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At least 343 records · Page 19Linked to original sources
PubMed1983

The 4-6 HZ tremor during sustained contraction in normal human subjects.

Continuous elevation of the middle finger for 15-60 min gave rise to modulation of the e.m.g. at 4-6 Hz. A marked peak (50-150% of the amplitude of the coexisting 8-12 Hz peak) at 4-6 Hz was produced in sixteen out of twenty-one subjects. The 8-12 Hz peak was also enhanced (2-14 times with respect to its initial amplitude in eighteen subjects) during the course of the prolonged contraction but its frequency did not change. The 4-6 Hz and the 8-12 Hz peaks were present simultaneously; it is concluded that the two phenomena are separate entities. A step-function mechanical perturbation of the finger generates, time-locked to the stimulus, a train of waves at the frequency of the slow tremor, which can be abolished by local ischaemia. It is proposed that this slow tremor is due to an oscillatory process, possibly involving the reflex arc, but entailing a longer neuronal delay than that responsible for 8-12 Hz tremor.

Adolescent↗
PubMed1987

Patellar clonus: an autonomous central generator.

The mechanisms underlying clonus are considered in relation to current theories. By the use of a lever attached to a printed motor forces have been applied to the upper edge of the patella, a steady stretching force in suitable hemiplegic patients started the clonic oscillations. With rhythmic forces it has been found that the underlying rhythm is very resistant to entrainment. The oscillation provoked by a steady bias is increased in amplitude but unchanged in frequency when inertia is added to the apparatus. The frequency of clonus at the ankle, patella and wrist is similar. These and other considerations lead to the conclusion that clonus is not due to the self re-excitation of stretch reflexes but to an autonomous central generator.

Electromyography↗
PubMed2002

Non-invasive proportional assist and pressure support ventilation in patients with cystic fibrosis and chronic respiratory failure.

BACKGROUND: Patients with advanced cystic fibrosis can benefit from non-invasive positive pressure ventilation (NPPV) for the treatment of acute decompensation as well as for the management of chronic respiratory failure. This study was undertaken to compare the physiological effects of non-invasive proportional assist ventilation (PAV) and pressure support ventilation (PSV) on ventilatory pattern, transcutaneous blood gas tensions, and diaphragmatic effort in stable patients with cystic fibrosis and chronic CO2 retention. METHODS: In 12 patients two periods of spontaneous breathing were followed randomly by PSV (12 (3) cm H2O) and PAV (flow assist 4.9 (1.3) cm H2O/l.s, volume assist 18.9 (5.1) cm H2O/l) set for the patient's comfort and administered for 40 minutes with 2 cm H2O continuous positive airway pressure. Ventilatory pattern, transcutaneous blood gas tensions, and surface diaphragmatic electromyography were measured in the last 10 minutes of each application. RESULTS: On average, both PSV and PAV improved ventilation (+30%), tidal volume (+30%), and transcutaneous CO2 (-7%) while reducing diaphragmatic activity (-30% with PSV, -20% with PAV). Mean inspiratory airway pressure was lower during PAV than during PSV (9.7 (1.9) and 12.9 (2.7) cm H2O, respectively; p<0.05). The mean coefficient of variation of tidal volume was about 20% (range 11-39%) during spontaneous breathing and did not change with either PAV or PSV. CONCLUSIONS: These results show that short term administration of nasal PAV and PSV to patients with stable cystic fibrosis with chronic respiratory insufficiency is well tolerated, improves ventilation and blood gas tensions, and unloads the diaphragm.

Adult↗
PubMed1978

The influence of a visual cue on muscle stretch reflexes.

Evidence has recently been presented indicating that muscle stretch reflexes have a large supraspinal component. The finding introduces the possibility that stretch reflex parameters may be modifiable by stimuli involving other modalities besides stretch. In this investigation, the effects of a visual cue on the reflex portions of the EMG activity following a sudden muscle stretch were examined. The results, obtained from the flexor carpi radialis muscles of six normal awake subjects, failed to show any significant change in the EMG parameters as a result of visual cues occurring at the instant of onset of muscle stretch. This was interpreted as indicating that visual inputs do not reach the areas of brain involved in the supraspinal reflex in sufficient time to modify the reflex.

