Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Reflex, Stretch”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

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

At least 19 recordsLinked to original sources
PubMed1976

Improvement in linearity and regulation of stiffness that results from actions of stretch reflex.

We studied stretch reflexes of soleus muscles of intercollicularly decerebrated cats using a new technique for estimating the component of a stretch reflex that results from the purely mechanical properties of the active muscle (mechanical response). The difference between a net stretch reflex and its underlying mechanical response provided a direct measure of reflex action. 1. The relative contributions of reflex action and the mechanical response are different for stretch and release. With stretch, reflex action is generally large and the mechanical response small. The opposite is true with release. The property that remains relatively constant, when stretch and release are compared, is the net stiffness in opposition to length change. We concluded that reflex action compensates for variations in the inherent stiffness of the muscle. 2. Compensation is effective over a range of intermediate values of initial force, but it fails whenever the reflex force approaches zero or the maximal force at that length. 3. Reflex action is capable of modifying muscular force within 22 ms of the onset of length change. This indicates that even during a fast gallop, there is sufficient time for reflex action. 4. The mechanical properties of the active soleus muscle are highly nonlinear; e.g., muscular stiffness becomes negative transiently during stretch. In stable decerebrate preparations we found that reflex action resulted in a considerable improvement in linearity. 5. Our results support two complementary hypotheses: a) stiffness may be the regulated property of the stretch reflex, and b) the main function of autogenetic reflexes may be to conpensate for variations in the properties of skeletal muscle rather than to oppose changes in load.

Animals↗
PubMed1976

An investigation of the servobehavior of the stretch reflex.

The stretch reflex is often described as a device for assisting in the regulation of muscle length or as a spinal servomechanism. Observation of the response to experimental interruption of voluntary movements fails to demonstrate a significant role for spinal reflexes. Functional responses with a latency of 120 ms, implying supraspinal mediation, are observed.

Electromyography↗
PubMed1976

Regulatory actions of human stretch reflex.

1. The stretch reflex in the elbow flexor musculature was studied in 23 human subjects. The subjects were required to establish an initial force equivalent to 10% maximum at a prescribed initial length; mechanical disturbances delivered at random times increased load force to 15% or reduced it to 5%. We measured arm force, displacement, and EMG (usually biceps); acceleration was calculated from displacement, and average responses from sets of 10 like trials. 2. Modification of the stretch reflex was studied by comparing average responses obtained with different instructions, but with the same disturbance. The usual introductions were "compensate for arm deflection" and "do not intervene voluntarily". The initial response did not depend on instruction; changes in response that depended on instruction began abruptly after a latent period which ranged from 70 to 320 ms (measured from force and acceleration), depending on conditions and subject. The latency became longer (10-50 ms) and more variable when the subject did not know the direction of disturbance in advance. This and other observations indicate that modifications of the stretch reflex are not produced by servo actions. They are produced by triggered reactions, which occur at both short and long latencies and which have properties resembling the movements produced in a reaction-time task. 3. We confirmed that most subjects can suppress triggered reactions when the instruction calls for no intervention, leaving an unmodified reflex response. This response consists of a compliant deflection of the arm in the direction of the disturbance. 4. The compensatory actions associated with unmodified stretch (and unloading) reflexes were assessed from EMG responses of biceps. During a 300-ms transient phase, EMG changes were notably asymmetric when responses to symmetric disturbances were compared. Increased force stretched biceps and produced a prominent increase in EMG, whereas decreased force allowed biceps to shorten and produced either an EMG decrease of smaller magnitude or an actual increase. These asymmetric reflex actions produced quite symmetric mechanical responses (arm displacements and forces), which implies the existence of and compensation for nonlinear muscle mechanical properties. This result is discussed in relation to the hypothesis that the function of the stretch reflex is to compensate for variations in muscle properties, thus maintaining stiffness. 5. Effective control of muscle length or joint position does not result from servo action by the stretch reflex. Errors in position are corrected only when triggered reactions are superimposed on the reflex response.

Adult↗
PubMed1978

Reciprocal inhibition during the tonic stretch reflex in the decerebrate cat.

