Discrete kink dynamics in hydrogen-bonded chains I: The one-component model

We study topological solitary waves (kinks and antikinks) in a nonlinear one-dimensional Klein-Gordon chain with the on-site potential of a double-Morse type. This chain is used to describe the collective proton dynamics in quasi-one-dimensional networks of hydrogen bonds, where the on-site potential plays role of the proton potential in the hydrogen bond. The system supports a rich variety of stationary kink solutions with different symmetry properties. We study the stability and bifurcation structure of all these stationary kink states. An exactly solvable model with a piecewise ``parabola-constant'' approximation of the double-Morse potential is suggested and studied analytically. The dependence of the Peierls-Nabarro potential on the system parameters is studied. Discrete travelling-wave solutions of a narrow permanent profile are shown to exist, depending on the anharmonicity of the Morse potential and the cooperativity of the hydrogen bond (the coupling constant of the interaction between nearest-neighbor protons).Comment: 12 pages, 20 figure

Model of P- and T-electroreceptors of weakly electric fish.

To clarify the microscopic mechanisms by which P- and T-receptors encode amplitude modulation and zero crossing time of jamming signals, we present a model of P- and T-receptors based on their physiological and anatomical properties. The model consists of a receptor cell, supporting cells, and an afferent nerve fiber. The basal membrane of the receptor cell includes voltage-sensitive Ca2+ channels, Ca(2+)-activated K+ channels, and leak channels of Na+, K+, and Cl-. The driving force of potential change under stimulation is generated by the voltage-sensitive Ca2+ channels, and the suppressing force of the change is generated by Ca(2+)-activated K+ channels. It has been shown that in T-receptor cells the driving force is much stronger than the suppressing force, whereas in P-receptor cells the driving force is comparable with the suppressing force. The difference in various kinds of response properties between P- and T-receptors have been consistently explained based on the difference in the relative strengths of the driving and suppressing forces between P- and T-receptor cells. The response properties considered are encoding function, probability of firing of afferent nerve, pattern of damped oscillation, shape of tuning curves, values of the optimum frequency, and response latency

Electroreceptor model of the weakly electric fish Gnathonemus petersii. I. The model and the origin of differences between A- and B-receptors.

We present an electroreceptor model of the A- and B-receptors of the weakly electric fish Gnathonemus petersii. The model consists of a sensory cell, whose membrane is separated into an apical and basal portions by support cells, and an afferent fiber. The apical membrane of the cell contains only leak channels, while the basal membrane contains voltage-sensitive Ca2+ channels, voltage-sensitive and Ca2+-activated K+ channels, and leak channels. The afferent fiber is described with the modified Hodgkin-Huxley equation, in which the voltage-sensitive gate of the K+ channels is a dynamic variable. In our model we suggest that the electroreceptors detect and process the information provided by an electric organ discharge (EOD) as follows: the current caused by an EOD stimulus depolarizes the basal membrane to a greatly depolarized state. Then the release of transmitter excites the afferent fiber to oscillate after a certain time interval. Due to the resistance-capacitance structure of the cells, they not only perceive the EOD intensity, but also sense the variation of the EOD waveform, which can be strongly distorted by the capacitive component of an object. Because of the different morphologies of A- and B-cells, as well as the different conductance of leak ion channels in the apical membrane and the different capacitance of A- and B-cells, A-receptors mainly respond to the EOD intensity, while B-receptors are sensitive to the variation of EOD waveform

Effect of syncytium structure of receptor systems on stochastic resonance induced by chaotic potential fluctuation.

To study a role of syncytium structure of sensory receptor systems in the detection of weak signals through stochastic resonance, we present a model of a receptor system with syncytium structure in which receptor cells are interconnected by gap junctions. The apical membrane of each cell includes two kinds of ion channels whose gating processes are described by the deterministic model. The membrane potential of each cell fluctuates chaotically or periodically, depending on the dynamical state of collective channel gating. The chaotic fluctuation of membrane potential acts as internal noise for the stochastic resonance. The detection ability of the system increases as the electric conductance between adjacent cells generated by the gap junction increases. This effect of gap junctions arises mainly from the fact that the synchronization of chaotic fluctuation of membrane potential between the receptor cells is strengthened as the density of gap junctions is increased

Electroreceptor model of the weakly electric fish Gnathonemus petersii I The model and the origin of differences between A- and B-receptors

We present an electroreceptor model of the A- and B-receptors of the weakly electric fish Gnathonemus petersii. The model consists of a sensory-cell, whose membrane is separated into an apical and basal portions by support cells, and an afferent fiber. The apical membrane of the cell contains only leak channels, while the basal membrane contains voltage-sensitive Ca2+ channels, voltage-sensitive and Ca2+-activated K+ channels, and leak channels. The afferent fiber is described with the modified Hodgkin;Huxley equation, in which the voltage-sensitive gate of the K+ channels is a dynamic variable; in our model we suggest that the electroreceptors detect and process the information provided by an electric organ discharge (EOD) as follows: the current caused by an EOD stimulus depolarizes the basal membrane to a greatly depolarized state. Then the release of transmitter excites the afferent fiber to oscillate after a certain time interval. Due to the resistance-capacitance structure of the cells, they not only perceive the EOD intensity, but also sense the variation of the EOD waveform, which can be strongly distorted by the capacitive component of an object. Because of the different morphologies of A- and B-cells, as well as the different conductance of leak ion channels in the apical membrane and the different capacitance of A- and B-cells, A-receptors mainly respond to the EOD intensity, while B-receptors are sensitive to the variation of EOD waveform