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Blanchette, Andreanne K., Aditi A. Mullick, Karina Moïn-Darbari y Mindy F. Levin. "Tonic Stretch Reflex Threshold as a Measure of Ankle Plantar-Flexor Spasticity After Stroke". Physical Therapy 96, n.º 5 (1 de mayo de 2016): 687–95. http://dx.doi.org/10.2522/ptj.20140243.
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Background Commonly used spasticity scales assess the resistance felt by the evaluator during passive stretching. These scales, however, have questionable validity and reliability. The tonic stretch reflex threshold (TSRT), or the angle at which motoneuronal recruitment begins in the resting state, is a promising alternative for spasticity measurement. Previous studies showed that spasticity and voluntary motor deficits after stroke may be characterized by a limitation in the ability of the central nervous system to regulate the range of the TSRT. Objective The study objective was to assess interevaluator reliability for TSRT plantar-flexor spasticity measurement. Design This was an interevaluator reliability study. Methods In 28 people after stroke, plantar-flexor spasticity was evaluated twice on the same day. Plantar-flexor muscles were stretched 20 times at different velocities assigned by a portable device. Plantar-flexor electromyographic signals and ankle angles were used to determine dynamic velocity-dependent thresholds. The TSRT was computed by extrapolating a regression line through dynamic velocity-dependent thresholds to the angular axis. Results Mean TSRTs in evaluations 1 and 2 were 66.0 degrees (SD=13.1°) and 65.8 degrees (SD=14.1°), respectively, with no significant difference between them. The intraclass correlation coefficient (2,1) was .851 (95% confidence interval=.703, .928). Limitations The notion of dynamic stretch reflex threshold does not exclude the possibility that spasticity is dependent on acceleration, as well as on velocity; future work will study both possibilities. Conclusions Tonic stretch reflex threshold interevaluator reliability for evaluating stroke-related plantar-flexor spasticity was very good. The TSRT is a reliable measure of spasticity. More information may be gained by combining the TSRT measurement with a measure of velocity-dependent resistance.
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Zhang, Li-Qun, Sun G. Chung, Yupeng Ren, Lin Liu, Elliot J. Roth y W. Zev Rymer. "Simultaneous characterizations of reflex and nonreflex dynamic and static changes in spastic hemiparesis". Journal of Neurophysiology 110, n.º 2 (15 de julio de 2013): 418–30. http://dx.doi.org/10.1152/jn.00573.2012.
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This study characterizes tonic and phasic stretch reflex and stiffness and viscosity changes associated with spastic hemiparesis. Perturbations were applied to the ankle of 27 hemiparetic and 36 healthy subjects under relaxed or active contracting conditions. A nonlinear delay differential equation model characterized phasic and tonic stretch reflex gains, elastic stiffness, and viscous damping. Tendon reflex was characterized with reflex gain and threshold. Reflexively, tonic reflex gain was increased in spastic ankles at rest ( P < 0.038) and was not regulated with muscle contraction, indicating impaired tonic stretch reflex. Phasic-reflex gain in spastic plantar flexors was higher and increased faster with plantar flexor contraction ( P < 0.012) than controls ( P < 0.023) and higher in dorsi-flexors at lower torques ( P < 0.038), primarily because of its increase at rest ( P = 0.045), indicating exaggerated phasic stretch reflex especially in more spastic plantar flexors, which showed higher phasic stretch reflex gain than dorsi-flexors ( P < 0.032). Spasticity was associated with increased tendon reflex gain ( P = 0.002) and decreased threshold ( P < 0.001). Mechanically, stiffness in spastic ankles was higher than that in controls across plantar flexion/dorsi-flexion torque levels ( P < 0.032), and the more spastic plantar flexors were stiffer than dorsi-flexors at comparable torques ( P < 0.031). Increased stiffness in spastic ankles was mainly due to passive stiffness increase ( P < 0.001), indicating increased connective tissues/shortened fascicles. Viscous damping in spastic ankles was increased across the plantar flexion torque levels and at lower dorsi-flexion torques, reflecting increased passive viscous damping ( P = 0.033). The more spastic plantar flexors showed higher viscous damping than dorsi-flexors at comparable torque levels ( P < 0.047). Simultaneous characterizations of reflex and nonreflex changes in spastic hemiparesis may help to evaluate and treat them more effectively.
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Calancie, B. y P. Bawa. "Voluntary and reflexive recruitment of flexor carpi radialis motor units in humans". Journal of Neurophysiology 53, n.º 5 (1 de mayo de 1985): 1194–200. http://dx.doi.org/10.1152/jn.1985.53.5.1194.
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The order of recruitment of flexor carpi radialis (FCR) motor units was studied during voluntary and reflexive activation of the motoneuron pool for two adult subjects. During slow "voluntary" activation, the recruitment threshold for tonic motoneuron firing was determined, and then the twitch profile of the motor unit was computed by the spike-triggered averaging technique. A positive correlation (r = 0.79 and 0.68 for the two subjects, respectively) between recruitment threshold and twitch amplitude implies that recruitment of FCR motoneurons during slow ramp isometric contractions proceeds in order of increasing size. The accompanying paper describes the behavior of single motor units during the short- and long-latency periods of the stretch reflex. When the effects of sufficient voluntary facilitation (preload) combined with a sufficiently large torque step were just adequate to cause a motor unit to fire during the stretch reflex, its response was virtually always confined to the long-latency period. In addition, the first unit to begin responding to muscle stretch always had the lowest voluntary recruitment threshold relative to other units "visible" at that recording site. By making this unit tonic, the reflex response to the same load increased substantially during the short-latency reflex period, while a second unit increased its reflex response probability during the long-latency period. Thus the voluntary recruitment order of two or more motor units is preserved during the stretch reflex, and is in fact maintained within first the long-latency and then short-latency components of this reflex.
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Latash, Mark, Mindy Levin, John Scholz y Gregor Schöner. "Motor control theories and their applications". Medicina 46, n.º 6 (12 de junio de 2010): 382. http://dx.doi.org/10.3390/medicina46060054.
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We describe several infl uential hypotheses in the field of motor control including the equilibrium-point (referent confi guration) hypothesis, the uncontrolled manifold hypothesis, and the idea of synergies based on the principle of motor abundance. The equilibrium-point hypothesis is based on the idea of control with thresholds for activation of neuronal pools; it provides a framework for analysis of both voluntary and involuntary movements. In particular, control of a single muscle can be adequately described with changes in the threshold of motor unit recruitment during slow muscle stretch (threshold of the tonic stretch reflex). Unlike the ideas of internal models, the equilibrium-point hypothesis does not assume neural computations of mechanical variables. The uncontrolled manifold hypothesis is based on the dynamic system approach to movements; it offers a toolbox to analyze synergic changes within redundant sets of elements related to stabilization of potentially important performance variables. The referent confi guration hypothesis and the principle of abundance can be naturally combined into a single coherent scheme of control of multi-element systems. A body of experimental data on healthy persons and patients with movement disorders are reviewed in support of the mentioned hypotheses. In particular, movement disorders associated with spasticity are considered as consequences of an impaired ability to shift threshold of the tonic stretch reflex within the whole normal range. Technical details and applications of the mentioned hypo theses to studies of motor learning are described. We view the mentioned hypotheses as the most promising ones in the field of motor control, based on a solid physical and neurophysiological foundation.
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Calota, Andra y Mindy F. Levin. "Tonic Stretch Reflex Threshold as a Measure of Spasticity: Implications for Clinical Practice". Topics in Stroke Rehabilitation 16, n.º 3 (mayo de 2009): 177–88. http://dx.doi.org/10.1310/tsr1603-177.
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Calota, Andra, Anatol G. Feldman y Mindy F. Levin. "Spasticity measurement based on tonic stretch reflex threshold in stroke using a portable device". Clinical Neurophysiology 119, n.º 10 (octubre de 2008): 2329–37. http://dx.doi.org/10.1016/j.clinph.2008.07.215.
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Marques, Isabela Alves, Maristella Borges Silva, Andrei Nakagawa Silva, Luiza Maire David Luiz, Alcimar Barbosa Soares y Eduardo Lázaro Martins Naves. "Measurement of post-stroke spasticity based on tonic stretch reflex threshold: implications of stretch velocity for clinical practice". Disability and Rehabilitation 41, n.º 2 (2 de octubre de 2017): 219–25. http://dx.doi.org/10.1080/09638288.2017.1381183.
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Frenkel-Toledo, Silvi, John M. Solomon, Akash Shah, Melanie C. Baniña, Sigal Berman, Nachum Soroker, Dario G. Liebermann y Mindy F. Levin. "Tonic stretch reflex threshold as a measure of spasticity after stroke: Reliability, minimal detectable change and responsiveness". Clinical Neurophysiology 132, n.º 6 (junio de 2021): 1226–33. http://dx.doi.org/10.1016/j.clinph.2021.02.390.
