Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “REFLEX”

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 847 records · Page 47Linked to original sources
PubMed1998

The effect of repeated prepulse and reflex stimulus presentations on startle prepulse inhibition.

The magnitude of a startle reflex is inhibited if the reflex-eliciting stimuli is preceded by a prepulse stimulus at a short lead interval. Previous research in humans has shown that the extent of prepulse inhibition decreases over repeated presentations of reflex stimuli and prepulse-reflex stimulus pairings. The present study (N = 70) investigated the effect of repeated presentations of prepulse stimuli, reflex stimuli, or prepulse-reflex stimulus pairings on prepulse inhibition. Five groups of subjects were presented during habituation training with either (a) reflex stimuli, (b) prepulse-reflex stimulus pairings, (c) a random sequence of prepulse and reflex stimuli, (d) prepulse stimuli, or (e) experimentally irrelevant light stimuli. Prepulse inhibition was reduced if startle stimuli were presented during habituation ((a), (b), (c)), but not after repeated presentation of the prepulse or the light stimulus ((d), (e)). The reduction in prepulse inhibition was abolished after dishabituation of the startle reflex. The present results indicate that habituation of the startle reflex can result in a reduction of prepulse inhibition.

Acoustic Stimulation↗
PubMed1998

On the role of galanin in mediating spinal flexor reflex excitability in inflammation.

The effects of exogenous and endogenous galanin on spinal flexor reflex excitability was evaluated in rats one to eight days after the induction of inflammation by subcutaneous injection of carrageenan into the sural nerve innervation area. In normal rats, electrical stimulation of C-fibres in the sural nerve elicited a brisk reflex discharge. Conditioning stimulation of C-fibres (1/s) generated a gradual increase in reflex magnitude (wind-up), which was followed by a period of reflex hyperexcitability. Intrathecal galanin dose-dependently blocked reflex hyperexcitability induced by C-fibre conditioning stimulation whereas i.t. M-35, a high-affinity galanin receptor antagonist, moderately potentiated this effect. At one to three days after the injection of carrageenen, when inflammation was at its peak, the magnitude of the reflex was significantly increased and discharge duration became prolonged. However, wind-up and reflex hyperexcitability were significantly reduced. Furthermore, reduced reflex excitability during conditioning stimulation ("wind-down") and depression of the reflex were sometimes present, which are rarely observed in normal rats. Intrathecal galanin reduced hyperexcitability during inflammation, although its potency was weaker than in normals. However, the galanin receptor antagonist M-35 strongly enhanced wind-up and reflex hyperexcitability, similarly as in normal rats. The baseline flexor reflex, wind-up and C-fibre conditioning stimulation-induced facilitation were normalized four to eight days after carrageenan injection when signs of inflammation were diminishing. Interestingly, intrathecal galanin and M-35 failed to influence spinal excitability. The results suggest a complex functional plasticity in the role of endogenous galanin in mediating spinal excitability during inflammation. There appears to be an enhanced endogenous inhibitory control by galanin on C-afferent input during the peak of inflammation, which may explain the relative ineffectiveness of exogenous galanin. During the recovery phase there may be a reduction in galanin receptors, which may impair the action of endogenous and exogenous galanin. These results further support the notion that galanin is an endogenous inhibitory peptide in nociception.

Animals↗
PubMed2000

H-reflex changes under spinal loading and unloading conditions in normal subjects.

