current in an axon

x011 at Lehigh.EDU x011 at Lehigh.EDU
Wed May 3 13:05:04 EST 1995


In article <3o62tc$4gf at steele.ohsu.edu>, Matt Jones <jonesmat at ohsu.edu> writes:
>In article <799364933snz at longley.demon.co.uk> David Longley,
>David at longley.demon.co.uk writes:
>>Without wishing to sound like *Mr Angry*, can I suggest that (IMHO), one
>>of the worst things  you can teach  a young scientific mind is that
>>scientific concepts can be learned by analogy  or metaphor.  The essence of
>>scientific method and the value of scientific language  is that  it gets
>>away from all that mumbo jumbo.
>>
>>Those who can't accept it described in the terms it actually  happens
>>will not learn it anyway, and those who do want to understand it properly
>>will just have excess baggage.
>
>I respectfully disagree, for two main reasons:
>1)     Analogies are obviously useful tools for teaching students *what to
>expect* from a certain process, if not what is actually happening. For
>example, students can use fluid-flow analogies to make predictions about
>changes in membrane potential (pressure) when the membrane resistance
>(leakiness) of an axon (hose) is changed by the opening of ion channels
>(valves). This type of analogy allows students to get an idea for how
>things are expected to behave, if not how they actually are described in
>the scientific literature. At the high school level, this is probably
>much more important than being able to solve systems of differential
>equations  or run sophisticated compartmental modelling programs.
>2)     It is presumptuous of us to believe that *we* understand the way !it
>actually happens!. All we, as scientists, have at our disposal are
>theories (analogies) and models (metaphors). We do not actually know how
>voltage-gated channels respond to depolarization (in any real molecular
>sense), so we *hypothesize* that there must be a !gate!.  In fact, we
>know beyond a doubt that our best equations represent only approximations
>to the way !it really happens!, and that!s why we have statistics to tell
>us whether our equations are close enough approximations to be taken
>seriously or not.
>
>Sorry for the tirade. In fact, I happen to agree with David Longley!s
>sentiments in the case of action potential propagation. The concepts of
>resistance, capacitance, voltage and current should not be too difficult
>for high school students to understand if they are really interested,
>even including the simple math of Ohm!s law.  The only remaining aspects
>of action potential propagation are voltage-gated channels, which might
>take a little more explanation. But these can be considered as variable
>resistors that have built in voltage sensitive switches.
>
A visual model using eigenfunctional equivalence is suggested by
Sridhar's experiments with microwaves in rectangular cavities.
The interference pattern created by scars or memories of ossillations
reminds me of what the brain may be doing.  Source: Science News
April 29, 1995
Ron Blue x011 at lehigh.edu




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