Study of Cutaneous Reflex Compensation During Locomotion After Nerve Section in the Cat

2007 ◽  
Vol 97 (6) ◽  
pp. 4173-4185 ◽  
Author(s):  
Geneviève Bernard ◽  
Laurent Bouyer ◽  
Janyne Provencher ◽  
Serge Rossignol
Keyword(s):  
Vastus Lateralis ◽  
Locomotor System ◽  
Plantar Surface ◽  
Threshold Response ◽  
Cutaneous Reflex ◽  
Reflex Pathways ◽  
Flexor Muscles ◽  
Reflex Compensation ◽  
Central Reorganization ◽  
Stimulation Of

In the cat, section of all cutaneous nerves of the hindfeet except the tibial (Tib) nerve supplying the plantar surface results in a long-lasting decrease in the intensity of Tib stimulation needed for a threshold response in flexor muscles and an increase in the amplitude of the phase-dependent responses recorded in various muscles during locomotion. Stimulating through chronically implanted nerve cuffs ensured a stable stimulation over time. The increase in reflex amplitude was well above the small increase in the amplitude of the locomotor bursts themselves that results from the denervation. Short latency responses (P1) were seen in flexor muscles, especially at the knee (semitendinosus) and ankle (tibialis anterior and extensor digitorum longus), with stimuli applied in the swing phase and also to a lesser degree in the later part of the cycle. Longer latency responses (P2) were increased in hip, knee, and ankle flexors, as well as in a contralateral extensor (vastus lateralis) when applied in late stance. Responses evoked from stimulating the proximal end of sectioned nerves were not larger than before neurectomy. This suggests that the increased responsiveness to Tib stimulation is not simply caused by an increase in motoneuron excitability, because this would have resulted in a nonspecific increase of responses to stimulation of any nerve. It is concluded that the adult locomotor system is capable of central reorganization to enhance specific remaining cutaneous reflex pathways after a partial cutaneous denervation of the paw.

Effects on Peroneal Motoneurons of Cutaneous Afferents Activated by Mechanical or Electrical Stimulations

2000 ◽  
Vol 83 (6) ◽  
pp. 3209-3216 ◽  
Author(s):  
Jean-François Perrier ◽  
Boris Lamotte D'Incamps ◽  
Nezha Kouchtir-Devanne ◽  
Léna Jami ◽  
Daniel Zytnicki
Keyword(s):  
Electrical Stimulation ◽  
Mechanical Stimulation ◽  
Cutaneous Afferents ◽  
Postsynaptic Potentials ◽  
Electric Pulses ◽  
Plantar Surface ◽  
Cutaneous Reflex ◽  
Inhibitory Postsynaptic Potentials ◽  
Mixed Pattern ◽  
Stimulation Of

The postsynaptic potentials elicited in peroneal motoneurons by either mechanical stimulation of cutaneous areas innervated by the superficial peroneal nerve (SP) or repetitive electrical stimulation of SP were compared in anesthetized cats. After denervation of the foot sparing only the territory of SP terminal branches, reproducible mechanical stimulations were applied by pressure on the plantar surface of the toes via a plastic disk attached to a servo-length device, causing a mild compression of toes. This stimulus evoked small but consistent postsynaptic potentials in every peroneal motoneuron. Weak stimuli elicited only excitatory postsynaptic potentials (EPSPs), whereas increase in stimulation strength allowed distinction of three patterns of response. In about one half of the sample, mechanical stimulation or trains of 20/s electric pulses at strengths up to six times the threshold of the most excitable fibers in the nerve evoked only EPSPs. Responses to electrical stimulation appeared with 3–7 ms central latencies, suggesting oligosynaptic pathways. In another, smaller fraction of the sample, inhibitory postsynaptic potentials (IPSPs) appeared with an increase of stimulation strength, and the last fraction showed a mixed pattern of excitation and inhibition. In 24 of 32 motoneurons where electrical and mechanical effects could be compared, the responses were similar, and in 6 others, they changed from pure excitation on mechanical stimulation to mixed on electrical stimulation. With both kinds of stimulation, stronger stimulations were required to evoke inhibitory postsynaptic potentials (IPSPs), which appeared at longer central latencies than EPSPs, indicating longer interneuronal pathways. The similarity of responses to mechanical and electrical stimulation in a majority of peroneal motoneurons suggests that the effects of commonly used electrical stimulation are good predictors of the responses of peroneal motoneurons to natural skin stimulation. The different types of responses to cutaneous afferents from SP territory reflect a complex connectivity allowing modulations of cutaneous reflex responses in various postures and gaits.