OBJECTIVE: The soleus H- reflex is usually tested clinically in patients lying prone, with the H-latency always the criterion of choice for detecting abnormality. However, stresses on the spine vary during lying, standing, loading (weight lifting) and unloading. So the objective of this study was to measure changes in the H-reflex under 4 different loading conditions and to investigate whether mechanical loading of the spine would affect the H-reflex parameters. METHODS: Twenty healthy volunteers (22-46 years) with no history of significant low back pain or radiculopathy participated in the study. A Cadwell Excel electromyography unit was used to elicit and record the soleus H-reflex. The tibial nerve was stimulated at the popliteal fossa using 1 ms pulses at 0.2 pps of H-max. Each subject was tested under 4 different conditions: prone lying, free standing, standing while lifting 20% of his or her body weight, and standing while unloaded by 25% of his/or her body weight by a ZUNI II unloading system. For each subject, the peak-to-peak amplitudes of the maximum obtained H- reflex and the onset latencies of 8 separate traces were averaged for both lower extremities. Two-factor, repeated-measures ANOVAs were used to test the effect of the condition and side on the H-reflex amplitude and latency with ( approximately =0.025). RESULTS: The H-reflex was inhibited during standing, loading and unloading as compared with prone lying. The H-reflex was recovered during loading as compared with during standing. There were no significant changes in the H-reflex latency under the 4 different conditions. Both lower extremities showed similar pattern of changes in the H-reflexes. CONCLUSIONS: These results imply a significant interplay between peripheral and central mechanisms and their effects on the spinal motoneurons. This in turn suggests that testing of the H-reflex amplitude and latency under functional conditions, such as standing may be useful in detecting subtle changes in root impingement.

Adult↗
PubMed1978

Interaction between penile reflexes and copulation in male rats.

Intact, unanesthetized male rats were place in a supine position, with the penile sheath continuously retracted. Three forms of penile reflex were displayed: erections, cups, and flips. The reciprocal relation between copulation and the penile reflexes occurring in supine tests was explored in four experiments. In Experiment 1, sexual exhaustion depressed all penile reflexes, but the reflexes returned to baseline levels within 8 hr, long before copulatory potential. In Experiment 2, reflexes were depressed to exhaustion levels after fewer ejaculations than were required for sexual exhaustion, an indication that reflexes are more readily evoked during copulation than in supine tests. Experiment 3 determined that a rat's penile-reflex potential may be enhanced by placing the rat in a copulation-test cage, by allowing the male a few antecedent intromissions, or by allowing an antecedent ejaculation. The display of penile reflexes within 1 min after ejaculation suggests that the period of reduced sexual arousability following ejaculation is not due to reduced excitability in the spinal mechanisms controlling penile reflexes. In Experiment 4, 1 hr of penile-reflex elicitation had no effect on subsequent copulatory behavior. Thus, sexual stimulation may increase or decrease penile-reflex potential, but a reciprocal influence was not detectable.

Animals↗
PubMed1994

[Effect of anesthesia on the intraoperative elicited stapedius reflex].

Evaluation of the intraoperative electrically evoked stapedius reflexes during cochlear implant surgery has two purposes: (1) The functioning of the device and the peripheral auditory pathways can be proven immediately and (2) The data of reflex threshold can be used for the prediction of later threshold (T)- and maximum comfortable (C) levels. This is especially useful for the later fitting of the speech processor in very young children. When trying to use the stapedius reflex data for the prediction of T- and C-levels it must be considered that during surgery the drugs used for general anaesthesia influence the values of the stapedius reflex. Depending on the drug, the stapedius reflex threshold can be increased or the reflex can even be totally blocked. This is not only due to relaxants but also to anaesthetics. To investigate this influence we first determined the acoustically evoked stapedius reflex threshold in normal hearing adults under general anaesthesia with 7 different anaesthetics without additional relaxation. It was found that especially with Dormicum and Brevimytal the stapedius threshold increased only very lightly or did not change at all. In a second investigation the electrically evoked stapedius reflex thresholds were obtained in adults who underwent a cochlear implant surgery using the same anaesthetics for anaesthesia. The intraoperatively evaluated reflex data were compared with postoperatively obtained data. It was found that both reflex thresholds were similar if evaluated in Dormicum or Brevimytal anaesthesia. This suggests that only with the use of the right anaesthetics the data of the electrically evoked stapedius reflex obtained intraoperatively can be used for predicting T- and C-levels.

Anesthesia, General↗
PubMed1999

Impaired modulation of quadriceps tendon jerk reflex during spastic gait: differences between spinal and cerebral lesions.

