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PubMed1984

Characteristics of the spino-bulbo-spinal reflex with evoked EMGs in human subjects.

Training in sports medicine and rehabilitation medicine requires the establishment of conditioned reflexes. Reinforcement of a conditioned reflex is more effective when it is part of a set of two or three reflexes. The late spinal reflexes appearing after conditioning were resolved into a stretch reflex and a spino-bulbo-spinal (SBS) reflex. H and M waves on the tibialis anterior muscle induced by tibial nerve stimulation were determined from the escape potential of the triceps sural muscle contraction. The tibial nerve and peroneal nerve were stimulated bilaterally, and H and M waves from the triceps sural muscle and tibialis anterior muscle were recorded bilaterally. The complete separation method of the late response and the time course of the stretch reflex and SBS reflex that composed the late response are described in this paper.

Animals↗

PubMed1995

Nonlinear behavior of muscle reflexes at the human ankle joint.

1. Pulse inputs (similar to tendon jerks) were applied to the human ankle joint with the use of a hydraulic actuator. Inputs of only 1-2 degrees could elicit large responses (> 20% of maximum voluntary contraction). The magnitude of the response depended nonlinearly on a number of factors: the amplitude, direction, and duration of the pulse; the angle of the ankle; and the level of voluntary activation of the ankle muscles. 2. Pulses that flexed or extended the ankle could both produce reflex torques in the same direction (extensor torque). Although an extension of the ankle did not itself produce a response, it could affect the response to a subsequent flexion for up to 1 s. 3. The influence of random perturbations on the stretch reflex at the ankle was assessed. Responses to pulse displacements alone and to pulses superimposed on random perturbations were compared at the same level of voluntary activity. Reflex responses decreased in a graded manner with increasing amplitude or bandwidth of the random perturbations. 4. These results demonstrate that stretch reflexes can generate substantial torques, but in a highly nonlinear manner. In particular, passive joint movements markedly alter stretch reflex gain, and these changes must be considered in interpreting the functional significance of reflex actions.

Ankle↗

PubMed1994

Shaping static elbow torque-angle relationships by spinal cord circuits: a theoretical study.

Static torque-angle relationships (invariant characteristics) as measured by Feldman [Feldman A. G. (1980) Neuroscience 5, 81-90] at the human elbow joint for constant descending excitatory drive have a monotonic convex shape determining joint angle-dependent stiffness. In contrast, for constant activation of elbow flexors, the torque increases, peaks and decreases again with increasing angle because of related moment arm alterations [Hasan Z. and Enoka R. M. (1985) Expl Brain Res. 59, 441-450]. Conversion of such constant-excitation torque-angle shapes into an invariant characteristic might result from action of the stretch reflex which adds excitation with increasing joint angle. To test whether a simple linear model of the stretch reflex could convert constant excitation torque-angle relationships into invariant characteristics, the following assumptions were made. (1) Muscle fibre length increases linearly with joint angle. (2) Reflex muscle excitation (electromyogram) is linearly related to muscle (fibre) length. With these assumptions, invariant characteristic shape cannot be derived from constant excitation torque-angle relationships because it would be sigmoid at low and nearly straight at large joint angles, whilst real flexor invariant characteristics are more convex at large than small angles. It is suggested that recurrent inhibition via Renshaw cells contributes to bend the invariant characteristics into their right shape. Renshaw cells show a nonlinear saturating dependence on motor axon input rate and amount of excitation, i.e. number of active axon collateral synapses. These relationships can contribute to shape motoneuron output so as to yield convex invariant characteristics. Whilst it is not quite clear whether the gain of recurrent inhibition from and to skeleto-motoneurons is high enough to co-determine the invariant characteristic shape significantly, recurrent inhibition of Ia inhibitory interneurons mediating reciprocal inhibition between antagonists is supposed to be quite strong and may influence joint stiffness by interacting with reciprocal inhibition. The arguments presented here extend those of Feldman and co-workers concerning the role of recurrent inhibition and in addition provide a possible explanation for the functional role of mutual inhibition between Renshaw cells. Together with reflex feedback, recurrent inhibition thus contributes to fine-regulate force output and joint stiffness. To account for this cooperation and to make another step towards a general theory of spinal cord circuits, major traits of a new concept are briefly outlined.