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Balamurugan, S., Rachaveti Dhanush y S. K. M. Varadhan. "Role of Post-Trial Visual Feedback on Unintentional Force Drift During Isometric Finger Force Production Tasks". Motor Control 26, n.º 1 (1 de enero de 2022): 1–14. http://dx.doi.org/10.1123/mc.2020-0031.
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A reduction in fingertip forces during a visually occluded isometric task is called unintentional drift. In this study, unintentional drift was studied for two conditions, with and without “epilogue.” We define epilogue as the posttrial visual feedback in which the outcome of the just-concluded trial is shown before the start of the next trial. For this study, 14 healthy participants were recruited and were instructed to produce fingertip forces to match a target line at 15% maximum voluntary contraction. The results showed a significant reduction in unintentional drift in the epilogue condition. This reduction is probably due to the difference in the shift in λ, the threshold of the tonic stretch reflex, the hypothetical control variable that the central controller can set.
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Dutta, A. y A. Das. "Effects of transcutaneous lumbar spinal cord alternating current stimulation on tonic stretch reflex threshold in stroke - a case series". Brain Stimulation 8, n.º 2 (marzo de 2015): 371–72. http://dx.doi.org/10.1016/j.brs.2015.01.193.
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Kim, Keo Sik, Jeong Hwan Seo y Chul Gyu Song. "Portable measurement system for the objective evaluation of the spasticity of hemiplegic patients based on the tonic stretch reflex threshold". Medical Engineering & Physics 33, n.º 1 (enero de 2011): 62–69. http://dx.doi.org/10.1016/j.medengphy.2010.09.002.
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Pyndt, H. S. y J. B. Nielsen. "Modulation of Transmission in the Corticospinal and Group Ia Afferent Pathways to Soleus Motoneurons During Bicycling". Journal of Neurophysiology 89, n.º 1 (1 de enero de 2003): 304–14. http://dx.doi.org/10.1152/jn.00386.2002.
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Transmission in the corticospinal and Ia pathways to soleus motoneurons was investigated in healthy human subjects during bicycling. Soleus H reflexes and motor evoked potentials (MEPs) after transcranial magnetic stimulation (TMS) were modulated similarly during the crank cycle being large during downstroke [concomitant with soleus background electromyographic (EMG) activity] and small during upstroke. Tibialis anterior MEPs were in contrast large during upstroke and small during downstroke. The soleus H reflexes and MEPs were also recorded during tonic plantarflexion at a similar ankle joint position, corresponding ankle angle, and matched background EMG activity as during the different phases of bicycling. Relative to their size during tonic plantarflexion, the MEPs were found to be facilitated in the early part of downstroke during bicycling, whereas the H reflexes were depressed in the late part of downstroke. The intensity of TMS was decreased below MEP threshold and used to condition the soleus H reflex. At short intervals (conditioning-test intervals of −3 to −1 ms), TMS produced a facilitation of the H reflex that is in all likelihood caused by activation of the fast monosynaptic corticospinal pathway. This facilitation was significantly larger in the early part of downstroke during bicycling than during tonic plantarflexion. This suggests that the increased MEP during downstroke was caused by changes in transmission in the fast monosynaptic corticospinal pathway. To investigate whether the depression of H reflexes in the late part of downstroke was caused by increased presynaptic inhibition of Ia afferents, the soleus H reflex was conditioned by stimulation of the femoral nerve. At a short interval (conditioning-test interval: −7 to −5 ms), the femoral nerve stimulation produced a facilitation of the H reflex that is mediated by the heteronymous monosynaptic Ia pathway from the femoral nerve to soleus motoneurons. Within the initial 0.5 ms after its onset, the size of this facilitation depends on the level of presynaptic inhibition of the Ia afferents, which mediate the facilitation. The size of the facilitation was strongly depressed in the late part of downstroke, compared with the early part of downstroke, suggesting that increased presynaptic inhibition was indeed responsible for the depression of the H reflex. These findings suggest that there is a selectively increased transmission in the fast monosynaptic corticospinal pathway to soleus motoneurons in early downstroke during bicycling. It would seem likely that one cause of this is increased excitability of the involved cortical neurons. The increased presynaptic inhibition of Ia afferents in late downstroke may be of importance for depression of stretch reflex activity before and during upstroke.
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Chapple, William D. "Regulation of Muscle Stiffness During Periodic Length Changes in the Isolated Abdomen of the Hermit Crab". Journal of Neurophysiology 78, n.º 3 (1 de septiembre de 1997): 1491–503. http://dx.doi.org/10.1152/jn.1997.78.3.1491.
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Chapple, William. Regulation of muscle stiffness during periodic length changes in the isolated abdomen of the hermit crab. J. Neurophysiol. 78: 1491–1503, 1997. Reflex activation of the ventral superficial muscles (VSM) in the abdomen of the hermit crab, Pagurus pollicarus, was studied using sinusoidal and stochastic longitudinal vibration of the muscle while recording the length and force of the muscle and the spike times of three exciter motoneurons. In the absence of vibration, the interspike interval histograms of the two larger motoneurons were bimodal; cutting sensory nerves containing most of the mechanoreceptor input removed the short interval peak in the histogram, indicating that the receptors are important in maintaining tonic firing. Vibration of the muscle evoked a reflex increase in motoneuron frequency that habituated after an initial peak but remained above control levels for the duration of stimulation. Motoneuron frequency increased with root mean square (rms) stimulus amplitude. Average stiffness during stimulation was about two times the stiffness of passive muscle. The reflex did not alter muscle dynamics. Estimated transfer functions were calculated from the fast Fourier transform of length and force signals. Coherence was >0.9 for the frequency range of 3–35 Hz. Stiffness magnitude gradually increased over this range in both reflex activated and passive muscle; phase was between 10 and 20°. Reflex stiffness decreased with increasing stimulus amplitudes, but at larger amplitudes, this decrease was much less pronounced; in this range stiffness was regulated by the reflex. The sinusoidal frequency at which reflex bursts were elicited was ∼6 Hz, consistent with previous measurements using ramp stretch. During reflex excitation, there was an increase in amplitude of the short interval peak in the interspike interval histogram; this was reduced when the majority of afferent pathways was removed. A phase histogram of motoneuron firing during sinusoidal vibration had a peak at ∼110 ms, also suggesting that an important component of the reflex is via direct projections from the mechanoreceptors. These results are consistent with the hypothesis that a robust feedforward regulation of abdominal stiffness during continuous disturbances is achieved by mechanoreceptors signalling the absolute value of changing forces; habituation of the reflex, its high-threshold for low frequency disturbances and the activation kinetics of the muscle further modify reflex dynamics.
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Subramanian, Sandeep K., Anatol G. Feldman y Mindy F. Levin. "Spasticity may obscure motor learning ability after stroke". Journal of Neurophysiology 119, n.º 1 (1 de enero de 2018): 5–20. http://dx.doi.org/10.1152/jn.00362.2017.
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Previous motor learning studies based on adapting movements of the hemiparetic arm in stroke subjects have not accounted for spasticity occurring in specific joint ranges (spasticity zones), resulting in equivocal conclusions about learning capacity. We compared the ability of participants with stroke to rapidly adapt elbow extension movements to changing external load conditions outside and inside spasticity zones. Participants with stroke ( n = 12, aged 57.8 ± 9.6 yr) and healthy age-matched controls ( n = 8, 63.5 ± 9.1 yr) made rapid 40°–50° horizontal elbow extension movements from an initial (3°) to a final (6°) target. Sixteen blocks (6–10 trials/block) consisting of alternating loaded (30% maximal voluntary contraction) and nonloaded trials were made in one (controls) or two sessions (stroke; 1 wk apart). For the stroke group, the tonic stretch reflex threshold angle at which elbow flexors began to be activated during passive elbow extension was used to identify the beginning of the spasticity zone. The task was repeated in joint ranges that did or did not include the spasticity zone. Error correction strategies were identified by the angular positions before correction and compared between groups and sessions. Changes in load condition from no load to load and vice versa resulted in undershoot and overshoot errors, respectively. Stroke subjects corrected errors in 1–4 trials compared with 1–2 trials in controls. When movements did not include the spasticity zone, there was an immediate decrease in the number of trials needed to restore accuracy, suggesting that the capacity to learn may be preserved after stroke but masked by the presence of spasticity. NEW & NOTEWORTHY When arm movements were made outside, instead of inside, the range affected by spasticity, there was an immediate decrease in the number of trials needed to restore accuracy in response to a change in the external load. This suggests that motor learning processes may be preserved in patients with stroke but masked by the presence of spasticity in specific joint ranges. This has important implications for designing rehabilitation interventions predicated on motor learning principles.