scholarly journals Repeated and patterned stimulation of cutaneous reflex pathways amplifies spinal cord excitability

2020 ◽  
Vol 124 (2) ◽  
pp. 342-351 ◽  
Author(s):  
Gregory E. P. Pearcey ◽  
E. Paul Zehr
Keyword(s):  
Spinal Cord ◽  
Nervous System ◽  
Presynaptic Inhibition ◽  
Sensory Stimulation ◽  
Cutaneous Afferents ◽  
Reflex Excitability ◽  
Cutaneous Reflex ◽  
Reflex Pathways ◽  
Muscle Reflex ◽  
Stimulation Of

Priming via patterned stimulation of the nervous system induces neuroplasticity. Yet, accessing previously known cutaneous reflex pathways to alter muscle reflex excitability has not yet been examined. Here, we show that sensory stimulation of the cutaneous afferents that innervate the foot sole can amplify spinal cord excitability, which, in this case, is attributed to reductions in presynaptic inhibition.

Coordinated Interlimb Compensatory Responses to Electrical Stimulation of Cutaneous Nerves in the Hand and Foot During Walking

2003 ◽  
Vol 90 (5) ◽  
pp. 2850-2861 ◽  
Author(s):  
Carlos Haridas ◽  
E. Paul Zehr
Keyword(s):  
Electrical Stimulation ◽  
Motor Coordination ◽  
The Body ◽  
Emg Activity ◽  
Motor Tasks ◽  
Step Cycle ◽  
Reflex Responses ◽  
Cutaneous Reflex ◽  
Reflex Pathways ◽  
Stimulation Of

It has been shown that stimulation of cutaneous nerves innervating the hand (superficial radial, SR) and foot (superficial peroneal, SP) elicit widespread reflex responses in many muscles across the body. These interlimb reflex responses were suggested to be functionally relevant to assist in motor coordination between the arms and legs during motor tasks such as walking. The experiments described in this paper were conducted to test the hypothesis that interlimb reflexes were phase-dependently modulated and produced functional kinematic changes during locomotion. Subjects walked on a treadmill while electromyographic (EMG) activity was collected continuously from all four limbs, and kinematic recordings were made of angular changes across the ankle, knee, elbow, and shoulder joints. Cutaneous reflexes were evoked by delivering trains of electrical stimulation pseudorandomly to the SP nerve or SR nerves in separate trials. Reflexes were phase-averaged according to the time of occurrence in the step cycle, and phasic amplitudes and latencies were calculated. For both nerves, significant phase-dependent modulation (including reflex reversals) of interlimb cutaneous reflex responses was seen in most muscles studied. Both SR and SP nerve stimulation resulted in significant alteration in ankle joint kinematics. The results suggest coordinated and functionally relevant reflex pathways from the SP and SR nerves onto motoneurons innervating muscles in nonstimulated limbs during walking, thus extending observations from the cat to that of the bipedal human.

Differential modulation of disynaptic cutaneous inhibition and excitation in ankle flexor motoneurons during fictive locomotion

1996 ◽  
Vol 76 (5) ◽  
pp. 2972-2985 ◽  
Author(s):  
A. M. Degtyarenko ◽  
E. S. Simon ◽  
R. E. Burke
Keyword(s):  
Electrical Stimulation ◽  
Dorsal Surface ◽  
Extension Phase ◽  
Fictive Locomotion ◽  
Plantar Surface ◽  
Cutaneous Reflex ◽  
Adult Cats ◽  
Differential Control ◽  
Almost All ◽  
Stimulation Of

