[Clinico-physiological study on the central reflex arcs of blink reflex; with special reference to its diagnostic value of the posterior fossa lesions (author's transl)].
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Muscle, reflex and central components in the control of the ankle joint in healthy and spastic man.
In understanding the control of the ankle joint during different motor tasks, we have to investigate at least three components, namely the influence of i) the passive and intrinsic properties of the intact and active muscle system around the joint (termed the non-reflex component), ii) the mechanical importance of the stretch reflex in the stretched and unloaded muscles, and iii) the supraspinal control of the stretch reflex. This thesis is dealing with the importance of the three components in healthy and spastic persons during sitting, standing, and walking. The results are based on stretch reflex and H-reflex measurements from the ankle extensor muscles. During stretch reflex experiments the foot was mounted to a platform (portable during walking) from which the ankle joint torque and the position were measured. To elicit a stretch reflex, the ankle joint was rotated by a strong motor connected to the platform. The mechanical importance of the stretch reflex was investigated by measuring the changes in joint torque. Electrically, the stretch reflex was recorded as the compound muscle action potential through bipolar surface EMG electrodes placed over the soleus muscle. During H-reflex experiments, the tibial nerve was stimulated at the popliteal fossa and the H-reflex recorded over the soleus muscle as during stretch reflex experiments. To investigate how the contractile properties of a muscle in humans depend on the history of activation, we investigated the intrinsic stiffness of the ankle extensors in healthy subjects. At matched background contraction in sitting subjects, a prolonged contraction increased the intrinsic muscle stiffness by 49%. Muscle yielding has been considered especially important for understanding the reflex compensation. We found a general lack of muscle yield and a mechanically important non-reflex stiffness of the ankle extensors showing that non-reflex stiffness is a prominent factor in normal movements of the ankle joint. In both healthy and spastic persons, we found a mechanically strong stretch reflex in the isometric, contracted muscles during sitting. This posed the question; how is the reflex regulated during more functional motor tasks. This was dealt with by studying the H-reflex during isometric ramp contractions and during walking in healthy and spastic persons. In the healthy subjects the H-reflex was modulated in consistency with a task dependent control. In the spastic patients the H-reflex lacked a task dependent modulation. In consistency with earlier findings it was suggested that the decreased modulation could have been caused by decreased control of the pre-synaptic inhibition of the Ia terminals or a change in recruitment gain. To test if the stretch reflex behaved as the H-reflex, the short latency stretch reflex was investigated during walking. Here we found that the stretch reflex was strongly modulated during a step in healthy subjects as seen for the H-reflex, but when comparing the stretch reflex at matched excitation levels (same background EMGs) during standing and walking, no task-specific reflex modulation was found except the one relating to the excitation level. Therefore, the results emphasise that at least during walking and standing it is not always possible to draw conclusions about the stretch reflex based on observations of the H-reflex. When investigating the modulation of the short latency stretch reflex during walking in spastic patients, we found that the stretch reflex modulation was impaired in spastic patients at least to the extent demonstrated earlier for the H-reflex. The passive stiffness of the ankle joint was at the same time increased in the patients. At matched ankle extensor contraction levels, stretch responses were compared before and after reversible block of the common peroneal nerve and during an attempted, voluntary, fictive dorsiflexion after common peroneal nerve block. (ABSTRACT TRUNCATED)
Afferent Pathways↗
Differential effects of low-frequency depression, vibration-induced inhibition, and posttetanic potentiation on H-reflexes and tendon jerks in the human soleus muscle.
A comparison was made between the effects of repetition rate, muscle vibration, and tetanic stimulation of the tibial nerve on H-reflexes and tendon (T) jerks elicited in the relaxed soleus muscle of normal human. H- and T-reflexes with electromyographic (EMG) potentials of equivalent amplitude were elicited alternately in the same leg to ensure identical experimental conditions. H- and T-reflexes of identical EMG amplitude showed isometric twitch tensions of identical amplitude and time course. H- and T-reflexes were elicited at different repetition rates ranging from once every 6 s to 2/s. H-reflexes showed a significantly stronger low-frequency depression than T-reflexes. Inhibition of H- and T-reflexes was induced by 2-min vibration at 100 Hz of ankle extensors, ankle flexors, or knee flexors. Vibration of ankle extensors and flexors induced a stronger inhibition than vibration of knee flexors. In all three conditions, inhibition of H-reflexes was stronger than inhibition of T-reflexes. The difference was relatively greater during vibration of ankle extensors and flexors than during vibration of knee flexors. When tested together, the effects of low-frequency depression and vibration-induced inhibition of H- and T-reflexes were found to be independent if reflex amplitudes were expressed as a percentage of the control reflex amplitude. The cessation of vibration of ankle extensors was followed by a gradual recovery of H-reflexes from inhibition. On the contrary, T-reflexes showed a marked potentiation. Such postvibratory effects were generally not observed following vibration of ankle or knee flexors. When postvibratory effects were tested during low-frequency depression, percent postvibratory depression of H-reflexes and percent postvibratory potentiation of T-reflexes were found to be independent of the degree of low-frequency depression. Tetanic stimulation of the tibial nerve for 20 s at 200 Hz resulted in posttetanic potentiation (PTP) of H- and T-reflexes, the former being stronger than the latter. The extent of the changes in H- and T-reflex EMG amplitudes, due to changes in repetition rate, vibration, or tetanic stimulation, was generally inversely related to the intensity of the electrical or mechanical reflex stimuli. The observed discrepancies between the induced changes in H- and T-reflex amplitudes are interpreted in terms of the differences in afferent inputs between the two reflexes that were suggested by Burke and his colleagues (9-11).(ABSTRACT TRUNCATED AT 400 WORDS)
Adolescent↗
Prospective follow-up of primitive reflex profiles in high-risk infants: clues to an early diagnosis of cerebral palsy.
