Tendon Tap Research Articles

Interaction of the Jendrássik maneuver with segmental presynaptic inhibition.

Since its initial description in 1883, the Jendrássik maneuver (JM) has been used in clinical neurological practice as an effective means of potentiating the tendon tap in neurologically impaired patients. The JM also potentiates its electrical analogue, the Hoffman (H-) reflex, but the mechanism of the reflex modulation has not been clearly established. We studied soleus H-reflex modulation in neurologically intact subjects while at rest and during a mild plantarflexion contraction (EMG level equivalent to approximately 10% maximum voluntary contraction). The control H-reflex was elicited by stimulating the tibial nerve in the popliteal fossa with single pulses of 1 ms duration. Conditioning of the reflex was by: (1) increasing segmental presynaptic inhibition via common peroneal nerve (CP) stimulation; (2) pulling the arms and clenching the teeth (JM); or (3) applying both together (JM+CP). CP stimulation significantly (P<0.05) suppressed the H-reflex (50% Hmax), while JM significantly (P<0.05) facilitated it during contraction. From either an analysis of the grouped data or by a within-subject analysis, we found that the combined effect of stimulating JM+CP was significantly lower than JM alone, but did not differ from control values or from CP alone. The simplest mechanism would be that the effects of the two sum algebraically on the interneurones producing segmental presynaptic inhibition of the H-reflex.

Proprioceptive control of wrist extensor motor units in humans: dependence on handedness

The effectiveness of the monosynaptic proprioceptive assistance to the wrist extensor motoneurone activity was investigated during voluntary contraction in relation to the subjects' handedness. The reflex responses of 411 single motor units to homonymous tendon taps were recorded in the wrist extensor carpi radialis muscles in both arms of five right-handed and five left-handed subjects. In the right-handed subjects, the motor unit reflex responses were clearly lateralized in favour of their right arm, whereas no side-related differences were observed in the left-handed subjects, whatever the motor units' mechanical properties and firing rates. When the muscle spindle sensitivity was by-passed by electrically stimulating the primary afferents in both arms of three right-handed and three left-handed subjects, no side-related differences were observed in the Hoffmann reflex (H-reflex) amplitude in either of the two lateralization groups. The effectiveness of the primary afferent synapses on to the motoneurones therefore does not seem to depend on the subject's handedness. Without excluding the possibility of structural changes being involved at the periphery, the comparisons carried out on the data obtained using electrical vs mechanical stimulation suggest that the asymmetrical effectiveness of the proprioceptive assistance observed in favour of the right arm in the right-handed subjects might result from either the gamma or beta drive being more efficient. This asymmetry might result from the preferential use of the right hand in skilled movements. In a predominantly right-handed world, however, left-handed people might tend to develop the ability to use their right arm almost as skillfully as their preferred left arm, which could explain the symmetrical effectiveness of the proprioceptive assistance observed here in the left-handers' wrist extensor muscles.

Sensitivity of H-reflexes and stretch reflexes to presynaptic inhibition in humans.

The sensitivity of soleus H-reflexes, T-reflexes, and short-latency stretch reflexes (M1) to presynaptic inhibition evoked by a weak tap applied to the biceps femoris tendon or stimulation of the common peroneal nerve (CPN) was compared in 17 healthy human subjects. The H-reflex was strongly depressed for a period lasting up to 300-400 ms (depression to 48 +/- 23%, mean +/- SD, of control at a conditioning test interval of 70 ms) by the biceps femoris tendon tap. In contrast, the short-latency soleus stretch reflex elicited by a quick passive dorsiflexion of the ankle joint was not depressed. The soleus T-reflex elicited by an Achilles tendon tap was only weakly depressed (92 +/- 8%). The H-reflex was also significantly more depressed than the T-reflex at long intervals (>15 ms) after stimulation of CPN (H-reflex 63 +/- 14%, T-reflex 91 +/- 13%; P < 0. 01). However, the short-latency (2 ms) disynaptic reciprocal Ia inhibition evoked by stimulation of CPN was equally strong for H- and T-reflexes (H-reflex 72 +/- 10%, T-reflex 67 +/- 13%; P = 0.07). Peaks in the poststimulus time histogram (PSTH) of the discharge probability of single soleus motor units (n = 53) elicited by an Achilles tendon tap had a longer duration than peaks evoked by electrical stimulation of the tibial nerve (on average 5.0 ms as compared with 2.7 ms). All parts of the electrically evoked peaks were depressed by the conditioning biceps femoris tendon tap (average depression to 55 +/- 27% of control; P < 0.001). A similar depression was observed for the initial 2 ms of the peaks evoked by the Achilles tendon tap (69 +/- 48%; P < 0.001), but the last 2 ms were not depressed. Conditioning stimulation of the CPN at long intervals (>15 ms) also depressed all parts of the electrically evoked PSTH peaks (n = 34; average 65%; P < 0.001) but had only a significant effect on the initial 2 ms of the peaks evoked by the Achilles tendon tap (85%; P < 0.001). We suggest that the different sensitivity of mechanically and electrically evoked reflexes to presynaptic inhibition is caused by a difference in the shape and composition of the excitatory postsynaptic potentials underlying the two reflexes. This difference may be explained by a different composition and/or temporal dispersion of the afferent volleys evoked by electrical and mechanical stimuli. We conclude that it is not straightforward to predict the modulation of stretch reflexes based on observations of H-reflex modulation.