In healthy subjects, functionally appropriate modulation of short latency leg muscle reflexes occurs during gait. This modulation has been ascribed, in part, to changes in presynaptic inhibition of Ia afferents. The changes in modulation of quadriceps tendon jerk reflexes during gait of healthy subjects were compared with those of hemi- or paraparetic spastic patients. The spasticity was due to unilateral cerebral infarction or traumatic spinal cord injury, respectively. The modulation of the quadriceps femoris tendon jerk reflex at 16 phases of the step cycle was studied. The reflex responses obtained during treadmill walking were compared with control values obtained during gait-mimicking standing postures with corresponding levels of voluntary muscle contraction and knee angles. In healthy subjects the size of the reflexes was profoundly modulated and was generally depressed throughout the step cycle. In patients with spinal lesion the reflex depression during gait was almost removed and was associated with weak or no modulation during the step cycle. In patients with cerebral lesion there was less depression of the reflex size associated with a reduced reflex modulation on the affected side compared with healthy subjects. On the 'unaffected' side of these patients reflex modulation was similar to that of healthy subjects, but the reflex size during gait was not significantly different from standing control values. These observations suggest that the mechanisms responsible for the depression of reflex size and the modulation normally seen during gait in healthy subjects are impaired to different extents in spasticity of spinal or cerebral origin, possibly due to the unilateral preservation of fibre tracts in hemiparesis.

Adolescent↗
PubMed1994

The effect of therapeutic massage on H-reflex amplitude in persons with a spinal cord injury.

BACKGROUND AND PURPOSE: The effect of therapeutic massage on the H-reflex amplitude in persons without neurological impairment has been established. To investigate its effects in a sample of persons with a spinal cord injury (SCI), two independent but interrelated studies were undertaken. Study 1 investigated whether the recorded response (H-reflex amplitude) to massage with the subjects in the supine testing position was similar to that recorded in previous studies in which the subjects were tested in the prone position. This study was undertaken because the prone testing position was considered inappropriate for persons with SCI. In study 2, the therapeutic effect of massage (petrissage) on H-reflex amplitude in persons with SCI was examined. SUBJECTS: Seven persons without neurological impairment volunteered to participate in study 1, and 10 individuals with a traumatic SCI volunteered to participate in study 2. METHODS: The two studies shared many methodological features and involved the recording of 10 H-reflex and M-response peak-to-peak amplitudes from the triceps surae muscle during each of five sequential, 3-minute time periods. Massage treatment (MASS) was given during the third time period, and the premassage time periods (C1, C2) and postmassage time periods (C3, C4) served as control conditions. Study 2, in addition to recording the peak-to-peak amplitudes of the recorded responses, also included the recording of the H-reflex latencies. RESULTS: The results of study 1 showed that massage applied with the subjects in the supine position decreased the H-reflex amplitude during the massage. A 56% decrease in the H-reflex amplitude was recorded. Study 2 demonstrated a 27% mean group decrease in the H-reflex peak-to-peak amplitude during the massage for all subjects, with variations in individual responses ranging from an increase in the H-reflex amplitude of 20% to a decrease of 84%. An analysis of variance revealed that the H-reflex means of the five conditions were significantly different. Newman-Keuls post hoc analyses revealed that the mean of the MASS condition (2.01 mV) was significantly different from the means of C1, C2, and C4 (2.79, 2.81, 2.58 mV). The mean of C3 (2.42 mV) was not found to be statistically different from the means of the other conditions. These changes were noted against a stable M-response. CONCLUSION AND DISCUSSION: The results recorded in study 1 are comparable to those obtained with the subjects in the prone position. Based on these results, the supine position was adopted as the testing position for study 2. Study 2 further showed a decrease in H-reflex amplitude concomitant with massage in persons with SCI, but no long-term effects were noted.

Adult↗
PubMed2001

Effects of sleep on spinal nociceptive reflexes in humans.