Biomechanical Phenomena↗

PubMed1996

A comparison of clinical and laboratory measures of spasticity.

Clinical evaluation of spasticity was performed in lower extremities in 35 ambulatory multiple sclerosis patients and compared with the soleus stretch reflex and the Hoffman reflex. There was no relation between the muscle tone score of dorsiflexion of the foot and the biomechanical/electrophysiological parameters. In contrast, the Achilles tendon reflex score was significantly related to the amplitude (rho = 0.411, P < 0.05) and the slope of the stretch reflex (rho = 0.523, P < 0.01). The clinical examination at the ankle joint revealed 33% normal reflex examinations but only 7% normal muscle tone examinations. In contrast, the number of normal examinations of patellar reflex and muscle tone at the knee joint were similar. It is concluded that the muscle tone score overestimates the amount of spasticity because of changes in the non-reflex properties of the spastic extremity and that a reflex score should be used as a clinical measure of spasticity. In addition, biomechanical/electrophysiological evaluation of spasticity at the ankle joint relates to the over-all total muscle tone and reflex scores of lower extremities in this group of MS patients.

Adult↗

PubMed2000

Peripheral and central effect of baclofen on ankle joint stiffness in multiple sclerosis.

The effect of baclofen on the soleus stretch reflex and peripheral muscle function was tested in 10 multiple sclerosis (MS) patients with spasticity in the lower extremities. Peroral baclofen (15-60 mg daily) induced a decrease in the twitch torque of the soleus muscle elicited by supramaximal nerve stimulation. The torque was 15.1 +/- 5.5 Nm with baclofen and 17.1 +/- 5.0 Nm without baclofen (P = 0.03). The slope of the background torque/EMG relation was also changed from 1.53 Nm/microV with baclofen to 1.13 NM/microV without it (P = 0.03), and the soleus stretch reflex threshold decreased from 11.4 degrees /s (3.1-62.8) to 6.2 degrees /s (3.1-25.1) without baclofen medication (P = 0.03) in the relaxed muscle. Furthermore, baclofen induced an approximately 20% decrease in the total stiffness at the ankle joint at all contraction levels due to a decrease in the short-latency stretch reflex. From a clinical point of view, the peripheral action of baclofen may be unfortunate. Spasticity is often accompanied by weakness, which may be the major cause of any disability. Consequently, reduction in spasticity by the central effect of baclofen may be counteracted by its influence on muscle properties. In addition, treatment of spasticity by baclofen may unmask weakness.

Adult↗

PubMed1981

The activity of human muscle spindle endings in normal motor behavior.

In none of the above instances has the fusimotor system been found to be responsible for the described changes in stretch reflex gain. These findings do not prove that the fusimotor system is incapable of altering the gain of the stretch reflex; they do, however, establish that there are quite adequate mechanisms of gain control completely independent of the fusimotor system. One could reasonably question whether the fusimotor system ever operates primarily as a gain-controlling mechanism. That "more in" would probably result in "more out" cannot be disputed, but this may be of little real functional importance when compared with other possible sources of adaptive control of reflex activity. This conclusion has been reached by others in this department, working independently and using a quite different approach (79). Given that there are other adequate mechanisms of controlling reflex gain, one should question whether the fusimotor system plays any primary role in the disorders of stretch reflex gain that characterize spinal shock and cerebellar hypotonia on the one hand, and spasticity and Parkinsonian rigidity on the other hand.

Afferent Pathways↗

PubMed1997

Central modifications of reflex parameters may underlie the fastest arm movements.