To clarify reflex profiles in the first year of life in connection with categories of neurologic abnormality, eight primitive reflexes (i.e., the palmar grasp reflex, the plantar grasp reflex, the Galant response, the asymmetric tonic neck reflex, the suprapubic extensor reflex, the crossed extensor reflex, the Rossolimo reflex, and the heel reflex) were prospectively examined in 204 high-risk infants, of whom 58 developed cerebral palsy, 22 had developmental retardation, and 124 were normal at follow-up examination at 2 years of age. The change in the retention time of reflex activity for each of these reflexes was characteristic for each category or type of neurologic abnormality: retention of palmar grasp reflex, suprapubic extensor reflex, crossed extensor reflex, Rossolimo reflex, and heel reflex in spastic cerebral palsy, as well as retention of plantar grasp reflex, Galant reflex, and asymmetric tonic neck reflex in athetoid cerebral palsy and somewhat weaker retention of these reflexes in developmental retardation (statistical significance P < .001 compared with normally developed patients). These characteristic changes imply that a presumptive diagnosis can be made in neurologically high-risk infants by examination of the primitive reflexes, which are of specific significance among the other neurologic criteria within the first year of life.
Cerebral Palsy↗
Reflex excitability regulates prepulse inhibition.
Presentation of a weak stimulus, a prepulse, before a reflex-evoking stimulus decreases the amplitude of the reflex response relative to reflex amplitude evoked without a preceding prepulse. For example, presenting a brief tone before a trigeminal blink-eliciting stimulus significantly reduces reflex blink amplitude. A common explanation of such data are that sensory processing of the prepulse modifies reflex circuit behavior. The current study investigates the converse hypothesis that the intrinsic characteristics of the reflex circuit rather than prepulse processing determine prepulse modification of trigeminal and acoustic reflex blinks. Unilateral lesions of substantia nigra pars compacta neurons created rats with hyperexcitable trigeminal reflex blinks but normally excitable acoustic reflex blinks. In control rats, presentation of a prepulse reduced the amplitude of both trigeminal and acoustic reflex blinks. In 6-OHDA-lesioned rats, however, the same acoustic prepulse facilitated trigeminal reflex blinks but inhibited acoustic reflex blinks. The magnitude of prepulse modification correlated with reflex excitability. Humans exhibited the same pattern of prepulse modification. An acoustic prepulse facilitated the trigeminal reflex blinks of subjects with hyperexcitable trigeminal reflex blinks caused by Parkinson's disease. The same prepulse inhibited trigeminal reflex blinks of age-matched control subjects. Prepulse modification also correlated with trigeminal reflex blink excitability. These data show that reflex modification by a prepulse reflects the intrinsic characteristics of the reflex circuit rather than an external adjustment of the reflex circuit by the prepulse.
Acoustic Stimulation↗
Reflex control of the spine and posture: a review of the literature from a chiropractic perspective.