Controversy continues to surround the monosynaptic and polysynaptic spinal reflexes during the different stages of sleep. In animal studies both of these reflexes were found to be depressed during desynchronized sleep. In humans, the H reflex was unchanged whereas the second component of the nociceptive flexion reflex was increased. However, abolition of the H reflex and F waves during REM sleep has also been reported. The aim of this investigation was to examine the effects of different sleep stages on the polysynaptic nociceptive flexion reflex. Six healthy volunteers were studied. The RIII reflex was studied according to Willer's method (1977) during the different stages of NREM and REM sleep. The RIII reflex threshold was found to increase during stage 2 of NREM sleep. It remained higher during stages 3 and 4. During REM sleep a further increase in the reflex threshold was observed. The reflex latency was prolonged during stage 4 of NREM sleep. There was evidence of further latency prolongation during REM sleep. It was also during REM sleep that the maximum increase in the amplitude and duration of the reflex were recorded.

Adult↗
PubMed2004

Monitoring of immobility to noxious stimulation during sevoflurane anesthesia using the spinal H-reflex.

BACKGROUND: The spinal H-reflex has been shown to correlate with surgical immobility, i.e., the absence of motor responses to noxious stimulation, during isoflurane anesthesia. Here, the authors established individual concentration-response functions for H-reflex amplitude and tested the predictive power of the H-reflex for movement responses during sevoflurane anesthesia in comparison to electroencephalographic parameters. In addition, they investigated the effect of noxious stimulation on the H-reflex itself. METHODS: The authors studied 12 female patients during sevoflurane anesthesia before surgery. The sevoflurane concentration was increased, a laryngeal mask was inserted, and then the sevoflurane concentration was decreased until H-reflex amplitude (recorded over the soleus muscle) recovered. Thereafter, the end-tidal sevoflurane concentration was kept at a constant value close to the minimum alveolar concentration for suppression of movement responses after tetanic stimulation (MACtetanus), determined by the Dixon up-down method. Pharmacodynamic modeling of H-reflex amplitude and of the Bispectral Index was performed, and predictive values for motor responses to noxious electrical stimulation (50 Hz, 60 mA tetanus, volar forearm) were compared using the prediction probability. RESULTS: Concentration-dependent depression of H-reflex amplitude by sevoflurane was well modeled (median r2 = 0.97) by a sigmoid function with a median EC50 of 1.5 vol% and a median slope parameter of 3.7, much steeper than the slope for the Bispectral Index. MACtetanus calculated by logistic regression was 1.6 vol%. H-reflex amplitude predicted motor responses to noxious stimulation with a prediction probability of 0.76, whereas the prediction probability for Bispectral Index and spectral edge frequency (SEF95) were not different from chance alone. Noxious stimulation was followed by a substantial increase of H-reflex amplitude for several minutes, whereas the Bispectral Index and SEF95 exhibited no significant changes. CONCLUSIONS: Suppression of movement to noxious stimulation and suppression of H-reflex amplitude by sevoflurane follow similar concentration-response functions. Although this does not imply a causal relation, it explains the high predictive value of H-reflex amplitude for motor responses to noxious stimuli, even in a narrow concentration range around the MACtetanus.

Aged↗
PubMedDate not supplied

Late facilitation of the human soleus H reflex induced by sustained isometric maneuver.

Studying the effect of spinal cord reinforcement maneuvers (SCRMs) on H reflex assists in understanding aspects of motor control. Our objective was as follows: (1) to elucidate the effects of four neck positions (neck resting at neutral position (control); passive hyperflexion of the neck; hyperextension of the neck with simultaneous abdominal contraction; and sustained active neck hyperflexion); (2) to evaluate the temporal changes of soleus H reflexes repeatedly evoked after a period of sustained neck flexion. We used a prospective, intrinsically controlled trial of the effects of these SCRMs on the H reflexes and M-responses in ten healthy volunteers. Pre- and postmaneuver measures included H reflex and M-response latencies and amplitudes, H/M maximum amplitude ratio, and H threshold. The four maneuvers showed no significant effect on the H reflex or M-response measures. To investigate temporal changes in the H reflex amplitude, H reflexes were repeatedly evoked at two-minute intervals after a one-minute period of active neck flexion. The amplitude of the H reflex was enhanced (P = 0.0356; analysis of variance), and the post hoc least significant difference test was significant at four minutes postmaneuver. Peak magnitude of the H reflex occurred at four minutes after relaxation, and the response returned to pretest baseline at eight minutes. The results of this study document the time course of repeated H reflexes after SCRM, and the timing of the H reflex was found to be a contributing variable that should be considered in future study designs.