Task-dependence of muscle afferent monosynaptic inputs to human extensor carpi radialis motoneurones

The task-dependence of homonymous muscle afferent inputs was investigated in motor units of the extensor carpi radialis muscles during voluntary isometric contraction involving either the activation of agonist extensor muscles (wrist extension) or the co-activation of antagonist extensor and flexor muscles (hand clenching). The effectiveness of the muscle afferent monosynaptic inputs was tested by delivering either tendon taps or electrical stimulation to the radial nerve. In both cases, the motor unit responses, which took the form of narrow peaks in the peri-stimulus time histograms, were found to be significantly greater during hand clenching. The parallel enhancement of the responses to both mechanical and electrical stimulations observed during hand clenching could not be explained in terms of changes in the muscle spindle responsiveness. The enhancement of the motor units' responsiveness was apparent during the first 0.5 ms of the peaks in the peri-stimulus time histograms, taken to be uncontaminated by any polysynaptic components. It may therefore have reflected an increase in the amplitude of the excitatory monosynaptic potentials generated by the muscle spindle primary afferents. This is interpreted in terms of changes in the presynaptic inhibition, which might be depressed as the result of the large-scale activation of palm and finger cutaneous afferents liable to occur during hand clenching.

Consistency of multi-channel surface EMG recordings: Application in spinal cord injured subjects

We evaluated the consistency of serial polyelectromyographic recordings of altered motor control in spinal cord injured (SCI) individuals. Using 12 pairs of surface electrodes placed over major muscle groups of lower limb and trunk, we examined voluntary and involuntary and phasic and tonic features of motor control using a standardized protocol for brain motor control assessment (BMCA). The surface electromyographic (EMG) data were digitized and analysed on the basis of the root mean square (RMS) envelope of activity, with the exception of phasic tendon tap responses which were evaluated from full bandwidth EMG data. The average amplitudes of responses were calculated. The median correlation of the results from two successive examinations 1–2 weeks apart for all subjects was 0.98. Further analysis was based on ratios of corresponding elements from the two studies. Noise from null responses was suppressed by incorporating a threshold parameter T set to 1 μV RMS. With this value, pairs of studies in 52 subjects were virtually identical (mean ratio of 1.02 ± 0.1). Z-scores from two case studies in which pharmacological and physiological interventions changed motor control demonstrated the utility of the procedure. This method offers a reliable and appropriate means of studying altered motor control which is sensitive to changes induced after interventions.

The "size principle" and synaptic effectiveness of muscle afferent projections to human extensor carpi radialis motoneurones during wrist extension.

