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  • 1
    Electronic Resource
    Electronic Resource
    Die rhythmogenese der atmung beschrieben mit hilfe des Lotka-Volterra-modells: Experimente und simulation (1977)
    Springer
    Biological cybernetics 26 (1977), S. 81-91 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The aim of the present study was to simulate respiratory responses to vagal stimulation using theLotka-Volterra model, a system of two simultaneous non-linear differential equations. The experiments were carried out on vagotomized, artificially ventilated rabbits. Low-threshold, fast-conducting vagal afferent fibres were stimulated with relatively high frequencies (100–200 cps) at various stages of the respiratory cycle. The phrenic activity was recorded in order to analyze the latency and duration of exspiratory reactions with regard to the time relation between stimulatory and respiratory phase. The onset of the stimulatory phase was progressively delayed with regard to the onset of the inspiratory or expiratory phase, stimulation ceasing at the onset of the ensuing respiratory cycle. Real-time simulation was carried out on a hybrid computer. The vagal stimulation was imitated by altering the values of one of the system parameters. The onset of parameter changes was progressively delayed with regard to the onset of the inspiratory or expiratory phase of the model, and the parameters were reset to the initial values as soon as the following respiratory phase began. Comparison of experimental and model data revealed satisfactory agreement between the time-dependent system properties of both respiratory centre and model. The results are discussed with regard to the central nervous processes underlying the genesis of respiratory rhythm. Further light is also thrown on the central processing of afferent vagal input subserving inspiratory inhibitory reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00801212
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  • 2
    Electronic Resource
    Electronic Resource
    Size principle and information theory (1997)
    Springer
    Biological cybernetics 76 (1997), S. 11-22 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract. The motor units of a skeletal muscle may be recruited according to different strategies. From all possible recruitment strategies nature selected the simplest one: in most actions of vertebrate skeletal muscles the recruitment of its motor units is by increasing size. This so-called size principle permits a high precision in muscle force generation since small muscle forces are produced exclusively by small motor units. Larger motor units are activated only if the total muscle force has already reached certain critical levels. We show that this recruitment by size is not only optimal in precision but also optimal in an information theoretical sense. We consider the motoneuron pool as an encoder generating a parallel binary code from a common input to that pool. The generated motoneuron code is sent down through the motoneuron axons to the muscle. We establish that an optimization of this motoneuron code with respect to its information content is equivalent to the recruitment of motor units by size. Moreover, maximal information content of the motoneuron code is equivalent to a minimal expected error in muscle force generation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004220050317
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Influences of morphology and topography of motoneurons and muscle spindle afferents on amplitude of single fiber excitatory postsynaptic potentials in cat (1989)
    Springer
    Experimental brain research 74 (1989), S. 493-500 
    Details
    ISSN: 1432-1106
    Keywords: Spinal cord ; Motoneurons ; Single-fiber e.p.s.p.s ; Muscle spindle afferents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Excitatory postsynaptic potentials (e.p.s. p.s) elicited by impulses in single muscle spindle afferent fibers from the medial gastrocnemius (m.g.) muscle were recorded intracellularly from homonymous and heteronymous motoneurons in order to study factors that influence the amplitudes of such responses. Impulses in large afferent fibers elicited larger single-fiber e.p.s.p.s than those in smaller afferents. Mean e.p.s.p. amplitudes were related exponentially to afferent conduction velocities of both Ia and spindle group II fibers. The closer a motoneuron was to the spinal entry point of an afferent fiber, the larger was the mean e.p.s.p. amplitude evoked in it. Impulses in the same afferent fiber elicited larger e.p.s.p.s in small than large motoneurons when the two cells were located at the same craniocaudal levels. Other factors being equal, the single-fiber e.p.s.p.s evoked in homonymous and heteronymous motoneurons were approximately equal in amplitude. Relatively simple morphological and topographical explanations for the findings were advanced and their functional significance for orderly recruitment in partitioned and unpartitioned reflexes was described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00247351
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  • 4
    Electronic Resource
    Electronic Resource
    A comparison of homonymous and heteronymous connectivity in the spinal monosynaptic reflex arc of the cat (1989)
    Springer
    Experimental brain research 74 (1989), S. 480-492 
    Details
    ISSN: 1432-1106
    Keywords: Spinal cord ; Motoneurons ; Spindle Ia afferents ; Spindle group II afferents ; Connectivity ; Species recognition ; Topographic connectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Multi-unit spike triggered averaging was used to determine functional connectivity between spindle afferent fibers from the medial gastrocnemius muscle and the motoneurons innervating the medial (homonymous connections) and the lateral gastrocnemius-soleus muscle (heteronymous connections). As many as 288 possible connections between 24 motoneurons and 12 afferent fibers were studied in single, acute experiments. The influences of morphological and topographical factors, as well as of motoneuron species on functional connectivity were analysed. The probability that a motoneuron would receive functional connections from a given population of afferent fibers was related to its size and its proximity to the spinal entry level of the afferent fibers. The faster the axonal conduction velocity of the motoneuron (i.e. the larger the motoneuron) and the closer its location to the entry zone of the afferent fibers, the higher was its probability of receiving functional connections. The greater the conduction velocity (i.e. diameter) of a stretch receptor afferent fiber, the higher was its probability of making functional connections with motoneurons. These relationships were qualitatively similar for homonymous and heteronymous connections. 58% (233/399) of the Ia and group II afferents (combined) had functional connections with homonymous motoneurons, 32% (75/234) with heteronymous motoneurons. However, homonymous and heteronymous motoneurons of similar sizes were equally likely to receive functional connections when located at the same craniocaudal level. Differences in the locations and mean sizes of homonymous and heteronymous motoneurons however, cannot account completely for the observed overall differences in homonymous and heteronymous connectivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00247350
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    Paper (German National Licenses)
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