1. The aim of this study was to investigate post-synaptic reciprocal Ia inhibition during the stretch reflex; particularly the extent to which an increased Ia excitation of the Ia inhibitory interneurones will be counteracted by recurrent inhibition from motor axon collaterals. For this purpose we investigated depression of monosynaptic test reflexes antagonist flexors (reciprocal inhibition) during static stretch of quadriceps or triceps surae in unanaesthetized decerebrate cats. 3. With increasing stretch of the extensor muscle there was first a linear augmentation of reciprocal inhibition, but along with the stretch reflex in the extensor a plateau appeared in the inhibition of the flexors, although the extensor stretch reflex (judged by the e.m.g.) increased with further stretching. Within the range of stretching of triceps surae which gave increased stretch reflexes the plateau in the reciprocal inhibition was usually maintained, while during stretching of quadriceps a second phase of augmenting reciprocal inhibition often appeared. Stretch beyond the level which increased the stretch reflex activity gave augmenting reciprocal inhibition both in case of quadriceps and triceps surae. 3. Excitability measurements from central terminals of Ia afferents revealed that the increasing reciprocal inhibition during increasing stretch reflex activity in quadriceps was associated with a primary afferent depolarization in knee flexor Ia afferents; there was no corresponding effect in ankle flexor Ia afferents during stretch reflexes in triceps surae. 4. The primary afferent depolarization evoked in knee flexor Ia afferents by electrical nerve stimulation was then compared with the presynaptic inhibition of knee flexor monosynaptic test reflexes produced by the same stimuli. The results suggest that the second phase of increasing reciprocal inhibition in knee flexors is due to presynaptic inhibition and accordingly that the depth of post-synaptic reciprocal inhibition remains constant at different degrees of stretch reflex activity in both knee and ankle extensors. 5. It is postulated that during increasing stretch reflex activity the increment in Ia excitation and recurrent inhibitio; on to the Ia inhibitory interneurones almost exactly balance each other. It is suggested that recurrent inhibition of Ia inhibitory interneurones may serve as a segmental autoregulatory mechanism to keep 'alpha-gamma-linked reciprocal inhibition' at a constant depth during different levels of agonist activity.

Animals↗
PubMed1976

Stretch reflex and servo action in a variety of human muscles.

1. In the long flexor of the thumb the latency of the stretch reflex and of other manifestations of servo action is some 45 msec, roughly double the latency of a finger jerk. 2. Tendon jerks are feeble or absent in the long flexor of the thumb even in subjects with brisk long-latency stretch reflexes in this muscle. This, and other facts, suggests that the nervous mechanism of the tendon jerk is different from that of the stretch reflex. 3. A muscle that has feeble tendon jerks may show a late component in the response to a tendon tap, with a latency similar to that of the long-latency stretch reflex. 4. On the hypothesis that the excess latency of the stretch reflex over that of a tendon jerk is because the stretch reflex employs a cortical rather than a spinal arc, the excess would be expected to be larger in magnitude for the long flexor of the big toe and smaller for the jaw closing muscles. This is confirmed, 5. An alternative hypothesis that the long latency of stretch reflexes in thumb and toe is because they are excited by slow-conducting afferents is made improbable by the finding that stretch reflexes with an equal or greater excess latency are also found in proximal arm muscles. 6. The long-latency stretch reflex in proximal muscles was seen most distinctly in a healthy subject who happened to have feeble or absent tendon jerks. In ordinary subjects there is often a large, short-latency, presumably spinal component of the stretch reflex in proximal muscles; and short-latency responses to halt and release are also seen, The significance of this spinal latency servo action in proximal muscles remains to be explored. 7. The Discussion argues that the available data on conduction time to and from the cerebral cortex are compatible with the hypothesis that the long-latency component of the stretch reflex uses a transcortical reflex arc, and that none of the experiments described in the present paper are inimical to this view.

Biomechanical Phenomena↗
PubMed1991

Stretch reflex variation in the relaxed and the pre-activated quadriceps muscle of normal humans.