Adaptation, Physiological↗
PubMed2004

Cervico-ocular reflex in normal subjects and patients with unilateral vestibular hypofunction.

OBJECTIVE: To determine whether the cervico-ocular reflex contributes to gaze stability in patients with unilateral vestibular hypofunction. STUDY DESIGN: Prospective study. SETTING: Tertiary referral center. PATIENTS: Patients with unilateral vestibular hypofunction (n = 3) before and after vestibular rehabilitation and healthy subjects (n = 7). INTERVENTIONS: Vestibular rehabilitation. MAIN OUTCOME MEASURES: We measured the cervico-ocular reflex in patients with unilateral vestibular hypofunction before and after vestibular rehabilitation and in healthy subjects. To measure the cervico-ocular reflex, we recorded eye movements with a scleral search coil while the trunk moved at 0.3, 1.0, and 1.5 Hz beneath a stabilized head. To determine whether the head was truly stabilized, we measured head movement using a search coil. RESULTS: We found no evidence of cervico-ocular reflex in any of the seven healthy subjects or in two of the patients with unilateral vestibular hypofunction. In one patient with chronic unilateral vestibular hypofunction, the cervico-ocular reflex was present before vestibular rehabilitation only for leftward trunk rotation (relative head rotation toward the intact side). After 5 weeks of placebo exercises, there was no change in the cervico-ocular reflex. After an additional 5 weeks that included vestibular exercises, cervico-ocular reflex gain for leftward trunk rotation had increased threefold. In addition, there was now evidence of a cervico-ocular reflex for rightward trunk rotation, potentially compensating for the vestibular deficit. CONCLUSION: The cervico-ocular reflex appears to be a highly inconsistent mechanism. The change of the cervico-ocular reflex in one patient after vestibular exercises suggests that the cervico-ocular reflex may be adaptable in some patients.

Adult↗
PubMed2006

Disturbed paraspinal reflex following prolonged flexion-relaxation and recovery.

STUDY DESIGN: Repeated measures experimental study of the effect of flexion-relaxation, recovery, and gender on paraspinal reflex dynamics. OBJECTIVE: To determine the effect of prolonged flexion-relaxation and recovery time on reflex behavior in human subjects. SUMMARY OF BACKGROUND DATA: Prolonged spinal flexion has been shown to disturb the paraspinal reflex activity in both animals and human beings. Laxity in passive tissues of the spine from flexion strain may contribute to desensitization of mechanoreceptors. Animal studies indicate that recovery of reflexes may take up to several hours. Little is known about human paraspinal reflex behavior following flexion tasks or the recovery of reflex behavior following the flexion tasks. METHODS: A total of 25 subjects performed static flexion-relaxation tasks. Paraspinal muscle reflexes were recorded before and immediately after flexion-relaxation and after a recovery period. Reflexes were quantified from systems identification analyses of electromyographic response in relation to pseudorandom force disturbances applied to the trunk. RESULTS: Trunk angle measured during flexion-relaxation postures was significantly higher following static flexion-relaxation tasks (P < 0.001), indicating creep deformation of passive supporting structures in the trunk. Reflex response was diminished following flexion-relaxation (P < 0.029) and failed to recover to baseline levels during 16 minutes of recovery. CONCLUSION: Reduced reflex may indicate that the spine is less stable following prolonged flexion-relaxation and, therefore, susceptible to injury. The absence of recovery in reflex after a substantial time indicates that increased low back pain risk from flexion-relaxation may persist after the end of the flexion task.

Adult↗
PubMed1999

Differential effects of angiotensin II on cardiorespiratory reflexes mediated by nucleus tractus solitarii - a microinjection study in the rat.