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Hasanbarani, Fariba, Marc Aureli Pique Batalla, Anatol G. Feldman y Mindy F. Levin. "Mild Stroke Affects Pointing Movements Made in Different Frames of Reference". Neurorehabilitation and Neural Repair 35, n.º 3 (29 de enero de 2021): 207–19. http://dx.doi.org/10.1177/1545968321989348.
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Background Motor performance is a complex process controlled in task-specific spatial frames of reference (FRs). Movements can be made within the framework of the body (egocentric FR) or external space (exocentric FR). People with stroke have impaired reaching, which may be related to deficits in movement production in different FRs. Objective To characterize rapid motor responses to changes in the number of degrees of freedom for movements made in different FRs and their relationship with sensorimotor and cognitive impairment in individuals with mild chronic stroke. Methods Healthy and poststroke individuals moved their hand along the contralateral forearm (egocentric task) and between targets in the peripersonal space (exocentric task) without vision while flexing the trunk. Trunk movement was blocked in randomized trials. Results For the egocentric task, controls produced the same endpoint trajectories in both conditions (free- and blocked-trunk) by preserving similar shoulder-elbow interjoint coordination (IJC). However, endpoint trajectories were dissimilar because of altered IJC in stroke. For the exocentric task, controls produced the same endpoint trajectories when the trunk was free or blocked by rapidly changing the IJC, whereas this was not the case in stroke. Deficits in exocentric movement after stroke were related to cognitive but not sensorimotor impairment. Conclusions Individuals with mild stroke have deficits rapidly responding to changing conditions for complex reaching tasks. This may be related to cognitive deficits and limitations in the regulation of tonic stretch reflex thresholds. Such deficits should be considered in rehabilitation programs encouraging the reintegration of the affected arm into activities of daily living.
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Miller, J. F., K. D. Paul, R. H. Lee, W. Z. Rymer y C. J. Heckman. "Restoration of extensor excitability in the acute spinal cat by the 5-HT2 agonist DOI". Journal of Neurophysiology 75, n.º 2 (1 de febrero de 1996): 620–28. http://dx.doi.org/10.1152/jn.1996.75.2.620.
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1. The decerebrate cat preparation with an intact spinal cord is characterized by a high degree of excitability in extensor motoneuron pools, which is eliminated by acute spinalization. Subtype-specific agonists for serotonin (5-HT) were investigated in terms of their effectiveness in restoring the extensor excitability following spinalization. 2. Our hypothesis was that 5-HT2 receptors have the primary role in enhancement of extensor reflex excitability, whereas 5-HT1A and 5-HT1B/D receptors are relatively unimportant. Reflex excitability was assessed from the tonic levels of force and electromyographic (EMG) output from the ankle extensors medial gastrocnemius (MG) and soleus (SOL), and from the reflex forces in both these muscles generated by ramp-and-hold stretches of MG. 3. Before spinal transection, MG and SOL usually exhibited a small amount of tonic background EMG activity and force output. Ramp-and-hold stretch of MG generated a large-amplitude reflex response. Spinal transection at the level of T10 virtually abolished tonic background activity in both extensors and greatly attenuated the MG stretch reflex. Ventral topical application of the selective 5-HT2A/2C agonist (+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-amino-propane hydrochloride (DOI) restored the amplitude of the MG stretch reflex in a dose-dependent fashion. However, a considerable portion of the DOI-mediated restoration of MG stretch reflex force was due to elevation of tonic background force levels above previous intact cord levels. 4. The DOI-induced increase in extensor tonic background excitability and facilitation of MG stretch reflex were reversed by ventral topical administration of the selective 5-HT2 antagonist ketanserin. No increase in extensor excitability was observed in spinalized preparations after administration of either the 5-HT1A agonist (+-)-8-hydroxy-dipropylaminotetralin hydrobromide or the 5-HT1B/1D agonist 7-trifluoromethyl-4-(4 methyl-1-piperazinyl)-pyrrolo[1,2- a]quinoxaline maleate. These data strongly suggest that the DOI-induced facilitation of extensor stretch reflex and tonic activity in spinalized preparations is mediated through an action on spinal 5-HT2 receptors. 5. One important difference between the actions of DOI in spinalized versus intact states was that the DOI-induced tonic and reflex forces in the spinalized state were subject to irregular oscillations. In contrast, DOI did not noticeably affect the smoothness of reflex force generation in the intact state. This discrepancy was probably due to the effects of clasp knife inhibition from muscular free nerve endings, which have potent reflex actions in the spinalized but not intact states. Thus DOI elevated excitability levels but did not alter the effects of spinalization on stretch reflex patterns.
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Chapple, W. D. "Reflex control of dynamic muscle stiffness in a slow crustacean muscle". Journal of Neurophysiology 54, n.º 2 (1 de agosto de 1985): 403–17. http://dx.doi.org/10.1152/jn.1985.54.2.403.
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The properties of a stretch reflex in the ventral superficial muscle of the hermit crab abdomen were studied in an isolated abdominal preparation to determine how the reflex affects the mechanical properties of the muscle and whether the reflex is controlling length, force, or stiffness. The reflex was elicited by stretch of hypodermal mechanoreceptors in the cuticle and resulted in the activation of excitor motoneurons to both circular and longitudinal layers of the muscle, thus stiffening the abdomen. The medial motoneuron of the longitudinal layer of the right fourth segment was selected for detailed analysis. It was tonically active and responded to stretch with a phasic burst having a latency of 100 ms. Reflex muscle tension began to increase at 130 ms and reached a peak at 300 ms. Reflex-burst frequency increased slightly with stretch amplitude. Peak force was an approximately linear function of stretch amplitude. No tonic component to the reflex was found in the medial motoneuron, in the central motoneuron (the smallest excitor to the muscle), or in the medial motoneuron studied in intact animals. The reflex-burst frequency was a function of stretch velocity, increasing between two and one-half to four times for a 10-fold increase in stretch velocity. Peak force was essentially independent of stretch velocity over this range. The reflex-burst frequency was not a function of the initial length of the muscle on the ascending limb of the length-tension relation. Active peak force (between two and three times passive peak force) was relatively constant over this range. The dynamic active stiffness (the resistance to stretch of the muscle when the nervous system was intact) was separated into two components. One component is that due to the tonic frequency of the motoneurons, the other to the reflex burst. The reflex component makes up a substantial part of the total active stiffness. Dynamic active stiffness is relatively constant under the conditions of these experiments and, when normalized, is similar to that observed in mammalian myotatic reflexes. This constancy, however, cannot be due to negative feedback control of stiffness, as in mammals. It is suggested that constant reflex stiffness arises from the combination of the low-pass filter characteristics of the muscle and the high-pass filter characteristics of the reflex over a restricted range of velocities.(ABSTRACT TRUNCATED AT 400 WORDS)
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Longo, Diego, Giulio Cherubini, Vanessa Mangè, Paolo Lippi, Leonardo Longo, Daniela Melchiorre y Maria Angela Bagni. "Effects of laser therapy and Grimaldi’s muscle shortening maneuver on spasticity in central nervous system injuries". Laser Therapy 29, n.º 2 (30 de junio de 2022): 121–28. http://dx.doi.org/10.4081/ltj.2022.299.
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Background an Aims: For 2003 year until today we treated hundreds of patients with Central Nervous System Injuries (CNSI), using Non-Surgical Laser Therapy (NSLT) obtaining good results in terms of sensibility and movement. In order to increase muscle strength and to further explore new emerging synergies, we have also started using a physical therapy practice based on the most current knowledge about the motor control, called Grimaldi’s Muscle Shortening Maneuver (GMSM). Spasticity is often the most disabling symptom and the current therapies are still not able to heal it at all. The goal of our study is to suggest a new way of treatment of spasticity, supporting it with objective measurements of muscle thresholds. Materials and Methods: In 2016-2017, 36 patients with traumatic or degenerative CNSI were enrolled. Lasers used were 808 nm, 10600 nm, and 1064 nm, applied with a first cycle of 20 sessions, four a day. Patients were subjected to Grimaldi’s Muscle Shortening Maneuver (MSM) twice a day, ten sessions at all, working selectively on hypertonic muscles and their antagonists. Before treatment, tonic stretch reflex thresholds (TSRTs) in Gastrocnemius Lateralis (GL) were assessed through a surface electromyography (sEMG) device paired with an electrogoniometer. Antagonist muscle force (Tibialis Anterioris) was assessed by some electronic hand-held dynamometers. For the clinical measure, we used the Modified Ashworth Scale (MAS). All tests have been performed at the baseline (before starting treatments), after one week (at the end of the last treatment) and after a month. Results: Results were considered positive if the instrumental assessment procedure showed modifications in TSRT values and subjects improved their antagonist muscle strength. Results showed modifications in TSRT values at every follow up. The average comparison between the follow-ups was always statistically significant (p .000). The increase in Tibialis Anterioris muscle strength was statistically significant as well (p .000). MAS showed some differences between followups but not all of them are statistically significant (T0-T1 p .063, T1-T2 p .001, T0-T2 p .000). Encouraging results suggest a possible correlation between laser and MSM therapies and modifications of TSRT in spastic muscles. Conclusion: Associating laser treatment and Grimaldi’s Muscle Shortening Maneuver (MSM) seems to be effective on spasticity in patients affected by traumatic or degenerative CNSI. Obviously, this kind of study design showed a lot of limits however this clinical series could be an important hint for every researcher working in the complex field of spasticity, a symptom that is poorly defined and hardly treated.