The stretch reflex to patellar tendon taps was quantified by force measurements at the ankle in 7 normal subjects. In each experiment the stretch reflex was elicited from 14 consecutive stretches by two types of hammers (an ordinary hand-held hammer and a motorized hammer) in the relaxed and the pre-activated quadriceps muscle. The coefficient of variation for the 14 stretch reflexes fell from 54% in the relaxed muscle to 39% in the contracting muscle (p less than 0.05). The stretch reflex varied less between the different levels of active contraction than between the relaxed state and the contracted level (p less than 0.05). The experiment was repeated in all subjects and at all contraction levels. The coefficient of variation of the mean for the two experiments fell non-significantly from a mean value of 27% in the relaxed muscle to 14% in the contracting muscle. The coefficients of variation for the two hammers were almost identical. It is concluded that quantification of the stretch reflex can be made more precisely in the contracting muscle.

Adult↗
PubMed1978

The stretch reflex in the Eaton Lambert syndrome, myasthenia gravis and myotonic dystrophy.

The stretch reflex at rest and after muscle work was studied in three cases of Eaton Lambert syndrome. After muscle work a potentiation of the stretch reflex was demonstrated clinically and electrophysiologically. The presence of muscle stretch reflexes and their potentiation after muscle work was correlated with the clinical stage of the disease. The enhancement of the stretch reflex after voluntary effort was absent in normal subjects, myasthenia gravis and myotonic dystrophy.

Action Potentials↗
PubMed1992

Evidence that a long latency stretch reflex in humans is transcortical.

1. The hypothesis that the long latency reflex response to muscle stretch in humans uses a transcortical pathway was tested by looking for convergence onto cortical neurones in eleven normal subjects. 2. Postsynaptic events in single flexor pollicis longus (FPL) motoneurones were derived from changes in the firing probability of individual FPL motor units. 3. Extension of the terminal phalynx of the thumb resulted in both short latency and long latency facilitations of individual FPL motoneurones. These were not reproduced by electrical stimulation of afferents in the terminal phalynx. Magnetic stimulation over the contralateral motor cortex produced strong, short latency facilitation of FPL motoneurones. 4. When the facilitation produced by stimulation over the cortex was superimposed on the long latency facilitation produced by extension of the thumb, the facilitation produced by both stimuli was greater than the sum of the individual facilitations produced by either stimulus given alone. This was not the case when the superimposition occurred on the short latency response to stretch. 5. We conclude that afferent systems excited by the stretch of FPL converge onto cortical neurones which are known to facilitate motoneurones. Thus the cortex is likely to contribute to the long latency stretch reflex in humans.

Adult↗
PubMed1977

An estimate of the secondary spindle receptor afferent contribution to the stretch reflex in extensor muscles of the decerebrate cat.

1. Vibration or stretch of the medial gastrocnemius muscle in the decerebrate cat each caused a significant increase in the tension of a synergist, the lateral gastrocenmius. 2. Simultaneous vibration and stretch of the medial gastrocnemius resulted in a substantial increase of lateral gastrocnemius tension which was greater that that produced by medial gastrocnemius vibration alone. The size of this force increase was proportional to the amplitude of medial gastrocnemius stretch, for the limited range of amplitudes examined. 3. Since the discharge of the medial gastrocnemius I a afferent fibres was held constant by vibration, the additional tension in lateral gastrocnemius provoked by medial gastrocnemius stretch must have resulted from the activation of an excitatory pathway separate from the I a afferent system. The secondary spindle afferent pathway was considered to be the most likely candidate. 4. The contributions of the Ia afferents and the additional stretch induced excitation to the stretch reflex were compared. The Ia potency was calculated from the ration of tonic vibration reflex force and the vibration frequency. The total Ia contribution to the stretch reflex, which was estimated from the product of this ratio and the primary ending stretch sensitivity, seemed modest, and was consistently smaller than the proposed secondary contribution. 5. The medial gastrocnemius nerve was subjected to anodal blockade at a strength sufficient to eliminate Ia transmission. Under these conditions, the lateral gastrocnemius excitation produced by medial gastrocnemius stretch or vibration was largely eliminated. When lateral gastrocnemius vibration was superimposed, the excitatory effect of medial gastrocnemius stretch was partly restored suggesting that some central facilitation by group Ia afferents may be necessary for group II pexcitatory effects to be manifested. 6. Although the additional excitatory actions of medial gastrocnemius stretch were examined exclusively in a synergist, it is suggested that similar effects are likely to occur in the homonymous stretch reflex.

