Q: dendrites/gates

kenneth collins kenneth.p.collins at worldnet.att.net
Sun Mar 20 23:12:44 EST 2005


"r norman" <rsn_ at _comcast.net> wrote in message news:nves31hde8kctll16ofpvn7t7o4l604e1m at 4ax.com...
| On Mon, 21 Mar 2005 13:27:21 +1100, Matthew Kirkcaldie
| <m.kirkcaldie-remove at unsw.edu.au> wrote:
|
| >In article <ir9s31tlhhpmmtpplufie8hdiov0qnnnrd at 4ax.com>,
| > r norman <rsn_ at _comcast.net> wrote:
| >
| >> Still, the real "transmission" of the action potential, as you say, is
| >> the successive replication of a completely new action potential at
| >> each node.  The longitudinal flow of current is simply the decremental
| >> spread of activity that is the mechanism underlying the triggering.
| >>
| >> If find that it usually takes two or three rounds of courses for
| >> students to really start to get it.  It starts in intro biology and
| >> continues in animal physiology.  By the third time in a specialized
| >> neuro course, it finally starts to really sink in and gel.
| >
| >I find the Mexican wave analogy does it every time - the action
| >potential corresponds to each person standing up and sitting back down,
| >nothing physically moves overall.  The length constant is how many seats
| >away you're looking to get your cue for when to stand, and the time
| >constant is what you use for the cue - the person starting to move, or
| >when they have fully stood, etc.  Myelin is empty seats between crowd
| >members - forces them to take their cues from further away.  I've had a
| >lecture audience do it for me!
| >
| >I find the analogy is surprisingly precise, to the extent that I
| >sometimes use it to remember this stuff myself!  Pity there's not really
| >anything you can liken to a current though.
| >
|
| I have done a cruder physical model.  I line up a long row of students
| in the front of the class and tell them that, if anything on either
| side should suddenly hit them, they have to retaliate by throwing both
| their arms out to the side, hitting both neighbors (current loops flow
| both ways).  The second instruction is that once they strike out, they
| can't do it again even if they get hit again (refractory period).  I
| then go to end and hit the end person.  The wave of hitting quickly
| spreads down to the other end, very visible to the rest of the class.
| I go to the other end and hit and the wave spreads back the other
| direction.  I go to the center and hit, starting a wave going both
| ways.
|
| I can't really show propagation velocity well, but students can easily
| understand that if everyone had arms that could reach out across three
| or four neighbors, the hitting would spread that much more rapidly.

It'd be a bit more to set-up, but you
could do this with "V"-mirrors.

Angle the V's in both directions down
the line, and, instead of being touched,
tell the Students to move their arms
when they see a person move both
arms in a mirror. [The "see-both-arms"
rule is to prevent the wave of a hand
from triggering the flow. [A sub-thresh-
hold event :-] The angles of the V's
set inter-node distance.]

With a little tweaking, you'll see indiv-
iduals, spaced at distances, waving
their arms in-sequence, and the Stu-
dents in-between remaining standing-
still.

| It is amazing what  effect a little physical activity can do in a
| large class!
|
| They also seem to like the toilet flush model of the neuron -- it
| clearly demonstrates all-or-none behavior with a threshold and a
| refractory period!  Now, maybe if I could line up a long row of
| toilets and somehow hook them together......!

Live in a trailer. There's always stuff
like that going'-on.

My Neighbor gave me an article about
a "drain bomb" today :-]

ken





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