Descending and reflex pathways usually converge on common interneurons and motoneurons. This implies that active movements may result from changes in reflex parameters produced by control signals conveyed by descending systems. Specifically, according to the lambda-model, a fast change in limb position is produced by a rapid change in the threshold of the stretch reflex. Consequently, external perturbations may be ineffective in eliciting additional reflex modifications of electromyographic (EMG) patterns unless the perturbations are relatively strong. In this way, the model accounts for the relatively weak effects of perturbations on the initial agonist EMG burst (Ag1) usually observed in fast movements. On the other hand, the same model permits robust reflex modifications of the timing and shape of the Ag1 in response to strong perturbations even in the fastest movements. To test the model, we verified the suggestion that the onset time of the Ag1, even in the fastest movements, depends on proprioceptive feedback in a manner consistent with a stretch reflex. In control trials, subjects (n = 6) made fast unopposed elbow flexion movements of approximately 60 degrees (peak velocity 500-700 degrees/s) in response to an auditory signal. In random test trials, a brief (50 ms) torque of 8-15 Nm either assisting or opposing the movement was applied 50 ms after this signal. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. In all subjects, the onset time of the Ag1 depended on the direction of perturbation: it was 25-60 ms less in opposing compared with assisting load conditions. Assisting torques caused, at a short latency of 37 ms, an additional antagonist EMG burst preceding the Ag1. The direction-dependent effects of the perturbation persisted when cutaneous feedback was suppressed. It was concluded that the direction-dependent changes in the onset time and duration of the Ag1 as well as the antagonist activation preceding the Ag1 resulted from stretch reflex activity elicited by the perturbations rather than from a change in the control strategy or cutaneous reflexes. The results support the hypothesis on the hierarchical scheme of sensorimotor integration in which EMG patterns and movement emerge from the modification of the thresholds and other parameters of proprioceptive reflexes by control systems.

Adult↗

PubMed2001

Physiologic and clinical monitoring of spastic hypertonia.

Spasticity has been defined as "a motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one component of the upper motor neuron syndrome." Increased motor neuron excitability and enhanced stretch-evoked synaptic excitation of motor neurons are potential neurophysiologic mechanisms to explain this phenomenon. The relative contribution of these two distinct mechanisms likely varies depending on the location of the lesion in the central nervous system. The patient history is an important component of the clinical evaluation focusing on potential nociceptive inputs that can worsen spasticity (e.g., urinary tract infections, skin breakdown). Assessment of the impact of the spasticity on function (positive and negative), position, care of the patient, and pain should be pursued. Clinical examination of spasticity is performed using methods to evoke and quantify spastic reflex responses to muscle stretch stimuli and to observe the patient performing functional tasks to note the impact of spasticity on their performance. Treatment is based on the negative impact of the spasticity on the patient, severity of the problems, and whether the hypertonicity is focal or diffuse in distribution (see article by Elovic elsewhere in this issue). First-line treatments include elimination of nociceptive stimuli, range of motion, seating and positioning, and other physical modalities. If additional intervention is necessary, oral medications are implemented for widespread spasticity, whereas focal problems are treated with prolonged stretching and splinting or casting to maintain muscle stretch and optimal positioning. In more severe cases, invasive procedures may be needed to supplement other treatments. Neurolytic procedures are pursued for focal tone problems. For generalized hypertonicity, intrathecal pump administration of medications or surgical interruption of reflex pathways has been helpful. Ultimately, the clinician must systematically approach the evaluation and treatment of spasticity. As decisions regarding moving from less to more invasive treatments are discussed, the potential risks and side effects of treatment options must be weighed versus the potential benefits that the patient might receive to maintain a rational approach to the management of spasticity.

Anti-Dyskinesia Agents↗

PubMed2001

Comparison of spinal myotatic reflexes in human adults investigated with cross-correlation and signal averaging methods.

