Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG.

The purpose of the study was to evaluate the influence of selected physiological parameters on amplitude cancellation in the simulated surface electromyogram (EMG) and the consequences for spike-triggered averages of motor unit potentials derived from the interference and rectified EMG signals. The surface EMG was simulated from prescribed recruitment and rate coding characteristics of a motor unit population. The potentials of the motor units were detected on the skin over a hand muscle with a bipolar electrode configuration. Averages derived from the EMG signal were generated using the discharge times for each of the 24 motor units with lowest recruitment thresholds from a population of 120 across three conditions: 1) excitation level; 2) motor unit conduction velocity; and 3) motor unit synchronization. The area of the surface-detected potential was compared with potentials averaged from the interference, rectified, and no-cancellation EMGs. The no-cancellation EMG comprised motor unit potentials that were rectified before they were summed, thereby preventing cancellation between the opposite phases of the potentials. The percent decrease in area of potentials extracted from the rectified EMG was linearly related to the amount of amplitude cancellation in the interference EMG signal, with the amount of cancellation influenced by variation in excitation level and motor unit conduction velocity. Motor unit synchronization increased potentials derived from both the rectified and interference EMG signals, although cancellation limited the increase in area for both potentials. These findings document the influence of amplitude cancellation on motor unit potentials averaged from the surface EMG and the consequences for using the procedure to characterize motor unit properties.     

Axis differentiation in two South American Nothofagus species (Nothofagaceae)

An analysis was carried out on the length, diameter and number of leaves, and the ratios between these variables for current-year growth units (sibling growth units) derived from different nodes of previous-year growth units (parent growth units) of young Nothofagus dombeyi and Nothofagus pumilio trees. Changes in sibling growth unit length, diameter, and number of leaves with position on the parent growth unit were assessed. In both species, sibling-growth unit morphology varied according to both the axis type of the parent growth unit and the position of the sibling growth unit on its parent growth unit. For the largest parent growth units, the length, diameter and number of leaves of their sibling growth units decreased from distal to proximal positions on the parent growth unit. Distal sibling growth units had a more slender stem and longer internodes than proximal sibling growth units. Sibling growth units in equivalent positions tended to have a more slender stem for N. dombeyi than for N. pumilio. Long main-branch growth units of N. pumilio had longer internodes than those of N. dombeyi; the converse was true for shorter growth units. The growth unit diameter/leaf number ratio was consistently higher for N. pumilio than for N. dombeyi. Nothofagus pumilio axes would go through a faster transition from an 'exploring' morphology to an 'exploiting' morphology than N. dombeyi axes. Within- and between-species variations in growth unit morphology should be considered when assessing the adaptive value of the branching pattern of plants.     

Neuromuscular organization of avian flight muscle: architecture of single muscle fibres in muscle units of the pectoralis (pars thoracicus) of pigeon (Columba livia)

The M. pectoralis (pars thoracicus) of pigeons (Columba livia) is comprised of short muscle fibres that do not extend from muscle origin to insertion but overlap ''in-series''. Individual pectoralis motor units are limited in territory to a portion of muscle length and are comprised of either fast twitch, oxidative and glycolytic fibres (FOG) or fast twitch and glycolytic fibres (FG). FOG fibres make up 88 to 90% of the total muscle population and have a mean diameter one-half of that of the relatively large FG fibres. Here we report on the organization of individual fibres identified in six muscle units depleted of glycogen, three comprised of FOG fibres and three comprised of FG fibres. For each motor unit, fibre counts revealed unequal numbers of depleted fibres in different unit cross-sections. We traced individual fibres in one unit comprised of FOG fibres and a second comprised of FG fibres. Six fibres from a FOG unit (total length 15.45 mm) ranged from 10.11 to 11.82 mm in length and averaged (± s.d.) 10.74 ± 0.79 mm. All originated bluntly (en mass) from a fascicle near the proximal end of the muscle unit and all terminated intramuscularly. Five of these ended in a taper and one ended bluntly. Fibres coursed on average for 70% of the muscle unit length. Six fibres from a FG unit (total length 34.76 mm) ranged from 8.97 to 18.38 mm in length and averaged 15.32 ± 3.75 mm. All originated bluntly and terminated intramuscularly; one of these ended in a taper and five ended bluntly. Fibres coursed on average for 44% of the muscle unit length. Because fibres of individual muscle units do not extend the whole muscle unit territory, the effective cross-sectional area changes along the motor unit length. These non-uniformities in the distribution of fibres within a muscle unit emphasize that the functional interactions within and between motor units are complex.     