1. The effect of microinjecting angiotensin II (ANGII) into the nucleus of the solitary tract (NTS) on both baroreceptor and peripheral chemoreceptor reflexes was compared. 2. Experiments were performed in a working heart-brainstem preparation of rat. Baroreceptors were stimulated by raising perfusion pressure and chemoreceptors were activated with aortic injections of sodium cyanide (0.025 %, 25-75 microl). Reflex changes in phrenic nerve activity and heart rate were measured after bilateral NTS microinjection (50 nl) of ANGII (0.5-5000 fmol). 3. NTS microinjection of 5 fmol ANGII elicited a transient (28.2 +/- 6 s; mean +/- s.e.m.) bradycardia (-18 +/- 3 beats min-1), and decreased phrenic nerve activity cycle length and amplitude (P < 0.05). At higher doses of ANGII a similar respiratory response was seen but heart rate changes were inconsistent. 4. The baroreceptor reflex bradycardia was depressed significantly by NTS microinjections of ANGII (5-5000 fmol) in a dose-dependent manner with the reflex gain decreasing from 1.7 +/- 0.16 to 0.66 +/- 0.1 beats min-1 mmHg-1 (P < 0.01) at 5000 fmol. Although the chemoreceptor reflex bradycardia was depressed at a low dose of ANGII (5 fmol), all higher doses (50-5000 fmol) produced a dose-dependent potentiation of the reflex bradycardia (maximally +64 +/- 8 %). The respiratory component was unaffected. The effects of ANGII on both reflexes were blocked by an ANGII type 1 (AT1) receptor antagonist, losartan (20 microM). 5. The potentiating action of ANGII on the chemoreceptor reflex cardiac response was abolished by a neurokinin type 1 (NK1) receptor blocker (CP-99,994, 5 microM) but this had no effect on the baroreceptor reflex. 6. AT1 receptors in the NTS can depress the baroreceptor reflex bradycardia which is independent of NK1 receptors. The ANGII effect on the cardiac component of the chemoreceptor reflex is bi-directional being inhibited at low concentrations and potentiated at higher concentrations; the latter involves NK1 receptors and presumably results from release of substance P.

Angiotensin II↗
PubMed2001

Neural control of rhythmic, cyclical human arm movement: task dependency, nerve specificity and phase modulation of cutaneous reflexes.

1. The organization and pattern of cutaneous reflex modulation during rhythmic cyclical movements of the human upper limbs has received much less attention than that afforded the lower limb. Our working hypothesis is that control mechanisms underlying the modulation of cutaneous reflex amplitude during rhythmic arm movement are similar to those that control reflex modulation in the leg. Thus, we hypothesized that cutaneous reflexes would show task dependency and nerve specificity in the upper limb during rhythmic cyclical arm movement as has been demonstrated in the human lower limb. 2. EMG was recorded from 10 muscles crossing the human shoulder, elbow and wrist joints while bilateral whole arm rhythmic cyclical movements were performed on a custom-made, hydraulic apparatus. 3. Cutaneous reflexes were evoked with trains (5 x 1.0 ms pulses at 300 Hz) of electrical stimulation delivered at non-noxious intensities (approximately 2 x threshold for radiating parasthesia) to the superficial radial, median and ulnar nerves innervating the hand. 4. Cutaneous reflexes were typically modulated with the movement cycle (i.e. phase dependency was observed). There was evidence for nerve specificity of cutaneous reflexes during rhythmic movement of the upper limbs. Task-dependent modulation was also seen as cutaneous reflexes were of larger amplitude or inhibitory (reflex reversal) during arm cycling as compared to static contraction. 5. While there are some differences in the patterns of cutaneous reflex modulation seen between the arms and legs, it is concluded that cutaneous reflexes are modulated similarly in the upper and lower limbs implicating similar motor control mechanisms.

Adult↗
PubMed1982

A range of different stretch reflex responses in the human thumb.

