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1
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Interspecies differences in the force-frequency relationship of the medial gastrocnemius motor units

100%
Mrowczynski W., Celichowski J., Krutki P.
Journal of Physiology and Pharmacology
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2006
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tom 57
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nr 3
Single, functionally isolated motor units were studied in the medial gastrocnemius (MG) muscle of cats and rats. Axons of their motoneurons were stimulated with trains of pulses at frequencies increasing from 1 to 150 Hz and forces developed by muscle fibers were measured and force-frequency curves were compared between species. The following observations were made: (1) the most steep parts of curves (related to unfused tetani of motor units) begun at lower frequencies of stimulations in all types of feline motor units, (2) for fast motor units, the same relative values of force of unfused tetani were achieved at significantly lower frequencies of stimulations in the cat than in the rat. Twitch time parameters of both species influenced the course of force-frequency curves. It was showed that the contraction times of feline units varied in the wide range (21-81 ms), and these units reached 60% of the maximum force at stimulation frequencies between 10 and 38 Hz. On the other hand, contraction times of rat units ranged from 10 to 34 ms, whereas stimulation frequencies necessary to reach 60% of the maximum force varied considerably, from 12 to 65 Hz. The correlations between the above parameters were found for motor units of each species. However, the regression lines drown for the collected population of cat and rat units did not form linear continuity. Thus it seems that interspecies differences in the twitch contraction times do not fully explain different force-frequency relationships in mammalian skeletal muscles.
2
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Relationship between the tension-time area and the frequency of stimulation in motor units of the rat medial gastrocnemius muscle

100%
Celichowski J., Grottel K., Bichler E.
Journal of Physiology and Pharmacology
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2000
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tom 51
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nr 2
3

The area under the record of contractile tension: estimation of work performed by a contracting motor unit

84%
Celichowski J., Grottel K., Bichler E.
Acta Neurobiologiae Experimentalis
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1998
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tom 58
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nr 2
4
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Force generated by fast motor units of the rat medial gastrocnemius muscle during stimulation with pulses at variable intervals

84%
Krutki P., Pogrzebna M., Drzymala H., Raikova R., Celichowski J.
Journal of Physiology and Pharmacology
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2008
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tom 59
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nr 1
During natural contractions of a muscle, motor units (MUs) are activated by irregular discharge patterns of motoneurones. The aim of this study was to analyze changes in contractile forces of MUs following patterns of stimulation at variable frequency. Experiments were performed on 33 functionally isolated MUs of the fast-type in the medial gastrocnemius (MG) muscle of adult Wistar rats, under pentobarbital anaesthesia. The MUs forces evoked at five different regular stimulation patterns of constant frequencies were compared to forces generated during five random patterns of irregular stimulation with the same mean values of interpulse intervals, between 10 and 75 ms, and variability of these intervals of ± 50% in each case. These values cover the natural range of the preferred firing rates of the MG motoneurones from unfused to nearly fused tetanic contractions. Analysis of changes in tetanic forces indicated a linear relationship between the interpulse interval as well as the initial level of the force and the amplitude of the force increase of the next contraction. It was demonstrated that variability of the instantaneous tetanic force during the irregular discharge pattern depends on the level of tetanic fusion. Moreover, it was demonstrated that for low and moderately-fused tetani, effectiveness of a MU contraction (expressed as the force-time area) is considerably higher for contractions evoked by irregular stimulation patterns. On the basis of the results of this study it was supposed that during voluntary contractions, the influence of changes in the motoneuronal firing rate on the motor unit force depends on the initial level of force.
5
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The rate of changes in tension within fused tetani of single motor units in rat medial gastrocnemius muscle

84%
Celichowski J., Bichler E.
Journal of Physiology and Pharmacology
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1998
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tom 49
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nr 4
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