The question of whether muscle spindle afferents might control human motoneurone activity on the basis of the "size principle" during voluntary contraction was investigated by recording the discharge of single motor units (n = 196) in wrist extensor muscles while stimulating the homonymous muscle spindles by means of tendon taps. The mechanical stimuli were delivered with a constant post-spike delay of 80 ms so that the resulting afferent volleys could be expected to reach the motoneurones towards the end of the inter-spike interval (mean +/- SD duration: 124.7 +/- 11.9 ms). In the six subjects tested, the response probability was found to be significantly correlated with the motor units' functional parameters. Differences in twitch rise times, twitch amplitudes, recruitment thresholds and macro-potential areas were found to account for 18%, 9%, 6% and 2% of the differences in the response probability observed within the whole population of motor units tested. These differences could not be due to differences in firing rate for two reasons: first, the motor units were found to discharge with a similar range of inter-spike intervals whatever their functional characteristics; secondly, the weak positive correlation observed between the response probability and the motor unit firing rate showed parallel regression lines between the late-recruited fast-contracting motor units and the first-recruited slowly contracting motor units, but the y-intercept was significantly higher in the latter case. This confirmed that the responses of the first-recruited slowly contracting motor units tended to be larger whatever the firing rates. In most of the pairs tested in the same experiment, the motor units which had the lowest recruitment thresholds, longest contraction times, smallest contraction forces or smallest motor unit macro-potentials tended to produce the largest responses, which also had the longest latencies. Taking the response latency to be an index of a motoneurone's conduction velocity and therefore of its size, the data obtained with this index and with other functional indices such as the twitch rise times and amplitudes, the macro-potential areas and the recruitment thresholds-can be said to be fully consistent with the "size principle", as previously found in anaesthetized animals. It can be inferred that the presynaptic inhibition which is liable to take action during voluntary contraction does not seem to alter the graded distribution of the muscle afferent projections to human wrist extensor motoneurones.

Comparison of peripheral Ia and corticomotoneuronal composite EPSPs in human motoneurons

The effects of excitatory inputs arising from Ia afferent and corticomotoneuronal volleys on repetitively firing flexor carpi radialis (FCR) motoneurons were compared in normal human subjects. Peripheral (Ia) volleys were produced by transcutaneous electrical stimulation of the median nerve and by mechanical taps to the FCR tendon. Transcranial magnetic stimulation (TMS) was used to activate the corticomotoneuronal pathway. The duration of the excitatory response peaks measured from peri-stimulus time histograms (PSTHs) and the time course of the response trajectories were both taken to reflect the shapes of the underlying composite excitatory postsynaptic potentials (EPSP)s acting upon that motoneuron. The duration of excitatory response peaks for the H-reflex and the first sub-peak (SP 1) of the motor unit's response to TMS were similar and were typically less than those arising from tendon taps. The response trajectories, which measure the excitability of the motoneuron during different phases of the afterhyperpolarization, overlapped for H-reflex and SP 1 responses, but were different for tendon tap inputs. Our results indicate that the SP 1 response of a motoneuron to TMS input and its response to near-synchronous Ia afferent activation are mediated by composite EPSPs with similar rise times. We suggest that a similar spatial distribution of synaptic boutons for both Ia and corticomotoneuronal input to motoneurons innervating FCR is likely.

Reflex response times of vastus medialis oblique and vastus lateralis in normal subjects and in subjects with patellofemoral pain syndrome.

Various authors have indicated that imbalance of the vastus medialis/vastus lateralis muscles might lead to patellofemoral pain syndrome. However, few reports have been published to substantiate such a hypothesis. The purpose of this study was to attempt to set a scale for the normal reflex response times of the vastus medialis oblique and vastus lateralis muscles after a patellar tendon tap and to determine if patellofemoral pain syndrome patients have an alteration in this firing sequence. A control group of 80 healthy adults was compared with a group of 19 patellofemoral pain syndrome patients. Results indicated that the reflex response time of the vastus medialis oblique was significantly shorter than the reflex response time of the vastus lateralis in the normal subjects (p < or = .01). When comparing these data in the patellofemoral pain syndrome group, a significant earlier firing was obtained from the vastus lateralis in comparison with the vastus medialis oblique (p < or = .01). These findings suggest that a reversal has occurred in the firing pattern of the vastus medialis oblique and vastus lateralis muscles in patellofemoral pain syndrome patients. The results indicate an alteration in the neuromuscular answer of the vastus medialis oblique and vastus lateralis muscles during a patellar tendon tap.

Clinical assessment of spasticity in spinal cord injury: a multidimensional problem.