Adult↗
PubMed1991

Effect of oxygenation on breath-by-breath response of the genioglossus muscle during occlusion.

We investigated the effect of different levels of O2 tension (hypoxia, normoxia, and hyperoxia) on the breath-by-breath onset and peak electromyographic (EMG) activity of the genioglossus (GG) muscle during a five-breath end-expiratory tracheal occlusion of 20- to 30-s duration. GG and diaphragmatic (DIA) EMG activity were measured with needle electrodes in eight anesthetized tracheotomized adult cats. In response to occlusion, the increase in the number of animals with GG EMG activity was different during hypoxia, normoxia, and hyperoxia (P = 0.003, Friedman). During hypoxia, eight of eight of the animals had GG EMG activity by the third occluded effort. In contrast, during normoxia, only four of eight and, during hyperoxia, only three of eight animals had GG EMG activity throughout the entire five-breath occlusion. Similarly, at release of the occlusion, more animals had persistent GG EMG activity on the postocclusion breaths during hypoxia than during normoxia or hyperoxia. Breath-by-breath augmentation of peak amplitude of the GG and DIA EMGs on each occluded effort was accentuated during hypoxia (P less than 0.01) and abolished during hyperoxia (P = 0.10). These results suggest that hypoxemia is a major determinant of the rapidity of onset, magnitude, and sustained activity of upper airway muscles during airway occlusion.

Airway Obstruction↗
PubMed1993

Effect of inspiratory muscle unloading on arousal responses to CO2 and hypoxia in sleeping dogs.

Chemical respiratory stimuli can induce arousal from sleep, but the specific mechanisms involved have not been established. Therefore, we tested the hypothesis that mechanoreceptor stimuli arising in the ventilatory apparatus have a role in the arousal responses to progressive hypercapnia and hypoxia by comparing arousal responses during spontaneous ventilation with those obtained when the inspiratory muscles were unloaded by mechanical ventilatory assistance. Studies were performed in three trained dogs in which the adequacy of inspiratory muscle unloading was verified by diaphragmatic electromyographic (EMG) recordings. In rapid-eye-movement (REM) sleep the arousal threshold during progressive hypercapnia increased from 68.4 +/- 0.5 (SE) mmHg during spontaneous runs to 72.3 +/- 0.8 mmHg during mechanically assisted runs (P < 0.01). In contrast there were no changes in arousal responses to hypercapnia during non-REM (NREM) sleep or to hypoxia in either NREM or REM sleep. However, during the assisted hypoxic runs, EMG activity of the transversus abdominis muscle was increased compared with the unassisted runs; therefore, the effects on arousal threshold of unloading the inspiratory muscles may have been offset by increased loading of the expiratory muscles. The findings indicate that even in the absence of added mechanical loads, mechanoreceptor stimuli probably arising in the respiratory muscles contribute to the arousal response to hypercapnia during REM sleep.

Animals↗
PubMed1996

Activation of pulmonary rapidly adapting receptors does not induce bronchoconstriction in dogs.

Activation of pulmonary rapidly adapting receptors (RARs) is believed to constrict airways by a vagally mediated reflex. We tested this hypothesis in dogs anesthetized with sufentanil citrate. We ventilated both lungs separately at a positive end-expiratory pressure of 4 cmH2O. We stimulated RARs in one lung under three different conditions: 1) deflation of the lung; 2) decrease in lung compliance; and 3) aerosolization of methacholine. We monitored the airway pressure in the nonstimulated lung as an index for airway muscle tone and could not detect increases in the pressure swing under these conditions. On the other hand, electrical stimulation of the distal end of cervical vagus nerve increased the pressure swing bilaterally (ipsilateral dominant), suggesting that reflex response could be detected in our preparation. Moreover, deflation (or inflation) of either lung increased (or suppressed) diaphragmatic activity. The results indicate intact vagal afferents and central response in our preparation. We conclude that activation of RARs located below the carina does not induce bronchoconstriction by a centrally mediated reflex. If any effect is present, it appears to be small.

