PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Reflex, Stretch”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 397 records · Page 22Linked to original sources
PubMed1981

Frequency response characteristics of a multi-loop representation of the segmental muscle stretch reflex.

This paper continues the investigation of a three-loop representation of the segmental muscle stretch reflex system introduced in a preceding communication. Frequency response characteristics were computed for open-loop conditions, control and disturbance signal inputs under a variety of conditions: (i) "in parallel" and "in series" peripheral arrangements of muscle compartments, (ii) various patterns of central connectivity, (iii) various recruitment levels of motor units, (iv) various overall reflex gains, (v) absence or presence of muscle spindle acceleration sensitivity. These computations disclose a number of mechanisms by which the nervous system might improve system stability and behaviour. These mechanisms are discussed with regard to physiological data.

Feedback↗
PubMed1977

C0-contraction and stretch reflexes in spasticity during treatment with baclofen.

Surface electromyograms were recorded from the quadriceps and hamstring muscles of 11 spastic patients during cyclical flexion and extension movements of the knee. A potentiometer strapped to the knee recorded the angle of the joint, the output signal being displayed on an oscilloscope. The patient used this signal to track a sine wave target for 20 cycles. The observer then moved the patient's limb through a further 20 cycles tracking the same target. Recordings were repeated at intervals for four hours after an oral dose of baclofen. Analysis of the recordings showed that the response of a spastic muscle to lengthening is not the same during passive movement as during voluntary movement. In mild spasticity stretch reflexes appear to be suppressed by voluntary effort whereas in severe spasticity they are enhanced. Baclofen suppressed the response to passive stretch by over 30% at plasma concentrations of over 250 ng/ml and by 50% at concentrations of over 400 ng/ml, but this effect was largely extinguised during voluntary movement.

Adolescent↗
PubMed1982

The effects of cerebellar stimulation on the stretch reflex in the spastic monkey.

The effects of stimulating the cerebellar surface on abnormal segmental reflexes were examined in monkeys rendered spastic by either bilateral or unilateral decortication of areas 1, 2, 3, 4 and 6. Rectified, integrated electromyographic (EMG) activity from the biceps and triceps as well as the torque were recorded and averaged during successive flexion-extension movements of the arm produced by a displacement controlled torque motor. Two movement paradigms were employed. The first consisted of a ramp and hold paradigm with an initial rapid flexion of the forearm, a subsequent two second period during which the arm position was held constant, and a rapid extension returning the limb to the initial position. In the second paradigm, the forearm was modulated sinusoidally at several different frequencies. Cerebellar stimulating electrodes were placed over the paravermal region bilaterally. Different frequencies (10 to 300 HZ) and different charge densities (1.5 to 10 microC/cm2) were used in each animal. In each experimental trial short periods of cerebellar stimulation (10 to 30 minutes) were interspersed between control periods. As observed in some types of clinical spasticity, flexion or extension of the extremity was capable of evoking coactivation of the biceps and triceps. Cerebellar surface stimulation reduced the amplitude of the phasic and tonic stretch reflexes recorded from the triceps during flexion and decreased the abnormal triceps response during passive shortening. The biceps response to stretch was increased by cerebellar stimulation and its abnormal response to flexion was decreased. These combined effects modified the organization of the segmental reflexes, producing a more normal reciprocal relationships of the EMG activity in the biceps and triceps. Evaluation of many different combinations of stimulus parameters revealed that not only the magnitude of the passive reflex but also the nature of the effect was dependent on stimulus parameters. Although these studies demonstrate an improvement in the abnormal reflexes present in spastic primates, they emphasize the complexities of the response evoked by cerebellar stimulation and the importance of stimulus parameters in the modifications produced by this technique.

Animals↗
PubMed1984

Corticomotoneuronal cells contribute to long-latency stretch reflexes in the rhesus monkey.

