Phasic Stretch Reflex Research Articles

Quantitated flexor response in acute spinal cord injury patients.

Flexor reflexes were compared with phasic stretch reflexes in 12 acute spinal cord injury patients with upper motor neuron lesions. Initial flexor reflex activity appeared later than initial stretch reflex activity in the majority of cases whereas maximal flexor reflexes developed at about the same time as maximal stretch reflexes. A quantitative method for evaluating flexor and stretch reflex activity at bedside is presented.

Expectancy effects in a psychophysiological experiment

The effect of the experimenter’s expectations about experimental outcomes on two physiological variables (EMG and EEG) were investigated in an experiment involving a tendon tap stimulus used to elicit a phasic stretch reflex. Experimenter’s and subject’s perceived locus of control scores were incorporated into the design to test their relevance as a mediating variable. Immediately after the presentation of the tendon tap stimulus, subject’s EEG alpha measures were found to be more biased in the direction of the experimenter’s expectations when experimenters and subjects were similar in their scores on the perceived locus of control scale. Biasing effects on EEG alpha measures in the direction of experimenter’s expectations were found early in the experimental session where subjects or their experimenters scored as internally controlled. The EMG measures increased or decreased in the direction of the experimenter’s expectations when subjects were internally controlled but there was a reversal of the direction of the experimenter’s expectations with subjects who scored as externally controlled so that no significant experimenter expectancy effect was observed.

Effects of skin cooling on stretch reflex activity in triceps surae of the decerebrate cat

The effects of selective skin stimulation by cooling on the stretch reflexes in triceps surae were studied in the midcollicularly decerebrated cat. Stretch reflexes were elicited with a muscle puller allowing the determination of responses to dynamic and static stretch. The skin overlying the lateral gastrocnemius was freed into a flap, and 8.6 cm 2 of this cooled with a thermoelectric cooling module. Lowering temperature to 10 ± 2 C produced an 11% decrease in the tonic component of the triceps surae stretch reflex, without significantly altering the amplitude of the phasic component. Cooling by applying ice cubes to the skin flap, a procedure involving mechanical stimulation, augmented both the tonic (11%) and the phasic (15%) stretch responses. The removal of the ice cubes depressed both responses for 30 sec. It is concluded that selective cooling of the skin receptors can depress tonic stretch reflexes of underlying muscle in the decerebrated cat. This effect differs from the facilitatory effect on phasic and tonic stretch reflexes characteristic of less selective forms of cutaneous stimulation.

Intermittent contralateral and ipsilateral hemiretinal stimulation and its effect on the phasic stretch reflex

The effect of visual stimulation on the phasic stretch reflex, measured isometrically by way of EMG recordings, was investigated with normal human subjects. Three experimental treatments were applied, namely 3 flashes of light presented as hemiretinal contralateral stimulation prior to tendon taps; similar hemiretinal stimulation presented ipsilaterally; and no flashes of light as a control condition. The analysis of variance showed that the MAP means and standard deviations for both of the lights conditions were significantly greater than for the control condition. Eleven out of 12 subjects showed a larger reflex response to stimulation of the brain ipsilateral to the tendon stimulated. The findings are discussed in terms of visual projections differentially affecting alpha and gamma motoneurons.

Afferent and efferent activation of human muscle receptors involved in reflex and voluntary contraction

