The Heat of Nervous Conduction: A Thermodynamic Framework

Early recordings of nervous conduction revealed a notable thermal signature associated with the electrical signal. The observed production and subsequent absorption of heat arise from physicochemical processes that occur at the cell membrane level during the conduction of the action potential. In particular, the reversible release of electrical energy stored as a difference of potential across the cell membrane appears as a simple yet consistent explanation for the heat production, as proposed in the "Condenser Theory." However, the Condenser Theory has not been analyzed beyond the analogy between the cell membrane and a parallel-plate capacitor, i.e. a condenser, which cannot account for the magnitude of the heat signature. In this work, we use a detailed electrostatic model of the cell membrane to revisit the Condenser Theory. We derive expressions for free energy and entropy changes associated with the depolarization of the membrane by the action potential, which give a direct measure of the heat produced and absorbed by neurons. We show how the density of surface charges on both sides of the membrane impacts the energy changes. Finally, considering a typical action potential, we show that if the membrane holds a bias of surface charges, such that the internal side of the membrane is 0.05 C m$^{-2}$ more negative than the external side, the size of the heat predicted by the model reaches the range of experimental values. Based on our study, we identify the change in electrical energy of the membrane as the primary mechanism of heat production and absorption by neurons during nervous conduction

U-Pb geochronology on zircon and columbite-group minerals of the Cap de Creus pegmatites, NE Spain

The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2 ± 2.5 to 301.9 ± 3.8 Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5 ± 2.5 and 292.9 ± 2.9 Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299 Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292 Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area

U-Pb geochronology on zircon and columbite-group minerals of the Cap de Creus pegmatites, NE Spain

The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2 ± 2.5 to 301.9 ± 3.8 Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5 ± 2.5 and 292.9 ± 2.9 Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299 Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292 Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area

National Sovereignty in the Belgian Constitution of 1831. On the Meaning(s) of Article 25

info:eu-repo/semantics/publishe