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Basic Neuron Questions

KP-PC k.p.collins at worldnet.att.net%remove%
Sat Apr 5 03:15:34 EST 2003


"BilZ0r" <BilZ0r at TAKETHISOUThotmail.com> wrote in message
news:Xns9354C35BBFAE7BilZ0rhotmailcom at 202.20.93.13...
| neo55592 at hotmail.com (Neo) wrote in
news:4b45d3ad.0304042219.2e905a42
| @posting.google.com:
|
| > 1. What is the average refractory period (the duration a neuron
needs
| > to recover before being able to create a successive action
potential)?
| > 2. If neurons were arranged linearly, approximately how neurons
will a
| > signal have traveled thru during an average refractory period?
TIA
| >
|
| The ABSOLUTE refractory period is between 4 and 5ms (the time it
takes
| for potassium channels to close).

In vivo, no such "absolute" exists. Everything occurs relative to
ionic concentration gradients.

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
period.

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
absolute
| 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.

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
4-5ms
| 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.

| If were dealing with a large mylinated neuron, were talking
100-120meters
| a second, to 100-120mm a millisecond, so in 4-5ms thats 400-600mm
or
| about half a meter. (Someone correct me if my maths is wrong).

Your conceptualizations are wrong.

Why have I jumped your post?

Because I gave the questioner the necessary instruction, but you
'override' my post with short-shrift stuff passing as 'knowledge'.

I jumped your post to 'protect' the questioner from the
'short-shrifting' influence inherent in your discussion [and because
you obviously wish to stand on the field of battle with respect to
Truth, giving Truth, itself, 'short-shrift'. There are no
'short-cuts' to understanding. If you endure in your quest, some day,
you'll thank me for the 'lesson' inherent.]

K. P. Collins





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