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Electrical current [was Consciousness]

r norman rsn_ at _comcast.net
Sat Nov 22 08:19:20 EST 2003

On Sat, 22 Nov 2003 05:21:23 GMT, Mark Zarella
<zarellam at nospam.twcny.nospam.rr.com> wrote:

>> The propagation of action potentials in neurons involves ionic currents 
>>  AND electrical conduction.
>Care to explain the difference?  I think this conversation is awfully 
>close to bordering on semantics.  So I suppose a definition of 
>electrical current and ionic current is in order.  I think we all agree 
>that ionic current can simply be characterized as the net flow of charge 
>  due to translational motion of ions.  So is "electrical current" that 
>current due to electron flow only, or can it be characterized simply by 
>net flow of charge?

It is posible to find definitions of "electric current" on the web
saying that is is the flow of electrons.  But then you can find all
sorts of nonsense on the web.

More properly electrical current is the rate of movement of electrical
charge.  And even more properly you must allow displacement current in
which charges do not move.  Displacement current, I = C dV/dt, is
usually called capacitative current in neurobiology terminology, and
is a major factor in current flow in neurons.

So in a typical action potential you have ionic current through
membrane channels caused by electrochemical gradients across the
mmbrane, you have capacitative current across the membrane where no
ions actually flow caused by temporal gradients in electrical
potential, you have ionic current down the axon caused by spatial
gradients in electrical potential, you have electron transport through
the redox reactions at the surface of your Ag/AgCl  recording or
stimulating electrodes, you have electron flow though your electronic
equipment, you have hole flow through P type semiconductors in the
equipment, you may even have electrons tunneling through barriers in
some semiconductor devices or ions flowing in plasmas in your display
devices.  Are there any other forms of current that I have forgotten?

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