Biomedical subjects

J Celichowski

Publications and source records attributed to J Celichowski.

At least 37 records · Page 2Linked to original sources

PubMed1999

Fatigability of motor units estimated by changes in work performed during their repetitive stimulation during the fatigue test.

In numerous studies resistance to fatigue is evaluated by measuring the peak tension of motor units in muscle. In the present study, the work performed within successive tetani during the fatigue test of rat medial gastrocnemius motor units was estimated by assessing of the area under the tension record. Resistance to fatigue was evaluated by a modified fatigue index which is expressed as the ratio of the area under a tetanus recorded two minutes after maximal potentiation of tension has been reached to the area under this maximally potentiated tetanus. The values of this modified fatigue index were compared to the standard fatigue index which was taken as the ratio of peak tensions for corresponding tetani. For fast fatigable units, values of the modified fatigue index were significantly lower than those of the standard index. This observation resulted from changes in the shape of unfused tetani accompanying developing fatigue. These changes strongly influenced the area under the tension record whereas the peak tension of these tetani diminished less significantly. For slow and a part of fast resistant to fatigue units (with the standard fatigue index above 0.85) the modified fatigue index was slightly higher than the standard one although the difference was not significant. This phenomenon was due to the prolongation of relaxation which was visible in the last part of the fatigue test. It is being concluded that the modified fatigue index describes more precisely the fatigue-induced changes in tetani during the fatigue test than the standard fatigue index, especially in fast fatigable units.

Animals↗

PubMed1998

Relationship between mechanomyogram signals and changes in force of human forefinger flexor muscles during voluntary contraction.

In previous studies on mechanomyogram (MMG) signals no analysis of these signals accompanying force generation has been performed. Therefore, we have recorded MMG signals (previously referred to as muscle sound or acoustomyographic signals) during voluntary contractions of forefinger flexor muscles in 31 young subjects. These subjects made contractions to produce force records of triangular or trapeziform shape. The peak target force amounted to 10, 20 or 40 N which represented less than 40% of maximal voluntary contraction. The MMG signals during the transient phases of force generation at three different rates were analysed. The MMG intensity level calculated for MMG records and the peak-to-peak amplitude of MMG signals correlated with both the velocity of force increase and the contraction force. The occurrence of the strongest MMG signals corresponded to changes in contractile force. Therefore, it is suggested that measurements of these parameters could be a useful tool in studies of changes in contractile force.

Adult↗

PubMed1998

The influence of a doublet of stimuli at the beginning of the tetanus on its time course.

The influence of a pair of stimuli generated in a short time sequence (doublet) at the beginning of stimulation on the time course of the following tetanus was investigated. Experiments were performed on single motor units in rat's medial gastrocnemius. The doublet evoked an increase in tetanic tension, tetanic fusion and the area under tension record. These effects were measured in tetani fused to varying degrees. It was found that for all types of motor units the strongest influence of the doublet was observed in half-fused tetani. Moreover, the doublet influenced the first part of tetanus significantly more as compared to the second. Slow motor units showed greater sensitivity of the tension and the tetanus area to the doublet than fast units. The results show that slow units are characterized by better summation of their tension at the beginning of a tetanus.

Animals↗

PubMed1998

The rate of changes in tension within fused tetani of single motor units in rat medial gastrocnemius muscle.

The time course of fused tetani of three main types of motor units: slow (S), fast resistant (FR) and fast fatigable (FF) was studied in the rat medial gastrocnemius. The rate of tension generation and of the relaxation within a tetanus was measured under isometric conditions. These measurements were performed at three points during both the contraction and relaxation: the beginning, the middle and the end of the phase of changes in tension. Significant differences were found in the rate of tension changes between fast and slow units. Comparison of FF and FR units showed less pronounced differences in their rates of the contraction and the relaxation. Moreover, slow units showed significantly greater slowing of both the contraction and relaxation within a tetanus in relation to the speed of their twitch when compared to fast motor units. The rate of changes in tetanic tension correlated to twitch time parameters and to tension generated during twitch or tetanus. The results point out that the well known difference in the speed of twitch contraction between fast and slow units is also visible in their fused tetani.

Animals↗

PubMed1997

Changes in tension-frequency relationship of motor units induced by their activity in rat muscle.

In 57 motor units of rats' medial gastrocnemius muscle the influence of activity on the course of 10 successively repeated tension-frequency curves (T-f curves) was observed. In slow motor units the steep parts of successive T-f curves usually shifted slightly towards higher frequencies. However, in some slow units of relatively short contraction these T-f curves shifted towards lower frequencies. In fast units, especially those of the FF type, more marked changes were observed in T-f curves. At first, a shift of the second to third curve towards lower frequencies was observed. Curves then shifted progressively towards higher frequencies. In all motor units greater changes in tension could be observed in unfused tetani than in fused tetani. In some motor units the tension of fused tetani showed a progressive decrease. Changes in the course of T-f curves related to changes in contraction and relaxation times. The results presented here explain how the duration of the activity can change the sensitivity of motor unit tension to the frequency of stimuli. The importance of the changes observed in the T-f relation in the process of fatigue is discussed.