Animals↗
PubMed1975

The mode of action of 5-hydroxytryptophan in facilitating a stretch reflex in the spinal cat.

1. Intravenous injection of 5-hydroxytryptophan (5-HTP) excites discharges of gamma motoneurones to extensor muscles of the hind limbs of decerebrate spinal cats and this occurs with a short latency (1-2 min). 2. 5-HTP also facilitates the stretch reflex in the spinal cat but, in contrast, there is a latency of about 10 min with a maximum action after 20 min. 3. Facilitation of the stretch reflex by 5-HTP still occurs when the gamma loop has been opened by cutting all ventral roots supplying the muscle. Thus excitation of gamma motoneurones by 5-HTP is not required for facilitation of the stretch reflex. 4. A possible contribution to the stretch reflex from the increased discharge of gamma motoneurones has been assessed. Selectively removing gamma activity rarely altered the reflex response to stretch and in only 3 out of 15 spinal cats could we conclude that gamma discharges contributed towards facilitation of the stretch reflex by 5-HTP; 5; Methysergide (0.25 mg/kg) blocked completely the facilitation of the stretch reflex caused by 5-HTP in the spinal cat but only partially antagonised the reflex in the decerebrate cat, even when injected intra-arterially close to the lumbar spinal cord. 6. Lysergic acid diethylamide (LSD) was found to mimic the actions of 5-HTP. It facilitated the stretch reflex and excited extensor gamma motoneurones in the spinal animal.

5-Hydroxytryptophan↗
PubMed1979

Tonic stretch reflexes in lip, tongue and jaw muscles.

Despite considerable speculation it remains unclear as to whether stretch reflexes perform a functional role in speech articulator muscles. Recent research, however, has shown that long loop stretch reflex mechanisms are brought into play during voluntary contraction of limb muscles and a functional role in oscillatory damping has been suggested. It was decided, therefore, to use a method and a technique of analysis similar to that used in limb muscles to search for tonic stretch reflex (TSR) responses in lip, tongue and jaw muscles during sustained voluntary contraction. The term 'action TSR' is used to differentiate stretch reflex responses measured from voluntary activity from those measured at rest. Simultaneous electromyogram (EMG) recordings were taken from the lip, tongue and jaw musculature in normal, stutterer and cerebral spastic subjects. Subjects were instructed to hold the appropriate articulator in a fixed position while the experiment applied an irregular, continuously changing, stretching force. The stretch and EMG signals were analyzed using a cross correlation and spectral analysis technique. This provided a sensitive means of detecting any EMG fluctuations which covaried with applied stretch and might therefore be classified as reflex. No suggestion of such action TSR responses could be found in lip or tongue muscles of any of the subjects tested, including the cerebral spastic subjects with dysarthric speech. It is therefore concluded that action TSR mechanisms are not operative in control of lip and tongue muscles in man. Furthermore, dysarthric speech in cerebral spasticity cannot be attributed to exaggerated tone of lip and tongue muscles resulting from hypersensitivity of TSR mechanisms. In contrast, clear action TSR responses were demonstrable in jaw closing muscles while in jaw opening muscles, small amplitude responses were detected but were not substantial in comparison with background activity. Since the action TSR is present in jaw and limb muscles, but absent in lip and tongue muscles, the suggestion of a functional role of this reflex in damping mechanical oscillations associated with inertial loads is further supported.

Adult↗
PubMed1979

The effects of cold-induced muscle spindle secondary activity on monosynaptic and stretch reflexes in the decerebrate cat.

