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    Hi, Do we need to know summation (Temporal and spatial summation) for edexcel unit 4??? Its in my notes, by I cant find it anywhere on the syllabse!! And I'd rather not learn it if its not on the syllabse. :tsr: :eek:

    umm im talking about Biology by the way :eek: :tsr:
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    (Original post by senshi)
    Hi, Do we need to know summation (Temporal and spatial summation) for edexcel unit 4??? Its in my notes, by I cant find it anywhere on the syllabse!! And I'd rather not learn it if its not on the syllabse. :tsr: :eek:

    umm im talking about Biology by the way :eek: :tsr:
    I do the main edexcel Biology course (not human) and have never even heard of these things! Are they in the Nelson textbooks? Anyway, if it aint in the syllabus, which im pretty sure its not, you don't need to know it.
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    i do edexcel, have never heard of summation
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    Never ever heard of it! Maybe its in an option. However I've now covered options A and C (the only one I havn't read is option B) and have never heard of it! Hopefully the answer is that we don't need to learn it then!
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    its not in b either
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    no, its not in the options, (im doin C) its in my notes for the core material. Its a large section which is quite hard and scary, but I couldnt find it in the syllabse. So if its not on, i guess I'l just skip it.

    Thanks a lot
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    Summation

    Summation is the process that occurs at synapses

    Often one the action potential in the presynaptic neurone is not sufficient in order to generate an action potential in the post synaptic neurone

    This is mainly due to the fact that insufficient neurotransmitter (acetylcholine) diffuses down the synapse, therefore not enough binds to the receptors in the post-synaptic neurone and so not enough Na+ ions would diffuse into the axon membrane in order for an action potential to occur. (since the threshold level is not reached)

    However, this problem can be over come by summation. Summation is where more than two presynaptic neurones share the same post synaptic neurone. Therefore, causing twice as much neurotransmitter in the synapse, which dramatically increases the chances of an action potential being generated in the post-synaptic neurone.

    Btw, i do Edexcel biology and it this is part of the core unit 4.

    I learnt summation in the context of rod and cone cells. Cone cells only synapse with one bipolar neurone whereas two or more rod cells share the same bipolar neurone. Summation explains why rod cells are adapted for detecting low intensities of lights whereas cone cells are adapted to high intensities of light (and colour).
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    yeh, thats what my notes say prety much, but thers two types of summation, temporal and spatial. Im confused, so many people said it isn't in syllbse, but one is saying it is

    *confused*
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    Isn't it in with the function of the eye, especially rod cells? I'm not doing that board, but that's where mine is and you wouldn't necessarily look there.

    Temporal summation is where several little impulses in one pre-synaptic neurone cause an impulse in the post synaptic neurone.

    Spatial summation is where several pre-synaptic neurones converge on one post-synapitc neurone and several impulses from several different neurones stimulate an impulse in the post synaptic neurone.

    Think spatial = space, many impulses from different points in space, i.e. different neurones.
    Temporal = time, many different impulses over a short space of time (nothing to do with lots of neurones).

    Does that make sense? PM me if you want me to go over it again.
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    well... it was in my revision guide that is written for the Edexcel syllabus only had summation in, nothing about two different types.

    ok... i was explaining spatial summation (see the post above for a good explanation)
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    I have this in my notes, so I think I am going to revise it just incase?
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    I stand corrected...it is also in my notes on the eye. But it doesn't seem too nasty anyway.
 
 
 
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