Aerosols↗
PubMed2003

Contribution of cutaneous inputs from the hindpaw to the control of locomotion. II. Spinal cats.

The goal of these experiments was to define the contribution of hindpaw cutaneous inputs in the expression of spinal locomotion in cats. In 3 cats, some (n = 1) or all (n = 2) cutaneous nerves were cut bilaterally at ankle level before spinalization. This denervation caused small deficits that were gradually compensated as reported in the companion study. After spinalization, the completely denervated cats never recovered plantar foot placement or weight bearing of the hindquarters despite more than 35 days of treadmill training. Although normal electromyographic rhythmic activity developed at the hip and knee, ankle flexors and extensors were abnormally coactivated during stance. In contrast, the partially denervated cat regained foot placement and weight support 15 days after spinalization. However, after completing the denervation, foot placement and weight bearing were lost as in previous cats. In a 4th cat, spinalization was performed before denervation and the cutaneous nerves were cut sequentially in the right hindlimb only. Rapid locomotor adaptation occurred after cutting the deep peroneal, saphenous, and sural nerves. Later, cutting the superficial peroneal nerve produced paw drag, which was compensated within 8 days. On cutting the last cutaneous nerve (tibial), plantar foot placement was lost despite another 71 days of training. On the one hand, these experiments show that some cutaneous inputs are necessary for appropriate plantar foot placement and weight bearing of the hindquarters during spinal locomotion and, on the other hand, that locomotor compensation to partial cutaneous denervation after spinalization reveals important adaptive capacities of the spinal cord.

Adrenergic alpha-Agonists↗
PubMed2004

Discharge rate variability influences the variation in force fluctuations across the working range of a hand muscle.

The goal of this study was to improve the ability of a motor unit model to predict experimentally measured force variability across a wide range of forces. Motor unit discharge characteristics were obtained from 38 motor units of the first dorsal interosseus muscle. Motor unit discharges were recorded in separate isometric contractions that ranged from 4 to 85% of the maximal voluntary contraction (MVC) force above recruitment threshold. High-threshold motor units exhibited both greater minimal and peak discharge rates compared with low-threshold units (P < 0.01). Minimal discharge rate increased from 7 to 23 pps, and peak discharge rate increased from 14 to 38 pps with an increase in recruitment threshold. Relative discharge rate variability (CV) decreased exponentially for each motor unit from an average of 30 to 13% as index finger force increased above recruitment threshold. In separate experiments, force variability was assessed at eight force levels from 2 to 95% MVC. The CV for force decreased from 4.9 to 1.4% as force increased from 2 to 15% MVC (P < 0.01) and remained constant at higher forces (1.2-1.9%; P = 0.14). When the motor unit model was revised using these experimental findings, discharge rate variability was the critical factor that resulted in no significant difference between simulated and experimental force variability (P = 0.22) at all force levels. These results support the hypothesis that discharge rate variability is a major determinant of the trends in isometric force variability across the working range of a muscle.

Action Potentials↗
PubMed1980

Response to sudden torques about ankle in man. II. Postmyotatic reactions.

1. Torques were applied to dorsiflex or plantarflex the ankle joint of normal human subjects who were instructed to react to them in various ways. Myoelectric and mechanical responses were recorded and analyzed. 2. Myoelectric responses in triceps surae or tibialis anterior with times of onset between 100 and 200 ms are conditional on the instruction to the subject and not the direction of the applied torque. These responses are termed postmyotatic responses. 3. The latency of the postmyotatic response is the same in both triceps surae and tibialis anterior. It is not dependent on the direction of the applied torque and consequently is not a "stretch reflex," but a triggered reaction. 4. When the subject is sitting relaxed and instructed to resist the applied torque, the magnitude of the postmyotatic response is highly and linearly correlated with the rate of ankle rotation produced by the disturbing torque. 5. Tonic contraction of the muscles prior to the onset of a stretching torque has only a slight effect on the magnitude of the postmyotatic response and usually reduces it. Prior tonic contraction of the antagonist also has a modest effect in reducing the response. 6. Instructing the subject to resist a torque as quickly and strongly as possible increases the magnitude of the postmyotatic response but has little effect on its linear functional relationship to the magnitude of the mechanical stimulus. 7. The postmyotatic response, although voluntary and kinesthetically triggered, is not completely equivalent to a visually triggered voluntary reaction because under experimental situations designed to measure simple reaction times and choice reaction times of the postmyotatic response, no significant difference is found between the two conditions. 8. It is suggested that the peripheral afferent pathways of the stretch reflex play a dual role in determining postmyotatic responses. First, they provide to supraspinal centers one early proprioceptive signal about limb perturbation that can trigger a previously selected mode of response. Second, they modulate that response by convergence, at the segmental level, of peripheral afferent signals with the descending command signals.