A cross-correlation method for recording spinal myotatic reflexes has been developed to meet the need for brief test periods in babies and children and subjects with central neurological pathology. In normal adult subjects the method has been validated by comparing excitatory and inhibitory reflexes obtained with cross-correlation with those obtained with conventional signal averaging. In the cross-correlation method a pseudo-random binary sequence of 64 brief tendon taps was delivered in <1.5 s, and in the averaging method 20-150 taps at one per second. The reflexes were expressed as unit impulse responses to enable direct, quantitative comparisons to be made. With cross-correlation the responses were slightly expanded in time, had lower peak amplitudes, and onset latencies advanced by 10 ms, the clock period of the pseudo-random binary sequence. The amplitude of biceps phasic stretch reflex increased with muscle contraction in a similar manner with both methods. In tests for stationarity the amplitude of biceps phasic stretch reflex varied <10% in the first six repeats of the pseudo-random binary sequence. The tap force required at threshold for cross-correlation was approximately half that for averaging, but with both methods the magnitude of biceps phasic stretch reflex varied linearly with tap force over the range of one to two times threshold. The validity of responses obtained with cross-correlation was assessed by a statistical procedure. In conclusion, the cross-correlation method is robust and gives similar results to those obtained with averaging.

Adult↗

PubMed1997

Simultaneous and nonlinear identification of mechanical and reflex properties of human elbow joint muscles.

The naturally coexisting intrinsic mechanical and reflex properties of the human elbow joint were identified simultaneously using nonlinear, time-delay, continuous-time, and dynamic models. Angular random perturbations of small amplitude and low bandwidth were applied to the joint using a computer-controlled servomotor, while the subject maintained various levels of mean background muscle torque. Joint neuromuscular dynamics were identified from the measured elbow angle and torque. Stretch reflexes were modeled nonlinearly with both dynamic and static reflex gains. A continuous-time system identification method was developed to estimate parameters of the nonlinear models directly from sampled data while retaining realistic physical or physiological interpretations. Results from six subjects showed that dynamic stretch reflex gains, joint stiffness, and viscosity generally increased with mean background muscle torque; and that dynamic stretch reflex gain was higher during muscle stretch than that during muscle shortening. More importantly, the study provided realistic simultaneous estimates of the relative contributions of intrinsic mechanical and reflex actions to net joint torque. In particular, reflexively-mediated stiffness generated a significant portion of the total joint stiffness and the percentage varied systematically with background muscle torque.

Biomechanical Phenomena↗

PubMed1998

Muscle hysteresis and movement control: a theoretical study.

In this study we have tried to elaborate necessary theoretical approaches for the adequate analysis of the central motor commands to a mammalian muscle in the equilibrium states and during transition movements between these states. At present, the equilibrium point hypothesis has obtained a wide distribution in this field. The muscle is considered in the framework of the theory as an executive element of the reflex circuits originating in the muscle proprioceptors and being closed at the level of spinal cord and the supraspinal motor centres. The main parameter defining the muscle state is supposed to be the threshold of the stretch reflex--the minimal length value at which muscle begins to resist to the externally applied force. We have attempted to show that the theory has an essential shortcoming because it does not take into account such important non-linearity in the muscle behaviour as hysteresis. In the framework of the equilibrium point hypothesis, the muscle behaviour within the stretch reflex system does not depend on movement direction. The stretch and unloading reflexes are supposed to have the same length tension dependencies when the muscle is stretching or contracting with a rather slow velocity. However, powerful hysteresis of the stretch reflex system requires taking into account the direction of the current movement, the after-effects of previous movement led to a principal uncertainty in the muscle steady-state. We would like to stress that any process of active muscle shortening should be controlled by dynamic components in efferent inflow. At the same time, the resulting steady-state develops by using effective hysteresis mechanism for its maintenance. The following hypothesis was proposed to explain the length clamping mechanisms in shortening transition movements. A significant decrement of the arrived efferent activity at the phase of the length fixation can evoke an internal elongation of the contractile elements within the muscle and corresponding hysteresis-like enhancement of the contractile effectiveness. Hence, instead of considering the quasi-static and dynamic components of movement commands as in the equilibrium point hypothesis, it is preferable to adopt a model of the shared coding of both the final position and movement velocity. The dynamic component of the efferent discharge seems to be required for a complete definition of the final steady-state, but maintenance of the state is closely associated with energetically advantageous hysteresis mechanisms. It was concluded that the dynamic phase of efferent activity should play an extremely important role in the central coding of the real movements produced, in particular, by contraction of agonists in the absence of antagonist activation.

Animals↗

PubMed1988

Involvement of different receptors in the regulation of human posture.