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Woolacott, Adam J. y John A. Burne. "The tonic stretch reflex and spastic hypertonia after spinal cord injury". Experimental Brain Research 174, n.º 2 (6 de mayo de 2006): 386–96. http://dx.doi.org/10.1007/s00221-006-0478-7.
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Nielsen, Jørgen F., Jacob B. Anderson y Thomas Sinkjær. "Baclofen increases the soleus stretch reflex threshold in the early swing phase during walking in spastic multiple sclerosis patients". Multiple Sclerosis Journal 6, n.º 2 (abril de 2000): 105–14. http://dx.doi.org/10.1177/135245850000600209.
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The effect of baclofen on walking performance was examined in nine spastic multiple sclerosis patient. In addition, nine healthy subjects were tested as controls. The modulation of the short latency soleus stretch reflex was closer to normal with baclofen compared to the recordings without baclofen, the modulation index being 74% (range: 60-100) with baclofen and 62% (range: 20 -100) without baclofen, P=0.03. In healthy subject the modulation index was 100% (range: 52 -100). In the early swing phase the threshold of the soleus stretch reflex was significantly higher during baclofen medication being 139 degls (range: 63 -302) compared with 93 degls (range: 37-187) with out baclofen, P=0.004. The relation between the stretch velocity (input) and the amplitude of the stretch reflex (output) in early swing phase was unchanged being 0.27 μVs/deg (range: 0.1-1.51) in patient with baclofen and 0.24 μVs/deg (range: 0.08-0.79) without baclofen, P=0.25. Baclofen induced no change in input-output properties of the stretch reflex during walking compared with findings in a sitting position at matched EMG activity. There was a significant correlation between clinical spasticity score and stretch reflex threshold in the early swing phase (p=-0.61, P=0.04) and between clinical spasticity score and the slope of the best linear fit in the early swing phase (p=0.72, P=0.009).
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Iwasaki, Masazumi, Ayako Ohata, Yoshinori Okada, Hideo Sekiguchi y Akiyoshi Niida. "Functional organisation of anterior thoracic stretch receptors in the deep-sea isopod Bathynomus doederleini: behavioural, morphological and physiological studies". Journal of Experimental Biology 204, n.º 20 (15 de octubre de 2001): 3411–23. http://dx.doi.org/10.1242/jeb.204.20.3411.
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SUMMARY The relationship between segmental mobility and the organisation of thoracic stretch receptors was examined in the deep-sea isopod Bathynomus doederleini, which shows a developed adaptive behaviour during digging. The movements of segments during digging were analysed from video recordings, which showed that a large excursion occurred in the anterior thoracic segments. Dye-fills of axons revealed four types of thoracic stretch receptor (TSR): an N-cell type (TSR-1), a differentiated N-cell type (TSR-2), a muscle receptor organ (MRO)-type with a long, single receptor muscle (TSR-3) and an MRO-type with a short, single receptor muscle (TSR-4 to TSR-7). Physiologically, TSR-1 and TSR-2 are tonic-type stretch receptors. TSR-3 to TSR-7 show two kinds of stretch-activated responses, a tonic response and a phasico-tonic response in which responses are maintained as long as the stretch stimulus is delivered. Both TSR-2, with a long muscle strand, and TSR-3, with a single, long receptor muscle, have a wide dynamic range in their stretch-activated response. In addition, TSR-2 is controlled by an intersegmental inhibitory reflex from TSR-3. These results suggest that, although TSR-1 has no receptor muscle and TSR-2 has a less-differentiated receptor-like muscle, they are fully functional position detectors of segmental movements, as are the MRO-type receptors TSR-3 to TSR-7.
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Stein, R. B., I. W. Hunter, S. R. Lafontaine y L. A. Jones. "Analysis of short-latency reflexes in human elbow flexor muscles". Journal of Neurophysiology 73, n.º 5 (1 de mayo de 1995): 1900–1911. http://dx.doi.org/10.1152/jn.1995.73.5.1900.
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1. A motor and digital controller have been developed to apply rapid stretches to the human elbow joint. The digital controller returns the forearm to the initial position before the reflex contraction. Thus short-latency reflex responses can be cleanly separated in time from the mechanical effects of the stretch under a wide variety of loading conditions. 2. The reflex force varies linearly with the velocity of stretch over nearly 2 orders of magnitude. The reflex force also varies linearly with the tonic level of force over the entire range of forces studied (0-100 N). This contrasts sharply with, for example, the human ankle joint, which shows a very limited linear range. 3. As the digital controller is made more compliant (less stiff), reflex shortening increases dramatically and becomes more prolonged, whereas the reflex force becomes somewhat smaller and shorter. With compliant loads and the brief stretches we applied, the reflex shortening is approximately equal to the stretch that generated it. 4. Simulations of the results confirm that the dependence of reflex shortening and force on the stiffness of the load is mainly determined by the mechanics of the limb and muscles. The simulations also indicate that 1) the gain of the reflex is as high as it can be without causing instability and 2) the presence of a rectification nonlinearity (e.g., lengthening the muscle produces a reflex, but shortening the muscle does not) is mainly responsible for preserving the stability of the elbow system.
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Clements, Linda G. y William A. Mackay. "Respiratory and Head Position Influences on Late Stretch Reflexes". Canadian Journal of Occupational Therapy 60, n.º 2 (junio de 1993): 61–69. http://dx.doi.org/10.1177/000841749306000202.
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The purpose of this study was to determine the relative effects of the asymmetric tonic neck reflex (ATNR) and of respiration on the upper limb, as measured by their influence on the stretch reflexes. Long latency stretch reflexes (M2 and M3) were induced in elbow muscles of human subjects. The subject's right forearm was strapped into a manipulandum. The forearm was perturbed with a torque test pulse at a fixed interval prior to an intended forearm movement. It was found that both the M2 and M3 reflexes, in triceps or brachialis muscles were significantly increased when perturbations were delivered during inspiration as compared to expiration. Rotated head positions to the right or left could also significantly alter reflex magnitude but there was no consistent pattern among subjects. The clinical implications of these findings are discussed.
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Onushko, Tanya, Allison Hyngstrom y Brian D. Schmit. "Hip proprioceptors preferentially modulate reflexes of the leg in human spinal cord injury". Journal of Neurophysiology 110, n.º 2 (15 de julio de 2013): 297–306. http://dx.doi.org/10.1152/jn.00261.2012.
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Stretch-sensitive afferent feedback from hip muscles has been shown to trigger long-lasting, multijoint reflex responses in people with chronic spinal cord injury (SCI). These reflexes could have important implications for control of leg movements during functional activities, such as walking. Because the control of leg movement relies on reflex regulation at all joints of the limb, we sought to determine whether stretch of hip muscles modulates reflex activity at the knee and ankle and, conversely, whether knee and ankle stretch afferents affect hip-triggered reflexes. A custom-built servomotor apparatus was used to stretch the hip muscles in nine chronic SCI subjects by oscillating the legs about the hip joint bilaterally from 10° of extension to 40° flexion. To test whether stretch-related feedback from the knee or ankle would be affected by hip movement, patellar tendon percussions and Achilles tendon vibration were delivered when the hip was either extending or flexing. Surface electromyograms (EMGs) and joint torques were recorded from both legs. Patellar tendon percussions and Achilles tendon vibration both elicited reflex responses local to the knee or ankle, respectively, and did not influence reflex responses observed at the hip. Rather, the movement direction of the hip modulated the reflex responses local to the joint. The patellar tendon reflex amplitude was larger when the perturbation was delivered during hip extension compared with hip flexion. The response to Achilles vibration was modulated by hip movement, with an increased tonic component during hip flexion compared with extension. These results demonstrate that hip-mediated sensory signals modulate activity in distal muscles of the leg and appear to play a unique role in modulation of spastic muscle activity throughout the leg in SCI.
