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Z Wünsch

Publications and source records attributed to Z Wünsch.

At least 19 recordsLinked to original sources
PubMed2002

Model of spike propagation reliability along the myelinated axon corrupted by axonal intrinsic noise sources.

We investigated how selected electromorphological parameters of myelinated axons influence the preservation of interspike intervals when the propagation of action potentials is corrupted by axonal intrinsic noise. Hereby we tried to determine how the intrinsic axonal noise influences the performance of axons serving as carriers for temporal coding. The strategy of this coding supposes that interspike intervals presented to higher order neurons would minimally be deprived of information included in interspike intervals at the axonal initial segment. Our experiments were conducted using a computer model of the myelinated axon constructed in a software environment GENESIS (GEneral NEural SImulation System). We varied the axonal diameter, myelin sheath thickness, axonal length, stimulation current and channel distribution to determine how these parameters influence the role of noise in spike propagation and hence in preserving the interspike intervals. Our results, expressed as the standard deviation of spike travel times, showed that by stimulating the axons with regular rectangular pulses the interspike intervals were preserved with a microsecond accuracy. Stimulation with pulses imitating postsynaptic currents, greater changes of interspike intervals were found, but the influence of implemented noise on the jitter of interspike intervals was approximately the same.

Action Potentials↗
PubMed2002

Model of spike propagation reliability along the myelinated axon corrupted by axonal intrinsic noise sources.

We investigated how selected electromorphological parameters of myelinated axons influence the preservation of interspike intervals when the propagation of action potentials is corrupted by axonal intrinsic noise. Hereby we tried to determine how the intrinsic axonal noise influences the performance of axons serving as carriers for temporal coding. The strategy of this coding supposes that interspike intervals presented to higher order neurons would minimally be deprived of information included in interspike intervals at the axonal initial segment. Our experiments were conducted using a computer model of the myelinated axon constructed in a software environment GENESIS (GEneral NEural SImulation System). We varied the axonal diameter, myelin sheath thickness, axonal length, stimulation current and channel distribution to determine how these parameters influence the role of noise in spike propagation and hence in preserving the interspike intervals. Our results, expressed as the standard deviation of spike travel times, showed that by stimulating the axons with regular rectangular pulses the interspike intervals were preserved with a microsecond accuracy. Stimulating the axons with pulses imitating postsynaptic currents, greater changes of interspike intervals were found, but the influence of implemented noise on the jitter of interspike intervals was approximately the same.

Action Potentials↗
PubMed1998

[Dendrites, neurons and simulation models].

The dendritic tree, this morphologically remarkably structured and typically diversified portion of the neuron reveals gradually its till recently little known complex functional possibilities. The size of the dendritic membrane participates in the latter similarly as their morphological pattern and their electronic structure which has a marked effect also due to its passive cable properties on the spread and interaction of potential changes on the membrane. Moreover the presence of a complex, differentiated mosaic of ion channels of different types provides dendrites with non-linearities with a wide scope of dynamic phenomena and active properties. The dendritic membrane can e.g. actively reinforce signals proceeding along the thin dendrite fibres and may make the development of action potentials or their retrograde movement from the membrane of the cell body possible. The possible operations above the spatial and temporal structures of signals equipped by differently located excitation and inhibition synapses are enriched by the action of ions entering via ion channels into the cell when the membrane potential changes. Manifestations of neuroplasticity lend these properties further temporal and functional dimensions. The neuron is no longer a one-way polarized and passive transmitter of synaptic input signals four output action potentials; it is a complicated non-linear hierarchic dynamic system with possible complex temporal and spatial analogue signal transformations in dendritic structures. New findings are the result of the cooperative use of empirical and theoretical procedures based on the morphophysiological methods with a high differentiating capacity and the methodology of studies of dynamic systems and computer simulation.

Action Potentials↗
PubMed1998

[The beginnings of cybernetics and its introduction into the biomedical arena in the Czech Republic].

During fifties at most few tens of persons were in Czechoslovakia who believed in the future of computers and cybernetics. At the sixties, the Czechoslovak Cybernetics was established and in 1962 the Main Problem Committee for the Medical Cybernetics was founded at the Ministry of Health. The first tentative lectures on this topics at the Charles University Medical faculty were introduced in the late sixties. The growing interest enabled to hold national and international conferences since the middle of seventies. There is mentioned the whole spectrum of these goal-directed activities so important for the future.

Cybernetics↗
PubMed1998

[Medical cybernetics in Czechoslovakia--the first steps].

During fifties there were at most few tens of persons in this country who believed in the future of computers and cybernetics. One group of such enthusiasts, headed by Antonín Svoboda, was working at a construction of the first Czech computer SAPO. The other group tried to analyse, anticipate, and prepare in advance various applications for the new systemic conceptions and for the information processing machines. Members of both groups met for discussions which opened prospects to the future and influenced many of other activities for a long time. At the early sixties, the Czechoslovak Cybernetic Society was established at the Czechoslovak Academy of Sciences and in 1962 the Main Problem Committee for the Medical Cybernetics was founded at the Department of Health. It coordinated majority of the research programmes in the medical cybernetics and informatics. In 1967-1969 the Committee prepared an extensive project of a medical information system (ZIS), but its accomplishment was finally blocked by the then authorities. However, interests for that topics kept growing and the new working places equipped with available computer technology were formed at the health and clinical centres. The first tentative lectures in medical cybernetics and biocybernetics at our faculty were introduced into the students curricula in the late sixties. Thematically, medical cybernetics subsequently differentiated into the medical informatics, simulations of biological and medical systems, and the biosignal analysis. The growing interest enabled to hold conferences since the middle of seventies, some of which were held periodically, sometimes with international participation. It is not possible in brevity to include the whole spectrum to those goal-directed activities nor to appraise adequately their future significance.

