Functional relationships between myotatic reflex arcs of the lower limb in man: investigation by excitability curves.

Abstract

SYNOPSISIn 30 normal subjects, the influence of the reflex activation of one myotatic reflex arc on the excitability of other myotatic reflex arcs of the lower limb has been investigated using excitability curves. Soleus, quadriceps, and short biceps tendon reflexes as well as H reflex at two different intensities (liminal and H max/2) were used either as conditioning or as conditioned responses. The reflex activation of the soleus muscle has opposite effects on antagonistic muscle groups of the thigh: facilitation of the quadriceps myotatic arc and inhibition of the short biceps myotatic reflex arc. Conversely, activation of both quadriceps and short biceps muscles leads to a marked and long lasting (±5000 ms) inhibition of the soleus myotatic reflex arc. The differences of functional organization between proximal and distal myotatic reflex arcs are emphasized and the role of the afferent impulses secondary to the conditioning muscular contraction is discussed.In normal man, muscular contractions of the lower limb are well coordinated in activities such as walking.Within the central nervous system, this coordination is achieved by several neuronal networks. The cerebellum plays a determining role in this function but even at the spinal level reciprocal influences between motor nuclei are operating (Lloyd, 1944).The proprioceptive and exteroceptive peripheral afferent nerves influence this coordination at different levels in the nervous system.In this study, we have investigated the influence of the reflex activation of one myotatic reflex arc of the lower limb on the excitability of other myotatic arcs. We used the method of excitability curves described by Magladery et al. (1951) and Paillard (1955). These curves, performed with experimental conditions excluding any voluntary contraction, indicate how proprioceptive afferent fibres can modify

Periodic modulation of repetitively elicited monosynaptic reflexes of the human lumbosacral spinal cord

“…Coupling effects are also put forward by the observation that not all possible phase relations of reflex modulation between muscle groups occurred with the same odds. Influences affecting different motoneuron pools may arise from interconnections of myotatic reflex arcs (Cheng et al 1995;Delwaide et al 1976;Meunier et al 1990) as well as crossed spinal connections (Koceja and Kamen 1992;Mezzarane and Kohn 2002). For instance, recurrent inhibition of Ia inhibitory interneurons would periodically release antagonistic motoneurons from their tonic inhibitory activity, a phenomenon known as recurrent facilitation (Hultborn et al 1971b;Pierrot-Desseilligny and Burke 2012).…”

“…Conditioning inputs through stimulation of other peripheral nerves activate spinal circuits that are otherwise not engaged and lead to different patterns of H-reflex modulation (Mao et al 1984;Meunier et al 1993;PierrotDeseilligny and Burke 2012). Such conditioning test paradigms have described various time-dependent facilitatory or inhibitory processes, based on the widespread spinal interconnections between the reflex circuits of different motoneuron pools (Delwaide et al 1976).…”

Recovery cycles of posterior root-muscle reflexes evoked by transcutaneous spinal cord stimulation and of the H reflex in individuals with intact and injured spinal cord

“…We further hypothesized that the recovery cycles of the H reflex and the PRM reflex would differ significantly with respect to within-subject group comparisons. We assumed that these differences would result from the multi-root input associated with transcutaneous SCS, the heteronymous connections in the human spinal cord [48,53,54] and their repeated activation [55,56]. The depression of the PRM reflex would thus depend on a wider range of spinal inhibitory mechanisms, which are altered after SCI.…”

Excitability relationships between lower limb myotatic arcs in spasticity.

“…Without excluding a more detailed analysis of the different phases of the curves (Paillard, 1955;Delwaide et al, 1976), three periods may be considered, on the basis of latency. The first period, with a duration of approximately 80 ms, essentially reflects purely spinal mechanisms, since the latencies for the appearance of known suprasegmental mechanisms are longer (functional stretch reflex (Melvill-Jones and Watt, 1971), transcortical reflex (Marsden et al, 1976;Nashner, 1976), spino-bulbo-spinal reflex (Shimamura et al, 1964).…”