1. Imposed sinusoids were used to assess the resistance to movement at the thumb interphalangeal joint.2. The resistance to high-frequency movements (> 12 Hz) increased when the subject exerted a large voluntary flexing force; this increase was attributable to a greater non-reflex resistance of the contracting flexor muscles. This resistance was essentially ;visco-elastic', and the force was phase-advanced on joint position. At moderately large forces (up to half maximal), however, the resistance changed with changing frequency, and over a range 4-12 Hz the vectors which represented joint stiffness described the wide path that is characteristic of an active stretch reflex (Brown, Rack & Ross, 1982a). At frequencies between about 4 and 6 Hz the force was sometimes phase-delayed on position, and the joint exhibited a negative viscous stiffness. When the voluntary flexing force was very large the reflex contributed less to the resisting force, which was then phase-advanced on position at all frequencies of movement.3. Large amplitude movements did not generate correspondingly large reflex responses; as the amplitude of movement was increased, the reflex component of the resisting force became relatively smaller and the total resisting force was then phase-advanced on joint position at all frequencies.4. The reflex component of the resisting force (as indicated by the excursion of the joint stiffness vectors) varied from subject to subject and from time to time; the reflex usually became more active late in an experiment when the subject had exerted flexing forces against the imposed movement for some minutes. Extreme fatigue, however, diminished the amount of reflex force.5. In some subjects the joint-stiffness records indicated a particularly vigorous reflex response at 8-11 Hz, in contrast to a rather feeble response at 6 or 7 Hz. It is suggested that the reflex pathways then had a relatively low impedance to afferent signals that were modulated at 8-11 Hz, related perhaps to the firing patterns of the most recently recruited motoneurones.6. Under the conditions of these experiments, it appears that the stretch reflex has too small a gain to function as a very effective error-controlled position servo-mechanism.

Adult↗
PubMed1982

Cutaneous reflex responses and their central nervous pathways studied in man.

1. Cutaneous reflex responses have been recorded in human first dorsal interosseous and extensor digitorum brevis muscles following electrical stimulation of the digital nerves of the index finger and second toe respectively.2. Recordings have been made in normal subjects and in patients with central nervous lesions.3. Cutaneous reflex responses in first dorsal interosseous were triphasic, consisting of initial short latency excitation, followed by inhibition, followed by prominent long latency excitation. Cutaneous reflex responses in extensor digitorum brevis were biphasic, consisting of short and long latency periods of excitation.4. Estimated central delay for the initial excitatory components of the cutaneous reflex in first dorsal interosseous and extensor digitorum brevis muscles ranged from 2.4 to 6.2 ms (mean 4.6 ms) and 0.6 to 4.1 ms (mean 2.3 ms) respectively.5. Differences in latency between short and long latency excitatory components of the cutaneous reflexes recorded in first dorsal interosseous and extensor digitorum brevis muscles ranged from 16 to 18 ms (mean 17.3 ms) and 27 to 32 ms (mean 29.3 ms) respectively.6. Differences in time delay between short and long latency excitation in first dorsal interosseous and extensor digitorum brevis muscles when compared in individual subjects ranged from 9 to 14 ms (mean 12 ms). These values lay within 0-7 ms (mean 4 ms) of estimates in each subject of conduction time along central pathways between T12 and C7 spinal segments.7. Differences in latency between short and long latency excitatory components of the cutaneous reflex recorded in first dorsal interosseous were 3.5-8.5 ms longer than the estimated minimum time for impulse conduction along a pathway travelling through the dorsal columns to cerebral cortex and returning by way of the corticospinal tract.8. The long latency excitatory component of the cutaneous reflex in first dorsal interosseous muscle is reduced and often delayed in patients with dorsal column lesions.9. The long latency excitatory and short latency inhibitory components of the cutaneous reflex in first dorsal interosseous muscle are absent in patients with damage to motor cortex.10. The long latency excitatory component of the cutaneous reflex in first dorsal interosseous muscle is reduced in amplitude and often delayed in patients with motoneurone disease causing damage to the corticospinal tract. The timing of short latency excitatory and inhibitory components is unchanged.11. It is concluded that the short latency excitatory and inhibitory components of the cutaneous reflex response of first dorsal interosseous muscle have a spinal pathway and that the interneurones mediating the inhibitory component are under descending extrapyramidal control from systems whose inputs are deranged by damage to motor cortex.12. It is concluded that the long latency excitatory component of the cutaneous reflex response of first dorsal interosseous muscle is of supraspinal origin requiring transmission of afferent impulses through the dorsal columns, a relay in the sensori-motor cortex and then descending transmission to the lower motoneurone pool by way of the corticospinal tract.