Single-unit activity from muscle nerve fibers was recorded with tungsten electrodes from the median nerve in unanaesthetized normal human subjects. Afferents were identified from individual Golgi tendon organs or muscle spindles during the phasic stretch reflex and the electrically stimulated twitch contraction. When the phasic reflex was initiated during a slight voluntary contraction, Golgi tendon organ firing was recorded in the postreflex silent period. In the electrically induced twitch contraction the muscle spindle fired a phasic burst of impulses during the relaxation phase of the contraction. This latter test proved to be highly reproducible and useful in verifying the dynamic sensitivity of the spindle. In a voluntary contraction, the Golgi receptor was activated in relation to the force of contraction, and during the relaxation phase of the contraction the receptor was inactivated. Muscle spindle firing was usually coactivated with the EMG, but not in a strict relation to the force of contraction. From some muscle spindles on minimal contraction a decrease in firing frequency was seen, and with stronger contraction the firing frequency was increased. At rest the spontaneous firing of muscle spindles was irregular, with the frequency varying with the degree of subject attention. Such tests as mental activity and acoustic arousal facilitated muscle spindle firing while Golgi tendon organs were not activated. During reinforcement maneuvers initiated by the contraction of remote leg muscles, muscle spindle spontaneous firing from the forearm flexor muscles was accelerated. The results supplement the criteria for individual human muscle receptor identification and establish the role of the receptors during reflex and voluntary muscle contraction and involuntary efferent receptor activation.

Muscle afferent potential ('A-wave') in the surface electromyogram of a phasic stretch reflex in normal humans.

The experiments reported in this paper tested the hypothesis that the afferent potential elicited by a tendon tap in an isometrically recorded phasic stretch reflex can be detected in the surface EMG of normal humans when appropriate techniques are used. These techniques involved (1) training the subjects to relax mentally and physically so that the EMG was silent before and immediately after the diphasic MAP which reflects a highly synchronous discharge of afferent impulses from low threshold muscle stretch receptors after a tendon tap, and (2) using a data retrieval computer to summate stimulus-locked potentials in the EMG over a series of 16 samples using taps of uniform peak force and duration on the Achilles tendon to elicit the tendon jerk in the calf muscles. A discrete, diphasic potential (`A-wave') was recorded from EMG electrodes placed on the surface of the skin over the medial gastrocnemius muscle. The `A-wave' afferent potential had the opposite polarity to the corresponding efferent MAP. Under control conditions of relaxation the `A-wave' had a latency after the onset of the tap of 2 msec, the peak to peak amplitude was of the order of 5 μV and the duration was in the range of 6 to 10 msec. Further experiments were conducted to show that the `A-wave' (1) was not an artefact of the instrumentation used, (2) had a threshold at low intensities of stimulation, and (3) could be reliably augmented by using a Jendrassik manoeuvre compared with the potential observed during control (relaxation) conditions. The results support the conclusion that the `A-wave' emanates from the pool of muscle spindles which discharges impulses along group Ia nerve fibres in response to the phasic stretch stimulus because the primary ending of the spindles is known to initiate the stretch reflex and the spindles can be sensitized by fusimotor impulses so that their threshold is lowered as a result of a Jendrassik manoeuvre. The finding has important implications for the investigation of the fusimotor system in intact man.

Electromyogram and myogram responses under pre-strain conditions in normal humans as an index of fusimotor sensitization of muscle spindles.

Comparisons of the EMG and myogram responses in a phasic stretch reflex between normal resting tension (control) and three pre-strain conditions show that (i) there is a positive, linear relationship between these two variables but the correlation coefficient decreases with increase in force of pre-strain, (ii) when the relationship is plotted, the regression lines for control and pre-strain separate but the slopes for the regressions are not dissimilar, (iii) there is a progressive decrease in the variance of responses with increase in force of pre-strain and (iv) there is a high product-moment correlation coefficient between the peak force of the myogram and the area of the myogram. Explanations for these results are discussed in terms of muscle spindle physiology.

Stretch reflex and shortening reaction. A quantitative analysis of phasic and tonic stretch reflex in clinical states of spasticity and rigidity : E. Esslen (Zürich, Switzerland)

Stretch reflex and shortening reaction. A quantitative analysis of phasic and tonic stretch reflex in clinical states of spasticity and rigidity : E. Esslen (Zürich, Switzerland)

Relationship between the electromyogram and isometric reflex response in pre-strain conditions in normal humans.