OBJECTIVE: This review details the anatomy and interactions of the postural and somatosensory reflexes. We attempt to identify the important role the nervous system plays in maintaining reflex control of the spine and posture. We also review, illustrate, and discuss how the human vertebral column develops, functions, and adapts to Earth's gravity in an upright position. We identify functional characteristics of the postural reflexes by reporting previous observations of subjects during periods of microgravity or weightlessness. BACKGROUND: Historically, chiropractic has centered around the concept that the nervous system controls and regulates all other bodily systems; and that disruption to normal nervous system function can contribute to a wide variety of common ailments. Surprisingly, the chiropractic literature has paid relatively little attention to the importance of neurological regulation of static upright human posture. With so much information available on how posture may affect health and function, we felt it important to review the neuroanatomical structures and pathways responsible for maintaining the spine and posture. Maintenance of static upright posture is regulated by the nervous system through the various postural reflexes. Hence, from a chiropractic standpoint, it is clinically beneficial to understand how the individual postural reflexes work, as it may explain some of the clinical presentations seen in chiropractic practice. METHOD: We performed a manual search for available relevant textbooks, and a computer search of the MEDLINE, MANTIS, and Index to Chiropractic Literature databases from 1970 to present, using the following key words and phrases: "posture," "ocular," "vestibular," "cervical facet joint," "afferent," "vestibulocollic," "cervicocollic," "postural reflexes," "spaceflight," "microgravity," "weightlessness," "gravity," "posture," and "postural." Studies were selected if they specifically tested any or all of the postural reflexes either in Earth's gravity or in microgravitational environments. Studies testing the function of each postural component, as well as those discussing postural reflex interactions, were also included in this review. DISCUSSION: It is quite apparent from the indexed literature we searched that posture is largely maintained by reflexive, involuntary control. While reflexive components for postural control are found in skin and joint receptors, somatic graviceptors, and baroreceptors throughout the body, much of the reflexive postural control mechanisms are housed, or occur, within the head and neck region primarily. We suggest that the postural reflexes may function in a hierarchical fashion. This hierarchy may well be based on the gravity-dependent or gravity-independent nature of each postural reflex. Some or all of these postural reflexes may contribute to the development of a postural body scheme, a conceptual internal representation of the external environment under normal gravity. This model may be the framework through which the postural reflexes anticipate and adapt to new gravitational environments. CONCLUSION: Visual and vestibular input, as well as joint and soft tissue mechanoreceptors, are major players in the regulation of static upright posture. Each of these input sources detects and responds to specific types of postural stimulus and perturbations, and each region has specific pathways by which it communicates with other postural reflexes, as well as higher central nervous system structures. This review of the postural reflex structures and mechanisms adds to the growing body of posture rehabilitation literature relating specifically to chiropractic treatment. Chiropractic interest in these reflexes may enhance the ability of chiropractic physicians to treat and correct global spine and posture disorders. With the knowledge and understanding of these postural reflexes, chiropractors can evaluate spinal configurations not only from a segmental perspective, but can also determine how spinal dysfunction may be the ultimate consequence of maintaining an upright posture in the presence of other postural deficits. These perspectives need to be explored in more detail.
Journal Article↗
Variation of magnitude and timing of wrist flexor stretch reflex across the full range of voluntary activation.
This paper reports an investigation of the magnitude and timing of the stretch reflex over the full range of activation of flexor carpi radialis. While it is well established that the magnitude of the reflex increases with the level of muscle activation, there have been few studies of reflex magnitude above 50% of maximum voluntary contraction (MVC) and virtually no study of the timing of the response in relation to activation level. Continuous small amplitude (approximately 2 degrees) perturbations were applied to the wrist of 12 normal subjects while they maintained contraction levels between 2.5-95% MVC, monitored via surface electromyography (EMG). Both narrow band (4-5 Hz) and broad band (0-10 Hz) stretch perturbations were employed. The gain (EMG output/stretch input) and phase advance of the reflex varied with the level of muscle activation in a similar manner for both types of stretch, but there were significant differences in the patterns of change due to stretch bandwidth. Consistent with previous studies, the group average reflex gain initially increased with muscle activation level and then saturated. Inspection of individual data, however, revealed that the gain reached a peak at about 60% MVC and then decreased at higher contraction levels, the pattern across the full range of activation being well described by quadratic functions (mean r2=0.82). This quadratic pattern has not been reported previously for the neural reflex response in any muscle but is consistent with the pattern that has been reliably observed in studies of the mechanical reflex response in lower limb muscles. In contrast to the pattern for reflex gain, the phase advance of the reflex (at a stretch frequency of 4.5 Hz) decreased linearly from approximately 130 degrees at the lowest contraction levels to approximately 50 degrees as maximum voluntary contraction was reached (mean r2=0.69). This decrease corresponds to a delay of 49 ms introduced centrally in reflex pathways. All subjects showed clearly defined quadratic functions relating reflex gain and linear functions relating reflex phase to activation level, but there were considerable individual differences in the slopes of these functions which point to systematic differences in synaptic behaviour of the motoneuron pool. Thus, there was wide inter-subject variation in both the contraction level at which the reflex gain reached a peak (31-69% MVC) and the highest target contraction level that could be sustained during reflex measurement (47-95% MVC). A high correlation between these variables (r2=0.78) suggests a linear relation between afferent support of contraction and muscle fatigability. The decline in reflex gain at high levels of muscle activation signals a failure of muscle afferent input and subjects in whom the gain reached a peak and declined early were unable to sustain higher target contraction levels. The results of the study show that both the timing and magnitude of the stretch reflex vary markedly over the full range of voluntary muscle activation. The pattern of variation may account for why the stretch reflex contributes most effectively to muscle mechanics over the lower half of the range of activation, while progressive reductions in both gain and phase advance at higher levels render the reflex mechanically less effective and make tremor more likely.
