The Problem of Excitability
Kluwer Academic/Plenum Publishers (Verlag)
978-0-306-30593-1 (ISBN)
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The relationship between the various parameters of excitability (threshold potential, threshold current, useful time), accommodation, and the action potential on the one hand, and the constants of ionic permeability of the nerve fiber membrane, on the other hand, is subjected to detailed examination in this context. To do this, the author has made extensive use not only of experimental results obtained on isolated fibers (especially single nodes of Ran- vier), but also the results of his own investigations on mathematical models of excitable membranes.
I. Excitability and Relationships Between the Initial and Critical Values of the Membrane Potential.- Changes in Vt associated with primary shifts of Er.- Physiological electrotonus.- Effect of afferent stimulation.- Wedensky's "pessimal" inhibition.- Relative refractoriness.- Effects of potassium ions.- Changes in Vt resulting from a primary shift of Ec.- Effects of calcium ions.- Effects of local and general anesthetics.- II. The Resting Potential.- III. Passive and Subthreshold Active Changes in the Membrane Potential.- Passive changes of membrane potential.- The local response.- Historical.- Method of detecting the local response.- Properties of the local response.- Role of the local response in critical membrane depolarization.- IV. The Action Potential.- Historical.- Effect of changes in external and internal sodium and potassium ion concentrations on action potential generation.- Movement of ions through the membrane during activity.- Investigation by the use of labeled atoms.- Investigation of ionic currents by the voltageclamp method.- Evidence for subdivision of the ionic currents.- The sodium current.- The potassium current.- Changes in ionic permeability.- Quantitative description of ionic currents.- A mathematical model of the membrane of the squid giant axon.- Medullated nerve fibers.- The use of the mathematical model to analyze the kinetics of ionic currents in different phases of development of the action potential.- V. Dependence of Action Potential Parameters on the Constants of Membrane Ionic Permeability.- Maximal sodium permeability $$/rm /overline P _{Na} $$Na.- Steady-state sodium inactivation (1 - h?) and time constant Th.- Reactivity of the sodium system (sensitivity of PNa to changes in membrane potential).- The threshold potential.- Maximal steepness of rise of the ascending phase of the action potential.- Amplitude of the action potential.- Duration of the action potential.- Time constant of sodium activation Tm.- Maximal potassium permeability $$/rm /overline P _K $$.- Reactivity of the potassium system (sensitivity of $$/rm /overline P _K $$ to changes in membrane potential).- Effects of an increase in reactivity of thepotassium system.- Effects of a decrease in reactivity of the potassium activating system.- Time constant of potassium activation (Tn).- Assessment of the character of changes in ionic permeability of the membrane from changes in the action potential.- VI. Analysis of Threshold Conditions of Stimulation and the Relationship Between the Threshold Current and Threshold Potential.- The strength versus duration curve.- Character of critical depolarization of the membrane during the action of pulses of current of different duration. Nature of the utilization time.- Relationship between the threshold current and the passive and active properties of the membrane.- The rheobase.- The rheobase and passive properties of the membrane.- Relationship between rheobase and constants of ionic permeability of the membrane.- Threshold current for stimuli of short duration. Dependence on passive properties of the membrane.- Capacitance of the membrane (Cm).- Resistance of the membrane (Rm).- Threshold current for short stimuli as a function of the active properties of the membrane.- Time constant of sodium activation.- Maximal sodium and potassium permeabilities.- VII. Role of the Rate of Change of the Stimulus. The Phenomenon of Accommodation.- The accommodation curve.- The mechanism of accommodation.- Minimal gradient as a function of the constants of ionic permeability of the membrane.- Accommodation and repetitive responses.- VIII. Cable Properties and Geometry of Excitable Structures and Parameters of Their Electrical Activity.- The propagated action potential.- Threshold conditions of stimulation.- The threshold potential.- The threshold current.- The strength versus duration curve.- Repetitive responses in a continuous axon.- Effects of stimulation of excitable structures with a functionally nonuniform membrane.- The relationship between the velocity of conductance of the action potential and the cable properties and excitability of the fiber.- Conduction of impulses along a nonuniform fiber.- Some properties of spike conduction from a medullated into a nonmedullated segment of a nerve fiber.- Compensatory changes in ionic currents during conduction of the impulse along a nonuniform fiber.- IX. Molecular Mechanisms of Ionic Permeability of the Excitable Membrane.- Functional architecture of the excitable membrane.- Enzymes.- Cations.- Anions.- Dilution of electrolytes in the internal medium.- Poisons.- The hypothesis of ionic carriers.- The hypothesis of ion pores.- Specificity of the ion channels.- The possible role of Ca++ ions in the mechanism of opening and closing of the ionic channels.- Hypotheses on conformational changes in the membrane.- Investigations of mechanisms of the changes in ionic permeability on artificial membranes.- Precipitation membranes.- Phospholipid membranes.- Conclusion.- Addendum.
| Übersetzer | B. Haigh |
|---|---|
| Zusatzinfo | biography |
| Sprache | englisch |
| Maße | 150 x 230 mm |
| Gewicht | 660 g |
| Themenwelt | Schulbuch / Wörterbuch |
| Naturwissenschaften ► Biologie ► Zoologie | |
| ISBN-10 | 0-306-30593-3 / 0306305933 |
| ISBN-13 | 978-0-306-30593-1 / 9780306305931 |
| Zustand | Neuware |
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