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Misiaszek, J. E., S. J. de Serres, R. B. Stein, W. Jiang y K. G. Pearson. "Stretch and H Reflexes in Triceps Surae Are Similar During Tonic and Rhythmic Contractions in High Decerebrate Cats". Journal of Neurophysiology 83, n.º 4 (1 de abril de 2000): 1941–50. http://dx.doi.org/10.1152/jn.2000.83.4.1941.
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During locomotion in decerebrate and spinal cats the group Ia afferents from hind leg muscles are depolarized rhythmically. An earlier study concluded that this locomotor-related primary afferent depolarization (PAD) does not contribute to modulation of monosynaptic reflex pathways during locomotion. This finding indicated that the neural network generating the locomotor rhythm, the central pattern generator (CPG), does not presynaptically inhibit monosynaptic reflexes. In this investigation we tested this prediction in decerebrate cats by measuring the magnitude of reflexes evoked in ankle extensor muscles during periods of tonic contractions and during sequences of rhythmic contractions. The latter occurred when the animal was induced to walk on a treadmill. At the similar levels of activity in the soleus muscle there was no significant difference in the magnitude of the soleus H reflex in these two behavioral situations. Similar results were obtained for reflexes evoked by brief stretches of the soleus muscle. We also examined the reflexes evoked by ramp-and-hold stretches during periods of rhythmic and tonic activity of the isolated medial gastrocnemius (MG) muscle. At similar levels of background activity, the reflexes evoked in the MG muscle were the same during rhythmic and tonic contractions. Our failure to observe a reduction in the magnitude of H reflexes and stretch reflexes during rhythmic contractions, compared with reflexes evoked at the same level of background activity during tonic contractions, is consistent with the notion that the CPG for stepping does not presynaptically inhibit monosynaptic reflexes during the extension phase of locomotor activity. Our results indicate that presynaptic inhibition of the monosynaptic reflex associated with normal locomotion in cats or humans arises from sources other than the extensor burst generating system of the central pattern generator.
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Mullick, Aditi A., Nadine K. Musampa, Anatol G. Feldman y Mindy F. Levin. "Stretch reflex spatial threshold measure discriminates between spasticity and rigidity". Clinical Neurophysiology 124, n.º 4 (abril de 2013): 740–51. http://dx.doi.org/10.1016/j.clinph.2012.10.008.
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Le Pellec, A. y B. Maton. "Influence of tonic neck reflexes on the upper limb stretch reflex in man". Journal of Electromyography and Kinesiology 6, n.º 2 (junio de 1996): 73–82. http://dx.doi.org/10.1016/1050-6411(95)00018-6.
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Silva, Maristella Borges, Andrei Nakagawa Silva, Eduardo Lázaro Martins Naves, Evanisi Teresa Palomari y Alcimar Barbosa Soares. "An improved approach for measuring the tonic stretch reflex response of spastic muscles". Computers in Biology and Medicine 80 (enero de 2017): 166–74. http://dx.doi.org/10.1016/j.compbiomed.2016.12.001.
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Shinohara, Minoru, Chet T. Moritz, Michael A. Pascoe y Roger M. Enoka. "Prolonged muscle vibration increases stretch reflex amplitude, motor unit discharge rate, and force fluctuations in a hand muscle". Journal of Applied Physiology 99, n.º 5 (noviembre de 2005): 1835–42. http://dx.doi.org/10.1152/japplphysiol.00312.2005.
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The purpose of this study was to compare the influence of prolonged vibration of a hand muscle on the amplitude of the stretch reflex, motor unit discharge rate, and force fluctuations during steady, submaximal contractions. Thirty-two young adults performed 10 isometric contractions at a constant force (5.0 ± 2.3% of maximal force) with the first dorsal interosseus muscle. Each contraction was held steady for 10 s, and then stretch reflexes were evoked. Subsequently, 20 subjects had vibration applied to the relaxed muscle for 30 min, and 12 subjects received no vibration. The muscle vibration induced a tonic vibration reflex. The intervention (vibration or no vibration) was followed by 2 sets of 10 constant-force contractions with applied stretches (After and Recovery trials). The mean electromyogram amplitude of the short-latency component of the stretch reflex increased by 33% during the After trials ( P < 0.01) and by 38% during the Recovery trials ( P < 0.01). The standard deviation of force during the steady contractions increased by 21% during the After trials ( P < 0.05) and by 28% during the Recovery trials ( P < 0.01). The discharge rate of motor units increased from 10.3 ± 2.7 pulses/s (pps) before vibration to 12.2 ± 3.1 pps ( P < 0.01) during the After trials and to 11.9 ± 2.6 pps during the Recovery trials ( P < 0.01). There was no change in force fluctuations or stretch reflex magnitude for the subjects in the Control group. The results indicate that prolonged vibration increased the short-latency component of the stretch reflex, the discharge rate of motor units, and the fluctuations in force during contractions by a hand muscle. These adjustments were necessary to achieve the target force due to the vibration-induced decrease in the force capacity of the muscle.
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Sukhdeo, S. C. y C. H. Page. "Abdominal postural motor responses initiated by the muscle receptor organ in lobster depend upon centrally generated motor activity". Journal of Experimental Biology 162, n.º 1 (1 de enero de 1992): 167–83. http://dx.doi.org/10.1242/jeb.162.1.167.
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1. Stretch stimulation of the abdominal muscle receptor organ of the lobster Homarus americanus initiated spike discharge of its tonic sensory neuron (SR1). This sensory response evoked a series of tonic postural reflex responses in the motor neurons that innervate the superficial extensor and flexor muscles of the abdominal postural system. The type of motor response depended on whether a flexion or extension pattern of spontaneous activity was being generated by the postural efferents. Spontaneous shifts between these centrally generated motor activities completely changed the SR1-evoked reflex responses. 2. During spontaneous centrally initiated flexion activity, tonic SR1 neuron discharge elicited an assistance response that included excitation of a medium-sized flexor excitor (f3) and the peripheral extensor inhibitor (e5), and inhibition of at least one extensor excitor. Neither the other flexor excitors nor the peripheral flexor inhibitor (f5) were affected by SR1 excitation. 3. During spontaneous centrally initiated extension activity, SR1 activity elicited a response that included excitation of the extensor excitors and the flexor peripheral inhibitor (f5) only, f3 and e5 spontaneous activities were unchanged. This response was a resistance reflex, since SR1 discharge normally resulted from an imposed abdominal flexion. 4. The SR1-initiated control of postural motor activity in lobster differs from previously published results in the crayfish Procambarus clarkii.
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St John, W. M. y D. Zhou. "Reductions of neural activities to upper airway muscles after elevations in static lung volume". Journal of Applied Physiology 73, n.º 2 (1 de agosto de 1992): 701–7. http://dx.doi.org/10.1152/jappl.1992.73.2.701.
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We evaluated the hypothesis that the tonic discharge of pulmonary stretch receptors significantly influences the respiratory-modulated activities of cranial nerves. Decerebrate and paralyzed cats were ventilated with a servo-respirator, which produced changes in lung volume in parallel with integrated phrenic activity. Activities of the facial, hypoglossal, and recurrent laryngeal nerves and nerves to the thyroarytenoid muscle and triangularis sterni were recorded. After a stereotyped pattern of lung inflation, tracheal pressure was held at 1, 2, 4, or 6 cmH2O during the subsequent ventilatory cycle. Increases in tracheal pressure caused progressive reductions in both inspiratory and expiratory cranial nerve activities and progressive elevations in triangularis sterni discharge; peak levels of phrenic activity declined modestly. Similar changes were observed in normocapnia and hypercapnia. We conclude that the tonic discharge of pulmonary stretch receptors is an important determinant of the presence and magnitude of respiratory-modulated cranial nerve activity. This reflex mechanism may maintain upper airway patency and also regulate expiratory airflow.
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Duval, Laura, Lei Zhang, Anne-Sophie Lauzé, Yu Q. Zhu, Dorothy Barthélemy, Numa Dancause, Mindy F. Levin y Anatol G. Feldman. "Effect of Object Texture and Weight on Ipsilateral Corticospinal Influences During Bimanual Holding in Humans". Motor Control 26, n.º 1 (1 de enero de 2022): 76–91. http://dx.doi.org/10.1123/mc.2021-0096.
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We tested the hypothesis that the ipsilateral corticospinal system, like the contralateral corticospinal system, controls the threshold muscle length at which wrist muscles and the stretch reflex begin to act during holding tasks. Transcranial magnetic stimulation was applied over the right primary motor cortex in 21 healthy subjects holding a smooth or coarse block between the hands. Regardless of the lifting force, motor evoked potentials in right wrist flexors were larger for the smooth block. This result was explained based on experimental evidence that motor actions are controlled by shifting spatial stretch reflex thresholds. Thus, the ipsilateral corticospinal system is involved in threshold position control by modulating facilitatory influences of hand skin afferents on motoneurons of wrist muscles during bimanual object manipulation.