Action Potentials↗
Characteristic appearances of the H-reflex and F-wave with increased stimulus intensity in patients with cerebrovascular disease.
We experienced H-reflex may be evoked with supramaximal stimulation in patients with cerebrovascular disease (CVD). In this study, we investigated the relationship between the characteristic appearances of H-reflex and F-wave with increased stimulus intensity and neurological signs. We examined the H-reflex and F-wave of the affected arm with increased stimulus intensity during muscle relaxation in 31 patients (17 males and 14 females) with hemiparesis caused by CVD. Mean patient age was 56.0 (range 30-82) years. 30 healthy subjects, mean age of 56.2 (range 28-80) were investigated using the same method as controlled group. H-reflex and F-wave with increased stimulus intensity after the median nerve stimulation at the wrist were recorded from the opponence pollicis muscle on the affected side in patients with CVD or right arm in the healthy subjects. Appearance patterns of the H-reflex and F-wave with increased stimulus intensity was separated into four types. Type 1: F-wave appeared with increased stimulus intensity, but there was no H-reflex. Type 2: H-reflex and F-wave both appeared with increased stimulus intensity, but the F-wave followed disappearance of the H-reflex with increased stimulus intensity. Type 3: H-reflex and F-wave both appeared with increased stimulus intensity, but the F-wave appeared during the H-reflex with increased stimulus intensity. Type 4: Only the H-reflex appeared with increased stimulus intensity, but there was no F-wave. Neurological findings including muscle tone and tendon reflex were also evaluated. Findings on muscle tone and tendon reflex were classified into increased (markedly, moderately and slightly), normal and decreased. Results were analyzed as follows; 1) The characteristic appearances of H-reflex and F-wave in the healthy subjects and 2) The relationship between characteristic appearances of waves with increased stimulus intensity and neurological signs in patients with CVD. 1) Pattern of the H-reflex and F-wave with increased stimulus intensity in all healthy subjects were type 1. 2) Patterns of the H-reflex and F-wave with increased stimulus intensity in patients with markedly increased muscle tone and tendon reflex were almost always type 4. Those with moderately increased signs in this parameter demonstrated type 2 or 3. Those with slightly increased signs in this parameter demonstrated type 1 or 2. Those with normal or decreased signs were type 1. These findings suggest that the characteristic appearances of the H-reflex and F-wave was influenced by grade of neurological signs.
Adult↗
Postural reflexes in Parkinson's disease during 'resist' and 'yield' tasks.
Postural reflexes in leg muscles appear to be set at a fixed gain in Parkinson's disease. To further investigate gain adaptation, we instructed 16 patients with idiopathic Parkinson's disease (studied during the 'off' phase) and 21 healthy controls to either 'resist' or 'yield' in response to 20 serial 4 degrees toe-up perturbations of a supporting platform on which they were standing. We bilaterally recorded destabilizing medium latency (ML) reflexes from stretched gastrocnemius muscles and corrective long latency (LL) reflexes from shortened tibialis anterior muscles. We also assessed changes in center of foot pressure (CFP) and center of gravity (COG). During the 'resist' condition, patients had increased destabilizing ML reflexes, decreased corrective LL reflexes, increased backward displacement of the COG and increased forward (destabilizing) displacement of the CFP. In addition, the backward (corrective) displacement of CFP between 150 and 250 ms was delayed. During the 'yield' condition, reflex gains were modified in controls: LL reflexes were markedly attenuated, whereas ML reflexes were markedly increased. Although this reflex pattern resembled the 'resist' condition in patients, it was not associated with an increased forward displacement of the CFP, but only with a strongly delayed backward displacement of CFP which started after 150 ms. In patients, ML reflex amplitudes remained unchanged during the 'yield' condition, suggesting a fixed reflex gain. LL reflex amplitudes were reduced in patients but significantly less compared to controls, which again suggests a fixed reflex gain. This 'inflexibility' of postural reflexes was reflected by the CFP which showed much smaller changes between 0 and 250 ms in patients than controls. These results could not be ascribed to a different ability to yield because posterior displacement of the COG was identical in patients and controls during the 'yield' condition. We conclude that (1) patients with Parkinson's disease have abnormal and 'inflexible' postural reflexes, associated with delayed corrective movements about the ankle joint and increased body sway; and (2) the increased forward displacement of the CFP in patients likely reflects high stiffness in ankle muscles because reflex changes in controls only affected the CFP more than 150 ms after the perturbation. The increased muscle stiffness and inflexibility of postural reflexes in Parkinson's disease may contribute to balance impairment in daily life.
Adaptation, Physiological↗
Cervical root compression monitoring by flexor carpi radialis H-reflex in healthy subjects.