Limitations of the surface electromyography technique for estimating motor unit synchronization

Motor unit synchronization was estimated from the surface electromyograms (EMG) of the first dorsal interosseus muscle of human volunteers by a simplified surface-EMG technique (Milner-Brown et al. 1973, 1975). Single motor units were identified from intramuscular recordings and were used to obtain a spike-triggered average of the surface-EMG. The discharge rate of a reference motor unit was controlled at two levels (high and low), and the effect of motor unit activity on the surface-EMG estimate of synchronization was studied in 56 motor units. The surface-EMG estimate of motor unit synchronization was significantly higher when the reference motor unit discharged at the high rate than when it discharged at the low rate. A regression analysis indicated that the synchronization ratio calculated from the surface EMG was significantly correlated with the level of EMG activity in the muscle. Motor unit synchronization was also estimated from surface-EMG measurements that were derived by computer simulation. The simulation permitted manipulation of motor unit activity (discharge rate and recruitment) with a complete absence of synchrony among the units in the pool. The stimulated surface-EMG index was influenced by an artifact associated with signal rectification, and this effect changed non-monotonically with motor unit activity. Furthermore, the increase in the motor unit activity reduced the signal-to-noise ratio of the spike-triggered surface EMG average, and consequently decreased the sensitivity of the surface-EMG index as an estimate of motor unit synchronization. We conclude that the simplified surface-EMG method (Milner-Brown et al. 1973, 1975) does not provide a useful index of motor unit synchronization due to its inability to accurately distinguish the synchronization from methodological effects related to a rectification artifact and variation in the signal-to-noise ratio.     

Molecular dynamics simulations of a double unit cell in a protein crystal: volume relaxation at constant pressure and correlation of motions between the two unit cells

Eight molecular dynamics simulations of a double crystal unit cell of ubiquitin were performed to investigate the effects of simulating at constant pressure and of simulating two unit cells compared to a single unit cell. To examine the influence of different simulation conditions, the constant-pressure and constant-volume simulations were each performed with and without counterions and using two different treatments of the long-range electrostatic interactions (lattice-sum and reaction-field methods). The constant-pressure simulations were analyzed in terms of unit cell deformation and accompanying protein deformations. Energetic and structural properties of the proteins in the simulations of the double unit cell were compared to the results of previously reported one-unit-cell simulations. Correlation between the two unit cells was also investigated based on relative translational and rotational movements of the proteins and on dipole fluctuations. The box in the constant-pressure simulations is found to deform slowly to reach convergence only after 5-10 ns. This deformation does not result from a distortion in the structure of the proteins but rather from changes in protein packing within the unit cell. The results of the double-unit-cell simulations are closely similar to the results of the single-unit-cell simulations, and little motional correlation is found between the two unit cells.     

Attachment of the main chain to the linkage unit in biosynthesis of teichoic acids

The main chain of teichoic acids can be assembled in cell-free membrane preparations by the transfer of residues from the appropriate nucleotide precursors to an incompletely characterized amphiphilic molecule, lipoteichoic acid carrier (LTC). However, in the cell wall, the main chain is attached to peptidoglycan through a linkage unit which is synthesized independently. It is believed that, in these cell-free systems, lipid intermediates carrying linkage units are also able to accept residues directly from nucleotide precursors to build up the main chain. In this paper, we have shown that the main chain attached to LTC was transferred from LTC to lipids containing the linkage unit. Thus, in these systems, there appear to be two routes to the biosynthesis of teichoic acid-linkage unit complexes, one by direct assembly of the main chain on linkage unit lipids and the other by transfer of the preassembled main chain from LTC to the linkage unit. It was also shown that linkage unit lipids from different organisms were interchangeable and that these were used for polymer synthesis by Bacillus subtilis 3610, in which the teichoic acid is a poly(glycerol phosphate).     