To determine the relation between various components of spasticity evaluated clinically in persons with spinal cord injury (SCI). Case series evaluating spasticity using clinical scales commonly referenced in contemporary literature, including the Penn Spasm Frequency Scale, the Ashworth Scale, and standard scales of tendon taps, clonus, and plantar stimulation. SETTING. A Veterans Affairs Medical Center Spinal Cord Injury Center. PATIENTS. Eighty-five spinal cord injured individuals with varying degrees of spasticity. Correlations demonstrated weak relationships between Spasm Frequency Scale and self-report scales of interference with function (.407) and painful spasms (.312). No clinical examination score correlated with self-report scores greater than 0.4. Three clinical examination scores correlated modestly (> 0.5)-Ashworth score with patellar tendon taps (.553), ankle clonus with Achilles tendon tap (.663), and patellar tendon tap with adductor tendon tap (.512). Two other clinical scales correlated weakly (> 0.4)-Achilles tendon tap with patellar tendon tap (.417) and plantar reflex with adductor tendon taps (.423). Clinical scales currently used to evaluate spasticity in SCI correlate poorly with each other, suggesting that they each assess different aspects of spasticity. The use of any single scale is likely to underrepresent the magnitude and severity of spasticity in the SCI population. In the absence of agreement among these various scales and with the absence of an appropriate criterion standard for evaluation of spasticity, assessments of spasticity, whether clinical or neurophysiological in nature, should be comprehensive in scope.

Spinal motoneuron excitability after acute spinal cord injury in humans

Few studies in humans have assessed the ability of Ia afferent and antidromic motor volleys to activate motoneurons during spinal shock. Hence, little is known about the excitability state of the spinal motoneuron pool after acute spinal cord injury (SCI) in humans. In 14 patients with acute SCI involving anatomic levels T10 and above, we performed clinical and electrophysiologic studies early after injury (within 24 hours in seven subjects) and on day 10, 20, and 30 postinjury. Maximal H:M ratios, F-wave persistence, and tendon tap T-reflexes were recorded. Sixteen normal subjects and eight chronic SCI patients served as control subjects. Ten of 14 patients had spinal shock (complete paralysis, loss of sensation, absent reflexes, and muscle hypotonia below the injury) at the time of initial evaluation. F-waves were absent in patients with spinal shock, reduced in persistence in patients with acute SCI without spinal shock, and normal in persistence in patients with chronic SCI. H-reflexes were absent or markedly suppressed in patients with spinal shock within 24 hours of injury but recovered to normal amplitudes within several days postinjury. This recovery occurred despite absence of F-waves that persisted for several weeks postinjury. Deep tendon reflexes were proportionally more depressed in spinal shock than were H-reflexes. All patients had elicitable H-reflexes for days or weeks before the development of clinical reflexes. Rostral cord injury causes postsynaptic changes (hyperpolarization) in caudal motoneurons. This hyperpolarization is a major physiologic derangement in spinal shock. The rise in H-reflex amplitude despite evidence of persistent hyperpolarization is due to enhanced transmission at Ia fiber-motoneuron connections below the SCI. Finally, the observation that the stretch reflex is proportionally more depressed than the H-reflex is consistent with fusimotor drive also being depressed after SCI.

Age-dependent effects of muscle vibration and the Jendrassik maneuver on the patellar tendon reflex response

Objective: To explore possible effects of aging on the excitability of spinal reflexes. Design: Using a cross-sectional design, the influences of muscle vibration and the Jendrassik maneuver on patellar tendon reflex function were compared between 30 young adults and 15 older adults. Setting: Motor control research laboratory. Subjects: The young adults were volunteers of college age. The older adults (74.5 ± 4.14yr) were volunteers from the local community. All subjects were free of medications and neurological conditions that would affect normal neuromuscular responses. Main Outcome Measures: A force-time curve analysis of the patellar tendon reflex response was used to assess the inhibition and facilitation of spinal reflexes. In the experimental protocol to assess spinal reflex inhibition, 100Hz vibration was applied to the right quadriceps muscle. In another experimental protocol, spinal reflex facilitation was assessed using the Jendrassik maneuver. To perform the Jdnrassik maneuver, subjects were instructed to grasp their hands together and to pull as hard as possible while breathing normally. After a 2-second count, the tendon tap was delivered to the right leg and the subject was instructed to relax. In both experimental protocols, control patellar tendon reflexes were collected. Results: Analysis of variance for reflex peak force revealed a significant 30% reduction in the amount of vibration-induced reflex inhibition with increasing age, and a similar 33% reduction in the amount of Jendrassik maneuver facilitation observed for the older adults as compared with the younger adults. Conclusion: These results support the hypothesis that inhibitory and excitatory influences acting on the alpha motoneuron pool are different in young and older adults.