Animals↗

PubMed1996

Axonal conduction velocity of motor units of rat's medial gastrocnemius muscle.

Axonal conduction velocity and its relations to different contractile properties of motor units of medial gastrocnemius muscle were investigated in nine Wistar rats anaesthetized with pentobarbitone. Functionally isolated motor units were identified as slow (S), fast resistant (FR) and fast fatigable (FF). Axons of S motor units conducted significantly more slowly than of fast units, while there was considerable overlap between conduction velocities measured for FR and FF types. The mean values of conduction velocity were 50.9 m/s for S, 68.9 m/s for FR and 71.3 m/s for FF type motor units. Strong and significant negative correlation between conduction velocity and contraction time as well as half-relaxation time was demonstrated. However, only a weak correlation between conduction velocity and twitch tension, tetanic tension or fatigue index was found. The multiple regression analysis revealed that the major factor to determine conduction velocity was contraction time.

Action Potentials↗

PubMed1996

Changes in fusion index during the fatigue test of fast motor units in the medical gastrocnemius muscle of the rat.

Changes in the fusion of tetani were investigated in fatigue tests of 50 fast motor units of the rat medical gastrocnemius muscle. Fusion of the tetani was measured using the fusion index, being the ratio of the tension to which motor unit relaxed before the last component of tetanus to the peak tension of the last component. In both types of fast units (fast fatigable and fast resistant) the changes in the fusion index were similar to those in tetanic tension: first they increased and then decreased. However, the increase of the fusion index was longer than that of tension and the subsequent decrease in the fusion index smaller than that of tetanic tension. Furthermore, the initial increase in the fusion index of fast fatigable motor units was greater than in the tension. The dependence of the fusion index on twitch time enables the analysis of the influence of changes in the twitch time on changes in tension of unfused tetani observed during activity of fast motor units.

Animals↗

PubMed1995

Changes in tension of slow motor units in rat medial gastrocnemius during constant-rate stimulation at different frequencies.

Changes in tension of slow motor units in the medial gastrocnemius muscle of the rat were measured and compared in three fatigue tests, each of 4 min duration. In one of these tests motor unit tetani were evoked by repeated trains of stimuli of the standard frequency, 40 Hz, while in other tests frequencies of 20 and 60 Hz were used. Tetanic tension initially decreased in the majority of units during these three tests, then potentiated and, in the last part of the fatigue test, the tension was normally stable. Initial changes in tension were greatest in the fatigue tests with the lowest stimulation frequency (20 Hz) and smallest or even absent during tests with the stimulation frequency of 60 Hz. Moreover, initial changes in tension occurred for the longest period of time when the lowest frequency of stimulation (20 Hz) was used. Some of the motor units showed a slow decrease in tension in the last part of tests, especially when frequencies of 60 and 40 Hz were used. These results show that the tension of repeated unfused tetani of a slow motor unit is not constant, even during constant frequency stimulation, and changes in tension are greater in less fused tetani.

Animals↗

PubMed1995

The relationship between fusion index and stimulation frequency in tetani of motor units in rat medial gastrocnemius.

The relationship between tetanic fusion and frequency of stimulation was investigated in 81 motor units of the rat medial gastrocnemius. A fusion index was calculated for tetani evoked by trains with constant frequency stimuli. This index is expressed as the ratio of a/b, where a is the distance from a baseline to the maximal relaxation before the last component of tetanus and b is the peak amplitude of the last component. The fusion-frequency relation has a sigmoid shape. The steep portion of the relation corresponds to lower frequencies for slow motor units than for fast units. Among the fast units, FR motor units are fused at somewhat lower frequencies than FF ones. However, the increase in fusion index per 1 Hz change in frequency of stimulation for the three types of motor units is similar. This observation suggests a similar course of fusion within different motor units. The fusion index shows a correlation with the contraction time as well as with the half-relaxation time.

Animals↗

PubMed1994

Dual projections of the ventromedial lamina VI and the medial lamina VII neurones in the second sacral spinal cord segment to the thalamus and the cerebellum in the cat.

