Modulation of stretch reflexes during locomotion in the mesencephalic cat

Abstract

SUMMARY1. A cat preparation was used to study the modulation of stretch reflexes during locomotion. The brain stem was transacted and locomotion was induced by electrical stimulation of the mesencephalic locomotor region below the level of transaction. Three legs walked normally on a treadmill, while the fourth leg, which was denervated except for the soleus muscle, was held fixed. Brief length perturbations were applied to the soleus muscle at various phases of the stepping cycle.2. The stretch reflex in this muscle was deeply modulated during the step cycle, and reached its peak at or before the peak in soleus e.m.g. activity associated with the locomotion. A similar variation was observed when the sciatic nerve was stimulated electrically at a strength which elicited reflex activity (H wave), but did not directly elicit motor nerve activity (M wave). Variation in the reflex during electrical stimulation could not be accounted for by cyclic variation in fusimotor activity or in the afferent volley, but must be due to post-synaptic changes in a-motoneurones or in the presynaptic inputs to them.3. Large changes were also observed in intrinsic muscle stiffness during the step cycle. The maximum stiffness occurred near the time the limb would normally strike the ground during locomotion. A high stiffness would be useful in reducing the amount that the limb would yield under the weight of the body during the extension phase of the step cycle. The variation of the stretch reflex in parallel with stiffness suggests that reflexes could assist in this load compensation. The variation is not consistent with the idea that the stretch reflex is used to compensate for changes in intrinsic muscle properties, so that the total system behaves more like a spring of constant stiffness than does muscle alone.

Spinal Cats on the Treadmill: Changes in Load Pathways

“…In this study with chronic spinal cats, fictive stepping did not induce a significant decrease in monosynaptic EPSP amplitude compared with rest in both sham (by 31.2%) and trained (by 29.2%) cats. During walking, transmission in the monosynaptic reflex pathway is phasically modulated in the cat (Forssberg and Grillner, 1973;Akazawa et al, 1982;Gossard, 1996;Ménard et al, 1999) and in humans (Capaday and Stein, 1986;Simonsen and Dyhre-Poulsen, 1999), being maximal during stance in extensors when motoneuronal pools are depolarized. Figure 6 illustrates that the phases for maximal amplitude of monosynaptic EPSPs are opposite in a sham and a trained cat.…”

Biologically inspired adaptive walking of a quadruped robot

“…The muscle stiffness is high in a stance phase for supporting a body against the gravity and low in a swing phase for compliance against the disturbance (Akazawa et al 1982). All the joints of Tekken are proportional and derivative (PD) controlled to move to their desired angles in each of the three states (A, B, C) in figure 4 in order to generate each motion, such as swinging up (A), swinging forward (B) and pulling down/back of a supporting leg (C).…”

Regulation of soleus muscle spindle sensitivity in decerebrate and spinal cats during postural and locomotor activities.

“…Stretch reflex responses are highly modulated during locomotor activities in decerebrate cats (Akazawa, Aldridge, Steeves & Stein, 1982). The averaged stretch reflex in spinal cats is markedly lower during locomotion, compared with the resting state just prior to locomotion (Bennett, De Serres & Stein, 1995).…”