KNEE REFLEX FACILITATION INDUCED BY SYNERGISTIC CONTRACTION OF THE CONTRALATERAL LEG IN WEIGHT TRAINED MALES 1217

The purpose of this study was to determine whether graded knee flexion (KF) and knee extension (KE) by the contralateral leg during the patellar (knee) reflex would elicit a graded facilitation(FAC) or inhibition(IHB) of fractionated reflex time. FAC would be indicative of a crossed extensor patterning effect. Five college-aged weight trained males (20.6 yrs, 79.9 kg) reported to the lab on two consecutive days. On day 1,25% and 50% MVC values of isometric KF and KE were found. For the reflex trials, subjects sat with their knee joint angles at 90°, and a bipolar electrode on the motor point. A tendon tap hammer struck the patellar ligament from 60°. Fourteen baseline trials (7 normal, 7 Jendrassik facilitory maneuver, JM) were done each day, followed by 4 conditions, 7 trials each. Conditions were 25% and 50% MVC for both KF and KE of the contralateral leg prior to the knee reflex. Post-condition trials were done to detect if fatigue occurred during testing. Conditions were randomized, and EMG data were collected and analyzed for total reflex time (TRT) and its 2 components, reflex latency (RLT, central) and reflex motor time (RMT, peripheral) for each trial. Thetable summarizes results for days 1 and 2. The 25 and 50% MVC KF condition showed a significant decrease in RMT and TRT. This condition elicits FAC similar to the JM. The 25 and 50% MVC KE showed a significant IHB in TRT and RMT. Since RLT was not affected as seen in untrained people, these data suggest that training status may cause a decrease in RMT and TRT, leading to enhanced motor response during synergistic activity.

Neuromuscular adaptations in rats trained by muscle stretch-shortening.

The aim of this study was the analysis of neurophysiological, mechanical and histochemical parameters to demonstrate muscle adaptation with training. If the parameters studied were to show correlated changes, it would be possible to propose that the neural and the muscle components of motor units are both affected by the training programme used. The training consisted of repeated stretch-shortening cycles known to use extensively fast fibres. After the training period electromyographical reflex activities of the ankle plantar-flexors were recorded in awake rats and then mechanical and histochemical measurements were made on isolated soleus muscles of the control and trained rats. The reflexes studied were the H-response to electrical stimulation of the sciatic nerve and the T-response to an Achilles tendon tap. The H-response analysis indicated a decrease in reflex excitability of the trained muscles. The trained soleus muscle also presented a higher contractility as demonstrated by significantly smaller twitch contraction times and higher maximal velocities of shortening measured during tetanic contractions. The reflex and contractile muscle changes were accompanied by relative increases in the number of type II fibres. The T-response was not significantly modified by training despite the decrease in motoneuron excitability demonstrated by the decrease in H-response. This would suggest that the peripheral components of the reflex pathway such as tendon stiffness and/or spindle sensitivity might be modified by training. This would imply that both the motor and the sensory parts of a muscle are affected by training.

WS-23-3 Event-related potentials associated with memory retrieval and retention during a paired associate memory paradigm

The responsiveness of the tonically firing single motor units (SMU) to Ia afferent volleys elicited by either mechanical (T-reflex) or electrical nerve stimulation (H-reflex) was tested in the extensor carpi radialis muscle (ECR) while the subjects were maintaining a steady wrist extension force using visual feedback set either at low or high gain. The aim was to determine whether the proprioceptive control of tonic motoneuronal activity depends on the level of attentiveness required by the behavioural context. The response probability of the SMUs to tendon taps was significantly higher (p<0.0001) and that to electrical nerve stimulation was lower (p<0.001) during the more demanding task. Since these changes in SMU responsiveness were not accompanied by any differences in either the motor unit firing patterns or the mean levels of EMG muscle activity, it can be concluded that there were no attention-related changes in the net excitatory drive to the ECR motoneurons. These results are consistent with the idea that fusimotor sensitization of the muscle spindle may have occurred in the more demanding task: an increase in the mechanical sensitivity of the muscle spindles would certainly account for both the T-reflex facilitation and the H-reflex depression observed. The attention-demanding task therefore seemed to involve an independent fusimotor drive activation process. The results of this study suggest that an adaptation of the fusimotor system occurs in humans, depending on the levels of attention and accuracy required to perform the ongoing motor task, as previously reported to occur in animals.

Onset timing of electromyographic activity in the vastus medialis oblique and vastus lateralis muscles in subjects with and without patellofemoral pain syndrome.

