Global InformationSoliton model in neuroscience information
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The soliton hypothesis in neuroscience is a model that claims to explain how action potentials are initiated and conducted along axons based on a thermodynamic theory of nerve pulse propagation.[1] It proposes that the signals travel along the cell's membrane in the form of certain kinds of solitary sound (or density) pulses that can be modeled as solitons. The model is proposed as an alternative to the Hodgkin–Huxley model[2] in which action potentials: voltage-gated ion channels in the membrane open and allow sodium ions to enter the cell (inward current). The resulting decrease in membrane potential opens nearby voltage-gated sodium channels, thus propagating the action potential. The transmembrane potential is restored by delayed opening of potassium channels. Soliton hypothesis proponents assert that energy is mainly conserved during propagation except dissipation losses; Measured temperature changes are completely inconsistent with the Hodgkin-Huxley model.[3][4]
The soliton model (and sound waves in general) depends on adiabatic propagation in which the energy provided at the source of excitation is carried adiabatically through the medium, i.e. plasma membrane. The measurement of a temperature pulse and the claimed absence of heat release during an action potential[5][6] were the basis of the proposal that nerve impulses are an adiabatic phenomenon much like sound waves. Synaptically evoked action potentials in the electric organ of the electric eel are associated with substantial positive (only) heat production followed by active cooling to ambient temperature.[7] In the garfish olfactory nerve, the action potential is associated with a biphasic temperature change; however, there is a net production of heat.[8] These published results are inconsistent with the Hodgkin-Huxley Model and the authors interpret their work in terms of that model: The initial sodium current releases heat as the membrane capacitance is discharged; heat is absorbed during recharge of the membrane capacitance as potassium ions move with their concentration gradient but against the membrane potential. This mechanism is called the "Condenser Theory". Additional heat may be generated by membrane configuration changes driven by the changes in membrane potential. An increase in entropy during depolarization would release heat; entropy increase during repolarization would absorb heat. However, any such entropic contributions are incompatible with Hodgkin and Huxley model[9]
- ^ Andersen, S; Jackson, A; Heimburg, T (2009). "Towards a thermodynamic theory of nerve pulse propagation" (PDF). Progress in Neurobiology. 88 (2): 104–113. doi:10.1016/j.pneurobio.2009.03.002. PMID 19482227. S2CID 2218193.
- ^ Hodgkin AL, Huxley AF, Katz B (1952). "Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo". Journal of Physiology. 116 (4): 424–448. doi:10.1113/jphysiol.1952.sp004717. PMC 1392213. PMID 14946713.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
Hodgkin AL, Huxley AF (1952). "Currents carried by sodium and potassium ions through the membrane of the giant axon of Loligo". Journal of Physiology. 116 (4): 449–472. doi:10.1113/jphysiol.1952.sp004717. PMC 1392213. PMID 14946713.
Hodgkin AL, Huxley AF (1952). "The components of membrane conductance in the giant axon of Loligo". J Physiol. 116 (4): 473–496. doi:10.1113/jphysiol.1952.sp004718. PMC 1392209. PMID 14946714.
Hodgkin AL, Huxley AF (1952). "The dual effect of membrane potential on sodium conductance in the giant axon of Loligo". J Physiol. 116 (4): 497–506. doi:10.1113/jphysiol.1952.sp004719. PMC 1392212. PMID 14946715.
Hodgkin AL, Huxley AF (1952). "A quantitative description of membrane current and its application to conduction and excitation in nerve". J Physiol. 117 (4): 500–544. doi:10.1113/jphysiol.1952.sp004764. PMC 1392413. PMID 12991237. - ^ Margineanu, D.-G; Schoffeniels, E. (1977). "Molecular events and energy changes during the action potential". PNAS. 74 (9): 3810–3813. Bibcode:1977PNAS...74.3810M. doi:10.1073/pnas.74.9.3810. PMC 431740. PMID 71734.
- ^ Hasenstaub, A; Callaway, E; Otte, S; Sejnowski, T (2010). "Metabolic cost as a unifying principle governing neuronal biophysics". Proceedings of the National Academy of Sciences of the USA. 107 (27): 12329–12334. Bibcode:2010PNAS..10712329H. doi:10.1073/pnas.0914886107. PMC 2901447. PMID 20616090.
- ^ Tasaki, Ichiji (13 October 1995). "Mechanical and Thermal Changes in the Torpedo Electric Organ Associated with Its Postsynaptic Potentials". Biochemical and Biophysical Research Communications. 215 (2): 654–658. doi:10.1006/bbrc.1995.2514. PMID 7488005.
- ^ Howarth, J V; Keynes, R D; Ritchie, J M; Muralt, A von (1 Jul 1975). "The heat production associated with the passage of a single impulse in pike olfactory nerve fibres". The Journal of Physiology. 249 (2): 349–368. doi:10.1113/jphysiol.1975.sp011019. PMC 1309578. PMID 1236946.
- ^ Tasaki, I; Byrne, P. M. (1993). "Rapid heat production associated with electrical excitation of the electric organs of the electric eel". Biochem Biophys Res Commun. 197 (2): 910–915. doi:10.1006/bbrc.1993.2565. PMID 8267630.
- ^ Tasaki, K; Kusano, K; Byrne, PM (1989). "Rapid thermal and mechanical changes in garfish olfactory nerve associated with a propagated impulse". Biophys J. 55 (6): 1033–1040. Bibcode:1989BpJ....55.1033T. doi:10.1016/s0006-3495(89)82902-9. PMC 1330571. PMID 2765644.
- ^ Howarth, J. V. (1975). "Heat Production in Non-Myelinated Nerves". Philosophical Transactions of the Royal Society. 270 (908): 425–432. Bibcode:1975RSPTB.270..425H. doi:10.1098/rstb.1975.0020. JSTOR 2417341. PMID 238239.