The distal hindlimb musculature of the cat

Abstract

In order to better understand the organization of the locomotor control system, we examined the temporal patterns of distal hindlimb muscle responses to brief electrical stimulation of cutaneous nerves during walking on a treadmill. Electromyographic recordings were made from twelve muscles; stimuli were applied individually to three nerves at random times throughout the step cycle. A new graphical technique was developed to assist detailed examination of the time course and gating of complex reflex patterns. The short latency reflexes were of two primary types: inhibition of extensors and excitation of flexors; these responses were only evident during locomotor phases in which the respective motoneuron pools were active. Longer-latency response components were gated in a similar but not identical manner, suggesting some independence from the basic locomotory influence on the motoneuronal pool. The phase-dependent gating of reflexes appeared to be consistent with a functional role for reflex responses during locomotion. The reflex responses of muscles with complex anatomical actions were often correspondingly complex.

Coordination of medial gastrocnemius and soleus forces during cat locomotion

“…Our results also do not exclude the possibility that a net speed-dependent inhibition might exist for movements performed at greater speeds than galloping, for example, during a paw shake or a scratch response; i.e. movements that are performed at frequencies of 5-10·Hz (Smith et al, 1980;Abraham and Loeb, 1985;Fowler et al, 1988; M. Kaya, T. Leonard and W. Herzog, unpublished observations). It has been suggested that SOL activity is strongly inhibited by increasing MG force in decerebrate cats (Nichols, 1994).…”

“…Therefore, a substantial increase in SOL force above that obtained for slow walking is only possible if activation goes towards maximum, or if the muscle is stretched at full activation. Although the size principle of motor unit recruitment is not applicable across muscles, but only within a given muscle (see paw-shake response in cat SOL and MG; Smith et al, 1980;Abraham and Loeb, 1985), it is feasible to assume that the 95-100% slow SOL is recruited to a much greater extent for standing and slow walking than the 70-80% fast MG. Consequently, there is less room for SOL force and activity modulation from the slow walking baseline, compared to MG force and activity modulation.…”

“…This is understandable as these measurements are extremely difficult and time consuming to do, so publication of results based on single (Gregor et al, 2001) or a very few animals (Walmsley et al, 1978;Hodgson, 1983;Whiting et al, 1984;Abraham and Loeb, 1985;Gregor et al, 1988;Pierotti et al, 1989;Fowler et al, 1993;Herzog et al, 1993) has been the norm in this area of research. Thus, the mechanisms of control of SOL activity are not well understood, and systematic, quantitative analysis of SOL EMG data are not available at present, but are essential to discuss changes in SOL activation associated with movement demands.…”

The Mechanical Action of Proprioceptive Length Feedback in a Model of the Cat Hindlimb

“…There are many activation patterns that would match the intended endpoint force pattern. Our choice of activations emphasized the deeper antigravity muscles -soleus and VI -while keeping the average activation level low (Sherrington, 1910;Abraham & Loeb, 1985;Roy et al, 1991). Changes in initial activation on the order of 10-15% had little effect on the qualitative results.…”

“…The initial activation pattern (table 1) was chosen to mimic the pattern of stance activation, i.e. predominantly the deep, "slow" anti-gravity muscles, (Roy et al, 1991;Abraham & Loeb, 1985) and to result in a stance-like force at the toe (Macpherson, 1994). The choice of initial activations is clearly critical to the results presented here, and little direct data are available.…”