Inappropriate neural control of the quadriceps femoris muscle group has been implicated in patellofemoral pain syndrome (PFPS). This study investigated the timing of initial electromyographic (EMG) activity of the vastus medialis oblique muscle (VMO) and the vastus lateralis muscle (VL) in asymptomatic subjects and subjects with PFPS during reflex and voluntary muscle activity. Fifteen symptomatic subjects (SYMP group) (9 with bilateral symptoms) and 12 asymptomatic subjects (ASYMP group) participated. Both knees were tested in the ASYMP group and only the symptomatic knees were tested in the SYMP group, resulting in a total of 24 data sets from each group. Electromyographic data were recorded from the VMO and VL under three conditions: reflex knee extension (RFLX) elicited by a patellar tendon tap, and active knee extension in non-weight-bearing (NWB) and weight-bearing (WB) situations. For each condition, EMG activity onset times for the VMO and VL were determined from ensemble averages of four trials. There were no differences between the SYMP and ASYMP groups with respect to the relative timing of initial VMO and VL activity under any of the three conditions tested. Mean timing differences for both groups were less than 0.25 milliseconds under reflex conditions and less than 4 milliseconds for active knee extension under both WB and NWB conditions. These findings contradict a previous report of differences in reflex timing related to PFPS. Differences in the relative timing of onset of EMG activity of the VMO and VL during voluntary knee extension were not significant between SYMP and ASYMP groups, and were not related to the relative timing differences observed during reflex testing.

Reciprocal inhibition between wrist flexors and extensors in man: a new set of interneurones?

1. Interneurones mediating reciprocal inhibition between wrist flexors and extensors in man are characterized using both Renshaw cells and transarticular group I afferent activation. 2. Renshaw cells were activated by reflex discharges evoked by a tendon tap. The tendon tap was applied to the tendon of the muscles from which the Ia fibres responsible for the reciprocal inhibition originated. Contrary to what was observed both in the cat hindlimb and in human elbow muscles, this Renshaw cell activation never resulted in a long depression of the reciprocal inhibition between wrist flexors and extensors. 3. Convergence from group I elbow muscle afferents and antagonistic group I afferents onto interneurones mediating reciprocal inhibition between wrist muscles was revealed in post-stimulus time histogram (PSTH) experiments using the technique of spatial facilitation. 4. The characteristics of the interneurones mediating reciprocal inhibition between wrist flexors and extensors could therefore be summarized as follows: (a) they are fed by antagonistic group I afferents and group I afferents originating from both flexor and extensor elbow muscles; (b) they are not inhibited by Renshaw cells; (c) they are not excited by low threshold cutaneous afferents; and (d) they are probably interposed in a disynaptic pathway. 5. It is therefore concluded that interneurones mediating reciprocal inhibition between wrist flexors and extensors in man differ both from Ia interneurones and from interneurones interposed in the Ib reflex pathways and these characteristics are related to the complex circumduction movements developed in the wrist.

Human myotatic reflex development of the lower extremities.

Lower extremity (LE) myotatic reflexes were tested by percussion (taps) to the patellar and Achilles tendons. Surface electromyographic recordings were obtained from 5 LE muscles during tendon taps. Results indicated that LE myotatic reflexes underwent considerable change during early human development. The changes were non-linear and highly variable. Reflex irradiation (the presence of reflex responses in muscles other than the one being directly stimulated by a tendon tap) was present in the newborn but to a lesser extent than was in evidence later on during the first year of life. The percentage of time reflex irradiation was detected in heteronymous muscle groups appeared to achieve maximal levels during the first year and then progressively decline. The decline in reflex irradiation was most dramatic between the first and second years of life. Irradiated responses were still recorded from 2 year-old children but with less frequency than in children less than 1 year of age. With the exception of responses in muscles that were direct antagonists to the stimulated muscle, irradiation was not observed in children 3-5 years of age.

Long-lasting conditioning of the human soleus H reflex following quadriceps tendon tap

Percussion of the quadriceps tendon was used to test the hypothesis that knee extensor muscle spindle discharge initiates down-regulation of the gain of the soleus H reflex. Seven subjects participated. Soleus H reflex magnitude was observed for up to 15 s, following conditioning tendon taps of 60 N or 80 N force and 10 ms or 100 ms duration, with the knee at 60° or 90° of flexion. The tap elicited quadriceps stretch reflexes in four subjects, with a mean latency of 42 ms. The major component of the conditioning of the soleus H reflex was significant attenuation of magnitude by 30–90% of controls, starting as early as 36 ms post-percussion and lasting as long as 3–8 s. The attenuation of reflex magnitude was evident, whichever combination of duration and force of tap was used. Preceding and/or following this inhibition, there was mild facilitation. Static stretch of quadriceps also significantly reduced soleus H reflex magnitude. These results support the spindle receptor origin for the gain attenuation seen during movement. The time course of the gain attenuation suggests a spinal route, by which the spindle discharge of the heteronymous extensor muscles initiates presynaptic inhibition of transmission through the reflex pathway.