Neurons of origin of the crossed spinocerebellar and/or spinothalamic tracts giving off axon collaterals at supraspinal levels were antidromically identified and labeled with horseradish peroxidase in lower sacral spinal cord segments of cats. Their cell bodies were located mainly in the medial part of lamina VII and rarely in the ventromedial aspect of lamina VI. In the S2 segment 77 neurons with axons in the opposite dorsolateral funiculus were recorded; 36 of them were invaded from only the thoracic level, 21 from both the thoracic level and the restiform body, 3 from both the thoracic level and the thalamus, and 17 from both the thoracic level, the restiform body and the thalamus on the contralateral side. These termination areas suggest that the S2 neurons under study transmit peripheral signals of proprioceptive, exteroceptive and nociceptive sensations.

Animals↗

PubMed1994

Primary and secondary afferent discharges from the same spindle during chain fibre contraction in cat tenuissimus muscle.

Pairs of Ia and II afferent fibres supplying primary and secondary endings lying in the same tenuissimus spindles were prepared in barbiturate anaesthetized cats in order to compare the variability in the rhythm of discharge of the two endings during responses elicited by the contraction of different intrafusal muscle fibres, especially by chain fibres. In these spindles, the intrafusal muscle fibres supplied by single static gamma-axons were identified with a recently developed technique based on the types of primary ending activation observed during gamma stimulation at 30 and 100 stimuli/s. The responses of the secondary endings to contraction of chain fibres either alone or with bag2 fibres were smaller and much more regular than the responses of the primary endings lying in the same spindles. This difference is probably related to the position of secondary endings along the intrafusal muscle fibres and to the mechanical properties of the muscle fibre regions on which the terminals lie. The dynamic properties of the encoding site of primary afferent impulses probably contribute to the difference. The different degrees of variability observed among secondary ending responses elicited either by chain fibres alone or by chain and bag2 fibres are not related to the type of activated intrafusal muscle fibres.

Animals↗

PubMed1994

Distribution of static gamma axons in cat peroneus tertius spindles determined by exclusively physiological criteria.

1. The intrafusal muscle fiber(s) activated in cat peroneus tertius spindles by single static gamma (gamma s) axons were identified by exclusively physiological criteria based on the different contractile properties of chain and bag2 fibers. 2. The identification rested both on the features of primary ending discharges observed during gamma s electrical stimulation at a rate of 30 pulses per second (stimulation at 30/s) and on cross-correlograms constructed during stimulation at 100/s. Three types of primary ending activation could be distinguished. 3. Type F (fast) activations are characterized, at 30/s, by either a 1-to-1 driving or a very irregular increase in firing arising from a level close to the frequency of stimulation and by the presence in cross-correlograms of significant peaks. They are ascribed to chain fibers whose contractions, at 30/s, present large oscillations and, at 100/s, are still incompletely fused. 4. Type S (slow) activations are characterized, at 30/s, by a sustained and generally regular increase in firing and by the absence of significant peaks in cross-correlograms constructed during stimulation at 100/s. They are ascribed to bag2 fibers whose contractions are nearly fused at 30/s and completely fused beyond 60-70/s. 5. Type M (mixed) activations are characterized, at 30/s, by an irregular increase of discharge above a level distinctly higher than the frequency of stimulation and by the presence of significant peaks in cross-correlograms. They are ascribed to the coactivation of chain and bag2 fibers for two reasons: first, they have some features of both type F and type S activations; and second, they are readily reproduced by stimulating together two axons supplying the same spindle, one exerting a type F activation, the other a type S activation. 6. In seven experiments the distribution of 42 single gamma s axons was determined by observing the type of activation they exerted on several spindles (from 3 to 6). Thirty-five axons (83%) were classified "nonspecific" because the type of activation (F, S, or M) varied from one spindle to the other. Seven axons (17%) were classified "specific" because the type of activation was the same in all spindles: either type F for five axons (12%) or type S for two axons (5%). A statistical analysis of the distribution of all activations showed that the proportions of specific axons were not significantly different from those predicted by chance.

Animals↗

PubMed1993

Twitch/tetanus ratio and its relation to other properties of motor units.

The ratio of single twitch tension to maximal tetanic tension (Tw/Tet ratio) represents one of the physiological properties of single motor units. In our study, in agreement with the results of other studies, the mean Tw/Tet ratio of slow motor units was lower than that of fast motor units. But we found that the Tw/Tet ratios of the slow motor units with twitch tension between 0.75 and 1.5 g were higher than those of fast motor units with twitch tension in the same range. A significant linear relation between Tw/Tet ratio and twitch tension was obtained for the three types of motor units. This relationship could be due to the increasing number of muscle fibres within a motor unit with the twitch tension.

Animals↗

PubMed1993

Load compensatory response of external intercostal muscles during assisted ventilation in rabbits.