STUDY DESIGN: One-group, pretest-postest experimental research with repeated measures. OBJECTIVE: To determine the effect of head postural modification on the flexor carpi radialis H-reflex in healthy subjects. SUMMARY OF BACKGROUND DATA: H-reflex testing has been reported to be useful in evaluating and treating patients with lumbosacral and cervical radiculopathy. The idea behind this technique is that postural modification can cause further H-reflex inhibition, indicating more compression of the impinged nerve root, or recovery, indicating decompression of the root. Such assumptions cannot be supported unless the influence of normal head postural modification on the H-reflex in healthy subjects is studied. METHODS: Twenty-two healthy subjects participated in this study (14 men, 8 women; mean age, 39 +/- 9 years). The median nerve of the subjects at the cubital fossa was electrically stimulated (0.5 msec; 0.2 pulses per second [pps] at H-max), whereas the flexor carpi radialis muscle H-reflex was recorded by electromyography. The H-reflexes were recorded after the subject randomly maintained the end range of head-forward flexion, backward extension, rotation to the right and the left, lateral bending to the right and the left, retraction and protraction. These were compared with the H-reflex recorded during comfortable neutral positions. Data were recorded after the subject maintained the position for 30 seconds, to avoid the effect of dynamic postural modification on the H-reflex. Four traces were recorded in each position. During recording, the H-reflex was monitored by the M-response to avoid any changes in the stimulation-recording condition. RESULTS: Repeated multivariate analysis of variance was used to evaluate the significance of the difference among the H-reflex, amplitude, and latency, in various head positions. The H-reflex amplitude showed statistically significant changes (P < 0.001) with head postural modification. All head positions, except flexion, facilitated the H-reflex. Extension, lateral bending, and rotation toward the side of the recording produced higher reflex facilitation than the other positions. These results indicate that H-reflex changes may be caused by spinal root compression-decompression mechanisms. It may also indicate that relative spinal root decompression occurs in most head-neck postures except forward flexion. CONCLUSIONS: Head postural modification significantly influences the H-reflex amplitude but not the latency. This indicates that the H-reflex is a more sensitive predictor of normal physiologic changes than are latencies. The H-reflex modulation in various head positions may be-caused by relative spinal root compression-decompression mechanisms.
Adult↗
Postural proprioceptive reflexes in standing human subjects: bandwidth of response and transmission characteristics.
1. This study investigated the reflex control of postural sway during human bipedal stance. The experiments were designed to: (i) find evidence for the operation of 'stretch reflex' pathways during quiet stance, (ii) determine the bandwidth of the reflex response, (iii) describe the reflex transmission characteristics in standing subjects, and (iv) assess the ability of subjects to make a task-dependent change in the reflex. 2. A continuous random perturbation that did not threaten stability was applied at waist level to nine standing subjects. The effects of the perturbation on ankle torque, ankle movement and soleus electromyographic activity (EMG) were identified by cross-correlation. The bandwidth of the reflex response and the transmission characteristics of reflexes that respond to ankle movement were identified by spectral analysis. Changes in these reflex responses were investigated when subjects attempted to stand as still as possible, had their eyes closed, or balanced a load equivalent to their own body in a situation in which neither visual nor vestibular reflexes would be activated. 3. When standing, a reflex response coherent with the perturbation was seen in soleus EMG at frequencies up to 5 Hz, with maximal coherence at 1.0-2.0 Hz. Reflex gain increased with frequency, and there was a frequency-dependent phase advance of soleus EMG on ankle movement reaching 135 deg at 3 Hz. When attempting to minimize sway, subjects produced a more coherent reflex response and significantly increased reflex gain. 4. The response and transmission characteristics of the lower limb proprioceptive reflex in freely standing subjects were similar to those in subjects balancing a load at the ankle, a situation in which vestibular and visual inputs could not contribute. 5. It is concluded that reflex feedback related to ankle movement contributes significantly to maintaining stance, and that much of the reflex response originates from lower limb mechanoreceptors stimulated by ankle rotation. Although reflex gain may be relatively low during quiet stance it can be increased when necessary to maintain stability.
Adult↗
Gain of the triceps surae stretch reflex in decerebrate and spinal cats during postural and locomotor activities.