Compensatory electromyographic (EMG) responses and several biomechanical parameters were studied following impulsive disturbance of the lower limbs during stance on a treadmill. Treadmill acceleration impulses were backwards or forwards directed, or their direction was inverted after 30 ms. Backwards directed impulses were followed by gastrocnemius and forwards directed ones by tibialis anterior EMG responses (latency 65-75 ms) whose duration depended on impulse duration. When the direction of the impulse was inverted, the respective antagonistic leg muscles were activated, with a delay of 68 to 75 ms after onset of stretch of these muscles. The behaviour of the EMG responses could best be correlated to the displacement at the ankle joint and may be described in terms of a stretch reflex response. The function of this stretch reflex mechanism is suggested to be connected with the control of the body's centre of gravity in order to prevent falling. Head movements induced by the impulses showed little correlation with the appearance of the EMG responses, suggesting that the vestibular system is unlikely to be significantly involved in the generation of these responses.

Biomechanical Phenomena↗

PubMed1977

Effects of 1,3-dimethyl-5-aminoadamantane hydrochloride (DMAA) on the stretch-induced reflex tension of flexor muscles and the excitability of the gamma-loop in decerebrate and spinal cats.

The effects of 10 mg/kg i.v. 1,3-dimethyl-5-aminoadamantane hydrochloride (memantine, DMAA) on the stretch-induced reflex tension of flexor muscles extensor digitorum longus and tibialis anterior (EDL/TA) and on the excitability of the neurons relaying transmission in the gamma-loop have been investigated in decerebrate and spinal cats. DMAA essentially reduced the relfex excitability of flexors EDL/TA induced by fusimotor activity in the decerebrate preparation. The drug did not stimulate the reflex activity in acute spinal cats. In the concentration used, DMAA suppressed largely the transmission of the fusimotor reflex in the decerebrate as well as in the spinal preparation, although in spinal cats DMAA increased the average firing rate of muscle spindle primaries originating from EDL/TA muscles. The possible mechanism of action of the compound on dopaminergic and serotonergic systems as well as its basic effects on neuronal membranes is discussed.

Amantadine↗

PubMed1996

Spasticity and muscle contracture following stroke.

It has become increasingly recognized that the major functional deficits following brain damage are largely due to "negative' features such as weakness and loss of dexterity rather than spasticity. A variety of studies suggest that spasticity is a distinct problem and separate from the loss of dexterity, but that it may be implicated in the formation of muscle contracture and even in the recovery of strength. In order to address these issues, we examined the relationship between spasticity, contracture, strength and dexterity in the affected upper limb following stroke. Spasticity was measured both as increased tonic stretch reflexes and increased resistance to passive stretch (hypertonia). Twenty-four patients were recruited non-selectively from three rehabilitation units within 13 months of their stroke. Few patients exhibited increased tonic reflexes but half were found to have muscle contracture, the earliest at 2 months following stroke. Hypertonia was associated with contracture but not with reflex hyperexcitability. Increased tonic stretch reflexes were observed only in a subgroup of those with contracture and where present could usually be elicited only at the end of muscle range. This findings suggests that instead of spasticity causing contracture, contracture may actually potentiate spasticity in some patients. However, the majority of patients with contracture did not have increased tonic stretch reflexes. In addition, we found no relationship between spasticity and either weakness or loss of dexterity. Therefore, while hypertonia remains an important problem following cerebral lesions, it would appear that the amount of attention directed to reflex hyperexcitability associated with spasticity is out of proportion with its effects. Consequently, hypertonia needs to be clearly distinguished from reflex hyperexcitability in patients with spasticity.

Adult↗

PubMedDate not supplied

Relation of early neuromotor and cranial signs with neuropsychological outcome at 4 years.