Phrenic and external intercostal motor responses to inspiratory load were studied in anaesthetized rabbits and after bilateral vagotomy. Animals were ventilated with a phrenic nerve driven respirator set at different gains, i.e. volume to phrenic-signal ratio. Load was imposed by occluding the trachea at the end of expiration for the period of one breath. It was found that vagally mediated low threshold facilitation may be observed in rabbits on late-inspiratory external intercostal motor units. After vagotomy, external intercostal EMG response to load depended on the given of the servorespirator set during the period of assisted ventilation.

Adaptation, Physiological↗

PubMed1992

Motor units of medial gastrocnemius muscle in the rat during the fatigue test. II. Changes in the time course of sequential tetani of fatigue test.

Seventy motor units (MUs) of 3 types: fast fatigable (FF), fast resistant to fatigue (FR) and slow (S) were studied in medial gastrocnemius muscle of the rat. The fatigue test time course showed significant variability. It was found, that slow MUs, apart from greater resistance to fatigue, had less variable tetanic time course during the fatigue test than the fast MUs. The tetani of fast MUs were unfused with a marked sag. At the beginning of fatigue test the tension of fast motor units increased. The increase appeared to be greater and more rapidly developing in FF than in FR MUs. In the next part of fatigue test, when decrease in the tetanic tension was observed, the tetanic time course was changing in FF but not in FR MUs. During the first tetanus of fast MUs the sag exhibited a significant variability of its time course. In a proportion of fast MUs the sag appeared again when their tension was potentiated but in such a case it showed a different time course. The obtained results point to high degree of specialization of MUs in the studied muscle.

Animals↗

PubMed1992

The dependence of the twitch course of medial gastrocnemius muscle of the rat and its motor units on stretching of the muscle.

The relationship between the force of a single twitch of the medial gastrocnemius muscle of the rat and contraction and half-relaxation times, on one hand, and the load of the muscle on the other, was studied. Twitches of the whole muscle and its individual motor units were induced. The optimal load, at which the majority of motor units reached the greatest twitch force, was 10 G. Mean optimal loads for twitches of different types of motor units were very similar. Slow motor units reached a slightly greater twitch force at greater loads (12.5 G) than at 10 G. However, the optimal load for the twitch of the whole muscle was much greater. It was 47 G on the average. The contraction and half-relaxation times of motor units, as well as of the whole muscle, became longer as the force stretching the muscle increased. Half-relaxation time changed more rapidly than contraction time. Both parameters were undergoing the greatest changes in slow motor units.

Animals↗

PubMed1992

Motor units of medial gastrocnemius muscle in the rat during the fatigue test. I. Time course of unfused tetanus.

Time course of tetanus recorded during 40 Hz stimulation was examined on 70 motor units (MUs) of medial gastrocnemius muscle in 41 rats. Three types of MUs were distinguished: slow(S), fast resistant to fatigue (FR) and fast fatigable (FF). In fast MUs of either type, the stimulation induced unfused tetanus with noticeable sag. It was found that in cases of tetani in FF MUs, the sag developed earlier than in FR MUs. Timing of tetanic peak before the sag appeared correlated with contraction time. Some fast MUs demonstrated a distinct time course of tetanus: the weakly accentuated sag appeared early and it was followed by a relatively significant rise in tetanic tension. However, in slow MUs, 40 Hz stimulation induced fused or fused-like tetani. In these MUs the sag was never observed. The obtained results indicate the relation between the sag time course in tetanus and the extent of tetanus fusing.

Animals↗

PubMed1991

Changes in motor unit action potentials during the fatigue test.

The studies were performed on medial gastrocnemius motor units of the rat. Changes in amplitude, duration and latency of motor unit action potentials were monitored in the course of fatigue test in the three types of motor unites: FF (fast twitch, fatigable), FR (fast twitch, resistant), and S (slow twitch, resistant) motor unit. In a majority of the motor units the amplitude of action potential decreased. The most pronounced decrease took place in FF units, less pronounced one in FR units, while in S type motor units the decrease was insignificant. However, in a part of investigated motor units the amplitude of their action potential transiently increased at the beginning of the fatigue test and, then decreased or was maintained at the same level till the end of the fatigue test. In a few motor units, particularly the slow ones, no changes in action potential amplitude were observed. In the studied material, a decrease in action potential amplitude was on the average less pronounced than a decrease in tetanus tension in the course of the fatigue test. In a majority of studied motor units the duration of action potential was becoming prolonged, which was most pronounced in FF type motor units and least pronounced in S type ones. In few slow motor units the duration showed no alterations. Changes in action potential duration were much more marked than changes in their amplitude. The changes in action potential in fast motor units were less pronounced than changes in their tetanus tension, while in the slow motor units they resembled each other in intensity. Comparison of motor unit action potential changes with changes in their tetanic tension in the course of fatigue test demonstrated no clear-cut relationship between the two phenomena.

Action Potentials↗