# The physical laws of thermodynamics tell us that electrical impulses must produce heat?

Health - Controversial New Idea: Nerves Transmit Sound, Not Electricity - By Robert Roy Britt, LiveScience Managing Editor posted: 14 March, 2007 1:00 pm ET Rendering shows a biological membrane at its melting point. The green molecules are liquid, and the red are solid. Molecules of anesthetic reduce the number of red areas so that the sound pulse can no longer transport its signal. The nerve is anesthetized. Credit: Heiko Seeger, Ph.D. Niels Bohr Institute Nerves transmit sound waves through your body, not electrical pulses, according to a controversial new study that tries to explain the longstanding mystery of how anesthetics work. Textbooks say nerves use electrical impulses to transmit signals from the brain to the point of action, be it to wag a finger or blink an eye. "But for us as physicists, this cannot be the explanation," says Thomas Heimburg, a Copenhagen University researcher whose expertise is in the intersection of biology and physics. "The physical laws of thermodynamics tell us that electrical impulses must produce heat as they travel along the nerve, but experiments find that no such heat is produced."

How should I read:

"The physical laws of thermodynamics tell us that electrical impulses must produce heat as they travel along the nerve, but experiments find that no such heat is produced." ?

I learned:

If only resistive [being coupled to an electrical resistance] electrical signal transmission takes place, there is dissipation of electric energy in the relevant resistance and hence development of heat.

But also, I learned:

If the signal is purely capacitive [a circuit of ideal capacitors] or inductively [ideal coils], no energy is dissipated.

Under ideal capacitors and inductors current and voltage differ always 90 ° in phase.

Therefore φ = 90 °.

If the current I and the voltage V, then the energy dissipation is always given by: I × V × cosφ

And because cos 90 ° = 0, is also the dissipation 0.

Is "purely capacitive" or "inductively" not the explanation why no such heat is produced?

## 1 Answer

The quote you give is very vague and hand waving. Various theories have been proposed of how nerve cells transmit information, which one can find by googling. The models are complex and this seems to be one more in the row.

You are correct in that inductive and capacitive transfers would not heat the nerve. It seems that they expect the signal transfer if electric to be resistive. It is not an extreme assumption because it is hard to model capacitive or inductive transfer in the messy environment of a nerve.

One needs more information to see whether their assumption of sound transfers is reasonable or not. Others have been proposing a type of superconductivity to explain nerve message transfers.