How is information transmitted in a nerve?
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How is information transmitted in a nerve? Michel Peyrard1 Received: 12 August 2020 / Accepted: 10 September 2020 / © Springer Nature B.V. 2020
Abstract In the last 15 years, a debate has emerged about the validity of the famous Hodgkin-Huxley model for nerve impulse. Mechanical models have been proposed. This note reviews the experimental properties of the nerve impulse and discusses the proposed alternatives. The experimental data, which rule out some of the alternative suggestions, show that while the Hodgkin-Huxley model may not be complete, it nevertheless includes essential features that should not be overlooked in the attempts made to improve, or supersede, it. Keywords Nerve cell · Nerve impulse · Axon · Hodgkin-Huxley model
1 Introduction In high school biology courses, a standard experiment shows how a small voltage applied to a dead-frog muscle can induce its contraction. Actually, it reproduces the first observation made by Luigi Galvani in the eighteenth century. In 1850, Hermann von Helmholtz designed an experiment to measure the velocity of the signal that propagates along the sciatic nerve of a frog [1–3]. A quantitative description of the propagation of an electrical signal in a nerve was proposed in 1952 by A.L. Hodgkin and A.F. Huxley [4] after a careful series of experimental investigations. For a long time, this Hodgkin-Huxley model, recognized in 1963 by the Nobel Prize for Physiology or Medicine, stayed as the unquestioned basic model of this phenomenon, which launched a new field of research [5, 6]. According to this model, the nerve impulse is due to voltage-controlled flows of sodium and potassium ions through the axon membrane. However, the phenomena are more complex. Experiments also detect heat transfer and a slight deformation of the axon together with the electrical signal. In the last 15 years, this led some scientists to raise questions about the Hodgkin-Huxley model and even to propose an alternative picture in which the propagation of a mechanical signal is the main feature [7, 8].
Michel Peyrard
[email protected] 1
Laboratoire de Physique de l’Ecole Normale Sup´erieure de Lyon, 46 All´ee d’Italie, 69364 C´edex 07, Lyon, France
M. Peyrard
This article reviews the main experimental data accumulated over more than a century on the propagation of the nerve impulse, paying attention to some aspects which are particularly relevant for the ongoing discussion on the validity of the Hodgkin-Huxley model. Then, it discusses the proposals to replace, or complete, this model. The final discussion contains some comments on these attempts.
2 Experimental studies of the electrical properties of axons The German school of “organic physicists” played a major role in creating modern physiology in the second half of the nineteenth century [9]. Hermann von Helmoltz (1821–1894), who worked in Heidelberg, was the first to measure the velocity of the signal along a nerve, and Julius Bernstein (1839–1917), who was trained under von Helmholtz, designed a clever apparatus which allowed
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