Reflex influences on muscle spindle activity in relaxed human leg muscles

1986 ◽  
Vol 56 (1) ◽  
pp. 159-170 ◽  
Author(s):  
S. C. Gandevia ◽  
S. Miller ◽  
A. M. Aniss ◽  
D. Burke
Keyword(s):  
Muscle Spindle ◽  
Tibialis Anterior ◽  
Tibial Nerve ◽  
Triceps Surae ◽  
Motor Threshold ◽  
Muscle Spindle Afferents ◽  
Posterior Tibial ◽  
Leg Muscles ◽  
Low Threshold ◽  
Electrical Stimuli

The study was designed to determine whether low-threshold cutaneous and muscle afferents from the foot reflexly activate gamma-motoneurons innervating relaxed muscles of the leg. In 15 experiments multiunit recordings were made from 21 nerve fascicles innervating triceps surae or tibialis anterior. In a further nine experiments the activity of 19 identified single muscle spindle afferents was recorded, 13 from triceps surae, 5 from tibialis anterior, and 1 from extensor digitorum longus. Trains of electrical stimuli (5 stimuli, 300 Hz) were delivered to the sural nerve at the ankle (intensity, twice sensory threshold) and the posterior tibial nerve at the ankle (intensity, 1.1 times motor threshold for the small muscles of the foot). In addition, a tap on the appropriate tendon at varying times after the stimuli was used to assess the dynamic responsiveness of the afferents under study. The conditioning electrical stimuli did not change the discharge of single spindle afferents. Recordings of rectified and averaged multiunit activity also revealed no change in the overall level of background neural activity following the electrical stimuli. The afferent responses to tendon taps did not differ significantly whether or not they were preceded by stimulation of the sural or posterior tibial nerves. These results suggest that low-threshold afferents from the foot do not produce significant activation of fusimotor neurons in relaxed leg muscles, at least as judged by their ability to alter the discharge of muscle spindle afferents. As there may be no effective background activity in fusimotor neurons innervating relaxed human muscles, it is possible that these inputs from the foot could influence the fusimotor system during voluntary contractions when the fusimotor neurons have been brought to firing threshold. In one subject trains of stimuli were delivered to the posterior tibial nerve at painful levels (30 times motor threshold). They produced an acceleration of the discharge of a spindle in soleus at a latency of approximately 125 ms, in advance of detectable activity in skeletomotor neurons and before an increase in muscle length was noted. It presumably resulted from activation of gamma-motoneurons innervating soleus by small myelinated afferents (A-delta range).

Reflex changes in muscle spindle discharge during a voluntary contraction

1988 ◽  
Vol 59 (3) ◽  
pp. 908-921 ◽  
Author(s):  
A. M. Aniss ◽  
S. C. Gandevia ◽  
D. Burke
Keyword(s):  
Muscle Spindle ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Triceps Surae ◽  
Sensory Threshold ◽  
Single Motor ◽  
Posterior Tibial ◽  
Single Motor Units ◽  
Flexor Muscles ◽  
Electrical Stimuli

1. This study was undertaken to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the foot reflexly affect fusimotor neurons innervating the plantar and dorsiflexors of the ankle during voluntary contractions. 2. Recordings were made from 29 identified muscle spindle afferents innervating triceps surae and the pretibial flexors. Trains of electrical stimuli (5 stimuli, 300 impulses per second) were delivered to the sural nerve at the ankle (intensity: 2-4 times sensory threshold) and to the posterior tibial nerve at the ankle (intensity: 1.5-3 times motor threshold for the small muscles of the foot). The stimuli were delivered while the subject maintained an isometric voluntary contraction of the receptor-bearing muscle, sufficient to accelerate the discharge of each spindle ending. This ensured that the fusimotor neurons directed to the ending were active and influencing the spindle discharge. The effects of these stimuli on muscle spindle discharge were assessed using raster displays, frequencygrams, poststimulus time histograms (PSTHs) and cumulative sums ("CUSUMs") of the PSTHs. Reflex effects onto alpha-motoneurons were determined from poststimulus changes in the averaged rectified electromyogram (EMG). Reflex effects of these stimuli onto single-motor units were assessed in separate experiments using PSTHs and CUSUMs. 3. Electrical stimulation of the sural or posterior tibial nerves at nonnoxious levels had no significant effect on the discharge of the 14 spindle endings in the pretibial flexor muscles. The electrical stimuli also produced no significant change in discharge of 11 of 15 spindle endings in triceps surae. With the remaining four endings in triceps surae, the overall change in discharge appeared to be an increase for two endings (at latencies of 60 and 68 ms) and a decrease for two endings (at latencies of 110 and 150 ms). The difference in the incidence of the responses of spindle endings in tibialis anterior and in triceps surae was significant (P less than 0.05, chi 2 test). 4. For both triceps surae and pretibial flexor muscles the electrical stimuli to sural or posterior tibial nerves had clear effects on the alpha-motoneuron pool, whether assessed using surface EMG or the discharge of single-motor units. Based on EMG recordings using intramuscular wire electrodes, the reflex effects differed for the gastrocnemii and soleus. 5. In this study, reflex changes in the discharge of human spindle endings were more difficult to demonstrate than comparable changes in the discharge of alpha-motoneurons.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Effects of tonic muscle pain on fusimotor control of human muscle spindles during isometric ankle dorsiflexion

