Entropy measures of signal in the presence of noise: evidence for ‘byte’ versus ‘bit’ processing in the nervous system

Summary A method for detecting signal in the presence of noise in a highly specific was is described. Using action potential interval data from 12 neurons in rat cerebellum, we have demonstrated that the sequential ordering of spike intervals contains both noise and signal. We have identified and quantified the magnitude of relative entropy (uncertainty) for specified sets of interval patterns, ranging in length from 3–5 successive intervals. Some of these sets have exceptionally low entropy and thus seem to be especially meaningful as a set (word) to the brain.     

Supernormal responses to premature stimulation in Ca-dependent action potentials.

The responses of Ca-dependent action potentials to premature stimulation were studied in the isolated canine ventricular muscle. When very premature stimuli were applied, supernormally augmented responses with propagation occurred, while responses with long preceding intervals were small and not conducted.     

Contributions of cellular electrophysiology to the understanding of the electrocardiogram

The understanding of cardiac action potential and membrane currents has broadened the theoretical foundation and enhanced the clinical usefulness of the electrocardiogram. An improved understanding of the morphology of the electrocardiographic waveform has resulted from: correlations between Vmax of depolarization and QRS complex, plateau of the ventricular action potential and S-T segment, terminal repolarization and T-wave, from definitions of action potential differences responsible for the T-wave, and recordings of action potential alternans. Cellular electrophysiology has contributed to the understanding of certain mechanisms of cardiac standstill. Many disturbances of conduction and refractoriness associated with ventricular arrhythmias can be attributed to the following derangements at the cellular level: slowing of terminal repolarization, development of diastolic depolarization in fibers with stable resting membrane potential, after-depolarizations, currents of injury resulting from non-uniform polarization, increased dispersion of action potential durations, and co-existence of slow conduction and short premature action potentials.     

Contributions of cellular electrophysiology to the understanding of the electrocardiogram

Summary The understanding of cardiac action potential and membrane currents has broadened the theoretical foundation and enhanced the clinical usefulness of the electrocardiogram. An improved understanding of the morphology of the electrocardiographic waveform has resulted from: correlations between V_max of depolarization and QRS complex, plateau of the ventricular action potential and S-T segment, terminal repolarization and T-wave, from definitions of action potential differences responsible for the T-wave, and recordings of action potential alternans. Cellular electrophysiology has contributed to the understanding of certain mechanisms of cardiac standstill. Many disturbances of conduction and refractoriness associated with ventricular arrhythmias can be attributed to the following derangements at the cellular level: slowing of terminal repolarization, development of diastolic depolarization in fibers with stable resting membrane potential, afterdepolarizations, currents of injury resulting from non-uniform polarization, increased dispersion of action potential durations, and co-existence of slow conduction and short premature action potentials.     

Zur wirkung hypertoner Lösungen auf die markhaltige Nervenfaser

Summary The effect of hypertonic solutions on the action potential of single myelinated nerve fibres is described. Hypertonicity mainly changes the duration of the action potential: Short action potentials obtained in normal Ringer's solution at room temperature are prolonged, long action potentials due to 0.1–1.0 mM NiCl₂-Ringer's solution and low temperature are shortened by hypertonicity. The changes in action potential duration are accompanied by small changes in action potential amplitude. In addition, hypertonicity reduces the depolarization produced by 20 mM KCl; inactivation of the sodium-carrying system under cathodal polarization is enhanced.

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Die Untersuchungen wurden mit Unterstützung der Deutschen Forschungsgemeinschaft ausgeführt.     

Effects of intracellular or extracellular application of tetraethylammonium on the action potential in cultured chick embryonic heart muscle cell

Summary The effects of tetraethylammonium (TEA) on the action potential in cultured chick embryonic heart muscle cells were investigated. The onset of prolongation of the action potential occurred within 10 min following intracellular iontophoretic application of TEA, but after more than 50 min following extracellular application. These facts suggest that the major site of action of TEA is on the inner surface of the membrane in these cells.     

Tetrodotoxin slightly shortens action potential duration in ventricular but not in atrial heart muscle

Tetrodotoxin (TTX), at concentrations significantly decreasing maximal upstroke velocity (dV/dtmax) of the action potential, exerted variable effects on action potential duration (APD) in different myocardial preparations. APD was virtually unchanged by tetrodotoxin in the guinea pig atrium, but slightly shortened in the guinea pig ventricle at maximally effective concentrations. In the human ventricle, both dV/dtmax and APD were reduced in the same concentration range of TTX. These results suggest that a TTX-sensitive sodium current significantly contributes to the repolarization phase of the action potential in ventricular but not in atrial heart muscle.     

In situ observations of spontaneous contractions of the peripheral lymphatic vessels in the rat mesentery: effects of temperature

By means of an intracellular glass microelectrode, action potential changes were successfully recorded in situ from the endothelial cells of rat mesenteric lymphatics over the temperature range of 27-40 degrees C. The frequency of action potential and the lymphatic contraction rate correlated well with temperature.     

A new stimulation technique of the crista ampullaris of the lateral canal in the adult cat: study of the action potential of the vestibular nerve.

The stimulation of the crista ampullaris of the lateral canal by a short ampullopetal liquid flux produces on the pre-ganglionic vestibular fibres the appearance of a bimodal action potential. The amplitude of this action potential increases with the intensity of the stimulation. This stimulation also provokes the birth of an evoked potential at the level of the vestibular nuclei as well as an ocular jerk.     

Excitation-contraction coupling in the myocardium of hibernating chipmunks

In the myocardium of nonhibernating chipmunks, replacing external Ca by Sr markedly prolongs the action potential plateau with an increase in contraction, while in preparations from hibernating animals this procedure inhibits both responses. Pretreatment with 4-aminopyridine causes a prolongation of the action potential plateau by Sr in hibernating animals.