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Results for “Neuromuscular adaptability”

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At least 271 records · Page 15Linked to original sources

PubMed1992

A short-term epidemiological study of median nerve dysfunction in practicing dental hygienists.

The purpose of this study was to assess over time changes in median nerve function in a group of 20 students who entered the University of Minnesota dental hygiene program in 1986. This is a follow-up report on 16 of the 20 students who were evaluated two years postgraduation in 1990. Comparisons were made with prior evaluations of the subjects completed at graduation in 1988, and one year postgraduation in 1989. Digital vibrometry was used to evaluate median nerve sensibility threshold at each of the time periods studied. Analysis revealed that after one year of clinical practice, there was a mean sensibility threshold shift of 11.04% in the left median nerve and 8.42% in the right median nerve as measured by digital vibrometry. Results at two years postgraduation indicated that the threshold shift observed in an earlier study had been arrested. The reasons appeared to be twofold: (1) a period of work hardening with a concept of neuromuscular ligamentous tissue hypertrophy or adaptation to the rigors of dental hygiene practice, and/or (2) the practicing dental hygienist had learned to become more efficient in the provision of hygiene procedures. There were no reported symptoms of median nerve dysfunction and none of the subjects had been diagnosed as having CTS at any time during the two years since graduation. Continued evaluations will be necessary to determine whether the observations noted during the second year postgraduation evaluation indicated temporary or permanent slowing of the conditions necessary for the development of CTS.

Adult↗

PubMed1988

Response of isolated muscle of the human cervix to electrofield stimulation.

Contractile activity was registered isometrically in isolated strip biopsies from the uterine cervix of nonpregnant, early pregnant and term pregnant women, and the influence of electrofield stimulation (EFS) was studied. In the great majority of women an excitatory effect was observed, but occasionally an inhibitory response occurred. The excitatory effect of EFS was reduced and, in many cases, changed to inhibition during treatment with guanethidine and phenoxybenzamine. These inhibitory effects were not antagonized by treatment with propranolol, indicating that the responses were not mediated by beta-adrenoceptors. Tetrodotoxin reduced or abolished the excitatory effect of EFS. The data suggest that contractile activity of the human cervix is influenced by both adrenergic and nonadrenergic neurons, which remain intact throughout pregnancy. This innervation may be a central part of neuromuscular control systems which undergo important adaptive changes during pregnancy and in connection with parturition.

Cervix Uteri↗

PubMed1988

Variation in neuromuscular activity during prey capture by trophic specialists and generalists (Pisces: Labridae).

Members of the marine teleost family Labridae are among the most abundant and morphologically diverse fish on coral reefs. A quantitative analysis was conducted of the neuromuscular activity patterns controlling movement of the jaws during prey capture by 4 labrid species ranging from trophic specialists to trophic generalists. A total of more than 800 captures of 3 prey types was analyzed. All 4 species showed significant modulation of electromyographic parameters in response to different prey types. Significant variation was also found between replicate experiments on the same individuals. To obtain valid assessments of interspecific variability, statistical analyses must take into account this potentially high degree of intraspecific variability. By partitioning the variance in a nested analysis of variance, a lack of significant differences in electromyographic parameters between species became apparent. In contrast to the closely related Cichlidae, trophic diversification in the Labridae has not been accompanied by the acquisition of unique neuromuscular activity patterns for prey capture. The dramatic adaptive radiation that has occurred in these 2 families has involved different processes of evolutionary diversification. Neuromuscular stereotypy of labrids may be associated with the lack of structural flexibility in their 'coupled jaw'. Additional study is needed to establish the extent to which labrid radiation into various trophic niches is related to the evolution of specialized morphologies and foraging behaviors.

Animals↗

PubMed2002

Adaptations in skeletal muscle disuse or decreased-use atrophy.