2019 ◽  
Vol 121 (4) ◽  
pp. 1143-1149
Author(s):  
Lyndon J. Smith ◽  
Vaughan G. Macefield ◽  
Ingvars Birznieks ◽  
Alexander R. Burton
Keyword(s):  
Muscle Spindle ◽  
Muscle Pain ◽  
Tibialis Anterior Muscle ◽  
Muscle Spindles ◽  
Muscle Spindle Afferents ◽  
Firing Rates ◽  
Leg Muscles ◽  
Tonic Muscle ◽  
Voluntary Contractions ◽  
Ankle Dorsiflexors

Studies on anesthetized animals have revealed that nociceptors can excite fusimotor neurons and thereby change the sensitivity of muscle spindles to stretch; such nociceptive reflexes have been suggested to underlie the mechanisms that lead to chronic musculoskeletal pain syndromes. However, the validity of the “vicious cycle” hypothesis in humans has yielded results contrasting with those found in animals. Given that spindle firing rates are much lower in humans than in animals, it is possible that some of the discrepancies between human experimental data and those obtained in animals could be explained by differences in background fusimotor drive when the leg muscles are relaxed. We examined the effects of tonic muscle pain during voluntary contractions of the ankle dorsiflexors. Unitary recordings were obtained from 10 fusimotor-driven muscle spindle afferents (6 primary, 4 secondary) supplying the ankle dorsiflexors via a microelectrode inserted percutaneously into the common peroneal nerve. A series of 1-min weak contractions was performed at rest and during 1 h of muscle pain induced by intramuscular infusion of 5% hypertonic saline into the tibialis anterior muscle. We did not observe any statistically significant increases in muscle spindle firing rates of six afferents followed during tonic muscle pain, although discharge variability increased slightly. Furthermore, a participant’s capacity to maintain a constant level of force, while relying on proprioceptive feedback in the absence of visual feedback, was not compromised during pain. We conclude that nociceptive inputs from contracting muscle do not excite fusimotor neurons during voluntary isometric contractions in humans. NEW & NOTEWORTHY Data obtained in the cat have shown that muscle pain causes a marked increase in the firing of muscle spindles, attributed to a nociceptor-driven fusimotor reflex. However, our studies of muscle spindles in relaxed leg muscles failed to find any effect on spindle discharge. Here we showed that experimental muscle pain failed to increase the firing of muscle spindle afferents during weak voluntary contractions, when fusimotor drive sufficient to increase their firing is present.

Reflex activation of muscle spindles in human pretibial muscles during standing

1990 ◽  
Vol 64 (2) ◽  
pp. 671-679 ◽  
Author(s):  
A. M. Aniss ◽  
H. C. Diener ◽  
J. Hore ◽  
D. Burke ◽  
S. C. Gandevia
Keyword(s):  
Muscle Spindle ◽  
Muscle Spindles ◽  
Muscle Afferents ◽  
Reflex Response ◽  
Muscle Stretch ◽  
Human Foot ◽  
Posterior Tibial ◽  
Flexor Muscles ◽  
Reflex Activation ◽  
Electrical Stimuli

1. Experiments were performed in standing subjects to determine whether low-threshold cutaneous and muscle afferents from mechanoreceptors in the human foot reflexly influence fusimotor neurons innervating pretibial flexor muscles. Recordings were made from 30 identified muscle-spindle afferents, four tendon-organ afferents, and one alpha-motor axon innervating the pretibial flexor muscles. The subjects stood without support or vision on a force platform while trains of electrical stimuli (5 stimuli, 300 Hz) were delivered at nonpainful intensities to the sural nerve or to the posterior tibial nerve at the ankle. 2. Seventeen of the 30 spindle endings had no background discharge, and none was activated by the sural or posterior tibial stimuli. Five silent afferents were given a background discharge by sustained pressure on the relevant tendon, but with two the discharge was dominated by a tremor rhythm obscuring any reflex response to the stimuli. Based on peristimulus time histograms (PSTHs), the sural stimuli then produced increases in discharge of two of the remaining three endings at latencies of 84 and 90 ms. These effects could not be explained by muscle stretch and are presumed to have been fusimotor mediated. 3. When the subjects stood freely without support or vision, 13 muscle-spindle endings had a background discharge, but with three endings tremor developed at the ankle and dominated the spindle discharge. Sural stimuli affected the discharge of five of nine endings unaffected by tremor. With three of these endings, there were changes in discharge that could be explained by muscle stretch.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Muscle spindles in human tibialis anterior encode muscle fascicle length changes