1. The triceps surae (TS) stretch reflex was measured in decerebrate cats during crossed extensor stimulation and after spinalization during rhythmic locomotor activity induced by clonidine and manual perineal stimulation. The TS force in response to sinusoidal stretch was measured at a given contraction level before and after deafferentation, and the 'reflex force' was computed by subtracting these two responses. Reflex 'gain' was computed as the ratio of the reflex and deafferented force responses (a unitless estimate of the open loop feedback gain). 2. Prior to locomotion the spontaneous muscle activity was low (less than 15% of maximum), but the reflex gain was relatively high (close to 1.0 with a 5 Hz stretch). When locomotion commenced the reflex gain was markedly lowered when measured at the same contraction level as before locomotion (25% of the gain prior to locomotion). At higher contraction levels the reflex gain was not significantly increased. The reflex force and EMG responses to stretch increased with the contraction level, but their effect on the total reflex gain was cancelled by an associated increase in the intrinsic muscle stiffness. 3. In the decerebrate cat, during weak tonic contractions (spontaneous), the reflex gain was high and comparable with the gain in the resting spinal cat. However, with increased tonic contractions produced by crossed extensor stimulation the reflex gain dropped. At higher contraction levels the gain was not significantly different from the gain during spinal locomotion. 4. When the frequency of stretch was increased from 3 to 20 Hz, EMG responses to stretch increased, but the reflex force decreased, since a more fused contraction developed with the more frequent reflex activations. Overall, the reflex gain decreased with frequency in both spinal and decerebrate cats. The phase lag of the reflex force, relative to the intrinsic muscle force, increased with increasing frequency, due to reflex delays, with a 180 deg lag occurring between 12 and 18 Hz (tremor frequencies). The mean gain was significantly lower and the phase lag was significantly greater during locomotion than during tonic crossed extensor contractions, suggesting different reflex mechanisms. 5. In conclusion, during locomotion in spinal cats afferent feedback from low frequency ankle movements, similar to those occurring during the normal step cycle, reflexly produces a small but significant fraction of the extensor force (about a quarter of the stretch-related force modulation). This fraction is remarkably constant at the different contraction levels of the step cycle. Afferent feedback during higher frequency movement is less effective, minimizing the chance of instability and tremor. In contrast during tonic contractions afferent feedback produces half of the total muscle force during perturbations, clearly contributing to the maintenance of posture.
Afferent Pathways↗
Mechanical actions of heterogenic reflexes among ankle stabilizers and their interactions with plantarflexors of the cat hindlimb.
1. The stretch-evoked reflex organization of muscles whose major action is to abduct [peroneus brevis (PB); peroneus longus (PL)] and adduct [tibialis posterior (TP); flexor digitorum longus (FDL); flexor hallucis longus (FHL)] the ankle, and their interactions with the hindlimb extensors gastrocnemius (G) and soleus (S), were studied in 27 unanesthetized decerebrate cats. Ramp-hold-release stretches of physiological amplitudes were applied to muscle tendons detached from their bony insertion, and muscle force output was measured in response to these perturbations. Flexion and crossed-extension reflexes were used to modulate baseline force. 2. PB and TP shared strong, length-dependent, short-latency inhibitory reflexes prominent when the muscles were either actively generating force or quiescent. The mechanical characteristics of this reflex suggest Ia reciprocal inhibition as the underlying mechanism. Just as reciprocal inhibition between S and tibialis anterior stiffens the ankle joint against sagittal perturbations, we propose that reciprocal inhibition between PB and TP stiffens the ankle joint against nonsagittal perturbations. 3. In all preparations (n = 7) and under all conditions examined, PB and PL shared well-demonstrated mutual excitation. The reflex responses were asymmetric (favoring excitation of PL), length dependent, and occurred simultaneously with the stretch reflex at a latency of 16-18 ms. Mutual monosynaptic projections previously described between these two muscles explain all of the above findings. Our data further demonstrate that, under certain conditions, the ensemble activity of this reflex interaction has a powerful effect on the mechanical behavior of the muscle. 4. The heterogenic reflex organization of the ankle adductors was as follows: FDL evoked a modest excitation on TP, whereas FHL evoked weak inhibition. Latency of the excitation from FDL onto TP (24 ms) was greater than expected if the reflex were mediated by heteronymous Ia afferents. In all preparations examined (n = 3), TP contributed no significant reflexes onto either FDL or FHL. 5. Mutual, asymmetric inhibition characterized interactions between PB and the plantarflexors S and G. Most remarkable was a novel, long-latency (72-74 ms) reflex inhibition evoked on both S and G by stretch of PB. When this inhibition occurred, it dramatically decreased the S (or G) stretch response. Longer PB lengths evoked greater inhibition of isometric S; regression analysis indicated that the model best predicting this inhibition contained muscle force and stiffness terms. No long-latency reflexes were noted from either G or S onto PB. The mechanism underlying long-latency inhibition is presently unknown; however, features of this interaction suggest interneurons receive either group II or group III afferent input. 6. G and TP shared short latency, mutually inhibitory, asymmetric reflexes favoring inhibition of TP. No long-latency interactions were noted, nor were there any mechanically significant interactions between S and TP. 7. Reflex interactions across the abduction/adduction axis thus favored inhibition of plantarflexion and adduction torques while emphasizing abduction torques: PB/S (or PB/G) interactions were mutual, asymmetric, and favored inhibition of G and S; TP/G interactions were mutual, asymmetric, and favored inhibition of TP; TP/PB interactions were approximately balanced. The overall mechanical outcome of these inhibitory interactions may partly underlie the global corrective strategy seen in intact cats subjected to linear perturbations. 8. No significant reflex interactions were demonstrated between PL and TP, G, or S, nor were any long-latency reflexes noted. Thus, whereas reflex interactions between the stereotypically activated PB and other stereotypically activated muscles (including TP, G, and S) were strong and well-demonstrated, interactions between the variably activated PL and these same muscles were far weaker.
