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Thread: Some questions about neuron mechanics

  1. #1
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    Some questions about neuron mechanics

    I looked in the web and readhttp://web.sfn.org/baw/pdf/brainfacts.pdf .But still didn't get it . So actually electrical signal triggers release of different neurotransmitters .

    Neurotransmitters actually serve like different signals . But is the amount of neurotransmitters realised in a single connection matter? Is it on/off thing (specifical neurotransmitter released/not released) ?

    How exactly electrical signal governs release of neurotransmitters ? Is there any difference in amplitude /shape of signal? How the right neurotransmiiter to be released is chosen (e.g. how it knows that it shoudl release dopamnine and not glutamate?)

    And how the all the weights (e.g. presence of neurotransmitters in all dendrites) in neuron are actually added and how the output electrical signal is generated? -E.g. how the actual proccessing of signals works? How a neuron ( a single cell) process all the amount of data from all the inputs and governs the distribution of electrical signals to its outputs?

  2. #2
    voltage gated ion channel Hercules Rockefeller's Avatar
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    <I><small>So actually electrical signal triggers release of different neurotransmitters.</small></I>

    Yes, electrical signals reaching a synapse cause the release of neurotransmitters. Release of neurotransmitters into the synaptic cleft and causes the subsequent activation of postsynaptic receptors and the propagation of the electric signal. Generally speaking, a single neuron releases only one type of neurotransmitter. (Some neuron-interneuron combinations can release more than one.) A single neurotransmitter can co-activate multiple receptor types. Furthermore, a single neuron can co-release its transmitter with neuropeptides that can modulate the effects of the neurotransmitter. So even though a given neuron releases only one neurotransmitter, there is still a great deal of signaling flexibility that can result.


    <I><small>But is the amount of neurotransmitters realized in a single connection matter? Is it on/off thing (specifical neurotransmitter released/not released)? </small></I>

    Yes, the level of signaling does matter. Synaptic signaling is not an ON/OFF system; there are often threshold levels of neurotransmitter signaling that need to be reached before the desired effect occurs. This is why the circuitry of the CNS is far and away more complex and powerful than any man-made circuitry. The functioning of every synaptic connection (and there are countless billions of them in the mammalian brain) can be subtly varied and modulated depending on the level of neurotransmitter release, the neuropeptides that are co-released and the effects of extrinsic factors such as inhibitors or facilitators of neurotransmitter re-uptake. It all results in an awesomely fine control of CNS functioning.


    <I><small>How exactly electrical signal governs release of neurotransmitters? Is there any difference in amplitude /shape of signal? How the right neurotransmitters to be released is chosen (e.g. how it knows that it shoudl release dopamnine and not glutamate?) </small></I>

    See above.


    <I><small>How a neuron (a single cell) process all the amount of data from all the inputs and governs the distribution of electrical signals to its outputs? </small></I>

    Itís amazing, isnít it? The functioning of the CNS is mind-boggling (pun intended). No one knows how it all comes together. I donít think we will ever fully understand the functioning of complex nervous systems, which I find rather ironical: our brains cannot understand how the brain works!

  3. #3
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    Are you sure its not ON/OFF? I read that it is either the potential passes the threshold - then we have excitant neuron .Either does not pass - then we have inhibitory one .

    Are all neurons essentially the same?

    The electrical signal is caused by potential change of the membrane ,but that should also mean that all axons of given neuron receive same electrical impulse. And should also mean that one neuron releases( not releases -depending on threshold) all the neurotransmitters in all axons simultaneously ?

    As far I understand threshold is greatly influenced (solely influenced? ) by chemical balance in brain -e.g. concentration of adrenalin and stuff. Does that mean that by rasing concentration if some neurotransmitter in blood we actually shifting whole brain chemical balance ?

    The actual release of neurotransmitters seems a lengthy process .Is there any kind of synchronization? (suppose no cause all functions are performed in parrallel on existing structure, -any change slowly changes structure , altering signal processing)


    Is there a determined functions of input/output for human neuron (e.g. electrical signal output depending on acquired neurotransmitters)? Is there any determined correlation of released neurotrasmitters depending on signal ( e.g. 0.5 v always releases X amount of alpha neurotransmitter , Y amount of beta)?

    Now I still wonder how a single neuron process info from say dozen inputs - is it only electrical potential of mebrane matters? E.g. -doesnt matter which neurottransmitters on which inputs were received, only matters that they changed the potential by X amount of volts.
    Last edited by DarkMadMax; 08-04-03 at 01:31 PM.

  4. #4
    voltage gated ion channel Hercules Rockefeller's Avatar
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    <I>Are you sure its not ON/OFF? I read that it is either the potential passes the threshold - then we have excitant neuron .Either does not pass - then we have inhibitory one.</I>

    I didnít explain that very well. Iíll try againÖ

    What I meant to say is that there is a threshold that needs to be reached befre a post-synaptic signal is generated, but itís not a case of no signal reaching the synapse or the threshold level of signaling reaching the synpase. In other words, itís not a case of all ON or all OFF. There is constant neurotransmitter signaling at synapses; each neurotransmitter-receptor interaction produces a very small potential Ė only a few millivolts (from memory). But their effects summate. So if enough excitatory potentials arrive simultaneously, the axon hillock will be excited above threshold and a spike is produced. Similarly, inhibitory potentials can summate to produce a greater degree of inhibition. Furthermore, excitatory and inhibitory potentials can summate, so if they arrive simultaneously they will cancel out.

    The final output of the postsynaptic neurone (which is expressed as frequency of action potentials) is determined by the results of integration of excitatory and inhibitory info.

  5. #5
    i haven't studied this subject much but i do remember a thing or two. it is kind of on/off in that the signal is all or none. reach the threshold voltage and the signal snaps across the membrane. but then more signals can be generated on top of the first like waves, amplifying the signal.

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