2017 ◽  
Vol 117 (4) ◽  
pp. 1489-1498 ◽  
Author(s):  
James Day ◽  
Leah R. Bent ◽  
Ingvars Birznieks ◽  
Vaughan G. Macefield ◽  
Andrew G. Cresswell
Keyword(s):  
Muscle Spindle ◽  
Tibialis Anterior ◽  
Tibialis Anterior Muscle ◽  
Muscle Length ◽  
Muscle Spindles ◽  
Muscle Spindle Afferents ◽  
Fascicle Length ◽  
Muscle Fascicle ◽  
Length Changes

Muscle spindles provide exquisitely sensitive proprioceptive information regarding joint position and movement. Through passively driven length changes in the muscle-tendon unit (MTU), muscle spindles detect joint rotations because of their in-parallel mechanical linkage to muscle fascicles. In human microneurography studies, muscle fascicles are assumed to follow the MTU and, as such, fascicle length is not measured in such studies. However, under certain mechanical conditions, compliant structures can act to decouple the fascicles, and, therefore, the spindles, from the MTU. Such decoupling may reduce the fidelity by which muscle spindles encode joint position and movement. The aim of the present study was to measure, for the first time, both the changes in firing of single muscle spindle afferents and changes in muscle fascicle length in vivo from the tibialis anterior muscle (TA) during passive rotations about the ankle. Unitary recordings were made from 15 muscle spindle afferents supplying TA via a microelectrode inserted into the common peroneal nerve. Ultrasonography was used to measure the length of an individual fascicle of TA. We saw a strong correlation between fascicle length and firing rate during passive ankle rotations of varying rates (0.1–0.5 Hz) and amplitudes (1–9°). In particular, we saw responses observed at relatively small changes in muscle length that highlight the sensitivity of the TA muscle to small length changes. This study is the first to measure spindle firing and fascicle dynamics in vivo and provides an experimental basis for further understanding the link between fascicle length, MTU length, and spindle firing patterns. NEW & NOTEWORTHY Muscle spindles are exquisitely sensitive to changes in muscle length, but recordings from human muscle spindle afferents are usually correlated with joint angle rather than muscle fascicle length. In this study, we monitored both muscle fascicle length and spindle firing from the human tibialis anterior muscle in vivo. Our findings are the first to measure these signals in vivo and provide an experimental basis for exploring this link further.

Force-sensitive mechanoreceptors of the dactyl of the crab: single-unit responses during walking and evaluation of function

1987 ◽  
Vol 57 (5) ◽  
pp. 1618-1637 ◽  
Author(s):  
F. Libersat ◽  
F. Clarac ◽  
S. Zill
Keyword(s):  
Motor Neurons ◽  
Carcinus Maenas ◽  
Sensory Stimulation ◽  
Mechanical Coupling ◽  
Leg Muscles ◽  
Low Threshold ◽  
Mechanical Bending ◽  
Electrical Stimuli ◽  
Phase Relationships ◽  
Stimulation Of

The activities of individual force-sensitive mechanoreceptors of the dactyl (terminal leg segment) of the crab, Carcinus maenas, have been recorded during free walking. These receptors have also been mechanically and electrically stimulated in freely moving animals to directly evaluate their function in locomotion. All force-sensitive mechanoreceptors fired during the stance phase of walking and were silent during swing. Receptor discharges showed regular phase relationships to bursts in motor neurons of leg muscles. Crabs walk laterally and use the legs of one side either in trailing to actively push the animal to the opposite side, or in leading, to less forcefully pull the animal in that direction. Individual force-sensitive mechanoreceptors differed in their patterns of activity during trailing or leading according to their location on the dactyl. Units of proximal receptors fired more vigorously when used in trailing than in leading. Discharges in trailing were also increased by loading of the animal. In contrast, distal receptors near the dactyl tip fired equally intensely during walking in either direction. Proximal receptors thus encode forces and loads applied to the leg. Distal receptors do not encode loads but can signal leg contact and, potentially, exteroceptive vibrations. Sensory stimulation of force-sensitive mechanoreceptors was produced during walking by a device that imposed continuous mechanical bending of the dactyl and by electrical stimulation of dactyl nerves. Intra- and inter-segmental reflexes were evaluated by myographic recordings from leg muscles. Continuous mechanical deformation of the dactyl increased the activity of the levator and decreased firing in the depressor muscles of the homonymous leg during walking. The same stimulus produced enhanced activity in depressor muscles of adjacent legs. The latter effect was not due to simple mechanical coupling resulting from reflexes in the stimulated leg. These reflexes can function to limit forces applied to a leg and provide compensatory adjustments in other legs. Brief low-threshold electrical stimuli applied to nerves in which the activities of force-sensitive mechanoreceptors were recorded produced reflex effects similar to those obtained by mechanical stimulation. These stimuli also reset the rhythm of motor neuron bursting in both homonymous and adjacent legs during walking. These studies confirm the importance of force-sensitive mechanoreceptors in adapting walking patterns and in determining leg coordination in locomotion.