Animals↗
On the cutaneous receptors contributing to withdrawal reflex pathways in the decerebrate spinal rat.
Previous studies indicate that the withdrawal reflex system in the rat has a "modular" organization, each reflex pathway performing a specific sensorimotor transformation. Here, we wished to clarify which cutaneous receptors contribute to this system and to determine whether there are differences in this respect between reflex pathways of different muscles. Withdrawal reflexes of the peroneus longus, extensor digitorum longus, and semitendinosus muscles were recorded with EMG techniques during high reflex excitability in decerebrate spinal rats (n=26). While maintained innocuous pressure on glabrous skin could elicit a sustained reflex activity in all muscles studied, vibration of glabrous skin (10-300 Hz) always failed to evoke a reflex response, suggesting that slowly adapting, but not rapidly adapting, low-threshold mechanoreceptive fibers from this type of skin contribute to withdrawal reflex pathways. Thermal stimulation in the innocuous range, i.e., cooling from 32 to 17 degrees C, or warming the skin from 32 to 41 degrees C, always failed to produce reflex responses, indicating that neither cold nor warm receptors contribute to withdrawal reflex pathways. When either cooling or warming the skin to the noxious temperatures of 1 degrees C or above 45 degrees C, respectively, a reflex discharge was often evoked in the muscles studied. Intradermal administration of histamine, a potent pruritogenic substance, produced very weak, or no, reflex response. In contrast, mustard oil produced vigorous reflex responses in all muscles studied. These findings suggest that some chemonociceptors contribute only weakly, or not at all, to withdrawal reflex pathways. The present data suggest that a selective set of cutaneous receptors contribute to withdrawal reflex pathways and that different withdrawal reflex pathways receive input from essentially the same cutaneous receptor types.
Animals↗
Supraspinal regulation of spinal reflex discharge into cardiac sympathetic nerves.
(1) In chloralose anaesthetized cats, reflex responses were recorded in inferior cardiac nerves following stimulation of intercostal nerves and hind limb afferent nerves. (2) In 80% of cats, a long latency reflex response alone was recorded, whereas, in the others, a short and long latency response was present to intercostal nerve stimulation. (3) In cats displaying only a long latency somatocardiac reflex response, damage to the ventral quadrant of the ipsilateral cervical spinal cord, through which runs a bulbospinal inhibitory pathway, resulted in the appearance of shorter latency reflexes to intercostal nerve stimulation. Lesions elsewhere in the cervical cord did not do this. (4) The characteristics of the early responses indicated that they were somatosympathetic reflexes and not dorsal root reflexes. (5) The early reflexes remained and the late reflex disappeared on subsequent complete transection of the spinal cord. The early reflexes were therefore spinal reflexes, and suppressed in the animal with cord intact. (6) Lesions at C4, which included a contralateral hemisection and a section of dorsal columns extending into the dorsal part of the lateral funiculus, abolished the inhibition of a sympathetic reflex that followed stimulation of some somatic afferent nerve fibres. These sections did not release the spinal reflex. Therefore, this reflex inhibition was not responsible for the suppression of the spinal somatosympathetic reflex. (7) The descending inhibitory influence on the segmental reflex pathway was not antagonized by strychnine, bicuculline or picrotoxin. (8) The possibility is discussed that the spinal reflex pathway into cardiac sympathetic nerves is tonically inhibited by a bulbospinal pathway originating from the classical depressor region of the ventromedial reticular formation.
Animals↗
Hip angle induced modulation of H reflex amplitude, latency and duration in spinal cord injured humans.
OBJECTIVES: To investigate the modulation of the soleus H reflex in spinal cord injured (SCI) subjects resulting from imposed changes in hip angle and to establish whether changes in H reflex amplitude co-vary with changes in reflex latency and duration. METHODS: H reflexes were recorded using conventional methods in 7 SCI subjects in the supine position. The right leg was secured by a leg brace and positioned at various angles of hip flexion (30 degrees, 40 degrees ) and at 10 degrees of hip extension. RESULTS: We found that imposing 10 degrees of hip extension resulted in a significant facilitation in the size of the soleus H reflex in all of the SCI subjects tested (200% of control reflex; recorded at 10 degrees of hip flexion). In contrast, positioning the hip at 30 degrees and at 40 degrees of flexion resulted in a significant reduction of the H reflex in 6 of 7 SCI subjects tested. In the remaining subject, an increase in the H reflex amplitude was observed. Modulation of H reflex amplitude coincided with shifts in both H reflex latency and duration. The reflex latency was prolonged when the reflex amplitude was reduced following hip flexion, while hip extension shortened the reflex latency. In contrast, the H reflex duration was prolonged with hip extended and shortened with hip flexed. CONCLUSIONS: When changes in static hip joint position are imposed in SCI subjects, changes in afferent feedback from hip proprioceptors are capable of promoting a switch between excitatory and inhibitory pathways. Associated changes in H reflex latency and duration are consistent with the hypothesis that oligosynaptic inputs contribute to the hip angle-induced H reflex modulation. Possible mechanisms for these effects are discussed.
