Biophysical journal
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Biophysical journal · Sep 1991
Analytical theory for extracellular electrical stimulation of nerve with focal electrodes. II. Passive myelinated axon.
The cable model of a passive, myelinated fiber is derived using the theory of electromagnetic propagation in periodic structures. The cable may be excited by an intracellular source or by an arbitrary, time-varying, applied extracellular field. When the cable is stimulated by a distant source, its properties are qualitatively similar to an unmyelinated fiber. ⋯ Several anatomic representations of the paranodal region are analyzed for their effects on the length and time constants of the fibers. Sensitivity of the model to parameter changes is studied. The linear model reliably predicts the effects of fiber size and electrode-fiber separation on threshold of cat dorsal column fibers to extracellular electrical stimulation.
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Biophysical journal · Jul 1984
Mechanisms of use-dependent block of sodium channels in excitable membranes by local anesthetics.
Many local anesthetics promote reduction in sodium current during repetitive stimulation of excitable membranes. Use-, frequency-, and voltage-dependent responses describe patterns of peak INa when pulse width, pulse frequency, and pulse amplitude are varied. Such responses can be viewed as reflecting voltage-sensitive shifts in equilibrium between conducting, unblocked channels and nonconducting, blocked channels. ⋯ We develop analytical expressions characterizing guarded receptors as "apparently" variable-affinity binding sites and predicting shifts in "apparent" channel inactivation in the hyperpolarizing direction. These results were confirmed with computer simulations. Furthermore, these results are in quantitative agreement with recent investigations of lidocaine binding in cardiac sodium channels.
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Biophysical journal · Feb 1978
Simulations of conduction in uniform myelinated fibers. Relative sensitivity to changes in nodal and internodal parameters.
Conduction of impulses in myelinated axons has been studied by a new method of computer simulation. The contributions of nodal and internodal characteristics and parameters were examined. ⋯ The conduction velocity also is relatively insensitive to the internodal length but much more sensitive to the myelin capacitance and axoplasm conductance. Qualitative change in theta with temperature depended on which temperature-sensitive parameters were included in the simulation.