rsn_ at _comcast.net
Fri Nov 21 17:48:35 EST 2003
On Fri, 21 Nov 2003 09:44:21 -0500, Joe Legris <jalegris at xympatico.ca>
>r norman wrote:
>> The orginal post, snipped away for being non-sensical, did refer to
>> the nervous system as supplying "electricity" to the body. However
>> silly that notion was, it is still true that electricity involves far
>> more than the movement of electrons -- that is how electric current is
>> manifested in metallic conductors. Bioelectricity was known since
>> Galvani's time.
>> Electrical forces are at work between any two charged bodies. The
>> energetics of ions moving across a membrane depend on their charge and
>> the electrical potential, the voltage, as much as they do on
>> concentrations and diffusion. The longitudinal flow of ions down
>> axons is almost entirely a response to electrical forces.
>> Yes, the real, physical, measurable electric currents that flow during
>> nerve activity are "electricity".
>Longitudinal flow of ions?? There are fast and slow tranport systems for
>moving proteins, vesicles, and other chemicals down (and up) the axon,
>but if you are talking about action potentials, the net movement of ions
>is perpendicular to the axon, not along it. The action potential is the
>only thing that "flows" along the axon in that sense, and it is a wave
>of depolarization and associated electrical fields, not an ionic
>current. If there was a longitudinal flow of ions down the axon there
>would have to be a mechanism for supplying them at one end and for
>getting rid of them at the other. No such mechanism exists to my knowledge.
This is very strange. In another post, you refer to the local current
loops that are responsible for the propagation of the action
potential. These closed loops do involve both transverse or membrane
currents crossing the membrane and longitudinal currents which travel
along the axon, up and down its length. The longitudinal currents are
caused by spatial variation in potential, dV/dx. Look at any diagram
in any text of a local current loop to see what I mean.
The loops are really quite lengthy. If an action potential propagates
at, say, 50 m/sec and lasts for 1 msec, then it is actually some 50 mm
or 5 cm long. The current loops, themselves, are of comparable size,
spreading a distance of centimeters down an axon. Lorente do No
(1947) mapped the electric field surrounding an axon conducting an
action potential. The current lines are easily calculated from the
isopotential lines and show the extensive longitudinal spread.
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