1. Intracellular recording from extensor digitorum longus (EDL) and tibialis anterior (TA) alpha-motoneurons during fictive locomotion was used to examine patterns of modulation of oligosynaptic postsynaptic potentials (PSPs) produced by electrical stimulation of the cutaneous superficial peroneal (SP) and medial plantar (MPL) nerves in unanesthetized, decerebrate adult cats. 2. In all 20 EDL motoneurons studied, electrical stimulation of the SP nerve with single pulses at about twice threshold for the most excitable fibers in the nerve (2xT) produced either no synaptic potentials or relatively small oligosynaptic excitatory or inhibitory PSPs (EPSPs or IPSPs), both at rest and during the extension phase of fictive stepping. However, at the onset of the flexion phase large, presumably disynaptic IPSPs (central latencies 1.7–2.0 ms) appeared in the SP responses. These IPSPs usually decreased in amplitude later in the flexion phase despite maintained membrane depolarization. 3. In most (7/8) TA motoneurons, SP stimulation produced oligosynaptic EPSPs at rest and during the extension phase of fictive stepping. These EPSPs were suppressed during flexion in a majority of TA cells studied (5/8) but no clearly disynaptic IPSPs were found in any TA motoneuron. 4. In most EDL and TA motoneurons, stimulation of the MPL nerve produced oligosynaptic EPSPs at rest and during the extension phase, most with latencies in the presumably disynaptic range (< or = 2.0 ms). When present, these MPL EPSPs were suppressed throughout the flexion phase of stepping in almost all EDL (18/ 20) and TA (6/8) motoneurons examined. 5. The available evidence suggests that these modulation effects during fictive stepping are due primarily to convergence of control information from the spinal central pattern generator (CPG) for locomotion onto segmental interneurons in the oligosynaptic cutaneous pathways. 6. These observations extend the evidence for precise differential control of transmission through cutaneous reflex pathways in the cat hindlimb by the locomotor CPG. Taken together with earlier evidence about locomotor modulation of cutaneous PSPs in flexor digitorum longus (FDL) motoneurons, the data suggest that cutaneous information from the dorsal surface of the foot, carried in part by the SP nerve, projects to digit motoneurons (FDL and EDL) through discrete sets of last-order interneurons that also receive powerful excitation from the locomotor CPG during flexion. In contrast, the last-order interneurons that convey excitatory information from the SP nerve to at least some TA motoneurons are inhibited by the CPG during flexion. 7. Another contrast resides in the fact that oligosynaptic cutaneous excitation from the plantar surface of the foot, via the MPL nerve, is suppressed in FDL, EDL, and TA motoneurons during the flexion phase of locomotion. The available information is consistent with the possibility that MPL effects may be delivered to these motor nuclei by common interneurons. 8. We suggest an interneuronal circuitry that could account for these observations and discuss possible functional implications of modulation of these sensory pathways during locomotion.

A kinematic and electromyographic study of cutaneous reflexes evoked from the forelimb of unrestrained walking cats

1987 ◽  
Vol 57 (4) ◽  
pp. 1160-1184 ◽  
Author(s):  
T. Drew ◽  
S. Rossignol
Keyword(s):  
Electrical Stimulation ◽  
Short Latency ◽  
Cutaneous Afferents ◽  
Mechanical Obstruction ◽  
Locomotor Rhythm ◽  
Cutaneous Reflex ◽  
Extensor Muscles ◽  
Flexor Muscles ◽  
Low Threshold ◽  
Stimulation Of

A kinematic and electromyographic (EMG) analysis was undertaken of the responses evoked in the forelimb of the cat by either mechanical obstruction of the forelimb during the swing phase of locomotion or by electrical stimulation of low-threshold cutaneous afferents during both swing and stance. Mechanical obstruction of the forelimb with a stiff metal rod evoked a complex response that allowed the cat to smoothly negotiate the obstacle without undue disruption of the overall locomotor rhythm. The initial movements were a flexion of the shoulder, together with a locking of the elbow joint, and a dorsiflexion of the wrist, which caused the limb to withdraw from the obstacle. They were followed by an extension of the shoulder, a flexion of the elbow, and a ventroflexion of the wrist, which together brought the limb forward and above the obstacle. The associated and complex pattern of short- and long-latency EMG responses was shown to be related to different aspects of the movement. At the shoulder there was a strong activation of flexor muscles; these responses were of long duration (greater than or equal to 100 ms) and generally lasted throughout the period of shoulder flexion. At the elbow, both flexor and extensor muscles were activated at short latency (9-13 ms). In flexors, this was followed by a cessation and subsequently an augmentation and prolongation of their activity. Dorsiflexors of both the wrist and digits were activated at short latency (10-12 ms) and remained active throughout the period of dorsiflexion of these joints. An injection of a local anesthetic into the area of skin contacted by the metal rod reduced or abolished all of the reflex responses, which suggests that the integrity of cutaneous reflex pathways is essential for the elaboration of these responses. Electrical stimulation of a cutaneous nerve innervating the distal forelimb (the superficial radial nerve) resulted in qualitatively similar, although weaker, responses to those obtained with the mechanical stimulation. Terminal experiments confirmed that these responses were mediated by low-threshold cutaneous afferents. Electrical stimulation also evoked short-latency excitatory responses (10-12 ms) in extensor muscles of the elbow. Generally, the largest reflex effects were obtained during the period of swing for flexor, extensor, and bifunctional muscles. During stance the stimulus was normally ineffective in exciting flexor muscles and in extensors evoked a short-latency inhibition, which was frequently followed by an increase in activity.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals An objective approach to assess colonic pain in mice using colonometry