Those factors that seem to play some role in inducing adaptations of skeletal muscle in vivo are discussed. The role of myogenesis in maintaining and repairing muscle during atrophic and hypertrophic states is discussed, including pointing out that the modulation of myonuclear number is one means of adapting to varying chronic levels of neuromuscular activity. Finally, we point out the potential consequences of muscle atrophy on the control of movement and the susceptibility to fatigue.

Adaptation, Physiological↗

PubMed2002

The vestibulo-ocular reflex in fourth nerve palsy: deficits and adaptation.

The effects of fourth nerve palsy on the vestibulo-ocular reflex (VOR) had not been systematically investigated. We used the magnetic scleral search coil technique to study the VOR in patients with unilateral fourth nerve palsy during sinusoidal head rotations in yaw, pitch and roll at different frequencies. In darkness, VOR gains are reduced during incyclotorsion, depression and abduction of the paretic eye, as anticipated from paresis of the superior oblique muscle. VOR gains during excyclotorsion, elevation and adduction of the paretic eye are also reduced, whereas gains in the non-paretic eye remain normal, indicating a selective adjustment of innervation to the paretic eye. In light, torsional visually enhanced VOR (VVOR) gains in the paretic eye remain reduced; however, visual input increases vertical and horizontal VVOR gains to normal in the paretic eye, without a conjugate increase in VVOR gains in the non-paretic eye, providing further evidence of selective adaptation in the paretic eye. Motions of the eyes after fourth nerve palsy exemplify monocular adaptation of the VOR, in response to peripheral neuromuscular deficits.

Adaptation, Physiological↗

PubMed2006

Neuromuscular-skeletal constraints on the acquisition of skill in a discrete torque production task.

The organisation of the human neuromuscular-skeletal system allows an extremely wide variety of actions to be performed, often with great dexterity. Adaptations associated with skill acquisition occur at all levels of the neuromuscular-skeletal system although all neural adaptations are inevitably constrained by the organisation of the actuating apparatus (muscles and bones). We quantified the extent to which skill acquisition in an isometric task set is influenced by the mechanical properties of the muscles used to produce the required actions. Initial performance was greatly dependent upon the specific combination of torques required in each variant of the experimental task. Five consecutive days of practice improved the performance to a similar degree across eight actions despite differences in the torques required about the elbow and forearm. The proportional improvement in performance was also similar when the actions were performed at either 20 or 40% of participants' maximum voluntary torque capacity. The skill acquired during practice was successfully extrapolated to variants of the task requiring more torque than that required during practice. We conclude that while the extent to which skill can be acquired in isometric actions is independent of the specific combination of joint torques required for target acquisition, the nature of the kinetic adaptations leading to the performance improvement in isometric actions is influenced by the neural and mechanical properties of the actuating muscles.

Adaptation, Physiological↗

PubMed1997

Height increase, neuromuscular function, and back pain during 6 degrees head-down tilt with traction.

BACKGROUND: Spinal lengthening and back pain are commonly experienced by astronauts exposed to microgravity. METHODS: To develop a ground-based simulation for spinal adaptation to microgravity, we investigated height increase, neuromuscular function and back pain in 6 subjects all of whom underwent two forms of bed rest for 3 d. One form consisted of 6 degrees of head-down tilt (HDT) with balanced traction, while the other was horizontal bed rest (HBR). Subjects had a 2-week recovery period in between the studies. RESULTS: Total body and spinal length increased significantly more and the subjects had significantly more back pain during HDT with balanced traction compared to HBR. The distance between the lower endplate of L4 and upper endplate of S1, as measured by ultrasonography, increased significantly in both treatments to the same degree. Intramuscular pressures in the erector spinae muscles and ankle torque measurements during plantarflexion and dorsiflexion did not change significantly during either treatment. CONCLUSION: Compared to HBR, HDT with balanced traction may be a better method to simulate changes of total body and spinal lengths, as well as back pain seen in microgravity.

Adaptation, Physiological↗

PubMed2006

Negative scotopic ERG and photopic ERG ON response impairment in a patient with normal dark adaptation.