Adult↗
Reliability of a new measure of H-reflex excitability.
OBJECTIVE: This study examined the intraclass reliability of different measures extracted from Hoffmann reflex (H-reflex) stimulus-response curve that are used to assess neuromuscular excitability. The following measures were compared: (1) the peak-to-peak amplitude of the H-reflex at a stimulus intensity associated with 5% of the maximum M-wave; (2) the slope of the regression line of the H-reflex stimulus-response curve; and (3) the peak of the first derivative of the H-reflex stimulus-response curve, a new measure introduced in this paper. METHODS: The H-reflex was elicited in the soleus for 24 subjects (12 males and 12 females) on 5 separate days. Vibration was applied to the Achilles tendon prior to stimulation to test the sensitivity of the measures on test day 4. The stimulus intensity was gradually increased from below the threshold for an H-reflex response to above the maximum M-wave (Mmax) response. The means of 5 evoked potentials at each intensity level were used to create both the H-reflex and M-wave stimulus-response curves for each subject across test days. Determination of reliability involves the consideration of both the stability and consistency of the measures. A repeated measures analysis of variance evaluated the stability of the group means across test sessions. The consistency of scores within individuals was determined by calculating the intraclass correlation coefficient (ICC). Calculation of the 95% confidence interval of estimation was used to assess significant differences between ICCs. RESULTS: The H-reflex measures were both stable and consistent across the first 3 test days. Achilles tendon vibration resulted in a profound reduction (59-70%) on test day 4, and then there was a return to baseline levels on test day 5. The ICC for H-reflex at a stimulus intensity associated with 5% of the maximum M-wave was 0.85. The ICC for the slope of the regression line of the H-reflex stimulus-response curve was 0.79, while it was 0.89 for the peak of the first derivative of the H-reflex stimulus-response curve. However, there was no statistical significance (P>0.05) between the 3 EMG measures of the H-reflex arc. Maximum M-wave amplitude had an ICC of 0.96 attesting to careful methodological controls. CONCLUSIONS: The peak of the first derivative of the H-reflex stimulus-response curve was shown to have comparable sensitivity and reliability as other more established measures. SIGNIFICANCE: The first derivative of the H-reflex stimulus-response curve provides the rate of change, rather than amplitude, making it a robust measure of reflex arc excitability. The higher ICC for the first derivative offers greater statistical power, which is of practical significance.
Achilles Tendon↗
Wideband reflectance measures of the ipsilateral acoustic stapedius reflex threshold.
OBJECTIVE: The purpose of this study was to develop a method for acoustically measuring the ipsilateral acoustic stapedius reflex threshold by using wideband shifts in energy reflectance and admittance. DESIGN: A group of 27 young adult subjects with normal hearing participated in the study. Contralateral reflex thresholds were first measured for a 4000 Hz activator tone (maximum level, 92 dB SPL), using a clinical method with a 226 Hz probe tone. Ipsilateral and contralateral reflex thresholds were then measured by using an experimental wideband reflectance and admittance system that used a band-filtered click (200 to 2000 Hz) as the probe stimulus, presented simultaneously with the 4000 Hz activator tone. Reflex thresholds for the wideband system were determined by using statistical tests of the magnitude of the reflex responses as well as their correlation with other reflex responses. RESULTS: Clinical and experimental reflex thresholds were obtained for 9 of the 27 subjects for all conditions. Clinical reflex thresholds were absent for 8 subjects for whom experimental reflex thresholds were present and were present for 5 subjects who had absent experimental reflex thresholds for one or more conditions. An additional 5 subjects had absent reflex thresholds in all conditions, consistent with the low maximum level of the activator. Wideband measures of contralateral reflex thresholds were approximately 3 dB lower than those obtained with the clinical system. The magnitudes of the group means of the reflex responses were similar for ipsilateral and contralateral stimulations. CONCLUSIONS: Wideband measures of reflectance and admittance may be used to estimate the ipsilateral acoustic stapedius reflex threshold by separating in frequency the spectral energies of the wideband probe stimulus from the activator stimulus. This technique holds promise for measuring reflex thresholds for individuals with absent reflex thresholds through the use of standard clinical methods.
Acoustic Impedance Tests↗