To test the hypothesis that a transcortical reflex contributes to the stretch-evoked long-latency electromyographic (e.m.g.) response we documented the responses of identified corticomotoneuronal (c.m.) cells and their target muscles to perturbations of active wrist movements. Macaque monkeys performed ramp-and-hold wrist movements against elastic loads, alternating between flexion and extension zones; brief (25 ms) torque pulses were intermittently applied during the hold period. C.m. cells were identified by a clear post-spike facilitation in spike-triggered averages of forelimb muscle e.m.g. activity. Activity of c.m. cells and twelve wrist and digit flexor and extensor muscles was recorded during: (a) active ramp-and-hold wrist movements, (b) passive ramp-and-hold wrist movements, and (c) torque perturbations applied during the hold phase of active flexion and extension which either lengthened or shortened the c.m. cell's target muscles. Muscle-lengthening perturbations evoked a reproducible pattern of average e.m.g. activity in the stretched muscles, consisting of two peaks: the first response (M1) had an onset latency of 11.2 +/- 2.1 ms (mean +/- S.D.), and the second (M2) began at 27.9 +/- 5.1 ms. Torque perturbations which shortened the active muscles also evoked a characteristic e.m.g. response consisting of an initial cessation of activity at 13.5 +/- 3.4 ms followed by a peak beginning at 33.9 +/- 3.0 ms. The responses of twenty-one c.m. cells which facilitated wrist muscles were documented with torque pulse perturbations applied during active muscle contraction. Twenty of twenty-one c.m. cells responded at short latency (23.4 +/- 8.8 ms) to torque perturbations which stretched their target muscles. For each c.m. cell-target muscle pair, transcortical loop time was calculated as the sum of the onset latency of the c.m. cell's response to lengthening perturbations (afferent time) and the onset latency of post-spike facilitation (efferent time). The mean transcortical loop time was 30.4 +/- 10.2 ms, comparable to the mean onset latency of the M2 peak (27.9 +/- 5.1). The duration of a c.m. cell's response to torque perturbations provides a further measure of the extent of its potential contribution to the M2 muscle response. In all cases but two, the c.m. cell response, delayed by the latency of the post-spike facilitation, overlapped the M2 e.m.g. peak.

Action Potentials↗
PubMed1979

A possible partitioning of segmental muscle stretch reflex into incompletely de-coupled parallel loops.

Based on previous investigations on focused signal transmission through the muscle stretch reflex system, a model is presented suggesting that different muscle areas (especially in large complex muscles such as the triceps surae muscle) may be regulated rather independently with respect to certain internal state variables, particularly internal length. Since the parallel localized reflex loops necessary for such local control tasks are inevitably coupled peripherally through the muscle and connective tissues, compensatory de-coupling elements would be required to reestablish at least partial independence. Whether and how this can be achieved at the level of spinal neuronal circuitry is investigated in connection with a discussion of the advantages of partially de-coupled reflex loops.

Animals↗
PubMed1983

Adaptive plasticity in the primate spinal stretch reflex: reversal and re-development.

Monkeys can gradually increase or decrease the amplitude of the segmentally mediated spinal stretch reflex (SSR) without change in initial muscle length or background EMG activity. Both increase (under the SSR increases mode) and decrease (under the SSR decreases mode) occur slowly, progressing steadily over weeks. The present study investigated reversal and re-development of SSR amplitude change. Over a period of months, following collection of control data, monkeys were exposed to one mode, then to the other, and then to the first mode again. Development, reversal, and re-development of change all took place over weeks, following very similar courses. These data are consistent with the hypothesis that persistent segmental alteration underlies SSR amplitude change. Such persistent segmental alteration would constitute a technically accessible substrate of memory.

Adaptation, Physiological↗
PubMed1993

Recovery of stretch reflex responses following mechanical stimulation.

The recovery behaviour of mechanically evoked stretch responses was investigated. Stimuli which promoted identical dorsiflexing movements around the ankle joint were applied to ten subjects in two positions, seated and upright. The experimental sets comprised single as well as double dorsiflexing displacements. In the latter the stimuli were elicited for durations of either 100, 200 or 400 ms. Stretch responses following the first displacements were related to the stretch velocity but not to the amplitude. The responses of the plantar flexors following the second mechanical dorsiflexion were reduced with respect to the delay time between the first and second displacement. In addition, the magnitudes of these responses depended on the functional task: the stretch responses recovered much faster in the standing position when the triceps surae muscle was only slightly activated, whereas in the relaxed sitting position the reflexes remained suppressed. Both reciprocal inhibition, as well as the time course of the reformation of intrafusal cross-bridge links, may help to explain the depression of the monosynaptic stretch reflex.