PURPOSE: To present ocular findings in a patient who showed negative scotopic electroretinogram (ERG) and reduced ON response, but normal dark adaptation. CASE: An 18-year-old Japanese male patient who complained of severe asthenopia. His corrected visual acuities were 1.2 in both eyes. His fundi were normal. He had normal contrast sensitivity and normal dark adaptation. METHODS: The patients underwent ERG (including the standard protocol and photopic long flash recordings). RESULTS: The amplitudes of the rod ERG b-wave were reduced. The scotopic standard combined ERG response showed negative configuration. The photopic response to long flash revealed the reduced b-wave (ON response), while the amplitude of the first peak of the d-wave (OFF response) was within the normal range. CONCLUSIONS: Postsynaptic abnormalities in both the rod and cone ON-pathways, which are often found in patients with night blindness, were suggested in the ERG findings, but the dark adaptation of our patient was normal. Neuromuscular evaluation of the patient and ophthalmological evaluation, including ERG, of his parents were normal. To our knowledge, the ophthalmological and electrophysiological findings of our patient cannot be attributed to any known clinical entity.

Adaptation, Ocular↗

PubMed1990

Cold adaptation in marine organisms.

Animals from polar seas exhibit numerous so called resistance adaptations that serve to maintain homeostasis at low temperature and prevent lethal freezing injury. Specialization to temperatures at or below 0 degrees C is associated with an inability to survive at temperatures above 3-8 degrees C. Polar fish synthesize various types of glycoproteins or peptides to lower the freezing point of most extracellular fluid compartments in a non-colligative manner. Antifreeze production is seasonal in boreal species and is often initiated by environmental cues other than low temperature, particularly short day lengths. Most of the adaptations that enable intertidal invertebrates to survive freezing are associated with their ability to withstand ariel exposure. Unique adaptations for freezing avoidance include the synthesis of low molecular mass ice-nucleating proteins that control and induce extracellular ice-formation. Marine poikilotherms also exhibit a range of capacity adaptations that increase the rate of some physiological processes so as to partially compensate for the effects of low temperature. However, the rate of embryonic development in a diverse range of marine organisms shows no evidence of temperature compensation. This results in a significant lengthening of the time from fertilization to hatching in polar, relative to temperate, species. Some aspects of the physiology of polar marine species, such as low metabolic and slow growth rates, probably result from a combination of low temperature and other factors such as the highly seasonal nature of food supplies. Although neuromuscular function shows a partial capacity adaptation in Antarctic fish, maximum swimming speeds are lower than for temperate and tropical species, particularly for early stages in the life history.

Adaptation, Physiological↗

PubMed1997

Functional neuromuscular stimulation controlled by surface electromyographic signals produced by volitional activation of the same muscle: adaptive removal of the muscle response from the recorded EMG-signal.

In order to use the volitional electromyography (EMG) as a control signal for the stimulation of the same muscle, it is necessary to eliminate the stimulation artifacts and the muscle responses caused by the stimulation. The stimulation artifacts, caused by the electric field in skin and tissue generated by the stimulation current, are relatively easy to eliminate by shutting down the EMG-amplifier at the onset of the stimulation pulses. The muscle response is a nonstationary signal, therefore, an adaptive linear prediction filter is proposed. The filter is implemented and for three filter lengths tested on both simulated and real data. The filter performance is compared with a conventional fixed comb filter. The simulations indicate that the adaptive filter is relatively insensitive to variations in amplitude of the muscle responses, and for all filter lengths produces a good filtering. For variations in shape of the muscle responses and for real data, an increased filter performance can be achieved by increasing the filter length. Using a filter length of up to seven stimulation periods, it is possible to reduce real muscle responses to a level comparable with the background noise. Using the shut-down circuit and the adaptive filter both the stimulation artifacts and the muscle responses can be effectively eliminated from the EMG signal from a stimulated muscle. It is therefore possible to extract the volitional EMG from a partly paralyzed muscle and use it for controlling the stimulation of the same muscle.

