Nerves Transmit Sound, Not Electricity

[Michaelangelica]

LiveScience.com - Controversial New Idea: Nerves Transmit Sound, Not Electricity

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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.

Controversial New Idea: Nerves Transmit ... - Care2 News Network

Controversial New Idea: Nerves Transmit Sound, Not Electricity
By Robert Roy Britt
LiveScience Managing Editor
posted: 14 March, 2007
1:00 pm ET


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."

The textbooks are not likely to be rewritten anytime soon, however.

Roderic Eckenhoff, a researcher in the Department of Anesthesiology and Critical Care at the University of Pennsylvania School of Medicine, called the sound pulse idea interesting. "But an enormous burden of proof exists and they have a very long way to go to beat electricity," he said.

The olive oil clue

Nerves are wrapped in a membrane of lipids and proteins. Biology textbooks say a pulse is sent from one end of the nerve to the other with the help of electrically charged salts that pass through ion channels in the membrane. But the lack of heat generation contradicts the molecular biological theory of an electrical impulse produced by chemical processes, says Heimburg, who co-authored the new study with Copenhagen University theoretical physicist Andrew Jackson.

Instead, nerve pulses can be explained much more simply as a mechanical pulse of sound, Heimburg and Jackson argue. Their idea will be published in the Biophysical Journal.

Normally, sound propagates as a wave that spreads out and becomes weaker and weaker. But in certain conditions, sound can be made to travel without spreading and therefore it retains its intensity.

The lipids in a nerve membrane are similar to olive oil, the scientists explain. And the membrane has a freezing point that is precisely suited to the propagation of these concentrated sound pulses [graphic].

Eckenhoff is not convinced, however.

"It is difficult to explain away an enormous number of real electrical recordings in the cell, tissue and whole animal as being some kind of artifact," Eckenhoff told LiveScience. "And I cannot easily discern how the sound might be generated."

Explaining anesthesia

The idea from Heimburg and Jackson, if it were proven true, could have implication for anesthetics, another mysterious process.. . .
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[freeztar]

Very interesting, but the information supplied is too sparse. I would like to see the actual journal article showing their methodology.

How are the waves propagated? How is the signal kept amplified? What does this say about ion channels? So many questions left hanging there...

[InfiniteNow]

I'd like to see their evidence that nerve impulses really don't produce heat, since this is the assumption prompting them to propose a new theory. Can they really state without a shadow of a doubt that transmission of signals down neural pathways is without heat generation?

You see, a nerve impulse DOES produce heat:

The Positive and Negative Heat Production Associated with a Nerve Impulse

The 'initial' heat production of a non-medullated nerve (Maia) has been reinvestigated with more rapid recording equipment than was previously available. In a single impulse at 0 degrees C a positive heat production was observed averaging about 9× 10-6 cal/g nerve: this is rapid and is probably associated with the active phase of the impulse. It is followed by a rather slower heat absorption averaging about 7× 10-6 cal/g nerve and lasting for about 300 ms. Previous methods were too slow to do more than record the difference between the two, the 'net heat', viz. about 2× 10-6 cal/g nerve: this is about one-third greater at 0 degrees C than at 18 degrees C.

It depends greatly on frequency of stimulation; at 'zero frequency' it was about 9× 10-8 mole/g x impulse.

[Michaelangelica]

Well I read some of the original abstracts, but am none the wiser, sorry

On soliton propagation in biomembranes and nerves - group of 7 »
T Heimburg, AD Jackson - Proceedings of the National Academy of Sciences, 2005 - National Acad Sciences
... nerves Thomas Heimburg * and Andrew D. Jackson. The ... changes. sound | action
potential | compressibility | Hodgkin–Huxley theory. ...
Cited by 6 - Related Articles - Web Search - BL Direct

The stability of solitons in biomembranes and nerves - group of 6 »
B Lautrup, AD Jackson, T Heimburg - Arxiv preprint physics/0510106, 2005 - arxiv.org
... B. Lautrup, AD Jackson and T. Heimburg Niels Bohr Institute ... These velocities are
closely related to the lateral sound velocities in the nerve membrane. ...
Cited by 2 - Related Articles - View as HTML - Web Search

On the action potential as a propagating density pulse and the role of anesthetics - group of 2 »
T Heimburg, AD Jackson - Arxiv preprint physics/0610117, 2006 - arxiv.org
... 21 . Page 2. Recently, Heimburg and Jackson 22,23 proposed that the ... This corresponds
to a localized piezoelectric sound pulse within the nerve membrane. ...
Related Articles - View as HTML - Web Search

The thermodynamics of general anesthesia - group of 2 »
T Heimburg, AD Jackson - Arxiv preprint physics/0610147, 2006 - arxiv.org
... Thomas Heimburg, ∗ and Andrew D. Jackson ... When supplemented by the empir- ical
observation that the sound velocity in lipid mixtures in- creases with ...
Cited by 1 - Related Articles - View as HTML - Web Search

[Boerseun]

Not that I'm an expert in the field in any way, but I really strongly doubt this theory. Nerve cells are flexible and will expand sideways too when a sound pulse travels through them. This will make sound pulses travelling through them fall in intensity pretty quickly, what with the intervening axons, and all.

Also, that nervous action don't cause any heat seems a bit presumptious. Warm-blooded animals are as a rule warmer than the environment. This is mostly due to chemical reactions in the bloodstream. But how can they be so sure that in this warm background, the nerves aren't contributing to the warmer-than-the-environment heat of their test subject? As another counterargument, more than 80% of a human's bodyheat is lost through the head - which also happens to be the seat of a huge big knot of nerve fibres, neurons and axons called a brain. Common knowledge is that the brain eats most of the body's bloodstream because the neurons are hungry for glucose and oxygen. It could also very well be that the brain is well-supplied by blood vessels that are there mostly to act as a radiator, to take the excess of heat generated by the neurons' electrical activity away. Definitely not impossible, and, in my mind, a valid counterargument to the contention that nerves don't generate any heat at all.