DATA have been reported which show a high positive correlation between the impulse of the isometric reflex contraction (area under the myogram) and the impulse of the synchronous muscle action potential (area of the diphasic spikes of the electromyogram) recorded from surface electrodes during a phasic stretch reflex in normal human subjects1. An explanation for this relationship was given in terms of consistency of gamma efferent control of muscle spindle sensitivity because the influence of supra-spinal centres of the central nervous system was reduced by (a) having the subjects well trained in Jacob-son's method of mental and physical relaxation2 and (b) conducting the experiments in a sound-proofed, electrically shielded and thermally insulated room3 to reduce sensory stimulation which can activate reticular neurones and augment gamma discharge.

Summation of motor units in a mechanically elicited phasic stretch reflex in human subjects.

IN a previous article1 brief reference was made to the results of preliminary investigations which revealed a high, positive correlation between the height and area of the myogram in a mechanically elicited patellar reflex. This relationship between the maximum force and the impulse (integral of force and time) of the isometric reflex contraction has now been confirmed repeatedly and the reasons for it have been established.

Motoneuron reflex response during intermittent visual stimulation as an indication of fusimotor activity

Abstract The effects of two types of weak visual stimuli (short and long trains of light flashes perceived binocularly) on alpha motoneuron response were investigated in a phasic stretch reflex in normal human subjects. These types of visual stimuli affect the frequency and amplitude of mesencephalic reticular neurons of intact cats in predictable ways. The reticular formation has connections with fusimotor neurons which can be readily and quickly activated along the pyramidal tract. Since fusimotor discharge has a powerful effect on alpha motor activity by biasing spindle sensitivity, it may be assumed that the arousal and attenuation characteristics of reticular neurons to visual stimulation will be reflected in alpha motoneuron response. Experimental results from five adults (three females, two males) showed that brief presentation of the intermittent visual stimuli increased both the variance and the mean amplitude of the muscle action potential whilst continued presentation reduced these measures at least to control level. The findings indicate that fusimotor activity may be determined by use of surface EMG, provided proper control is exercised over variables which affect the reflex response.

Effect of the Jendrassik manoeuvre on a phasic stretch reflex in normal human subjects during experimental control over supraspinal influences

Until recently theevidence gained bycomparisons between electrical (Hreflex) andmechanical (tendon jerk) stimulation during theJendrassik manoeuvre hasindicated thatthefusimotor (gammaefferent) systemplaystheparamount roleinfacilitating monosynaptic reflexes byheightening thesensitivity ofthemuscle spindles. Morerecent evidence, making useofthesametechniques, hasraised thequestion that itmaynotbenecessary topostulate facilitation during theJendrassik manoeuvre solely tobethe result of fusimotor biasing ofthespindle. This report deals withexperiments which examine this question bystudying theeffects oftheJendrassik manoeuvre during several conditions (other thanelectrical stimulation) designed tocontrol supraspinal influencesdifferentially. LandauandClare (1964), intheintroduction to their article, havepointed outthattheuseofthe Hoffmanntechnique ofelectrical stimulation of muscle afferents, bywhichtheeffect ofthespindle receptor maybeisolated fromthemotorresponse, hasenabled investigators toinfer that thefacilitation ofmonosynaptic reflexes during theJendrassik manoeuvre occurred bywayoffusimotor alteration ofthesensitivity ofthespindle. TheH reflex seemed resistant toaugmentation during themanoeuvre (Buller andDornhorst, 1957; Paillard, 1959) andit wasreasonable toassumethat thefusimotor neurones, which exclusively innervate theintrafusal fibres ofthespindle (Kuffler, Hunt,andQuilliam, 1951), wereresponsible fortheaugmentation phenomenon. Since 1961there havebeenreports oftheaugmentation oftheH reflex bycontraction ofremote muscles (Benson andGedye,1961;Landauand Clare, 1964). Inaddition, Clare andLandau(1964) haveusedthetechnique of differential nerve blockade (Matthews andRushworth, 1957) tostudy theeffect oftheJendrassik manoeuvre onreflexes Commonwealth postgraduate research scholar 34 which hadbeendepressed bytheselective blockade oftonicfusimotor discharge. Theyfoundthat augmentation ofthereflex becamemoreeffective and'whenthetendon jerk wasabsent, evenwith reinforcement, thedepressed H reflex could still be reinforced'.