Reversal of fusimotor reflex responses during locomotion in the decerebrate cat

Abstract

SUMMARYThe effect of brief trains of electrical stimulation, at 2, 3 and 20 x threshold (T), of cutaneous afferents in the medial plantar nerve on the discharges of single medial gastrocnemius static and dynamic y-efferents has been investigated at rest and during locomotion in a decerebrate cat preparation. The units were classified as dynamic (10 units) or static (10 units) indirectly on the basis of their resting and locomotor discharge characteristics. Responses were assessed by calculating the change in mean y-rate during the 100 ms after stimulus onset compared with a control period. At rest, most dynamic neurones were inhibited by stimulation at 2T (9 of 10 units) and above. In contrast, the resting responses of most static neurones were excitatory at 2T (9 of 10 units) and 3T, while 20T produced static y-effects that varied in sign. During locomotion the responses of both types of y-efferent were phase related. Two patterns were observed with dynamic units. For seven dynamic neurones, at stimulus levels of 2T (7 units) and above, responses during electromyogram (EMG) bursts were inhibitory while those between bursts were not significantly different from zero. However, for three other dynamic units, a phase-related reversal of reflex responses was observed at some stimulus intensities (always 2T, 3 units) comprising inhibition during, and excitation between, EMG bursts. For static neurones, inhibitory (never excitatory) responses occurred during walking at stimulus intensities of 2T (10 units) and above. The locomotor responses of static units were maximum during (3 units) or between (7 units) EMG bursts and were minimum in the opposite phase of EMG activity. A task-related reversal of reflex responses was thus generally apparent (9 of 10 units) to low intensity stimulation (2T) for static y-efferents during locomotion (inhibition) compared with rest (excitation). During locomotion there was a significant linear relation between the magnitude of response and the background y-rate for static units and those dynamic units that did not exhibit phase-related reflex

The effects of experimental muscle and skin pain on the static stretch sensitivity of human muscle spindles in relaxed leg muscles

“…It also means that the input–output relationship seen in one condition may even reverse if the context or state of the system is altered. Fusimotor reflex reversal has been demonstrated during walking in the cat (Murphy & Hammond, 1997) and this principle of motor control is well known (Lacquaniti et al 1991; De Serres et al 1995). This notion would also fit with the suggestion that muscle spindles represent the final step in an integrative network which joins information from muscle, skin and joint receptors (Johansson, 1985).…”

The Effect of Muscle Facilitation Using Kinesio Taping on Walking and Balance of Stroke Patients

“…The initial mechanism with regard to the enhancement of muscle strength and muscle control is that cutaneous fusimotor reflex increases fiber tension, resulting in excitation of primary and secondary nerve endings, thus, helping afferent sensory nerve activity 23 , 24 ) . The mechanism of taping is improvement of muscle strength by excitation of gamma motor nerves in skeletal muscle, as the taped part raises the tension of the fiber 25 , 26 ) . In addition, spatial summation makes neurotransmitter isolated and postsynaptic potential is generated without action potential of pre-synaptic nerve.…”

System identification of muscle–joint interactions of the cat hind limb during locomotion

“…However, the activity (EMG) of those muscles is more pronounced during the unstretched phase. Therefore, dynamic and phase-dependent control of the CPG on muscle spindle sensitivity through alpha-gamma co-activation is very important for stabilization of the gait (Murphy and Hammond 1997;Taylor et al 2000;Windhorst 2007). In addition, alpha-gamma co-activation varies with the task as well (Prochazka 1989;Rossignol et al 2006).…”

“…Duenas et al (1990) showed clear evidence for a phase dependency of the monosynaptic reflex during locomotion in the cat. The action of some of the reflex mechanisms, for instance fusimotor drive for the ankle extensor of the cat hindlimb (Murphy and Hammond 1997), could get reversed depending on the phase of the walking leg. Therefore, the system level analysis of the muscle-joint interactions at several positions throughout the step cycle will give more insight into the understanding of the controllability and the stability of the locomotion.…”