Changes in transmission across synapses of Ia afferents in spastic patients.

The transmission across synapses of Ia afferents on spinal motor neurons was investigated in 30 healthy subjects and 25 spastic multiple sclerosis patients. Slow passive stretch (17 degrees/s of the soleus muscle evoked a pronounced depression of the soleus Hoffmann reflex (H-reflex) lasting for more than 10 s in the healthy subjects. This depression was less pronounced and had a shorter duration in the spastic patients. A tap applied to the biceps femoris tendon also produced an inhibition of the soleus H-reflex, which was larger in the healthy subjects than in the spastic patients. This inhibition only lasted for 300-400 ms. Finally, stimulation of the femoral nerve (FN) produced a facilitation of the soleus H-reflex, which was larger in the spastic patients than in the healthy subjects. The inhibition of the H-reflex evoked by the biceps femoris tendon tap is known to be caused by presynaptic inhibition of the Ia afferents, which mediate the reflex. The facilitation of the soleus H-reflex produced by FN stimulation has also been shown to be influenced by changes in presynaptic inhibition. The increased facilitation from the FN and the decreased inhibition from the biceps femoris tendon tap onto the soleus H-reflex in spastic patients are thus both compatible with a deficient presynaptic inhibition in these subjects. The long lasting depression of the reflex evoked by a previous slow stretch of the soleus muscle is most likely caused by a decrease of the probability of transmitter release from the Ia afferents. The decrease of this depression in spastic patients suggests that mechanisms other than presynaptic inhibition may contribute to changes in the efficiency of transmission across the synapses of Ia afferents in spastic patients and thus contribute to the exaggeration of stretch reflexes seen in these patients.

Is presynaptic inhibition distributed to corticospinal fibres in man?

1. A tendon tap of the biceps femoris tendon was found to evoke a depression of the soleus and tibialis anterior H reflexes with a duration of 300-400 ms and with an onset at a conditioning-test interval of 20-30 ms. It is suggested that the depression is caused by presynaptic inhibition of the terminals of the Ia afferents mediating the reflexes. 2. This possibility was tested by a method in which the H reflex is facilitated by a monosynaptic Ia volley from the quadriceps muscle. The attenuation of this facilitation when another pathway is stimulated is probably caused by presynaptic inhibition of Ia afferents. It was shown that the biceps femoris tendon tap depressed the size of the femoral nerve-induced facilitation of the soleus and tibialis anterior H reflexes. This suggests that the depression of the reflexes by the tendon tap was indeed caused by presynaptic inhibition. 3. To investigate whether the terminals of descending fibres were similarly susceptible to presynaptic inhibition, the stimulation of the femoral nerve was replaced by magnetic stimulation of the contralateral motor cortex. This stimulation has been shown to evoke a facilitation of the tibialis anterior and soleus H reflexes which (within its initial 0.5-1 ms) is probably caused exclusively by direct monosynaptic projections from the cortex to the motoneurones. In contrast to the facilitation evoked by Ia afferents, the descending facilitation was not influenced by the biceps tendon tap. 4. Similarly, the monosynaptic peak in the post-stimulus time histogram (PSTH) of single voluntarily activated tibialis anterior motor units evoked by stimulation of the common peroneal nerve was depressed by the tendon tap, whereas this was not the case for the presumed monosynaptic peak evoked by brain stimulation. 5. It is suggested that the tendon tap evoked presynaptic inhibition of the terminals of flexor as well as extensor Ia afferents terminating on both soleus and tibialis anterior motoneurones. In contrast, the tap failed to elicit any presynaptic inhibition of the terminals of descending fibres on the motoneurones. We suggest that descending pathways in general are free from the presynaptic control which attenuates peripheral input to motoneurones. Through modulation of presynaptic inhibition the brain may thus selectively hinder the access of peripheral feedback mechanisms to the motoneurones, while still maintaining control of the output from the spinal cord through direct and indirect projections to the motoneurones.