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Bandaru, Samira P., Shujun Liu, Stephen G. Waxman y Andrew M. Tan. "Dendritic spine dysgenesis contributes to hyperreflexia after spinal cord injury". Journal of Neurophysiology 113, n.º 5 (1 de marzo de 2015): 1598–615. http://dx.doi.org/10.1152/jn.00566.2014.
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Hyperreflexia and spasticity are chronic complications in spinal cord injury (SCI), with limited options for safe and effective treatment. A central mechanism in spasticity is hyperexcitability of the spinal stretch reflex, which presents symptomatically as a velocity-dependent increase in tonic stretch reflexes and exaggerated tendon jerks. In this study we tested the hypothesis that dendritic spine remodeling within motor reflex pathways in the spinal cord contributes to H-reflex dysfunction indicative of spasticity after contusion SCI. Six weeks after SCI in adult Sprague-Dawley rats, we observed changes in dendritic spine morphology on α-motor neurons below the level of injury, including increased density, altered spine shape, and redistribution along dendritic branches. These abnormal spine morphologies accompanied the loss of H-reflex rate-dependent depression (RDD) and increased ratio of H-reflex to M-wave responses (H/M ratio). Above the level of injury, spine density decreased compared with below-injury spine profiles and spine distributions were similar to those for uninjured controls. As expected, there was no H-reflex hyperexcitability above the level of injury in forelimb H-reflex testing. Treatment with NSC23766, a Rac1-specific inhibitor, decreased the presence of abnormal dendritic spine profiles below the level of injury, restored RDD of the H-reflex, and decreased H/M ratios in SCI animals. These findings provide evidence for a novel mechanistic relationship between abnormal dendritic spine remodeling in the spinal cord motor system and reflex dysfunction in SCI.
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Gregson, J. M. y A. K. Sharma. "Measuring poststroke spasticity". Reviews in Clinical Gerontology 10, n.º 1 (febrero de 2000): 69–74. http://dx.doi.org/10.1017/s0959259800001076.
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What is spasticity?Spasticity is a well-recognized and potentially important clinical syndrome comprising inappropriate and involuntary high muscle tone. It has been variably defined, with debate still ongoing. Currently, the most widely accepted definition is that of Lance, stating that spasticity is ‘a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes (muscle tone) with exaggerated tendon jerks, resulting from hyper-excitability of the stretch reflex.’ Unfortunately, even this description does not fully encompass the multifactorial nature of spasticity, since resistance to movement, even in the normal state, is subject to varied contributors. These include patient volition, inertia, visco-elastic muscle forces and range of joint movement, as well as true muscle activation secondary to reflex action. In the real clinical world, it is often not possible to distinguish which of these features is/are dominant. Furthermore, spastic muscle undergoes physiopathological, rheologic change with stiffness, atrophy, fibrosis and finally contracture.
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Grider, John R. y Lea E. Langdon. "Physiological role of neuropeptide Y in the regulation of the ascending phase of the peristaltic reflex". American Journal of Physiology-Gastrointestinal and Liver Physiology 285, n.º 6 (diciembre de 2003): G1139—G1146. http://dx.doi.org/10.1152/ajpgi.00082.2003.
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The physiological role of neuropeptide Y (NPY) and of specific NPY receptors in regulating the intestinal peristaltic reflex was examined in three-compartment flat-sheet preparations of rat colon. Graded muscle stretch or mucosal stimulation applied to the central compartment inhibited NPY release in the orad compartment where ascending contraction was measured. NPY and the Y1-receptor agonist [Leu31, Pro34]NPY inhibited, whereas the selective Y1-receptor antagonist BIBP 3226 augmented ascending contraction and substance P (SP) release in the orad compartment induced by muscle stretch or mucosal stimulation. Neither agonist nor antagonist had any effect on descending relaxation or VIP release in the caudad compartment. The Y2-receptor agonist NPY13-36 and antagonist BIIE 0246 had no effect on peptide release or mechanical response. The results indicate that suppression of a tonic inhibitory influence of NPY neurons on excitatory neurotransmitter release contributes substantially to the orad contractile phase of the peristaltic reflex. The effect of NPY on neurotransmitter release is mediated by Y1 receptors.
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Gildenberg, Philip L., Robert J. Campos y Milan R. Dimitrijevic. "Characteristics of the Tonic Stretch Reflex in Spastic Spinal Cord and Head-Injured Patients". Stereotactic and Functional Neurosurgery 48, n.º 1-6 (1985): 106–10. http://dx.doi.org/10.1159/000101112.
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Powers, R. K., J. Marder-Meyer y W. Z. Rymer. "Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis". Annals of Neurology 23, n.º 2 (febrero de 1988): 115–24. http://dx.doi.org/10.1002/ana.410230203.
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Harris, Michael B. y Walter M. St.-John. "Phasic pulmonary stretch receptor feedback modulates both eupnea and gasping in an in situ rat preparation". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 289, n.º 2 (agosto de 2005): R450—R455. http://dx.doi.org/10.1152/ajpregu.00750.2004.
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The perfused in situ juvenile rat preparation produces patterns of phrenic discharge comparable to eupnea and gasping in vivo. These ventilatory patterns differ in multiple aspects, including most prominently the rate of rise of inspiratory activity. Although we have recently demonstrated that both eupnea and gasping are similarly modulated by a Hering-Breuer expiratory-promoting reflex to tonic pulmonary stretch, it has generally been assumed that gasping was unresponsive to afferent stimuli from pulmonary stretch receptors. In the present study, we recorded eupneic and gasplike efferent activity of the phrenic nerve in the in situ juvenile rat perfused brain stem preparation, with and without phrenic-triggered phasic pulmonary inflation. We tested the hypothesis that phasic pulmonary inflation produces reflex responses in situ akin to those in vivo and that both eupnea and gasping are similarly modulated by phasic pulmonary stretch. In eupnea, we found that phasic pulmonary inflation decreases inspiratory burst duration and the period of expiration, thus increasing burst frequency of the phrenic neurogram. Phasic pulmonary inflation also decreases the duration of expiration and increases the burst frequency during gasping. Bilateral vagotomy eliminated these changes. We conclude that the neural substrate mediating the Hering-Breuer reflex is retained in the in situ preparation and that the brain stem circuitry generating the respiratory patterns respond to phasic activation of pulmonary stretch receptors in both eupnea and gasping. These findings support the homology of eupneic phrenic discharge patterns in the reduced in situ preparation and eupnea in vivo and disprove the common supposition that gasping is insensitive to vagal afferent feedback from pulmonary stretch receptor mechanisms.
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Harris, Michael B. y Walter M. St.-John. "Tonic pulmonary stretch receptor feedback modulates both eupnea and gasping in an in situ rat preparation". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, n.º 1 (julio de 2003): R215—R221. http://dx.doi.org/10.1152/ajpregu.00112.2003.
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The perfused in situ juvenile rat preparation produces phrenic discharge patterns comparable to eupnea and gasping in vivo. These ventilatory patterns of eupnea and gasping differ in multiple aspects, including most prominently the rate of rise of inspiratory activity. Because gasping, but not eupnea, appeared similar after vagotomy in spontaneous breathing preparations, it has been assumed that gasping was unresponsive to afferent stimuli from pulmonary stretch receptors. In the present study, efferent activity of the phrenic nerve was recorded during eupnea and gasping in the in situ juvenile rat preparation. Gasping was induced in hypoxic-hypercapnia or ischemia. An increase in the pressure of tonic lung inflation from 1 to 10 cmH2O caused a prolongation of the duration between phrenic bursts in both eupnea or gasping. Bilateral vagotomy eliminated these changes. We conclude that the neural substrate mediating the Hering-Breuer reflex is retained in the in situ preparation and that the brain stem circuitry generating the respiratory patterns responds to tonic activation of pulmonary stretch receptors in a similar manner in eupnea and gasping. These findings support the homology of eupnea-like phrenic discharge patterns in the reduced in situ preparation and eupnea in vivo and disprove the common supposition that gasping is insensitive to vagal afferent feedback from pulmonary stretch receptor mechanisms.
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Hui-Chan, Christina W. Y. y Mindy F. Levin. "Stretch Reflex Latencies in Spastic Hemiparetic Subjects are Prolonged After Transcutaneous Electrical Nerve Stimulation". Canadian Journal of Neurological Sciences / Journal Canadien des Sciences Neurologiques 20, n.º 2 (mayo de 1993): 97–106. http://dx.doi.org/10.1017/s0317167100047636.