Cybernetics↗
PubMed1996

Isotonic contraction as a result of cooperation of sarcomeres--a model and simulation outcome.

The molecular level of the functional structure of the contractile apparatus of cross-striated muscle has been mapped out almost minutely. Most authors accept the basic principles of the theory of sliding filaments and the theory of operation of molecular generators of force which, of course, are progressively updated by integrating new knowledge. The idea of the model delineated below does not contradict these theories, for it refers to another level of the system's hierarchy. The definition of the system, hereafter referred to Ideal Sarcomere (IS), takes into account the fact that, during isotonic contraction, a large number of not wholly independently working sarcomeres and molecular generators of force is active in a synergistic way. The shortening velocity of isotonically contracting IS is determined by the relation between quantities conveying different tasks of active generators of force and the influence of the system parameters. Although IS is derived from simple axiomatic predicates, it has properties which were not premediated in defining the system and which, in spite of this, correspond to some properties of the biological original. The equations of the system allow us to calculate the shortening velocity of 'isotonic contraction' and other variables and parameters and show, inter alia, an alternative way to derive and interpret the relations stated in Hill's force-velocity equation. The simulation results indicate that the macroscopic manifestations of isotonic contraction may be also contingent on the properties of the cooperating system of the multitude of sarcomeres, which also constitutes one part of the functional structure of muscle.

Animals↗
PubMed1996

[Biocybernetics and physiology yesterday and today].

In the first part of the article authors characterize briefly the biocybernetics as a branch of science and substantiate why it should be considered as an integral constituent of biological sciences, and consequently of the physiology, too. In the second part they are paying attention to the reasons and policies for embodying selected biocybernetical subjects into the course of physiology.

Bionics↗
PubMed1987

A joint model of the contractile system of striated muscle (dynamic version).

The Joint Model of the Contractile System of Muscle is a theoretical construction and the question is whether it may express adequately some aspects of the biological original. In addition to the previous results which presented preliminary calculations, simulation experiments have been performed with a dynamic version of the model. The relations found between the variables studied (length, shortening velocity, isotonic contraction load, shortening heat production rate and excess of effective activity), did not essentially differ from those established by preliminary calculations; the choice of appropriate parameter values and the introduction of some additional features in the system made it possible to obtain a better approximation of relations known from measurements on the biological object. The model discloses some relevant general aspects of the contractile system of "independent" generators of force and thus contributes to a specification of the relationships between molecular and macroscopic levels of contraction phenomena. Future development or correction of the concepts under consideration depend on more suitable empirical data and further simulation experiments.

Biomechanical Phenomena↗
PubMed1986

Prolegomena to a joint model of the contractile system of striated muscle.

On the basis of some known properties of the contractile apparatus of muscle and, employing speculative premises, a mathematical model was formulated which makes it possible to express the relations between some macroscopic phenomena of muscle contraction and activities of idealized molecular generators of force quantitatively. With the exception of the sliding filament theory, which is generally accepted, no other published models have, as yet, been taken into consideration.

Animals↗
PubMed1986

A joint model of the contractile system of striated muscle (preliminary calculations).

Values of the variables of a model of the muscle contractile apparatus were calculated on the basis of a previously described theoretical system JMCSM (i.e. the Joint Model of the Contractile System of Muscle) and after introducing some necessary simplifying presuppositions. The calculations made it possible to compare the model with the original biological system and provided data needed for the subsequent stage of simulation experiments. The properties of the model are apparently not inconsistent with the properties of the original biological system. The basic equation of the theoretical model could be expressed in the form analogous to Hill's equation; the procedure by which the equations were derived and the interpretation of their parameters are mutually independent. The model also suggests a different interpretation of the dependence of the heat of shortening on other quantities of the system. It is necessary to consider these calculations and their results as preliminary with regard to the simplifying presuppositions and to the possible inaccuracies of the estimations of input data.

Animals↗
PubMed1982

Dynamic and steady state characteristics of the rabbit gastrocnemius muscle determined in series measurements.

1. Within the range of the given conditions of measuring static and dynamic properties of the rabbit gastrocnemius muscle the following results were obtained: a) the dependence of the maxima of isotonic shortening upon the relative length of the muscle at constant load is linear; b) the parameters of the non-linear dependence of the passive elastic force of the muscle upon its relative length (measured in series) were identified using asymptotic regression; c) the time course of isotonic contractions (at an interval from 0 to 0.3 s after the beginning of stimulation) could be satisfactorily approximated by responses of a linear system to a step-function; d) the time course of isometric contractions (at an interval from 0 to 0.3 s after the beginning of stimulation) could be closely approximated by responses of a linear system to a step-function. 2. The time constants of isotonic and isometric contractions were determined as the parameters of the corresponding linear systems. 3. The maximum rates of the isometric and isotonic contractions were determined as maxima of the first derivatives of the responses of the corresponding models. 4. The experimental set-up made it possible to compare the values of the parameters concomitantly followed at various muscle lengths and at various loads.

Animals↗
PubMed1980

Recording and evaluation of isotonic and isometric contractions of skeletal muscle in situ.

A procedure is described for obtaining records and identifying curves of isotonic and isometric contractions (both tetanic and twitch) of the gastrocnemius muscle of the rabbit in situ. The experimental conditions have made it possible to follow the above mentioned phenomena and to measure further parameters in series at sequentially altered muscle lengths and loads acting in the course of isotonic contractions.

Animals↗