Adult↗
PubMed1979

[The influence of benzoctamine on dopamine and norepinephrine contents in substantia nigra and on the muscle stretch reflex of the cat (author's transl)].

The concentration of dopamine (DA) and norepinephrine (NE) are decreased to a maximum of 40% and 20%, respectively, in the substantia nigra of precollicular and prenigral decerebrated cats previously treated with benzoctamine (Tacitin) (0.7 mg/kg i.v.), while the tyrosine-hydroxylase and MAO activities remain unchanged. Muscle stretch reflexes recorded simultaneously showed a significant decrease of stretch tension which is evoked by a clear reduction of Ia discharges of the primary muscle spindle afferents. It would appear that benzoctamine suppresses reflexly evoked gamma-motoneurone discharges.

Animals↗
PubMed1978

Spinal mechanisms of the functional stretch reflex.

A sudden and rapid angular displacement of the limb evokes, in human and monkey subjects, a segmented pattern of electromyographic activity in muscles which are stretched. While the first segment is acknowledged to represent a tendon jerk, it has been proposed that the second segment, occurring with a shorter latency than a reaction time, is mediated by a transcortical loop. The present experiments were conducted in cats to determine the properties of muscle responses to torque perturbations analogous to those used in the monkey, and to determine if the integrity of supraspinal pathways is required for the individual response segments to occur. Torque perturbations which flexed the forearm evoked a segmented response in the electromyogram of the cat triceps muscle. This response typically consisted of three early segments with latencies of 10, 30 and 60 msec which were similar to the M1, M2, and M3 segments described in the monkey. The M3 and occasionally M2 components were depressed when the cat followed rather than resisted the perturbation. A torque pulse of 10 msec duration was sufficient to elicit a near maximal M1 response while torque pulses in excess of 20 msec were required to evoke the M2 response. To determine if any of these components required mediation by the cerebral cortex, experiments were conducted in decerebrate and spinal cats. Similar torque perturbations produced segmented electromyographic responses in the triceps muscles which were indistinguishable in their timing from those observed in intact cats. The torque required to produce the segmented responses was comparable as well. All three segments were dependent upon the activation of receptors in the homonymous muscle and did not require cutaneous input. These observations show that receptor properties and/or spinal mechanisms involved in the stretch reflex are sufficient to produce a segmented response similar to that observed in intact animals.

Animals↗
PubMed1966

Postsynaptic versus presynaptic inhibition in antagonistic stretch reflexes.

Motoneurons of the cat gastrocnemius-soleus muscle were studied intracellularly with conventional glass micropipettes. Each of these motoneurons was made to fire repetitively by stretch of its own muscle (gastrocnemius-soleus), and by current injected through the impaling microelectrode. By comparing the amount of inhibitory influence from antagonistic stretch of posterior biceps on the repetitive firing in these two different situations, an estimate could be obtained of the relative contribution of postsynaptic inhibition in this type of antagonistic stretch reflex. Even when the experimental conditions were such as to favor presynaptic inhibition, only strong postsynaptic inhibitory effects were seen; presynaptic inhibition was not found.

Animals↗
PubMed2001

Transcranial magnetic stimulation and stretch reflexes in the tibialis anterior muscle during human walking.