The persistence and predictive value at 3-5 years of age of three signs detected within the first 18 months of life were investigated: phasic stretch reflex in one or both gastrocnemius muscles, imbalance in passive axial tone with an excess of dorsal extension, and a ridge on the squamous sutures. Phasic stretch reflex and at least one of the other signs were found in 14 children during repeated assessments within the first 18 months. The progress of these children was compared with that of 14 matched controls who had repeatedly normal neurological assessments during the first 18 months in the same clinic in Paris. At the age 3-5 years all the children were then assessed blindly by the second author from a pediatric neurological viewpoint and by two psychologists and two psychomotor therapists as well. The parents of the affected children reported significantly more problems in motor/praxis skills, language development and attention. Abnormal neurological signs were also significantly more frequent than in the controls. Suboptimal cognition did not reach significance. The neurological inclusion criteria were still present at 3-5 years old in 86% (vs. respectively 100% and 93% during the first 18 months of life) of this small group of children, while the cranial suture sign was still present in only 28% (vs. 64%). Findings of these three signs during the first 18 months of life may help in predicting long-term neurobehavioral or long-term neuropsychological problems.

Age Factors↗

PubMed1981

Effect of vibrating agonist or antagonist muscle of the reflex response to sinusoidal displacement of the human forearm.

1. The mechanical resistance of the human forearm to imposed sinusoidal movements has been determined. By means of a visual monitor, subjects maintained a steady force (typically 100 N) by flexing the elbow so as to pull with the wrist against an isometric force transducer. This was mounted upon a stretcher which displaced the forearm sinusoidally at frequencies of 7-11 Hz with a peak-to-peak amplitude of movement of about 1 mm. The average mechanical resistance over 10-40 sec of stretching was analysed into its vector components at the fundamental of the stretching frequency. Observations were made of both the normal resistance and that obtained while applying continuous vibration at 100 Hz to the tendon of either the biceps (agonist) or triceps (antagonist).2. In confirmation of Joyce, Rack & Ross (1974), at frequencies around 10 Hz the normal (unvibrated) response sometimes showed a component of ;negative viscosity' (force increasing during muscle shortening), rather than the simple ;positive viscosity' attributable to muscle visco-elasticity; this effect is attributable to the stretch reflex being appropriately delayed and of sufficient magnitude to over-ride the inherent properties of muscle. Vibration of either agonist or antagonist usually increased the extent of the ;negative viscosity' (negative quadrature component of force), as well as changing the ;elastic' stiffness of the arm (in-phase component of force).3. More commonly, the component of viscosity was initially positive. It was then normally reduced by vibration; that is, the vibration had (in formal terms) again added a component of negative viscosity.4. The vibration did not produce these effects by acting directly upon the contractile system of muscle to reduce its ;visco-elasticity'. On increasing the frequency of stretching the effect of vibration systematically shifted from being the addition of a negative viscosity, as above, to being the addition of a positive viscosity. These effects may all be attributed to an action of vibration on the stretch reflex, with the precise action of the reflex determined by the relation between the cycle time and the delays round the reflex pathway.5. In some experiments the activity of the flexor muscles was sampled by surface electromyograms from biceps and from brachioradialis; these were rectified, smoothed and averaged. For biceps, the absolute depth of e.m.g. modulation in relation to the cycle of stretching was sometimes, but not always, increased by vibration; but for brachioradialis the modulation was always reduced. Thus vibration cannot invariably produce its effects on the mechanical resistance of the arm by increasing the size (gain) of the stretch reflex. However, in all subjects the phase of the electromyographic modulation of both muscles was significantly delayed during vibration, whether of biceps or of triceps. In comparison with the normal, vibration introduced a phase lag on average of 18 degrees . In qualitative terms, this can be shown to explain the typical augmentation of ;negative viscosity'.6. The findings are discussed in relation to the genesis of tremor and to the reflex regulation of muscle contraction. They support the classical idea that afferent activity from the antagonist is as crucially implicated as that from the agonist.

Adult↗

PubMed1996

Reflex stimulation of continuously oscillatory firing alpha and gamma-motoneurons in patients with spinal cord lesion.