Artifacts↗

PubMedDate not supplied

Maintenance of transmitter release from neuromuscular junctions with different patterns of usage "in vivo".

The basic mechanisms underlying chemically-mediated neurotransmission at synapses are well established. Synaptic vesicles release their contents of neurotransmitter by exocytosis, and are then recycled and refilled before re-priming for re-release. It is less clear, however, what determines the differences in the quantitative aspects of this process at synapses with different in vivo activity patterns, and the extent to which they can be adapted to changing patterns of usage. The neuromuscular junction is particularly suited to investigations of these issues, due to the presence of distinctive muscle fibre types, with well-differentiated physiological roles and hence, activity patterns. The relative accessibility of NMJs means that chronic recording and manipulation of in vivo activity patterns of single motor neurones are possible. Several laboratories around the world now examining how transmitter release at NMJs is adapted to maintain (or not) release under these identified activity patterns. This review will cover the current state of knowledge and briefly highlight areas where more research is required. For example, current knowledge is largely derived from invertebrate preparations, indicating a need for more detailed comparisons at mammalian NMJs with different activity patterns. Finally, it is not yet clear in any species whether adaptations observed with imposed activity can be driven to complete transformation, with appropriate stimulus regimes.

Animals↗

PubMed2002

The role of proprioceptive feedback in the regulation and adaptation of locomotor activity.

Feedback from muscle afferents is essential for locomotion to be functional under changing external conditions. In this article, we review the role of afferent feedback in adapting locomotor activity to transient and more sustained changes in sensory input in reduced and walking cat preparations. Much of the work on muscle afferent regulation of locomotion has focused on the regulation of stance phase activity. Proprioceptive feedback from extensor muscles during the stance phase ensures that the leg does not go into swing when loaded and that the magnitude of extensor activity is adequate for support. Proprioceptive feedback from flexor muscles towards the end of the stance phase facilitates the initiation of the swing phase of walking. Evidence that muscle afferent feedback also contributes to the magnitude and duration of flexor activity during the swing phase has been demonstrated recently. The regulation of the magnitude and duration of extensor and flexor activity during locomotion is mediated by monosynaptic, disynaptic, and polysynaptic muscle afferent pathways in the spinal cord. In addition to allowing for rapid adaptation in motor output during walking, afferent feedback from muscle proprioceptors is also involved in longer-term adaptations in response to changes in the biomechanical or neuromuscular properties of the walking system.

Adaptation, Physiological↗

PubMed2005

Control of neuromuscular blockade in the presence of sensor faults.

The problem of embedding sensor fault tolerance in feedback control of neuromuscular blockade is considered. For tackling interruptions of feedback measurements, a structure based upon Bayesian inference as well as a predictive filter is proposed. This algorithm is general and can be applied to different situations. Here, it is incorporated in an adaptive automatic system for feedback control of neuromuscular blockade using continuous infusion of muscle relaxants. A significant contribution consists in the experimental clinical testing of the algorithm in patients undergoing surgery.

Algorithms↗

PubMed1982

Oculomotor effects of intermittent conduction block in myasthenia gravis and Guillain-Barré syndrome. An oculographic study with computer simulations.

Five abnormal oculographic patterns were identified in eight patients with either myasthenia gravis or Guillain-Barré syndrome (GBS). These could be differentiated into three intrasaccadic and two postsaccadic abnormalities. From our studies of computer simulations, and considering the established pathophysiology of myasthenia gravis and GBS, we believe that our oculographic findings were a consequence of defects in peripheral neural and neuromuscular conduction, together with a simple adaptive increase in duration of the saccadic burst of central innervation. We conclude that the eye movement abnormalities we observed are explained by intermittent block of peripheral conduction, and suggest that any disease causing intermittent blockage of neural signals to extraocular muscles will produce similar abnormalities of eye movement.

Adolescent↗

PubMed1996

Implantable multiprogrammable microstimulator dedicated to bladder control.