Electromyography↗
PubMed1989

Influence of central set on human postural responses.

1. The effect of central set on automatic postural responses was studied in humans exposed to horizontal support-surface perturbations causing forward sway. Central set was varied by providing subjects with prior experience of postural stimulus velocities or amplitudes under 1) serial and random conditions, 2) expected and unexpected conditions, and 3) practiced and unpracticed conditions. In particular, the influence of central-set conditions was examined on the pattern and magnitude of six leg and trunk electromyograph (EMG) activations and associated ankle torque responses to postural perturbations with identical stimulus parameters. 2. The scaling of initial agonist integrated EMG (IEMG) and torque responses to postural perturbation amplitude disappeared when perturbation amplitudes were randomized. This finding suggests that the initial magnitude of postural responses were centrally set to anticipated postural perturbation amplitudes based on sequential experience with the stimulus. 3. Expectation of postural stimulus amplitude had a significant effect on initial torque responses; subjects overresponded when a larger perturbation was expected and underresponded when a smaller perturbation was expected. Expectation of postural stimulus velocity had a smaller effect on initial torque responses, and subjects consistently overresponded when the velocity of the perturbation was unexpected. This difference in amplitude and velocity expectation may be because of the capacity to encode stimulus velocity, but not amplitude information, into the earliest postural responses of the current trial. The relative strength of amplitude and velocity central-set effects varied widely with individual subjects. 4. Central-set conditions did not affect initial EMG response latencies (100 +/- 20 ms, mean +/- SD) or the relative onset of proximal and distal agonists and antagonists. Unexpected or unpracticed stimulus amplitudes, however, were associated with significant late activation of ankle antagonist, tibialis. Thus errors in initial response magnitude because of central-set effects appear to be partially corrected by reciprocal antagonist activity. Agonist IEMG, however, did not always reflect significant changes in torque responses with central-set conditions. 5. Expectation of postural stimulus amplitude and velocity had two different types of effects on the magnitudes of postural responses: 1) a directionally specific, central-set effect consisting of either increased or decreased responses, depending on expectation of stimulus amplitude; and 2) a nonspecific enhanced response to novel stimulus velocities with a gradual reduction when a velocity was presented repeatedly. Two different neural mechanisms are proposed for these two adaptive effects. 6. Reduction of postural response magnitude and antagonist activity during practice may be partially explained by adaptive mechanisms based on expectation because of prior experience with stimulus velocity and amp

Adult↗
PubMed1992

Responses of cerebellar Purkinje cells to slip of a hand-held object.