Stretch of the ankle dorsiflexors was applied at different times of the walking cycle in 17 human subjects. When the stretch was applied in the swing phase, only small and variable reflex responses were observed in the active tibialis anterior (TA) muscle. Two of the reflex responses that could be distinguished had latencies which were comparable with the early (M1) and late (M3)components of the three reflex responses (M1, M2 and M3) observed during tonic dorsiflexion in sitting subjects. In the stance phase a single very large response was consistently observed in the inactive TA muscle. The peak of this response had the same latency as the peak of M3, but in the majority of subjects the onset latency was shorter than that of M3. The TA reflex response in the stance phase was abolished by ischaemia of the lower leg at the same time as the soleus H-reflex, suggesting that large muscle afferents were involved in the generation of the response. Motor-evoked potentials (MEPs) elicited in the TA by transcranial magnetic stimulation (TMS) were strongly facilitated corresponding to the peak of the stretch response in the stance phase and the late reflex response in the swing phase. A similar facilitation was not observed corresponding to the earlier responses in the swing phase and the initial part of the response in stance. Prior stretch did not facilitate MEPs evoked by transcranial electrical stimulation in the swing phase of walking. However, in the stance phase MEPs elicited by strong electrical stimulation were facilitated by prior stretch to the same extent as the MEPs evoked by TMS. The large responses to stretch seen in the stance phase are consistent with the idea that stretch reflexes are mainly involved in securing the stability of the supporting leg during walking. It is suggested that a transcortical reflex pathway may be partly involved in the generation of the TA stretch responses during walking.

Adult↗
PubMed1981

[Hand-stretching reflex in children of different age and sex indicative for left- or right-handedness (author's transl)].

Young boys and girls when opening their mouth show an involuntary movement of one or both hands, i.e. slight flexion with maximal extension of fingers. The highest incidence of this "hand-stretching reflex" (HSR) is found in the age group of 4 to 5. Below this age more girls than boys are found with a positive HSR, whereas at the age of eleven girls are outnumbered by boys. Beyond this age the reflex disappears. Lefthandedness and leftsided reflex seem to correspond and vice versa. Lack of this reflex in the age group of 4 to 5 as well as persistence over the age of eleven seems to indicate retarded cerebral maturation.

Age Factors↗
PubMed1991

Dependence of autogenic and heterogenic stretch reflexes on pre-load activity in the human arm.

1. Subjects held their right arm in a horizontal plane. The angle of the elbow was 90 deg. They exerted forces in several directions in the plane of the arm, varying independently the pre-load torques about shoulder and elbow. We measured electromyographic (EMG) activity in several arm muscles in response to force perturbations which extended the shoulder, without changing the elbow angle. 2. The EMG activity in flexors of both shoulder and elbow showed reflex responses at short latency (approximately 25 ms). In all muscles the reflex activity increased with the pre-load activity of that muscle. 3. The short-latency reflex activity of m. brachialis, which was not stretched by the perturbations, was independent of the pre-load activity of the muscles acting over the shoulder. 4. From these results we conclude that the force resulting from the short-latency reflex, assessed from the EMGs, does not counteract the perturbations exactly. Having found that the short-latency reflex is dependent on the pre-load direction, we argue that this dependence makes the short-latency reflex suitable for correcting fast movements for misjudgements of load. 5. At longer latencies (greater than 50 ms) the direction of the force resulting from the reflex, assessed from the EMGs, was almost independent of the direction of the pre-load. In our experiment the force resulting from the long-latency reflex counteracted the perturbations quite well.

Arm↗
PubMed1970

Oscillation in the stretch reflex arc and the origin of the rhythmical, 8-12 C-S component of physiological tremor.

1. A brief downward, stepwise displacement applied to the outstretched finger gives rise to a train of approximately sinusoidal movements of it, lasting often more than 1 sec. The frequency of these waves is the same, in any one subject, as that of physiological tremor.2. The oscillations are regular in form, and bear a constant phase relation to the applied displacement; they can be summated using an averaging computer (Biomac 1000) triggered by the mechanical stimulus.3. The oscillations are altered in the same way as is physiological tremor by a number of factors. Cooling the arm before recording lowers the frequency, warming raises it, while the application of an arterial cuff decreases the amplitude and tends to elevate the frequency. These factors have effects of similar magnitude on both the oscillations and the tremor. It thus appears highly likely that the waves produced by a mechanical input and physiological tremor waves are due to the same process, namely oscillation in an underdamped servo-system.4. The oscillation is not due simply to the mechanical, die-away resonance of the finger, because bursts of muscle action potentials can be recorded in phase with the finger movements both in the wave train evoked by the mechanical displacement and during normal tremor.5. It is concluded that physiological tremor in the 8-12 c/s band is due to oscillation in the stretch reflex servo-loop.

