r norman wrote:
> 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?
>>
Those definitions are pretty standard, though I think not having them
posted led to thet source of confusion in this discussion.