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1

Differences between małe and female motor unit properties of the medial gastocnemius muscle in rat

100%
Drzymala H., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2005
|
tom 65
|
nr 3
2
Content available remote

Differences between properties of male and female motor units in the rat medial gastrocnemius muscle

100%
Celichowski J., Drzymala H.
Journal of Physiology and Pharmacology
|
2006
|
tom 57
|
nr 1
Differences between motor units in hindlimb locomotor muscles of male and female Wistar rats were studied. The contractile and action potential properties of various types of motor units as well as proportions of these units in the medial gastrocnemius muscle were analyzed. Experiments were based on functional isolation and electrical stimulation of axons of single motor units. Composition of motor units was different for male and female subjects, with higher number of the fast fatigable and lower number of slow type units in male animals. The contraction and the half-relaxation times were significantly longer in male motor units, what might be due to differences in muscle size. Slower contraction of male motor units likely corresponds to lower firing rates of their motoneurons. On the other hand, no significant differences between sexes were observed with respect to force parameters of motor units (the twitch and the maximum tetanus forces), except the fast resistant units (higher force values in male muscles). The mass of the muscle was approximately 1.5 time bigger in male rats. However, the mean ratio of motor unit tetanus force to the muscle mass was almost twice smaller in this group, what indirectly suggests that muscles of male rats are composed of higher number of motor units. Finally, female muscles appeared to have higher fatigue resistance as the effect of higher proportion of resistant units (slow and fast resistant) and higher values of the fatigue index in respective motor unit types. The motor unit action potentials in female rats had slightly lower amplitudes and shorter time parameters although this difference was significant only for fast resistant units.
3

Nonlinear summation of motor unit forces in rat medial gastrocnemius muscle

81%
Drzymala H., Celichowski J., Krutki P.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
4

Influence of location of single motor unit within a muscle on shape of a mechanomyographic signal

81%
Celichowski J., Kaczmarek P., Drzymala H., Kasinski A.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
5

The successive contractions subtracted from unfused tetanus of fast and slow motor units

71%
Pogrzebna M., Raikova R., Drzymala H., Celichowski J., Aladjov H.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
6

Force generated by fast motor units during stimulation with pulses at variable intervals

71%
Krutki P., Pogrzebna M., Drzymala H., Raikova R., Celichowski J.
Acta Neurobiologiae Experimentalis
|
2007
|
tom 67
|
nr 3
7
Content available remote

Force generated by fast motor units of the rat medial gastrocnemius muscle during stimulation with pulses at variable intervals

71%
Krutki P., Pogrzebna M., Drzymala H., Raikova R., Celichowski J.
Journal of Physiology and Pharmacology
|
2008
|
tom 59
|
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.
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