The effect of activity during early postnatal development on motor unit size

At early stages of neuromuscular development, motor unit territory is expanded, with each muscle fibre being supplied by several axons. During postnatal development, some synapses are eliminated, motor unit size decreases, and the adult distribution of motor unit sizes emerges. This process depends on activity, since it proceeds more rapidly when the nerve is activated and is slower when activity is reduced. Here we studied whether, in addition to influencing the rate of retraction of motor unit territory, activity during the critical period of development affects the final outcome of the distribution of motor unit sizes. The sciatic nerve of 8- to 12-day-old rats was stimulated daily. One week later the tension of the extensor digitorum longus muscle and that of its individual motor units was recorded. The sizes of individual motor units were calculated and compared with those from animals that received no stimulation. The distribution of motor unit sizes from stimulated muscles was not significantly different from those from control muscles. Therefore, we conclude that although activity increases the rate at which motor units attain their adult size, it does not influence the final outcome of motor unit size distribution.     

A study of the motor unit action potential by means of computer simulation

In order to study the motor unit action potential a computer simulation model was developed. It is based on the superposition of single muscle fibre potentials of the fibres belonging to the motor unit. The parameters which characterize each fibre (spatial position, diameter, and a dispersion of arrival time of the potential at the electrode) are chosen from statistical distributions which can be derived from anatomical and physiological data. The electrode type, position and dimensions can be specified. Simulated motor unit action potentials are presented in the time and frequency domain. The simulation results refer to (1) the influence of the electrode position and dimensions with respect to the motor unit territory, (2) the meaning of this model for the study of pathological phenomena, (3) the variability of some parameters characterizing the motor unit, (4) the selectivity of uni- and bipolar electrodes and finally (5) the influence of the geometrical situation of the motor end-plates within the muscle, on the shape of motor unit action potentials.     

Programmed investigation unit.

The programmed investigation unit (PIU) is a inpatient unit where a full range of investigational medicine can be organised. It provides the basic minimum nursing care and is suitable for ambulant patients who can care for themselves. Requests for admission to the PIU at the Royal Victoria Infirmary, Newcastle upon Tyne, come directly from clinical units, and the staff of these units perform some of the tests and remain responsible for the patient while she is in the unit. At present the unit caters only for female medical patients. The average waiting time for admission is three weeks, and because the unit now deals with most investigations the waiting time for admission to the female general medical wards has fallen considerably. The staff of the unit have gained expertise in diagnostic methods, while the nurses of general medical wards have been free to concentrate on nursing those patients who need it. Separating patients who need investigations from those on general medical wards seems a logical way of using resources and staff to best effect.     

Comparison of force and EMG measures in normal and reinnervated tibialis anterior muscles of the rat.

The relationship between motor unit force and the recorded voltage produced by activated muscle unit fibres (electromyogram, EMG) was examined in normal and reinnervated rat tibialis anterior muscles. The number, cross-sectional area, and radial distance from the recording electrode of muscle fibres in a given unit, obtained directly from a sample of glycogen-depleted motor units, were analysed in relation to the magnitude of the EMG signal produced by that unit. EMG peak to peak amplitude and area varied as approximately the square root of twitch force in both normal and reinnervated units. Furthermore, the EMG amplitude increased approximately as the total cross-sectional area of the motor unit (number of muscle fibres x the average cross-sectional area of the fibres) and inversely with approximately the square root of the distance of fibres from the recording electrodes on the surface of the muscle.     

Motor unit acceleration maps and interference mechanomyographic distribution

The study analyses the two-dimensional distribution of surface mechanomyographic (MMG) signal generated by the activation of single motor units located in three transverse positions in the tibialis anterior muscle. In 12 healthy volunteers, surface MMG signals were recorded from the tibialis anterior muscle with a 3x4 grid of accelerometers spaced by 20 and 30mm in the transverse and longitudinal direction. Three intramuscular electromyographic (EMG) signals were recorded with wire electrodes inserted 20-mm apart, between the first and second most proximal accelerometers of each column of the grid. The subject was asked to activate three different motor units (target motor units) in three contractions with visual feedback from each of the three intramuscular recordings (three locations). The MMG signals from the 12 accelerometers were averaged using the intramuscular single motor unit action potentials as trigger in order to obtain surface motor unit acceleration maps (MUAMs). The peak-to-peak value of the averaged MMG depended on motor unit location (P<0.001) and on the transverse position of the accelerometer in the grid (P<0.05). Moreover, MUAM amplitude depended on the interaction between motor unit location and transverse accelerometer position (P<0.05), demonstrating an influence of motor unit location on the generated MUAM. The observed dependency of MUAMs on motor unit location provides a quantitative analysis of the effect of the volume conductor on the recorded surface MMG signal.     