PLoS ONE ◽  
2021 ◽  
Vol 16 (3) ◽  
pp. e0245410
Author(s):  
Liya Y. Qiao ◽  
Jonathan Madar
Keyword(s):  
Neurological Disorders ◽  
Stretch Reflex ◽  
Distal Colon ◽  
Saline Infusion ◽  
Noxious Stimulation ◽  
Trinitrobenzene Sulfonic Acid ◽  
Primary Afferent ◽  
Reflex Pathways ◽  
Constant Rate ◽  
Stimulation Of

The present study presents a non-surgical approach to assess colonic mechanical sensitivity in mice using colonometry, a technique in which colonic stretch-reflex contractions are measured by recording intracolonic pressures during saline infusion into the distal colon in a constant rate. Colonometrical recording has been used to assess colonic function in healthy individuals and patients with neurological disorders. Here we found that colonometry can also be implemented in mice, with an optimal saline infusion rate of 1.2 mL/h. Colonometrograms showed intermittent pressure rises that was caused by periodical colonic contractions. In the sceneries of colonic hypersensitivity that was generated post 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colonic inflammation, following chemogenetic activation of primary afferent neurons, or immediately after noxious stimulation of the colon by colorectal distension (CRD), the amplitude of intracolonic pressure (AICP) was markedly elevated which was accompanied by a faster pressure rising (ΔP/Δt). Colonic hypersensitivity-associated AICP elevation was a result of the enhanced strength of colonic stretch-reflex contraction which reflected the heightened activity of the colonic sensory reflex pathways. The increased value of ΔP/Δt in colonic hypersensitivity indicated a lower threshold of colonic mechanical sensation by which colonic stretch-reflex contraction was elicited by a smaller saline infusion volume during a shorter period of infusion time. Chemogenetic inhibition of primary afferent pathway that was governed by Nav1.8-expressing cells attenuated TNBS-induced up-regulations of AICP, ΔP/Δt, and colonic pain behavior in response to CRD. These findings support that colonometrograms can be used for analysis of colonic pain in mice.

Modulatory effects of nitric oxide on synaptic depression in the crayfish neuromuscular system

2000 ◽  
Vol 203 (23) ◽  
pp. 3595-3602 ◽  
Author(s):  
H. Aonuma ◽  
T. Nagayama ◽  
M. Takahata
Keyword(s):  
Nitric Oxide ◽  
Neuromuscular Transmission ◽  
Procambarus Clarkii ◽  
Synaptic Depression ◽  
Physiological Property ◽  
Muscle Fibres ◽  
Flexor Muscle ◽  
Bath Application ◽  
Flexor Muscles ◽  
Stimulation Of

A characteristic physiological property of the neuromuscular junction between giant motor neurones (MoGs) and fast flexor muscles in crayfish is synaptic depression, in which repetitive electrical stimulation of the MoG results in a progressive decrease in excitatory junction potential (EJP) amplitude in flexor muscle fibres. Previous studies have demonstrated that l-arginine (l-Arg) modulates neuromuscular transmission. Since l-Arg is a precursor of nitric oxide (NO), we examined the possibility that NO may be involved in modulating neuromuscular transmission from MoGs to abdominal fast flexor muscles. The effect of a NO-generating compound, NOC7, was similar to that of l-Arg, reversibly decreasing the EJP amplitude mediated by the MoG. While NOC7 reduced the amplitude of the EJP, it induced no significant change in synaptic depression. In contrast, a scavenger of free radical NO, carboxy-PTIO, and an inhibitor of nitric oxide synthase, l-NAME, reversibly increased the EJP amplitude mediated by MoGs. Synaptic depression mediated by repetitive stimulation of MoGs at 1 Hz was partially blocked by bath application of l-NAME. Bath application of a NO scavenger, a NOS inhibitor and NO-generating compounds had no significant effects on the depolarisation of the muscle fibres evoked by local application of l-glutamate. The opposing effects on EJP amplitude of NOC7 and of carboxy-PTIO and l-NAME suggest that endogenous NO presynaptically modulates neuromuscular transmission and that it could play a prominent role at nerve terminals in eliciting MoG-mediated synaptic depression in the crayfish Procambarus clarkii.

