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  • 1
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract An earlier proposed model of the de-efferented muscle spindle mechano-receptors has been developed further to simulate the effects of the dynamic fusimotor (γ D) activation of the group Ia afferents (primary endings). The rate sensitivity of the original second order receptor model might be increased simply by increasing the overall viscous damping of the simulated polar regions of the nuclear bag fibre. However, adequate simulation of the typical time course of the stretch response of the primary endings during γ D-activation required a subdivision of the polar regions into an active and a passive part. A reasonable behaviour of the model was obtained by simulating a local contraction covering about 50–90% of the polar regions of the nuclear bag fibres. The ramp response of the model showed a “quick” rate response component that increased by increasing the rate of the simulated stretch. This component was not significantly influenced by the simulated γ D-activation. A “slow” rate component appeared to increase approximately in the same proportion as the intensity of the simulated γ D-activation. The behaviour of the model closely corresponds to that of the biological prototype. The study demonstrates that the electrophysiological effects of activating the dynamic fusimotor fibres are indeed compatible with peripheral mechanical events associated with contraction phenomena within the polar regions of the nuclear bag intrafusal muscle fibres.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 10 (1972), S. 189-200 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract An earlier proposed mechanical model of the de-efferented muscle spindle endings has been developed further in order to study whether the functional effects of activating the static fusimotor fibres may be accounted for by relatively simple mechanical events in the intrafusal muscle fibres. Particular attention has been paid to important controversial problems related to the processes involved in the fusimotor activation of the mammalian muscle spindles. In order to develop an adequate model, preliminary simulation studies of the functional effects of various reasonable modifications of the original “de-efferented” model were first carried out by means of a convenient direct electronic analogue of the mechanical system. The following results apparently reflect pertinent details about the peripheral receptor mechanisms associated with the activation of the static fusimotor fibres: (1) The γ s-activation is most adequately accounted for by mechanical events occurring in the nuclear chain fibres. (2) Any uniform chain fibre contraction fails to account for the effects of the γ s-activation. (3) The simulation of a local chain fibre contraction could apparently account for all significant effects of the γ s-activation. (4) A reasonable increase of the position sensitivity and the vibration sensitivity of both the primary and the secondary endings could be accounted for by increasing the stiffness of about 1/4–1/2 of the length of the simulated nuclear chain fibre by a factor of about 2–10. (5) The powerful modulation of the background discharge of the receptor endings that is associated with the γ s-activation could be accounted for by an independent contraction force related to the intensity of the static fusimotor activity. (6) The model predicts a decrease of the rate sensitivity of the primary endings (group Ia) and a slight increase of the (moderate) rate sensitivity of the secondary endings. (7) By an adequate selection of the parameters, the simulated γ s-activation showed a negligible influence on the absolute level of the dynamic phase of the ramp response of the simulated primary endings, in spite of a considerable increase of the steady state (background) discharge before and after the termination of a simulated stretch.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 6 (1970), S. 205-213 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Summary With reference to experimental data and the failure of earlier proposed first order linear models of mammalian muscle spindles, a second order mechanical model of de-efferented primary endings is studied. The model takes into account the presence of two different types of intrafusal muscle fibres in a complete spindle organ. It further allows the incorporation of different gain of the mechano-electric conversion into a depolarization of the sensory terminals innervating the two types of fibres. It is shown that a closer approximation to the behaviour of the biological prototype is obtained if the transducer gain of the branch corresponding to the nuclear bag intrafusal fibres is chosen significantly higher than that corresponding to the nuclear chain branch. The marked nonlinear behaviour of muscle spindle primary endings as recently reported by Matthews and Stein (1968, 1969) is interpreted as a saturation effect of the high gain mechano-electric transducer of the nuclear bag branch. The saturation is considered to reflect a condition of complete depolarization of these sensory terminals. If a higher transducer gain actually is present, a complete depolarization of these terminals would occur at a lower degree of mechanical deformation than for the nuclear chain terminals. The mechano-electric transducer system of the nuclear chain fibres might thus behave approximately linearly within a larger range of input amplitudes. The greatly reduced gain of the primary endings at large emplitudes of imposed muscle vibrations as observed experimentally (Matthews and Stein, 1968, 1969) may thus be accounted for by the transducer gain of the nuclear chain fibres alone.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 7 (1970), S. 72-77 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Summary The depolarization of the sensory terminals of muscle spindle primary endings is studied in terms of a simplified core conductor model of the system. The terminals branching from a group Ia afferent fibre have different geometrical structures, depending on whether they innervate the nuclear bag or the nuclear chain intrafusal fibres of a muscle spindle. The depolarization of the two different structures as a function of space and time is analysed by digital simulation technique. The studies indicate that the tapered core conductor model of the bag-fibre terminals responds faster than a uniform system similar to the terminals innervating the nuclear chain fibres. The steady state response, on the other hand, appears to supply a more effective depolarization in the case of a uniform system with otherwise equivalent parameters. The results suggest that the bag fibre terminals are best suited for converting dynamical stimuli into an electrical signal, whilst the chain fibre terminals seem to yield a more effective steady state response. The results are discussed in relation to the functional properties of the mammalian muscle spindles and in relation to the earlier proposed models of the mechanical system represented by the two types of intrafusal muscle fibres.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 7 (1970), S. 122-128 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Summary A mechano-electric model of the secondary endings of the mammalian muscle spindle receptors has been developed. The model involves a mechanical system with second order transfer dynamics connected to a zero order mechano-electric transducer with constant gain. The mechanical system is supposed to describe the viscoelastic properties of the intrafusal muscle fibres, and this part of the model is identical to that used in connection with an earlier proposed model of the primary endings (Rudjord, 1970). The general transfer properties of the model are derived, together with a description of the particular response components obtained during a linear extension of the mechanical system. A simple direct electronic analogue was used for studying the effects of the individual parameters and for a preliminary estimate of an adequate set of parameter values. With appropriate parameter values, a close correspondence could be obtained between the behaviour of the model and the typical response properties of the secondary endings of the muscle spindles. The order of magnitude of the best parameter fit also appeared to correspond to the values previously found to yield an adequate description of the transfer properties of the primary endings. It is further shown that for the best fit of the mechanical parameters, the secondary ending model may be approximated by a simple first order system with lead-lag transfer behaviour. The transfer properties of this simplified model appear to agree with the reported response properties of typical secondary ending receptors except for extreme rates of stretch or very high vibrational frequencies of stretch during which the simplifying approximation evidently does not apply.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1741-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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