Adolescent↗
PubMed1983

Naloxone enhancement of spinal reflexes in the rabbit.

The effects of intravenous morphine, (-)-naloxone and (+)-naloxone have been studied on three ipsilateral cutaneo-muscular reflexes in spinal rabbits. Morphine, 3 mg/kg caused a slow-onset depression of all three reflexes. This effect was naloxone reversible. The ipsilateral extensor reflexes, sural to gastrocnemius medialis and saphenous to vastus lateralis were both enhanced to more than double control size following a 5 micrograms/kg dose of naloxone given in the absence of morphine. For the sural-gastrocnemius reflex, naloxone potentiated the reflex drive from all groups of myelinated afferent fibres. The ipsilateral flexion reflex, sural to semitendinosus, was only weakly enhanced by naloxone, the 5 micrograms dose leading to an increase in the size of the reflex to 130% of control. All observed actions of naloxone were stereospecific as the enantiomer (+)-naloxone failed to affect any of the reflexes even in a dose of 50 micrograms/kg. We conclude from these findings that opioid peptides are tonically released in rabbit spinal cord, and that they have differential effects in control of flexion and extension reflexes. It is suggested that the ipsilateral extension reflexes are held under a more powerful opioid-mediated depression than that operating upon the flexion reflexes, and that this difference may be related to the greater inhibitory inflow to extensor motoneurones from ipsilateral skin areas.

Action Potentials↗
PubMed1985

Development of the monosynaptic stretch reflex in the rat: an in vitro study.

The properties and development of the stretch reflex pathway were investigated in new-born and fetal rats using the isolated spinal cord-hind limb preparation. Muscle afferent discharge was elicited by small stretch of the triceps surae muscle in the new-born rat and in the fetus. It appeared as early as embryonic day 18.5. Ramp-and-hold stretch elicited only phasic discharges in most afferent fibres. A phasic reflex response was evoked in the triceps surae muscle by brief or ramp-and-hold stretch of the muscle in the new-born rat. The threshold stretch required for evoking the reflex response was close to that for eliciting the afferent discharge. A reflex response in the triceps surae muscle was also evoked by electrical stimulation of the triceps surae muscle nerve or the sciatic nerve in the new-born rat. Excitatory post-synaptic potentials (e.p.s.p.s) in the triceps surae motoneurones were evoked by stimulation of the muscle nerve in the new-born rat. The amplitude of the e.p.s.p.s was large enough to generate spike potentials. Homonymous e.p.s.p.s were significantly larger than heteronymous e.p.s.p.s. The amplitudes of the e.p.s.p.s were very susceptible to the rate of stimulus repetition. At a stimulus frequency of 10 Hz they were depressed to less than 10% of the control value. Presynaptic impulses evoked by stimulation of afferents in the muscle nerve appear in the motor nucleus less than 1.0 ms before the onset of synaptically evoked field potentials. The interval between the arrival of impulses evoked by dorsal root stimulation and the onset of e.p.s.p.s in motoneurones was 0.56 +/- 0.16 ms, indicating monosynaptic transmission from the primary afferents to the motoneurones. In the fetus, a reflex response in the triceps surae muscle was observed following a small stretch of the muscle (or electrical stimulation of the sciatic nerve) in all preparations at embryonic day 20.5 and in about half of those examined at embryonic day 19.5. Neither stimulation evoked a reflex response at embryonic day 18.5. Latencies of the reflex responses evoked by muscle stretch or by nerve stimulation were similar to those in the new-born rat. It is concluded that the monosynaptically evoked stretch reflex response in the triceps surae muscle first appear at embryonic day 19.5. Natural and electrical stimulation of the plantar skin evoked a reflex response with long latencies in flexor muscles. Such a cutaneous reflex was first present at embryonic day 17.5, two days earlier than the onset of the stretch reflex.

Action Potentials↗