Influence of gravitational forces on function of lower extremity muscles

1964 ◽  
Vol 19 (5) ◽  
pp. 999-1004 ◽  
Author(s):  
S. J. Houtz
Keyword(s):  
Lower Extremity ◽  
Tibialis Anterior ◽  
Body Position ◽  
The Body ◽  
Triceps Surae ◽  
Contralateral Limb ◽  
Gravitational Forces ◽  
Leg Muscles ◽  
Forward Bending ◽  
Muscle Groups

Action potentials were recorded by surface electrodes from the quadriceps, hamstrings, tibialis anterior, and triceps surae muscle groups as 12 normal adolescents performed a series of changes in posture. Postural movements consisted of sitting, standing, squatting, sit-ups, unilateral standing with contralateral lower extremity exercise, trunk forward bending with knee flexion and extension, and the head stand. Photographs were taken to assist in analyzing change in body position during the activities. The hamstrings and triceps surae resist forces tending to flex the supporting extremity when the trunk or contralateral limb is suspended anteriorly. The quadriceps and tibialis anterior act volitionally or by lengthening contraction to move the body vertically. The muscles participating in an activity and their specific functions are influenced by gravitational forces, the weight and position of various body segments, and the point of contact with the supporting surface. electromyography; thigh and leg muscles; postural exercises; human male and female Submitted on February 3, 1964

Changes in Crossed Spinal Reflexes After Peripheral Nerve Injury and Repair

2002 ◽  
Vol 87 (4) ◽  
pp. 1763-1771 ◽  
Author(s):  
Antoni Valero-Cabré ◽  
Xavier Navarro
Keyword(s):  
Sciatic Nerve ◽  
Action Potential ◽  
Peripheral Nerve ◽  
Nerve Injury ◽  
Peripheral Nerve Injury ◽  
Tibialis Anterior ◽  
Tibial Nerve ◽  
Spinal Reflexes ◽  
Injury And Repair

We investigated the changes induced in crossed extensor reflex responses after peripheral nerve injury and repair in the rat. Adults rats were submitted to non repaired sciatic nerve crush (CRH, n = 9), section repaired by either aligned epineurial suture (CS, n = 11) or silicone tube (SIL4, n = 13), and 8 mm resection repaired by tubulization (SIL8, n = 12). To assess reinnervation, the sciatic nerve was stimulated proximal to the injury site, and the evoked compound muscle action potential (M and H waves) from tibialis anterior and plantar muscles and nerve action potential (CNAP) from the tibial nerve and the 4th digital nerve were recorded at monthly intervals for 3 mo postoperation. Nociceptive reinnervation to the hindpaw was also assessed by plantar algesimetry. Crossed extensor reflexes were evoked by stimulation of the tibial nerve at the ankle and recorded from the contralateral tibialis anterior muscle. Reinnervation of the hindpaw increased progressively with time during the 3 mo after lesion. The degree of muscle and sensory target reinnervation was dependent on the severity of the injury and the nerve gap created. The crossed extensor reflex consisted of three bursts of activity (C1, C2, and C3) of gradually longer latency, lower amplitude, and higher threshold in control rats. During follow-up after sciatic nerve injury, all animals in the operated groups showed recovery of components C1 and C2 and of the reflex H wave, whereas component C3 was detected in a significantly lower proportion of animals in groups with tube repair. The maximal amplitude of components C1 and C2 recovered to values higher than preoperative values, reaching final levels between 150 and 245% at the end of the follow-up in groups CRH, CS, and SIL4. When reflex amplitude was normalized by the CNAP amplitude of the regenerated tibial nerve, components C1 (300–400%) and C2 (150–350%) showed highly increased responses, while C3 was similar to baseline levels. In conclusion, reflexes mediated by myelinated sensory afferents showed, after nerve injuries, a higher degree of facilitation than those mediated by unmyelinated fibers. These changes tended to decline toward baseline values with progressive reinnervation but still remained significant 3 mo after injury.

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