An implantable multiprogrammable microstimulator that is intended to restore normal bladder functions (retention and incontinence) to spinal cord injured patients is presented. The implantable microstimulator circuitry is externally controlled and is powered by a single encoded radio frequency carrier and has four bipolar (eight monopolar) independently controlled channels. It offers a higher degree of reprogrammability and flexibility and can be used in any neuromuscular applications. The implant system is adaptable to the patient's needs and to future developments in stimulation algorithms, without changing the implant. Features of the microstimulator include its capabilities to generate a wide range of waveforms and to combine up to four different programmable frequencies in each wave train. By using a forward error detection and correction communication protocol, the reliability of the implant is increased. The chip has been designed for structural testability by means of a scan-based test approach and uses circuit techniques to reduce power consumption and ensure long-term stability.

Electric Stimulation↗

PubMed2003

Expression profiling and pharmacogenomics of muscle and muscle disease.

Parallel technologies are emerging for the study of DNA (single nucleotide polymorphism genotyping and association studies), and RNA (microarrays and expression profiling). Muscle tissue has many intrinsic features that make it the tissue of choice to model the application of these newly emerging technologies. Well-preserved human biopsies are readily available both from volunteers undergoing specific muscle training protocols and from neuromuscular disease patients. Furthermore, the rapid adaptation of muscle to environmental cues (e.g. exercise, conditioning and weightlessness) makes it possible to conduct time series data in humans (molecular cause and effect). Muscle is also important in drug metabolism and adverse events, and the application of single nucleotide polymorphism association studies in muscle pharmacogenomics is a field of expected future growth.

Drug Design↗

PubMed1988

Endurance exercise alters the morphology of fast- and slow-twitch rat neuromuscular junctions.

The present investigation studied the effects of an endurance exercise program on the morphology of nerve terminals of phasic extensor digitorum longus (EDL) and tonic soleus (SOL) muscles from young mature female Sprague-Dawley rats. The animals were treadmill exercised for 30 consecutive days for 1 h/day at velocities up to 30 m/min. The area, perimeter, nerve longitudinal extent length, and fiber diameter of camera lucida drawings of zinc iodide osmium-stained nerve terminals were analyzed with a computerized morphometry system. Additionally, the number of nerve terminal branches and percentage of end-plates with sprouts were determined. Nerve terminals from exercised EDL and SOL had significantly greater areas than those from corresponding controls, with no changes in the perimeters. The magnitude of the changes were greater in the EDL. The exercised EDL nerve terminals were also significantly longer than controls and had more branches and sprouts. No training differences in fiber diameter were observed for either muscle. These data confirm previous suggestions that physical activity or exercise levels affect the morphology of the neuromuscular junction.

Adaptation, Physiological↗

PubMed1998

Identical responses of fast muscle to sustained activity by low-frequency stimulation in young and aging rats.

To investigate effects of sustained activity on major phenotypic properties, the left extensor digitorum longus muscle of young (15 wk) and aging (101 wk) male Brown Norway rats was subjected to 50 days of chronic low-frequency stimulation (CLFS; 10 Hz, 10 h/day). The contralateral muscle served as control. Changes in metabolic enzymes were analyzed by using glyceraldehyde-3-phosphate dehydrogenase and lactate dehydrogenase as reference enzymes of glycolysis and by using citrate synthase and 3-hydroxyacyl-CoA dehydrogenase as mitochondrial enzymes representative of aerobic-oxidative metabolism. Myosin heavy chain (MHC) isoforms were analyzed by SDS-PAGE. No differences existed between the enzyme activity profiles of control muscles from young and aging rats. CLFS induced similar increases in mitochondrial enzymes, as well as similar decreases in glycolytic enzymes. Although the MHC composition of the control muscles in the aging rats displayed a shift toward slower isoforms, the ultimate changes induced by CLFS led to nearly identical MHC phenotypes in both young and aging rats. These results demonstrate an unaltered adaptability of skeletal muscle to increased neuromuscular activity in the aging rat.

3-Hydroxyacyl CoA Dehydrogenases↗