Spatial analysis of motor unit potentials of the rat medial gastrocnemius

The spatial analysis of the potentials of single motor units of the rat medial gastrocnemius muscle evoked by stimulation of the fibres of split ventral roots was carried out with a bipolar electrode moving in the direction perpendicular to the longitudinal axis of the muscle fibres. During this movement of the electrode a variability was observed in the time of the biphasic potential from its maximum to minimum, and in the peak-to-peak amplitude of these potentials. The potentials recorded outside the territory of the motor unit had a lower amplitude in relation to the potentials from the territory of the unit. This made localization of the motor unit on the cross-section of the muscle possible. Differences in the duration of the potential from maximal to minimal amplitude (maximum-minimum amplitude time--M-MAT) of each investigated motor unit from successive recording sites reflected the number of fibres contributing to the action potential and the distance of the recording surface of the electrode from the zone of the motor end-plates of this motor unit. The greatest diameter of the territory of the observed motor units reached 2.5 mm.     

Portable multi-purpose device for monitoring of physiological informations

Unconstrained system that measures physiological information as skin temperatures and heart rate per unit time of a human subject was developed. The system contained portable device included memory control unit, instrumentation unit, timer and batteries, read-out unit, test unit and verify unit. Total number of data and channels, and interval were selected by switches in the memory control unit. The data from the instrumentation unit were transferred to memory control unit and stored in the Erasable Programmable ROM (EPROM). After measurement, EPROM chip was taken off the memory control unit and put on the read-out unit which transferred the data to the microcomputer. The data were directly calculated and analyzed by microcomputer. In application of the instrumentation unit, 8-channel skin thermometer was developed and tested. After amplification, 8 analog signals were multiplexed and converted into the binary codes. The digital signals were sequentially transferred to memory control unit and stored in the EPROM under controlled signal. The accuracy of the system is determined primarily by the accuracy of the sensor of instrumentation unit. The overall accuracy of 8-channel skin thermometer is conservatively stated within 0.1 degree C. This may prove to be useful in providing an objective measurement of human subjects, and can be used in studying environmental effect for human body and sport activities in a large population setting.     

Sequential nuclear magnetic resonance assignment of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of the pathogenic yeast Candida albicans NIH B-792 strain.

The H-1 and H-2 signals of beta-1,2-linked mannooligosaccharides isolated from the phosphomannan of Candida albicans NIH B-792 strain by mild acid hydrolysis were assigned by a sequential NMR assignment method that combines two-dimensional 1H-1H correlated spectroscopy (COSY) and two-dimensional nuclear Overhauser enhancement and exchange spectroscopy (NOESY). The results indicated that the H-1 and H-2 of each beta-1,2-linked mannopyranose unit show largely different signals compared with those of the alpha-linked ones and that the correlation between linkages and signals could not be explained by a conventional additivity rule. Furthermore, a regular proportional downfield shift of the H-1 signal was observed in the order of the mannose unit from the reducing terminal except those of the reducing and nonreducing terminal positions. Although the 1H NMR spectra of these oligosaccharides were complicated due to the presence of a large portion of the beta-anomer from the reducing terminal mannose unit, reduction of the oligosaccharides with NaBH4 to the corresponding alcohols gave simple and more readily interpretable 1H NMR spectra. Unexpectedly, however, a shift of H-1 signals by this reduction occurred not only on the second mannose unit but also on the third and fourth mannose units from the modified reducing terminal group of each oligosaccharide alcohol. This result indicates that the reducing terminal mannose unit is able to affect up to the fourth mannose unit from the reducing terminal. The presence of a long-distance interresidue NOE also suggests that the beta-1,2-linked mannooligosaccharides have a compactly folded conformation in solution.     

Tutorial: Analysis of motor unit discharge characteristics from high-density surface EMG signals

Recent work demonstrated that it is possible to identify motor unit discharge times from high-density surface EMG (HDEMG) decomposition. Since then, the number of studies that use HDEMG decomposition for motor unit investigations has increased considerably. Although HDEMG decomposition is a semi-automatic process, the analysis and interpretation of the motor unit pulse trains requires a thorough inspection of the output of the decomposition result. Here, we report guidelines to perform an accurate extraction of motor unit discharge times and interpretation of the signals. This tutorial includes a discussion of the differences between the extraction of global EMG signal features versus the identification of motor unit activity for physiological investigations followed by a comprehensive guide on how to acquire, inspect, and decompose HDEMG signals, and robust extraction of motor unit discharge characteristics.     