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ABSTRACT:Low-intensity repetitive electrical stimulation such as dorsal column and transcutaneous electrical nerve stimulation (TENS) reportedly decreases spasticity and improves voluntary motor control. However, the mechanisms mediating these effects are unclear. Recent findings suggest that spasticity may be characterized more appropriately by a decrease in the stretch reflex threshold than by an increase in gain. Our objectives were: (1) to examine possible changes in stretch reflex excitability following 45 min of TENS, (2) to map out the time course of possible post-stimulation effects via both latency and magnitude (amplitude or area) measurements, and (3) to determine the role of segmental versus non-segmental mechanisms involved in mediating these changes. The effects of 45 min of segmentally and heterosegmentally applied TENS on lower limb reflexes in ten spastic hemiparetic subjects were contrasted with those resulting from placebo stimulation. We found that both segmentally and heterosegmentally applied TENS caused an immediate increase in soleus H reflex latencies that was evident for up to 60 minutes post-stimulation in over 75% of the subjects. Similar increases for up to 60 and 40 minutes post-stimulation was noted for the stretch reflex latencies in 50% and 67% of the subjects respectively for segmental and heterosegmental stimulation. These results suggested that manipulation of segmental and heterosegmental afférents for 45 min may lead to a decrease of the otherwise augmented stretch reflex excitability accompanying hemiparetic spasticity.
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Chapple, W. D. "Dynamics of reflex cocontraction in hermit crab abdomen: experiments and a systems model". Journal of Neurophysiology 69, n.º 6 (1 de junio de 1993): 1904–17. http://dx.doi.org/10.1152/jn.1993.69.6.1904.
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1. Both stretch and release of the ventral superficial muscles (VSM) in the abdomen of the hermit crab, Pagurus pollicarus, activate the VSM motoneurons in the intact animal and in the isolated abdomen. 2. This reflex was studied by recording intracellularly from muscle fibers innervated by single motoneurons during stretch and release of the VSM. The three motoneurons of the right fourth segment respond to both stretch and release with a phasic burst lasting approximately 250 ms. The burst in the two tonic motoneurons has two components, a short burst lasting 10-20 ms, with a latency from the beginning of stretch of 60-90 ms, and a longer burst of variable length, with a latency of 120 ms. Ramp stretches of different amplitudes and velocities were used to show that the first component is proportional to the absolute value of the second derivative of force and the second component to the absolute value of the first derivative of force. 3. Stretch and release of the VSM also simultaneously evoke phasic bursts in the motoneurons of the dorsal superficial muscles and the VSM circular muscles (functional antagonists of the longitudinal VSM), as well as in contralateral homologues of the same segment and in ipsilateral homologues of the next anterior segment. The effect of this coactivation is to stiffen the abdomen in response to perturbations in any direction. 4. Stretch or release of phasic mechanoreceptors in the VSM evokes this reflex. Isometric electrical stimulation of the isolated muscle also activates them, showing that they are transducing changes in force and suggesting that they operate to increase muscle stiffness by positive feedback. 5. A mathematical systems model of this reflex, composed of two parallel pathways activating the motoneurons, was constructed. The first pathway produces a signal proportional to the absolute value of the second derivative of force, the second pathway a signal proportional to the first derivative of force. The sum of the signals from the two pathways is filtered by an adaptation process, which is followed by a low-pass filter representing muscle activation kinetics. The muscle activation signal is then fed back to multiple muscle force. 6. Simulations using this model generate the phasic bursts to stretch and release as well as reproducing the frequency dependence of this reflex. The predominant action of this reflex is to enhance muscle stiffness.
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D'Amico, Stephen C. y William F. Collins. "External urethral sphincter motor unit recruitment patterns during micturition in the spinally intact and transected adult rat". Journal of Neurophysiology 108, n.º 9 (1 de noviembre de 2012): 2554–67. http://dx.doi.org/10.1152/jn.00927.2011.
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In the rat, external urethral sphincter (EUS) activation during micturition consists of three sequential phases: 1) an increase in tonic EUS activity during passive filling and active contraction of the bladder (guarding reflex), 2) synchronized phasic activity (EUS bursting) associated with voiding, and 3) sustained tonic EUS activity that persists after bladder contraction. These phases are perturbed following spinal cord injury. The purpose of the present study was to characterize individual EUS motor unit (MU) patterns during micturition in the spinally intact and transected adult rat. EUS MU activity was recorded from either the L5 or L6 ventral root (intact) or EUS muscle (transected) during continuous flow cystometry in urethane-anesthetized adult female Sprague-Dawley rats. With the use of bladder pressure threshold and timing of activation, four distinct patterns of EUS MU activity were identified in the intact rat: low threshold sustained, medium/high threshold sustained, medium/high threshold not sustained, and burst only. In general, these MUs displayed little frequency modulation during active contraction, generated high-frequency bursts of action potentials during EUS bursting, and varied in terms of the duration of sustained tonic activity. In contrast, three general patterns of EUS MU activity were identified in the transected rat: low threshold, medium threshold, and high threshold. These MUs exhibited considerable frequency modulation during active contraction of the bladder, no bursting behavior and little to no sustained firing. The prominent frequency modulation of EUS MUs is likely due to the enhanced guarding reflex seen in EUS whole muscle electromyogram recordings in transected rats (D'Amico SC, Schuster IP, Collins WF 3rd. Exp Neurol 228: 59–68, 2011). In addition, EUS MU recruitment in transected rats more closely followed predictions by the size principle than in intact rats. This may reflect the influence of local synaptic circuits or intrinsic properties of EUS motoneurons that are active in intact rats but attenuated or absent in transected rats.
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Schreuder, J. J., J. R. Jansen y A. Versprille. "Hemodynamic effects of PEEP applied as a ramp in normo-, hyper-, and hypovolemia". Journal of Applied Physiology 59, n.º 4 (1 de octubre de 1985): 1178–84. http://dx.doi.org/10.1152/jappl.1985.59.4.1178.
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Nonlinear hemodynamic responses on positive end-expiratory pressure (PEEP) have been attributed to a rise of mean central venous pressure (Pcv), to compensatory cardiovascular control mechanisms, and to the occurrence of a lung stretch depressor reflex above a threshold lung stretch. We tested the hypothesis that the contribution of each of these mechanisms is dependent on the preexisting volemic load. PEEP was applied as a continuous rise (ramp) in piglets in three different volemic loads. In the normovolemic circulation cardiac output (CO) decreased nonlinearly in three phases during the PEEP ramp up to 15 cmH2O. CO decreased gradually in phase I, followed by a sharp decrease in phase II between a PEEP of 3 and 9 cmH2O and again a more gradual decrease in phase III up to a PEEP of 15 cmH2O. Heart rate (HR) and mean aortic pressure (PaO) also decreased during phase II, indicating the predominance of a lung stretch depressor reflex. In the hypervolemic circulation (loading 15 ml . kg-1 dextran) only phases I and II were observed with the onset of phase II at a higher level of PEEP (6 cmH2O). More lung stretch appeared to be necessary to elicit the lung stretch depressor reflex. In the hypovolemic circulation (hemorrhage 15 ml . kg-1) CO decreased linearly, Pao was stable after an initial decrease, and HR increased continuously, indicating a predominance of cardiovascular compensatory mechanisms.
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SKORUPSKI, PETER y KEITH T. SILLAR. "Central Synaptic Coupling of Walking Leg Motor Neurones in the Crayfish: Implications for Sensorimotor Integration". Journal of Experimental Biology 140, n.º 1 (1 de noviembre de 1988): 355–79. http://dx.doi.org/10.1242/jeb.140.1.355.
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We present electrophysiological evidence for the presence of central output synapses on crayfish walking leg motor neurones. The effect of these central outputs is that a motor neurone can exert tonic graded control over other motor neurones without the requirement for spiking. Excitatory interactions among synergists and inhibitory interactions among antagonists are described. This central coupling among leg motor neurones profoundly affects their responses to afferent input from an identified stretch receptor, the thoracocoxal muscle receptor organ (TCMRO). Injecting current into a motor neurone can change the gain of TCMRO reflexes in other motor neurones. Some motor neurones are also capable of reversing the sign of TCMRO reflexes by inhibiting reflex firing of antagonists and facilitating reflex activity in synergists. The implications of these central interactions of motor neurones in motor control are discussed.
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Manella, Kathleen J., Kathryn E. Roach y Edelle C. Field-Fote. "Operant conditioning to increase ankle control or decrease reflex excitability improves reflex modulation and walking function in chronic spinal cord injury". Journal of Neurophysiology 109, n.º 11 (1 de junio de 2013): 2666–79. http://dx.doi.org/10.1152/jn.01039.2011.