Action Potentials↗
PubMed1983

The effects of cutaneous mechanoreceptor stimulation on the stretch reflex.

The effects of cutaneous stimulation on tonic and phasic responses to stretch were studied in the triceps surae complex of unanesthetized, decerebrate cats. The tonic response was produced by a maintained stretch of the muscle group to 80-85% of its maximum length. Stretch was applied directly to the isolated tendon at the calcaneus. Phasic responses were elicited by a ramp stretch of 1.0 to 2.0 mm superimposed on the maintained stretch. Mild, brief, electrical or mechanical stimulation of the plantar cushion caused a sequence of inhibitory and excitatory changes in the tonic EMG activity in the soleus muscle. Mild stimuli, applied 0.01 to 5 ms before the start of ramp stretch, decreased the size of the phasic response to stretch and converted it into a biphasic response. It is suggested that stimulation of cutaneous mechanoreceptors may be responsible for variations in the initial burst of EMG activity seen in the agonist muscle during the response to perturbation or fast voluntary movement in animals and man.

Animals↗
PubMed2000

Studies of the human stretch reflex.

We recorded the late electromyographic (EMG) responses to predictable and unpredictable stretches of the wrist flexor and extensor muscles during ballistic movement or isometric contractions. We simultaneously recorded the accompanying cerebral responses. Our findings suggest that the late EMG responses are influenced by suprasegmental (cerebral) phasic mechanisms that seem to have a dual functional role, being involved in the control of limb stiffness and in a servomechanism to return the displaced limb to its intended position.

Electromyography↗
PubMed1991

Effect of muscle length on phasic stretch reflexes in humans and cats.

1. This is a report of the effects at different muscle lengths of the muscle's immediate history on the tendon jerk and Hoffman (H)-reflex in triceps surae of human subjects and cats. 2. In adult human subjects the size of the tendon jerk was measured as electromyogram (EMG) and torque in response to a tendon tap. Before each test tap the muscle was conditioned by a maximum voluntary contraction carried out with the foot either plantarflexed or dorsiflexed by 30 degrees from the test position. After a contraction with the foot dorsiflexed, the subsequent reflex response was smaller than after a contraction with the foot plantarflexed. 3. The same conditioning procedure was carried out with the H-reflex. The reflex was elicited by transcutaneous electrical stimulation of the tibial nerve in the popliteal fossa. Here the reflex after a contraction with the foot dorsiflexed was larger than after plantarflexion. In other words, the effects of conditioning were the opposite for the tendon jerk and H-reflex. 4. The effects of muscle conditioning were tested over a range of muscle lengths. As the test length was made progressively longer, that is, the foot more dorsiflexed, the difference in size of the tendon jerk following the two forms of conditioning became less, whereas for the H-reflex it remained the same. 5. These findings were confirmed in cats anesthetized with alpha-chloralose. The tendon jerk was elicited by a quick stretch applied to the triceps surae muscle group, and the H-reflex represented by the monosynaptic reflex recorded from the central, cut end of the ventral root in response to electrical stimulation of the triceps nerve. Muscle conditioning consisted of a 1-s period of stimulation at 20 pulses/s, at fusimotor strength, of the peripheral end of the cut ventral root at a muscle length 5 mm longer or shorter than the test length. In the cat, as in human subjects, the effect of conditioning on the tendon jerk reversed at long muscle lengths, whereas the monosynaptic reflex showed no reversal. 6. It had been proposed previously that the effects of conditioning on stretch reflexes could be explained by development of slack in the intrafusal fibers of muscle spindles after a contraction at a longer-than-test length. The presence of slack lowers the resting discharge of spindles and reduces the afferent response to a tendon tap.(ABSTRACT TRUNCATED AT 400 WORDS)

Achilles Tendon↗