Biomedical subjects

J M Elek

Publications and source records attributed to J M Elek.

5 recordsLinked to original sources

PubMed1995

Human motor units studied by intramuscular microstimulation.

We recorded twitch parameters of motor units of the human first dorsal interosseus muscle applying low-rate intramuscular microstimulation of motor axons (IMS) or spike-triggered averaging (STA). The values of contraction time, half-relaxation time and maximal rate of rise of force were significantly smaller in the STA studies. The reduction corresponded to the effect expected from partial twitch fusion. Twitch amplitudes, however, were not smaller than those in the IMS studies, indicating that other factors, such as motor unit synchronization, compensate for the effects of partial fusion.

Adult↗

PubMed1994

Assessment of human motor unit twitches--a comparison of spike-triggered averaging and intramuscular microstimulation.

We recorded twitches of single motor units (MUs) in the human first dorsal interosseus muscle using either spike-triggered averaging (STA; 236 MUs in 12 normal subjects) or low-rate intramuscular microstimulation of motor axons (IMS; 200 MUs in 20 normal subjects). We analysed twitch force (TF), maximal rate of rise of force (MRRF), contraction time (CT) and half-relaxation time (HRT). MRRF, CT and HRT were significantly smaller with STA than with IMS whereas TFs were fairly similar. Higher stimulus rates (up to 14 Hz) in IMS resembling the voluntary MU firing rates in STA were associated with a decrease of all twitch parameters because of partial fusion of the twitches (20 MUs). Concerning MRRF, CT and HRT, the reduced values matched those obtained by STA, suggesting that the underestimation of these parameters in STA can be mainly attributed to partial fusion. The reduction of TF with high rate IMS but not with STA reveals that other factors such as MU synchronization and non-linear force summation of MU contractions must counteract the effects of partial fusion in STA. We conclude that both STA and IMS are appropriate for assessing TFs in man while the time-dependent parameters MRRF, CT and HRT will be underestimated with STA.

Adult↗

PubMed1992

Parameters of human motor unit twitches obtained by intramuscular microstimulation.

Intramuscular microstimulation of motor axons was used to study twitch responses of 209 motor units (MUs) in the first dorsal interosseus muscle (FDI) of 20 normal subjects. Twitch peak force (TF), maximum rate of rise of force (MRRF), contraction time (CT) and one-half relaxation time (HRT) were determined. The distributions of TF (mean 16.0 mN, median 10.3 mN) and MRRF (mean 0.88 N s-1, median 0.66 N s-1) were skewed to the right with the majority of the values lying in the lower ranges, whereas CT (mean 63 ms, median 62 ms) and HRT (mean 61 ms, median 58 ms) were approximately normally distributed. TF was significantly correlated with MRRF, but not with CT in contrast with studies of cat gastrocnemius muscle. TF values were similar to those obtained by spike-triggered averaging in the same muscle. The method proved to be reliable and appropriate for use in patients. Examples of MU twitch parameters from three patients with chronic partial denervation of the FDI are described.

Adult↗

PubMed1991

Mechanical implications of paired motor unit discharges in pathological and voluntary tremor.

Paired motor unit discharges (PDs), i.e., two discharges of the same motor unit (MU) with short interval, and their relation to tremor amplitude were studied in the first dorsal interosseous muscle (FDI) of patients with parkinsonian or essential tremor and in normal subjects mimicking tremor. In both pathological and voluntary tremor, interdischarge intervals of PDs were inversely correlated with the amplitude of the subsequent tremor beat, i.e., PDs with shorter intervals were followed by higher tremor beats. To further assess their mechanical impact, PDs were simulated by applying paired stimuli to MUs of the FDI in normal subjects using intramuscular microstimulation. Following paired stimuli, summation of twitch responses was more than linear. This was also the case with the paired stimuli applied at a tremor-like repetition rate (5 Hz). These findings stress the importance of PDs for tremor expression.

Adult↗

PubMed1988

Silent periods in single orbicularis oculi motoneurones.

The activity of single motor units (MUs) of the orbicularis oculi muscle was recorded in normal volunteers. While the subject maintained a constant firing rate, electrical stimuli were applied to the ipsilateral supraorbital nerve. Peristimulus histograms were constructed showing 2 periods of discharge accumulation at times corresponding to the R1 and R2 component of the blink reflex, each followed by a silent period, called SP1 and SP2, respectively. Whereas SP1 may merely result from the synchronisation of discharges in the preceding R1, SP2 can only be explained by an inhibition of the motoneurone activity. These findings confirm the existence of silent periods in the orbicularis oculi muscle in spite of the absence of mechanisms probably responsible for silent periods in load-bearing muscles.

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