Basic Neuron Questions
BilZ0r at TAKETHISOUThotmail.com
Sun Apr 6 17:54:50 EST 2003
"KP-PC" <k.p.collins at worldnet.att.net%remove%> wrote in news:Ggwja.14342
$cO3.997264 at bgtnsc04-news.ops.worldnet.att.net:
> "BilZ0r" <BilZ0r at TAKETHISOUThotmail.com> wrote in message
> news:Xns9354C35BBFAE7BilZ0rhotmailcom at 188.8.131.52...
>| neo55592 at hotmail.com (Neo) wrote in
>| > 1. What is the average refractory period (the duration a neuron
>| > to recover before being able to create a successive action
>| > 2. If neurons were arranged linearly, approximately how neurons
> will a
>| > signal have traveled thru during an average refractory period?
>| The ABSOLUTE refractory period is between 4 and 5ms (the time it
>| for potassium channels to close).
> In vivo, no such "absolute" exists. Everything occurs relative to
> ionic concentration gradients.
Yes there is, Its defined by the time it takes for the potassium channels
to be available for opening again.
> The 'pat' answer 'applies', only weakly, in vitro, because the nerual
> energydynamics have, in fact, been isolated from their in vivo ionic
> concentration gradients.
>| But a neuron needs a much larger
>| stimulation to fire the directly after the absolute refractory
> Such results from the 'momentary' ionic concentration gradients, and
> can vary considerably as a function of such.
>| The relative refractory period is any time from the end of the
>| refractory period untill the neuron can generate an action
> potential by
>| the normal level of stimulation.
> Within Living nervous systems, there exists no such thing as "normal"
> levels of stimulation.
What? Yes there are. look at any monosynaptic nevous pathway.
> That is, the same activation 'state' never occurs twice within Living
> nervous systems.
> One can apply the same inputs in a rigorously-controlled experimental
> setup, but the neural tissue, itself, is never the same from trial to
> trial even within a rigorously controlled experimental setup.
> Neural tissue modifies itself as a function of the activation that
> occurs within it, and this is awesomely 'magnified' within a Living,
> intact [whole] nervous system.
> In other words, nervous systems "learn" - so there's nothing within
> their functioning that can be termed "normal". Such is just a TD
> E/I-minimization 'short-cut or 'convenience' on the parts of folks
> who wish to communicate the non-existent 'ideal case' - such
> in-the-ball-park stuff is useful for introductory purposes, but
> useless if the way nervous systems work is to be comprehended.
>| If we assume were dealing with a small, unmylinated neuron the AP
>| propigates at about 5 meters a second, or 5mm a millisecond, so in
>| it travels 20-25mm, about a 10th of an inch.
> Can't say this without discussing the neural architecture in which
> the neuron exists, and the activation that's occurring within it -
> especially with respect to unmyelinated neurons.
What I can't say how fast a action potentialtravels? Lol. Not exactly,
but I can give the accepted range.
>| If were dealing with a large mylinated neuron, were talking
>| a second, to 100-120mm a millisecond, so in 4-5ms thats 400-600mm
>| about half a meter. (Someone correct me if my maths is wrong).
> Your conceptualizations are wrong.
My 'conceptualizations' are just fine. I paraphrased my answer kandel and
schwatrz, principles of neural science 4th ed. Go argue with them.
They're at the centre for neruobiology and behaviour. College of
physicians & surgeons of Columbia University and the Howard huges medical
institute. I've got no time for your bizzare one tracked mind.
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