On spiking units in the first optic chiasm of the blowfly

We recorded from the spiking sustaining unit in the optic chiasm between lamina and medulla in the brain of the blowfly Calliphora vicina, and investigated both temporal and spatial properties of the light-adapted cell. The sustaining unit fails to follow the highest temporal frequencies followed by the photoreceptor, but its temporal resolution is substantially better than that of the on-off unit. The sustaining unit does not display the fast temporal adaptation as previously described in the on-off unit. As compared with the on-off unit, the sustaining unit has a high sensitivity to small contrasts. Although the sustaining unit continues spiking as long as the light is on, its response is also transient as it adapts rapidly after a change of intensity. The receptive field and the line spread function of the sustaining unit have a similar size and profile: a central lobe with a half-width of approximately 2° surrounded by a circular inhibitory zone located at about 3° off-axis.     

A study of synchronization of the sinus unit upon stimulation from auricles

The excitation of the sinoatrial unit from heart auricles of the frog has been studied. Potentials were recorded by means of microelectrodes inserted to pacemaker of the sinoatrial unit. It has been established that auricles can impart the rhythm to the sinoatrial unit due to electric and electromechanical influence, and electromechanical influence is of greater significance. Specific transitions accompanying the establishment of the stationary rhythm have been studied. A mathematical model of transitions of the establishment of the rhythm of the sinoatrial unit, which is based on diophant methods is offered. The catculations performed by means of the mathematical model coincide well with results of experimental studies. The stabilizing role of auricles in the formation of the rhythm of the sinoatrial unit has been established.     

The 5S DNA sequences in Hordeum bogdanii and in the H. brevisubulatum complex, and the evolution and the geographic dispersal of the diploid Hordeum species (Triticeae: Poaceae).

The molecular diversity of 5S rDNA from the closely related Asiatic diploid species, Hordeum bogdanii and the H. brevisubulatum complex has been catalogued and analysed. As in previous studies in Hordeum, we found that the sequences are constrained in such an manner that unit classes can be defined. The long H1 unit class, known to occur in all Eurasian species, was frequently found in these 2 taxa. In addition, we identified a new unit class, called the short H3 to reflect the H genome found in these 2 taxa. Although the 2 taxa are very close morphologically, the variation in the long H1 DNA units is constrained to such a great degree that, in many cases, the accessions in a unit class from a single species are clustered. In H. bogdanii, the majority of the sequences are grouped in this manner, whereas in the H. brevisubulatum complex, the tendency to be constrained is lower in some but not all subspecies. These results support keeping H. brevisubulatum ssp. violaceum and ssp. iranicum as 1 species with the long H1 and short H1 unit classes, while retaining ssp. nevskianum and ssp. turkestanicum in the H. brevisubulatum complex. We have summarized our work on the presence/absence of the 10 unit classes found in all diploid species of Hordeum. A phylogenetic analysis, based strictly on the presence/absence of unit classes, indicated clearly that all the South American diploids and all the North American diploids possess long H2 and long Y2 unit classes and, except for H. californicum and H. pusillum, which contain long H1 in addition to the long H2 and long Y2 classes, are devoid of the long H1 unit class. This suggests that the gene gain/loss process from a common ancestor has been concomitant with intercontinental dispersal between the Old and the New Worlds.     

Study of patients' psychological attitudes to a coronary care unit

Seventy-four consecutive male patients aged 38 to 63 years were admitted to a coronary care unit with their first myocardial infarction. Their attitude to the unit was studied by interview and personality tests. Only six patients found the unit anxiety-provoking. Dependency feelings were found to occur frequently, both after transfer from the unit to the general wards and after discharge from hospital. It is suggested that the weaning process from the unit should be gradual and that at least one follow-up outpatient appointment should be arranged, as well as good liaison between the family doctor and the hospital.     

不同地理单元尖吻蝮蛇毒蛋白组分比较研究

目的探讨不同地理单元尖吻蝮蛇毒蛋白组分有无差异性。方法采用非变性聚丙烯酰胺凝胶电泳(NativePAGE)方法,比较采自安徽黄山(黄山单元)和贵州梵净山(西部单元)尖吻蝮蛇毒组分。结果梵净山尖吻蝮的蛇毒蛋白表达量和条带数目均高于黄山尖吻蝮。结论黄山单元和西部单元的尖吻蝮蛇毒蛋白组分具有差异性。