Abstract
The collisions of two simultaneously generated impulses in the giant axons of both earthworms and lobsters propagating in orthodromic and antidromic direction are investigated. The experiments have been performed on the extracted ventral cords of Lumbricus terrestris and the abdominal ventral cord of a lobster, Homarus americanus, by using external stimulation and recording. The collision of two nerve impulses of orthodromic and antidromic propagation did not result in the annihilation of the two signals, contrary to the common notion that is based on the existence of a refractory period in the well-known Hodgkin-Huxley theory. However, the results are in agreement with the electromechanical soliton theory for nerve-pulse propagation, as suggested by Heimburg and Jackson [On Soliton Propagation in Biomembranes and Nerves, Proc. Natl. Acad. Sci. U.S.A. 102, 9790 (2005).].
- Received 31 March 2014
DOI:https://doi.org/10.1103/PhysRevX.4.031047
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Published by the American Physical Society
Synopsis
SynopsisNerve Pulses Pass by Each Other
Published 10 September 2014
Experiments on neuron fibers from earthworms and lobsters reveal that two nerve pulses that collide do not annihilate, contrary to common beliefs of nerve electrophysiology.
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Popular Summary
In nerve electrophysiology, it is widely believed that two colliding nerve pulses annihilate and cannot pass through each other. However, there is little evidence in the literature that this process actually occurs. We show that action potentials in the nerve fibers of earthworms and lobsters in fact pass through each other without inducing major perturbations.
We compare two different approaches for explaining the nerve pulse: the Hodgkin-Huxley model and a more recent electromechanical soliton model. The former does not allow for pulse penetration; the latter treats the nerve pulse as a nondissipative electromechanical pulse and predicts pulse penetration. Therefore, penetration experiments are critical for discriminating between the two approaches. We use the ventral cords of earthworms and lobsters, specifically the median and lateral giant axons. We stimulate the axons with two pairs of electrodes, one at each end of the nerve. Our measurements reveal that the myelinated fibers (from earthworms) and nonmyelinated fibers (from lobsters) yield no change in the shape or velocity of the colliding pulses, implying that action potentials propagate as electromechanical pulses. The presence of electromechanical pulses is consistent with the experimental finding that changes in nerve thickness are found and no heat is dissipated during the nerve pulse.
Our findings are not consistent with the Hodgkin-Huxley model, which has long been accepted as a description of nerve-pulse propagation.
