Date: September
10, 2014
Source: University
of Copenhagen - Niels Bohr Institute
Summary:
According to the traditional theory
of nerves, two nerve impulses sent from opposite ends of a nerve annihilate
when they collide. New research now shows that two colliding nerve impulses
simply pass through each other and continue unaffected. This supports the
theory that nerves function as sound pulses.
According
to the traditional theory of nerves, two nerve impulses sent from opposite ends
of a nerve annihilate when they collide. New research from the Niels Bohr
Institute now shows that two colliding nerve impulses simply pass through each
other and continue unaffected. This supports the theory that nerves function as
sound pulses.
The
results are published in the scientific journal Physical Review X.
Nerve
signals control the communication between the billions of cells in an organism
and enable them to work together in neural networks. But how do nerve signals
work?
Old
model
In
1952, Hodgkin and Huxley introduced a model in which nerve signals were
described as an electric current along the nerve produced by the flow of ions.
The mechanism is produced by layers of electrically charged particles (ions of
sodium and potassium) on either side of the nerve membrane that change places
when stimulated. This change in charge creates an electric current.
This
model has enjoyed general acceptance. For more than 60 years, all medical and
biology textbooks have said that nerves function is due to an electric current
along the nerve pathway. However, this model cannot explain a number of
phenomena that are known about nerve function.
New
model
Researchers
at the Niels Bohr Institute at the University of Copenhagen have now conducted
experiments that raise doubts about this well-established model of electrical
impulses along the nerve pathway.
"According
to the theory of this ion mechanism, the electrical signal leaves an inactive
region in its wake, and the nerve can only support new signals after a short
recovery period of inactivity. Therefore, two electrical impulses sent from
opposite ends of the nerve should be stopped after colliding and running into
these inactive regions," explains Thomas Heimburg, Professor and head of
the Membrane Biophysics Group at the Niels Bohr Institute at the University of
Copenhagen.
Thomas
Heimburg and his research group conducted experiment in the laboratory using
nerves from earthworms and lobsters. The nerves were removed and used in an
experiment in which allowed the researchers to stimulate the nerve fibres with
electrodes on both ends. Then they measured the signals en route.
"Our
study showed that the signals passed through each other completely unhindered
and unaltered. That's how sound waves work. A sound wave doesn't stop when it
meets another sound wave. Both waves continue on unimpeded. The nerve impulse
can therefore be explained by the fact that the pulse is a mechanical wave in
the form of a sound pulse, a soliton, that moves along the nerve
membrane," explains Thomas Heimburg.
The
theory is confirmed
When
the sound pulse moves through the nerve pathway, the membrane changes locally
from a liquid to a more solid form. The membrane is compressed slightly, and
this change leads to an electrical pulse as a consequence of the piezoelectric
effect. "The electrical signal is thus not based on an electric current
but is caused by a mechanical force," points out Thomas Heimburg.
Thomas
Heimburg, along with Professor Andrew Jackson, first proposed the theory that
nerves function by sound pulses in 2005. Their research has since provided
support for this theory, and the new experiments offer additional confirmation
for the theory that nerve signals are sound pulses.
Story
Source:
The
above story is based on materials provided by University of Copenhagen - Niels Bohr Institute. Note:
Materials may be edited for content and length.
Journal
Reference:
1.
Alfredo Gonzalez-Perez, Rima
Budvytyte, Lars D. Mosgaard, Søren Nissen, Thomas Heimburg. Penetration of
Action Potentials During Collision in the Median and Lateral Giant Axons of
Invertebrates. Physical Review X, 2014; 4 (3) DOI: 10.1103/PhysRevX.4.031047
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