1. Two monkeys were trained to grasp, lift, and hold a device between the thumb and forefinger for 1 s. The device was equipped with a position transducer and strain gauges that measured the horizontal grip force and the vertical lifting or load force. On selected blocks of 20-30 trials, a force-pulse perturbation was applied to the object during static holding to simulate object slip. The animals were required to resist this displacement by stiffening the joints of their wrists and fingers to obtain a fruit juice reward. Single cells in the hand representation area of the paravermal anterior lobe of the cerebellar cortex were recorded during perturbed and unperturbed holding. If conditions permitted, the cell discharge was also recorded during lifting of objects of various weights (15, 65, or 115 g) or different surface textures (sandpaper or polished metal), and when possible the cutaneous or proprioceptive fields of the neurons were characterized with the use of natural stimulation. 2. On perturbed trials, the force pulse was always applied to the manipulandum after it had been held stationary within the position window for 750 ms. The perturbation invariably elicited a reflexlike increase of electromyographic (EMG) activity in wrist and finger muscles, resulting in a time-locked increase in grip force that peaked at a latency between 50 and 100 ms. 3. The object-slip perturbation had a powerful effect on cerebellar cortical neurons at a mean latency of 45 +/- 14 (SD) ms. Reflexlike increases or decreases in simple spike discharge occurred in 55% (53/97) of unidentified cells and 49% (21/43) of Purkinje cells recorded in the anterior paravermal and lateral cerebellar cortex. 4. The perturbation failed to evoke complex spike responses from any of the Purkinje cells examined. All the perturbation-evoked activity changes involved modulation of the simple spike discharge. The perturbations stimulated the simple-spike receptive field of most Purkinje cells recorded here, which suggests that the short-latency unit responses were triggered by afferent stimulation. Only one Purkinje cell was found with a distinct complex-spike receptive field on the thumb, but this neuron did not respond to the perturbation. It appears that simple- and complex-spike to receptive fields are not always identical or even closely related. 5. The majority of Purkinje and unidentified neurons that responded to the perturbation had cutaneous receptive fields, although some had proprioceptive fields. Seventy-seven neurons were examined for peripheral receptive fields and were also tested with the perturbation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Rhythmic modulation of the responsiveness of locust sensory local interneurons by walking pattern generating networks.

1. Spiking local interneurons in the thoracic ganglia of the locust are known to process mechanosensory information from leg receptors and to contribute to postural reflexes. It is not clear, however, whether these interneurons are also involved in the control of leg movement during walking or whether their role in mediating local reflexes is phasically modulated by the walking pattern generating networks. To address these questions, intracellular recordings from spiking local interneurons in a midline population were made both in a "fictive walking" preparation reduced to isolated thoracic ganglia and in semi-intact locusts walking on a treadwheel. 2. In fictive walking (and therefore deafferented) preparations, rhythmic synaptic inputs were observed in 72% of the sampled local interneurons. These inputs resulted in a modulation of the interneurons' firing rate in phase with the centrally generated rhythm. A similar rhythmic drive was seen in spiking local interneurons recorded from semi-intact walking locusts. This drive persisted after amputation of the leg from which the interneurons received their sensory inputs. These results indicate that this population of interneurons receives inputs from central networks that participate in the generation of walking. 3. In fictive walking preparations where a hindleg was left attached to its segmental ganglion, individual local interneurons could be characterized physiologically by their receptive field properties. The central inputs were found to modulate the activity of members of all subclasses of interneurons (i.e., purely exteroceptive, purely proprioceptive, and with mixed receptive fields. The mode of modulation observed could oppose or assist the effect of sensory input expected to occur during normal walking.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Unexpected motor patterns for hindlimb muscles during slope walking in the cat.

1. Hindlimb kinematics and motor patterns were assessed from high-speed ciné film synchronized with electromyographic (EMG) data from cats trained to walk on a walkway placed at four grades (25, 50, 75, and 100%). 2. Flexor muscles of the hip (iliopsoas) and ankle (tibialis anterior) had similar activity patterns for the swing phase of up- and down-slope walking; both flexor muscles also had stance-related activity during down-slope walking and this was unexpected. Extensor muscles of the hip (anterior biceps femoris and anterior semimembranosus), knee [vastus lateralis (VL)], and ankle [lateral gastrocnemius (LG)] were active during the stance phase of up-slope walking. The VL and LG activity was reduced in duration during stance of down-slope walking and centered around paw contact. Hip extensors, however, were totally inactive during stance of down-slope walking, and this was not expected. 3. Flexor muscles at the hip and ankle (not extensor muscles) dominated the stance phase of down-slope walking, especially at the steeper slopes. This switch in motor patterns may be required to counterbalance external forces that produced extension at the hip and ankle joints during the stance phase of down-slope walking. Neural mechanisms for programming stance-related activity of flexor muscles are discussed.

Animals↗