NERVE IMPULSES CAN COLLIDE, CONTINUE UNAFFECTED
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 journalPhysical
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.
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