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

Abstract

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.

Single joint perturbation during gait: neuronal control of movement trajectory

“…The observation of a bilateral pattern of compensatory EMG responses made here for unilateral hip or knee displacements is in line with earlier observations on the co-ordination of stepping in cat (Grillner and Rossignol 1978;Gorassini et al 1994;Hiebert et al 1994Hiebert et al , 1996Schomburg et al 1998) and infants (Yang et al 1998;Pang andYang 2000, 2001). This pattern is based on the organisation of the central pattern generator.…”

Single joint perturbation during gait: Preserved compensatory response pattern in spinal cord injured subjects

“…Afferent information related to hip position has been shown to be critical for regulation of step cycle timing (Pang and Yang, 2000;Pearson and Rossignol, 1991;Hiebert et al, 1996;Andersson et al, 1978;Grillner and Rossignol, 1978). Our results are consistent with these works and indicate that hip joint related afferent input is most influential in the generation of a spinal pattern regardless of the degree of available supraspinal influence (Dietz et al, 2002).…”

“…We hypothesized that the temporal aspects of the response pattern would be similar across groups, on the basis that the spinal cord would be able to generate similar responses to an external stimulus even in individuals in whom supraspinal influence is absent. Further, we hypothesized that early hip perturbations would be associated with a larger responses as the hip is beginning to move from extension to flexion at this time and afferent signals from hip flexors appear to be critical for control of step timing (Pang and Yang, 2000;Pearson and Rossignol, 1991;Hiebert et al, 1996;Andersson et al, 1978;Grillner and Rossignol, 1978). In addition, we hypothesized that EMG responses in the contralateral limb would not be as large as those of the ipsilateral limb as the most direct effects of the perturbation would likely to be observed in the perturbed limb.…”

Stretch reflex coupling between the hip and knee: implications for impaired gait following stroke

“…In the human lower limb, stimulation of group-I and group-II afferents from intrinsic foot muscles has been shown to produce widespread reflex excitation throughout the lower limb (Marque et al 2001a(Marque et al , 2005. Furthermore, activity in hip muscle spindle afferents during gait appears to be critical in the initiation of both the stance to swing transition (Grillner and Rossignol 1978;Hiebert et al 1996) and the swing to stance transition (McVea et al 2005). What remains to be seen is how potential changes in these afferent-mediated, inter-joint connections contribute to leg muscle coordination following stroke.…”