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Ankle clonus is common after spinal cord injury (SCI) and is attributed to loss of supraspinally mediated inhibition of soleus stretch reflexes and maladaptive reorganization of spinal reflex pathways. The maladaptive reorganization underlying ankle clonus is associated with other abnormalities, such as coactivation and reciprocal facilitation of tibialis anterior (TA) and soleus (SOL), which contribute to impaired walking ability in individuals with motor-incomplete SCI. Operant conditioning can increase muscle activation and decrease stretch reflexes in individuals with SCI. We compared two operant conditioning-based interventions in individuals with ankle clonus and impaired walking ability due to SCI. Training included either voluntary TA activation (TA↑) to enhance supraspinal drive or SOL H-reflex suppression (SOL↓) to modulate reflex pathways at the spinal cord level. We measured clonus duration, plantar flexor reflex threshold angle, timed toe tapping, dorsiflexion (DF) active range of motion, lower extremity motor scores (LEMS), walking foot clearance, speed and distance, SOL H-reflex amplitude modulation as an index of reciprocal inhibition, presynaptic inhibition, low-frequency depression, and SOL-to-TA clonus coactivation ratio. TA↑ decreased plantar flexor reflex threshold angle (−4.33°) and DF active range-of-motion angle (−4.32°) and increased LEMS of DF (+0.8 points), total LEMS of the training leg (+2.2 points), and nontraining leg (+0.8 points), and increased walking foot clearance (+ 4.8 mm) and distance (+12.09 m). SOL↓ decreased SOL-to-TA coactivation ratio (−0.21), increased nontraining leg LEMS (+1.8 points), walking speed (+0.02 m/s), and distance (+6.25 m). In sum, we found increased voluntary control associated with TA↑ outcomes and decreased reflex excitability associated with SOL↓ outcomes.
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Nielsen, Jorgen F., Thomas Sinkjaer y Johannes Jakobsen. "Treatment of spasticity with repetitive magnetic stimulation; a double-blind placebo-controlled study". Multiple Sclerosis Journal 2, n.º 5 (diciembre de 1996): 227–32. http://dx.doi.org/10.1177/135245859600200503.
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The effect of repetitive magnetic stimulation on spasticity was evaluated in 38 patients with multiple sclerosis in a double-blind placebo-controlled study. One group was treated with repetitive magnetic stimulation (n=2l) and the other group with sham stimulation (n=l7). Both groups were seated twice daily for 7 consecutive days. Primary end-points of the study were changes in the patients self-score, in clinical spasticity score, and in the stretch reflex threshold. The self-score of ease of daily day activities improved by 22% (P=0.007) after treatment and by 29% (P=0.004) after sham stimulation. The clinical spasticity score improved 3.3±4.7 arbitrary unit (AU) in treated patients and 0.7±2.5 AU in sham stimulation (P-0.003). The stretch reflex threshold increased 4.3±7.5 degls in treated patients and-3.8±9.7 degls in sham stimulation (P=0.001). The data presented in this study supports the idea that repetitive magnetic stimulation has an antispastic effect in multiple sclerosis. Future studies should darify the optimal treatment regimen.
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Levin, Mindy F. y Anatol G. Feldman. "The role of stretch reflex threshold regulation in normal and impaired motor control". Brain Research 657, n.º 1-2 (septiembre de 1994): 23–30. http://dx.doi.org/10.1016/0006-8993(94)90949-0.
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MILSOM, WILLIAM K. y DAVID R. JONES. "Characteristics of Mechanoreceptors in the Air-Breathing Organ of the Holostean Fish, Amia Calva". Journal of Experimental Biology 117, n.º 1 (1 de julio de 1985): 389–99. http://dx.doi.org/10.1242/jeb.117.1.389.
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Single nerve fibre discharge was recorded from mechanoreceptors associated with the air-breathing organ in double-pithed specimens of the bowfin, Amia calva L. These receptors were innervated by the vagus nerve and although their exact location was difficult to determine, most appeared to be located along the anterio-ventral wall of the single lung. All receptors increased tonic discharge with step increases in lung volume, above a threshold level, and were slowly adapting. There was a dynamic, rate-sensitive burst of activity associated with lung inflation and a dynamic, rate-sensitive inhibition of discharge associated with deflation. These responses were qualitatively similar to those of the tonic stretch receptors found in fish swimbladder and mammalian gut. All receptors were insensitive to changes in intrapulmonary partial pressures of oxygen and carbon dioxide. These observations suggest that receptors capable of transducing the rate, as well as the degree, of inflation and deflation are associated with primitive lungs, and may have arisen from tonic gut receptors.
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Sirucek, Laura, Catherine Ruth Jutzeler, Jan Rosner, Petra Schweinhardt, Armin Curt, John Lawrence Kipling Kramer y Michèle Hubli. "The Effect of Conditioned Pain Modulation on Tonic Heat Pain Assessed Using Participant-Controlled Temperature". Pain Medicine 21, n.º 11 (16 de marzo de 2020): 2839–49. http://dx.doi.org/10.1093/pm/pnaa041.
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Abstract Objective Descending pain modulation can be experimentally assessed by way of testing conditioned pain modulation. The application of tonic heat as a test stimulus in such paradigms offers the possibility of observing dynamic pain responses, such as adaptation and temporal summation of pain. Here we investigated conditioned pain modulation effects on tonic heat employing participant-controlled temperature, an alternative tonic heat pain assessment. Changes in pain perception are thereby represented by temperature adjustments performed by the participant, uncoupling this approach from direct pain ratings. Participant-controlled temperature has emerged as a reliable and sex-independent measure of tonic heat. Methods Thirty healthy subjects underwent a sequential conditioned pain modulation paradigm, in which a cold water bath was applied as the conditioning stimulus and tonic heat as a test stimulus. Subjects were instructed to change the temperature of the thermode in response to variations in perception to tonic heat in order to maintain their initial rating over a two-minute period. Two additional test stimuli (i.e., lower limb noxious withdrawal reflex and pressure pain threshold) were included as positive controls for conditioned pain modulation effects. Results Participant-controlled temperature revealed conditioned pain modulation effects on temporal summation of pain (P = 0.01). Increased noxious withdrawal reflex thresholds (P = 0.004) and pressure pain thresholds (P < 0.001) in response to conditioning also confirmed inhibitory conditioned pain modulation effects. Conclusions The measured interaction between conditioned pain modulation and temporal summation of pain supports the participant-controlled temperature approach as a promising method to explore dynamic inhibitory and facilitatory pain processes previously undetected by rating-based approaches.
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Skorupski, P., B. M. Rawat y B. M. Bush. "Heterogeneity and central modulation of feedback reflexes in crayfish motor pool". Journal of Neurophysiology 67, n.º 3 (1 de marzo de 1992): 648–63. http://dx.doi.org/10.1152/jn.1992.67.3.648.
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1. Movement of the crayfish thoracocoxal leg joint is monitored by a muscle receptor organ (TCMRO) and a chordotonal organ (TCCO). Both receptors span the joint in parallel but signal opposite directions of leg movement. The TCMRO is innervated by afferents responsive to lengthening, which corresponds to leg remotion, whereas TCCO afferents are responsive to shortening of the chordotonal strand, which corresponds to leg promotion. 2. When both receptors are stimulated in parallel, in an otherwise isolated preparation, reflex responses of coxal promoter and remotor motor neurons occur on both stretch and release. By comparison with experiments where one or the other of these receptors is stimulated selectively, we conclude that reflexes evoked by stretch of the two receptors are due to the TCMRO and reflexes evoked by release are due to the TCCO. 3. Reflexes mediated by these receptors are both state dependent and phase dependent. In preparations that produce patterns of reciprocal motor activity in promotor and remotor motor neurons (the active state), the reflex effect depends on the phase of this centrally generated activity. In preparations that are quiescent, or that produce only tonic motor output (the inactive state), the reflex effect is stable, corresponding to a typical resistance (negative feedback) reflex for both directions of receptor movement. 4. In the active state, coxal promotor motor neurons are both excited and inhibited in a phase-dependent manner by stretching the TCMRO. A subgroup of promotor motor neurons is excited by shortening the TCCO. One subgroup of the antagonistic coxal remotor motor neurons receives phase-dependent excitation from stretch of the TCMRO, whereas a second subgroup receives phase-dependent excitation from shortening the TCCO. 5. There are, therefore, at least two ways in which reflex effects can be modulated. At the level of a single motor neuron, the reflex response can vary in gain, and in some cases in sign, in a manner depending on centrally generated motor activity. In addition, at the level of a pool of synergistic motor neurons, the reflex effect is not uniform; instead, different subgroups of motor neurons display different reflex effects, so that the relative levels of excitability of different motor neuron reflex subgroups can also determine the net reflex effect. 6. Excitation of promotor motor neurons by TCCO shortening and of remotor motor neurons by TCMRO lengthening are positive feedback reflexes. The subgroups of motor neurons in which positive feedback reflexes can be evoked in both promotor and remotor pools are termed group 1.(ABSTRACT TRUNCATED AT 400 WORDS)