Reciprocal Ia inhibition between ankle flexors and extensors in man.

Abstract

SUMMARY1. Reciprocal inhibition between antagonist muscle groups at the ankle has been investigated in sixty healthy subjects. Hoffmann reflexes (H reflexes) in the soleus and tibialis anterior muscles were used to assess changes in reciprocal inhibition evoked by electrical stimulation of antagonist muscle nerves.2. Inhibition of the soleus H reflex was evoked by a single conditioning stimulus to the common peroneal nerve, and inhibition of the tibialis anterior H reflex was elicited by one conditioning stimulus to the posterior tibial nerve. Symmetrical central connections between the antagonist flexors and extensors were assumed and under this assumption the central delay for the inhibition, in addition to the delay for monosynaptic I a excitation, was calculated to be about 1 ms. The inhibition was evoked by weak stimuli to the nerves from antagonist muscle groups; the threshold for the inhibition was around 0-6 x threshold for a direct motor response (Mthreshold). Furthermore, tendon taps to the Achilles tendon facilitated the soleus H reflex and inhibited the tibialis anterior reflex at short latencies. The short central delay, the low electrical threshold and the. actions of Achilles tendon taps strongly suggest that the early reciprocal inhibition is homologous to the disynaptic Ia inhibition previously studied in animal experiments.3. With the test soleus H reflex kept at 15-25 % of the maximum directly evoked motor response (M-response) and the strength of the conditioning peroneal nerve stimulation kept at 1-0 x M-threshold, the inhibition from the peroneal nerve ranged between 0 and 40 % (mean, 14-9 %) at rest.4. Changes in the amount of reciprocal inhibition from the peroneal nerve were studied both during tonic and dynamic dorsi-and plantarflexion. During tonic dorsiflexion there was no significant change of inhibition as compared to rest, while inhibition decreased during tonic plantarflexion. However, during ramp-and-hold dorsiflexion there was a transient increase in reciprocal inhibition of the soleus H reflex. This increase in inhibition from the peroneal nerve could be seen 50 ms prior to the onset of contraction. The increase in inhibition before and at the very beginning of the contraction cannot be due to sensory feed-back during contraction, but must depend on a supraspinal control of the spinal cord.5. At conditioning-test intervals of 4-6 ms, the inhibition of the soleus H reflex from the peroneal nerve was considerably larger during tonic dorsiflexion than at rest.6-2 C. CRONE AND OTHERS Thus, tonic dorsiflexion revealed an inhibition with long latency from the peroneal nerve, which was not seen at rest. This long-latency inhibition was probably of group I origin since the threshold for the inhibition was very low (0-6 x M-threshold).6. The results are discussed in relation to the hypothesis that a-motoneurones and 'Ia inhibitory interneurones' projecting to antagonist motoneurones are controlled in parallel from the brain.

Avaliação da inibição recíproca em humanos durante contrações isométricas dos músculos tibial anterior e sóleo

“…A diminuição da IR na flexão plantar pode estar associada a quatro mecanismos: (1) aumento da inibição mútua entre os interneurônios inibitórios Ia (INIa); (2) redução da inibição recorrente por atividade das células de Renshaw acopladas aos motoneurônios do mús-culo sóleo; (3) aumento da inibição pré-sináptica sobre as terminações das fibras aferentes Ia do M. tibial anterior sobre os INIa 4, 12,13 ; e (4) aumento da excitabilidade dos motoneurônios do sóleo. Esses fatores não se excluem e contribuem para a melhor ativação dos motoneurônios do sóleo.…”

“…A tendência de aumento da IR com a DF, por sua vez, pode estar relacionada ao aumento da excitabilidade dos INIa responsáveis pela IR, por maior ativação central, ou ainda por redução da inibição mútua entre os INIa. A falta de significância desses resultados pode estar relacionada à oclusão da via da IR na medula, entre os sinais descendentes e as aferências 12,14 .…”

The Phase Difference Between Neural Drives to Antagonist Muscles in Essential Tremor Is Associated with the Relative Strength of Supraspinal and Afferent Input

“…Ia afferent feedback was based on these mechanics. Motoneurons received supraspinal input, while afferent feedback was mediated by monosynaptic excitation (Jack et al, 1971;Finkel and Redman, 1983;Schieppati, 1987) and reciprocal disynaptic inhibition from Ia fibers (Jankowska and Roberts, 1972;Crone et al, 1987;Katz et al, 1991).…”

Differences in corticospinal excitability to the biceps brachii between arm cycling and tonic contraction are not evident at the immediate onset of movement

“…Activation of group Ia afferents takes place during arm cycling, which involves the rapid stretching and shortening of the biceps and triceps brachii as the motor output alternates between elbow flexion and extension. While their influence during cycling is mitigated by reciprocal inhibition, they still provide afferent feedback throughout the movement (Tanaka 1974;Crone et al 1987;Nielsen et al 1992). However, both the amplitude and the rate of stretch that would have occurred when measurements were taken during the condition 1 for arm cycling would have been diminished in comparison to steady-state arm cycling.…”