the change in action of the first leads to a sort of 'domino effect', so some will have the same response as with other neurones at one point in time, while other neurones will be in a differen state....I think...

    Unless you can find out otherwise, you may be better just accepting it


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    Okay, thank you.
 
 
 
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