Single nerve-fibre action potentials (APs) were recorded extracellularly from lower human sacral nerve roots, and simultaneous single-fibre impulse patterns of alpha and gamma-motoneurons and secondary muscle spindle afferents were analysed. Identified alpha and gamma-motoneurons fired oscillatory, due to the sustained stretch reflex of the external sphincters induced by an anal catheter (and, possibly, the bladder catheter). The motoneurons and the secondary muscle spindle afferents transiently synchronized their firing upon repetitive touch, pin-prick and dimpling stimulation of the perianal skin inside the anal reflex area, by reducing the duration of their oscillation period until resetting of the oscillation cycle. In one case, the anal reflex area extended approximately 6 cm laterally from the anus. The responses to pin-prick stimulation were different from those to touch stimulation in three aspects. Firstly, the response time till the shortening of the oscillation period was longer than the oscillation period (approximately 100 ms) for pin-prick, and it was shorter for touch. Second, the response to pain stimulus was longer (shortening of several oscillation periods) and stronger than for touch stimulation. Pin-prick stimulation reduced the oscillation period to between 5 and 40 ms (mean = 18 ms), and touch stimulation to between 8 and 28 ms (mean = 15 ms). Third, transient synchronization of afferents and efferents was most pronounced for pin-prick stimulation. The shortest latency following touch was approx. 10 ms when measuring from the afferent volley running in the direction of the spinal cord, and 30 ms when measuring from the beginning of the skin touch. It is discussed that repetitive touch stimulation reinforced the sustained stretch reflex of the anal sphincter which is possible with no network reorganization (variation of the same network state) and therefore fast, whereas repetitive pin-prick stimulation replaced the sustained stretch reflex by the protection reaction of the anal sphincter (change from one network state to a different one) which made time consuming network reorganization necessary. Different sacral reflexes were analysed by studying time-related activation changes of group conduction velocities in velocity distributions. During the reflex response to stretch of the external anal sphincter, the alpha 2-motoneurons (FR) (and the secondary muscle spindle afferents) were strongly activated whereas upon eliciting the bulbocavernosus reflex (squeezing of the glans penis) the alpha 3-motoneurons (S) were mainly activated. Sacral reflexes are discussed with respect to the organization and reorganization of preformated neuronal networks, and the synchronization of oscillatory firing networks is discussed with respect to the overlapping of synfire chains.

Action Potentials↗

PubMed2005

Interest of peripheral anesthetic blocks as a diagnosis and prognosis tool in patients with spastic equinus foot: a clinical and electrophysiological study of the effects of block of nerve branches to the triceps surae muscle.

OBJECTIVE: To evaluate clinically and electrophysiologically the effects of selective anesthetic blocks of motor nerve branches to the triceps surae muscle on lower limb stretch reflex in patients with spastic equinus foot. METHODS: Eleven patients were assessed before and after selective anesthetic block of the superior soleus nerve or the gastrocnemius nerves, performed by lidocaine injection. The stretch reflex (SR) of the ankle with the knee flexed or extended and the Achilles tendon reflex (TR) were scored clinically. Additionally, the direct M response and the H reflex to tibial nerve stimulation were recorded on the three heads of the triceps surae muscle. The ratio of H reflex to M response of maximal amplitudes (H(max)/M(max)) was calculated. RESULTS: The SR and TR mean scores were significantly reduced after soleus nerve block but not after gastrocnemius nerve block. Electrophysiologically, H(max) and H(max)/M(max) ratios were significantly reduced for the soleus muscle after soleus nerve block and for the lateral (but not medial) gastrocnemius muscle after gastrocnemius nerve block. CONCLUSIONS: Soleus nerve block appeared more appropriate than gastrocnemius nerve block to relieve spasticity clinically. In addition, the decrease in H(max)/M(max) ratio suggested that lidocaine preferentially blocked proprioceptive Ia fibers rather than A-alpha motor fibers. SIGNIFICANCE: Selective anesthetic blocks of nerve branches to the triceps surae muscle are useful in the assessment of lower limb spasticity and can benefit from H reflex investigation. H reflex recordings showed a preferential susceptibility of muscle spindle afferents to local anesthetics and supported the hypothesis of a prominent role of the soleus muscle in spastic ankle. The clinical and electrophysiological effects induced by anesthetic blocks may help to guide therapeutic interventions, such as neurotomy, neurolysis or botulinum toxin injection.

Adolescent↗