Basic question about electrical currents in EEG

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2 total messages Started by cwenhoo Mon, 30 Nov 2009 08:38

#77

Author: cwenhoo
Date: Mon, 30 Nov 2009 08:38

20 lines
2189 bytes

From Luck's book, p.32:

"When a dipole is present in a conductive medium such as the brain,
current is conducted throughout that medium until it reaches the
surface...Electricity does not just run directly between two poles of
a dipole in a conductive medium, but instead spreads out through the
conductor."

"Another important point is that electricity travels at nearly the
speed of light. For all practical purposes, the voltages recorded at
the scalp reflect what is happening in the brain at the same moment in
time."

My question is, what generates this current flow? I mean I can
understand if the conductive medium is a piece of metal, then a dipole
results in direct movement of electrons.

But what about the brain? What is even more confusing to me is that
action potentials are not even near the speed of light, so how can
this current resulting from the dipoles in the brain travel that fast?

Re: Basic question about electrical currents in EEG

#78

Author: Kalman Rubinson
Date: Mon, 30 Nov 2009 16:43

33 lines
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On Mon, 30 Nov 2009 00:38:42 -0800 (PST), cwenhoo
<ilangobi@yahoo.com> wrote:

>From Luck's book, p.32:
>
>"When a dipole is present in a conductive medium such as the brain,
>current is conducted throughout that medium until it reaches the
>surface...Electricity does not just run directly between two poles of
>a dipole in a conductive medium, but instead spreads out through the
>conductor."
>
>"Another important point is that electricity travels at nearly the
>speed of light. For all practical purposes, the voltages recorded at
>the scalp reflect what is happening in the brain at the same moment in
>time."
>
>My question is, what generates this current flow? I mean I can
>understand if the conductive medium is a piece of metal, then a dipole
>results in direct movement of electrons.

The dipoles are the neurons which, when activated, have
different voltages across different parts of their surface.

>But what about the brain? What is even more confusing to me is that
>action potentials are not even near the speed of light, so how can
>this current resulting from the dipoles in the brain travel that fast?

Action potentials are slowed by capacitance and by the time
taken for their underlying mechanisms.  Intra-axonal passive
current flow occurs at a rate equivalent to a substantial
proportion of the speed of light.

Kal

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