The effects of muscle spindle secondary ending activity on the stretch reflex were studied in unanesthetized decerebrate cats. Activation of secondary endings was accomplished by reducing the muscle temperature. This has been shown to cause a sustained asynchronous discharge from secondary endings. Cooling of the medial gastrocnemius or lateral gastrocnemius-soleus muscles caused an increase in the phasic and tonic components of their stretch reflexes. Cooling of the relaxed medial gastrocnemius muscle caused similar increases in the components of the stretch reflex of the synergistic lateral gastrocnemius-soleus muscle and an increase in its monosynaptic reflex. It was concluded that the facilitatory autogenetic and synergistic effects of muscle cooling on the stretch and monosynaptic reflexes were brought about by activity in group II afferents from muscle spindle secondary endings and could not be ascribed to any other type of muscle receptor. These results support the concept of an excitatory role for the secondary endings of the muscle spindle in the stretch reflex of the decerebrate cat.

Animals↗
PubMed1979

Somatosensory evoked potential of the stretch-reflex (T-reflex).

Averaging of EEG recorded monopolarly from C3, contralateral to the activated limb, in the stretch reflex shows the presence of somatosensory evoked potential (SSEP) with characteristic shape: four constant waves--P29, N84, P202 and N294, and four inconstant waves--N31, P74, P99 and N123. Comparison of this SSEP with the SSEP in children, evoked in the stretch reflex, shows shorter latencies of the waves in adults. On the basis of data from the different series of experiments, it is assumed that kinesthetic signalization plays a dominant role in the genesis of SSEP of the T-reflex. Studies have shown that SSEP of the T-reflex is succeptible to habituation upon long repetition of the stretch reflex.

Achilles Tendon↗
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↗
PubMed1992

The influence of the shape of mechanical stimuli on muscle stretch reflexes and SEP.

Stretching of human thenar muscle was carried out using mechanical stimuli of different amplitudes and velocities in 50 normal subjects. Amplitudes of early M1 and late M2 reflex responses as well as cortical evoked potentials were recorded. M1 and M2 increased with a larger mechanical stimulus. Steeper mechanical stimuli generated larger M1 amplitudes, whereas M2 remained unaffected. Amplitudes of early cortical evoked potentials increased with increase of both rise-time and amplitude of muscle stretch. The shape of the mechanical stimulus is critical for the resulting reflex response. The different behaviours of M1 and M2 with increasing stimulus velocity are in favour of their different origins. Our results support a participation of slowly conducting muscle spindle afferents in the generation of the late M2 response in distal human hand muscles.

Adult↗
PubMed1991

Radiation of phasic stretch reflex in biceps brachii to muscles of the arm in man and its restriction during development.

1. The phasic stretch reflex in biceps brachii has been recorded in 372 normal subjects aged from 31 weeks gestation to 55 years. The stimulus used was a brief mechanical pulse delivered by a hand-held electromagnetic vibrator and the response was measured in the surface electromyogram. 2. The threshold for eliciting the reflex was low in the newborn and increased over the first 6 years to values corresponding to those of adults. 3. On the basis of timing it is concluded that the phasic stretch reflex has a monosynaptic component at all ages. 4. The surface electromyogram was also recorded in triceps brachii, pectoralis major, deltoid and hypothenar muscles. In some subjects evoking the phasic stretch reflex in biceps brachii resulted in short latency responses in these muscles, a phenomenon termed radiated response. 5. The probability of occurrence of radiated responses and their magnitudes were greatest at birth and decreased over 2-4 years. 6. Experiments were performed to determine how far mechanical transmission of the stimulus to biceps through the tissues of the arm might account for the radiated responses in the other muscles studied. It was concluded that the responses observed in triceps brachii, pectoralis major, deltoid and hypothenar muscles, following vibration of the biceps tendon, are primarily due to the radiation of the activity carried in biceps muscle afferents to the alpha-motoneurones of the respective muscles. 7. On the basis of timing it is concluded that in subjects below 2 years the radiated responses in the muscles studied have a monosynaptic component.

Adolescent↗
PubMed1991

The human stretch reflex and the motor cortex.

The spinal stretch reflex, exemplified by the tendon jerk, appears to be less important in humans than a delayed 'long-latency' response. This is easily observed when muscles of the hand are stretched while they are already contracting voluntarily. On limited evidence, many have long held that the delayed response is a transcortical reflex and have tended to neglect alternative possibilities, particularly that it might be a spinal reflex dependent upon slow afferents. New experiments have now eliminated the alternatives, leaving the transcortical hypothesis in command of the field.

Animals↗