Patterns of Locomotor Drive to Motoneurons and Last-Order Interneurons: Clues to the Structure of the CPG

2001 ◽  
Vol 86 (1) ◽  
pp. 447-462 ◽  
Author(s):  
R. E. Burke ◽  
A. M. Degtyarenko ◽  
E. S. Simon
Keyword(s):  
Fictive Locomotion ◽  
Cutaneous Reflex ◽  
Reflex Pathways ◽  
Locomotor Control ◽  
Low Threshold ◽  
Experimental Findings ◽  
Differential Control ◽  
Flexor Digitorum ◽  
First Time ◽  
Shed Light

We have examined the linkage between patterns of activity in several hindlimb motor pools and the modulation of oligosynaptic cutaneous reflex pathways during fictive locomotion in decerebrate unanesthetized cats to assess the notion that such linkages can shed light on the structure of the central pattern generator (CPG) for locomotion. We have concentrated attention on the cutaneous reflex pathways that project to the flexor digitorum longus (FDL) motor pool because of that muscle's unique variable behavior during normal and fictive locomotion in the cat. Differential locomotor control of last-order excitatory interneurons in pathways from low-threshold cutaneous afferents in the superficial peroneal and medial plantar afferents to FDL motoneurons is fully documented for the first time. The qualitative patterns of differential control are shown to remain the same whether the FDL muscle is active in early flexion, as usually found, or during the extension phase of fictive locomotion, which is less common during fictive stepping. The patterns of motor pool activity and of reflex pathway modulation indicate that the flexion phase of fictive locomotion has distinct early versus late components. Observations during “normal” and unusual patterns of fictive stepping suggest that some aspects of locomotor pattern formation can be separated from rhythm generation, implying that these two CPG functions may be embodied, at least in part, in distinct neural organizations. The results are discussed in relation to a provisional circuit diagram that could explain the experimental findings.

Differential synaptic effects on physiological flexor hindlimb motoneurons from cutaneous nerve inputs in spinal cat

1991 ◽  
Vol 66 (2) ◽  
pp. 460-472 ◽  
Author(s):  
J. C. Leahy ◽  
R. G. Durkovic
Keyword(s):  
Stimulus Intensity ◽  
Nerve Stimulation ◽  
Mixed Effects ◽  
Saphenous Nerve ◽  
Short Latency ◽  
Cutaneous Nerve ◽  
Flexor Muscle ◽  
Inhibitory Circuits ◽  
Cutaneous Reflex ◽  
Reflex Pathways

1. We previously demonstrated in the spinal cat that superficial peroneal cutaneous nerve stimulation produced strong reflex contraction in tibialis anterior (TA) and semitendinosus (St) muscles but unexpectedly produced mixed effects in another physiological flexor muscle, extensor digitorum longus (EDL). The goal of the present study was to further characterize the organization of ipsilateral cutaneous reflexes by examining the postsynaptic potentials (PSPs) produced in St, TA, and EDL motoneurons by superficial peroneal and saphenous nerve stimulation in decerebrate, spinal cats. 2. In TA and St motoneurons, low-intensity cutaneous nerve stimulation that activated only large (A alpha) fibers [i.e., approximately 2-3 times threshold (T)], typically produced biphasic PSPs consisting of an initial excitatory phase and subsequent inhibitory phase (EPSP, IPSP). Increasing the stimulus intensity to activate both large (A alpha) and small (A delta) myelinated cutaneous fibers supramaximally (15-45 T) tended to enhance later excitatory components in TA and St motoneurons. 3. In EDL motoneurons, 2-3 T stimulation of the superficial peroneal nerve evoked initial inhibition (of variable magnitude) in 7/10 EDL motoneurons tested, with either excitation (n = 2) or mixed effects (n = 1) observed in the remaining EDL motoneurons. Saphenous nerve stimuli produced excitation either alone, or preceded by an inhibitory phase in EDL. Increasing the stimulus intensity enhanced later inhibitory influences from superficial peroneal and excitatory influences both from superficial peroneal and saphenous nerve inputs in EDL motoneurons. 4. Short-latency (less than 1.8 ms) EPSPs were observed in a few motoneurons in all reflex pathways examined, except for EPSPs in EDL motoneurons evoked by saphenous stimulation. IPSPs with central latencies less than 1.8 ms were also produced by both saphenous (TA, n = 1; EDL, n = 2) and superficial peroneal (EDL, n = 4) nerve stimulation. 5. The results, in comparison with other reports employing spinal and nonspinal preparations, suggest that removal of influences from higher centers reveals inhibitory circuits from the superficial peroneal and saphenous nerves to EDL motoneurons in the spinal preparation. The inhibitory inputs observed are thought to reflect the activation of "specialized" reflex pathways. Additionally, the demonstration of short-latency EPSPs and IPSPs suggest that the minimal linkage in both the excitatory and inhibitory cutaneous reflex pathways examined is disynaptic. The results are discussed in relation to previous studies on classically conditioned flexion reflex facilitation in spinal cat.

Contribution of hind limb flexor muscle afferents to the timing of phase transitions in the cat step cycle

1996 ◽  
Vol 75 (3) ◽  
pp. 1126-1137 ◽  
Author(s):  
G. W. Hiebert ◽  
P. J. Whelan ◽  
A. Prochazka ◽  
K. G. Pearson
Keyword(s):  
Electrical Stimulation ◽  
Stance Phase ◽  
Flexor Muscle ◽  
Step Cycle ◽  
Locomotor Rhythm ◽  
Ia Afferents ◽  
Group I ◽  
Flexor Muscles ◽  
Group Ii ◽  
Stimulation Of

1. In this investigation, we tested the hypothesis that muscle spindle afferents signaling the length of hind-leg flexor muscles are involved in terminating extensor activity and initiating flexion during walking. The hip flexor muscle iliopsoas (IP) and the ankle flexors tibialis anterior (TA) and extensor digitorum longus (EDL) were stretched or vibrated at various phases of the step cycle in spontaneously walking decerebrate cats. Changes in electromyogram amplitude, duration, and timing were then examined. The effects of electrically stimulating group I and II afferents in the nerves to TA and EDL also were examined. 2. Stretch of the individual flexor muscles (IP, TA, or EDL) during the stance phase reduced the duration of extensor activity and promoted the onset of flexor burst activity. The contralateral step cycle also was affected by the stretch, the duration of flexor activity being shortened and extensor activity occurring earlier. Therefore, stretch of the flexor muscles during the stance phase reset the locomotor rhythm to flexion ipsilaterally and extension contralaterally. 3. Results of electrically stimulating the afferents from the TA and EDL muscles suggested that different groups of afferents were responsible for the resetting of the step cycle. Stimulation of the TA nerve reset the locomotor step cycle when the stimulus intensity was in the group II range (2-5 xT). By contrast, stimulation of the EDL nerve generated strong resetting of the step cycle in the range of 1.2-1.4 xT, where primarily the group Ia afferents from the muscle spindles would be activated. 4. Vibration of IP or EDL during stance reduced the duration of the extensor activity by similar amounts to that produced by muscle stretch or by electrical stimulation of EDL at group Ia strengths. This suggests that the group Ia afferents from IP and EDL are capable of resetting the locomotor pattern generator. Vibration of TA did not affect the locomotor rhythm. 5. Stretch of IP or electrical stimulation of TA afferents (5 xT) during the flexion phase did not change the duration of the flexor activity. Stimulation of the EDL nerve at 1.8-5 xT during flexion increased the duration of the flexor activity. In none of our preparations did we observe resetting to extension when the flexor afferents were activated during flexion. 6. We conclude that as the flexor muscles lengthen during the stance phase of gait, their spindle afferents (group Ia afferents for EDL and IP, group II afferents for TA) act to inhibit the spinal center generating extensor activity thus facilitating the initiation of swing.

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