Summary
In decerebrate cats a train of impulses in Ia afferents may lead to a sustained increase in excitability of α-motoneurones of homonymous and heteronymous muscles. It was previously suggested that this long-lasting excitability increase reflects a maintained synaptic input to the motoneurones from excitatory interneurones. With intracellular recording from motoneurones we here demonstrate that the sustained increase of α-motoneurone activity is due to an all-or-none plateau depolarization. This plateau can be induced by a short train of excitatory synaptic potentials or a brief, intracellularly injected depolarizing current pulse and is terminated by a short train of inhibitory synaptic potentials or a hyperpolarizing current pulse. It is concluded that maintained motor unit firing triggered by a brief train of impulses in Ia afferent reflects an intrinsic bistable behaviour of α-motoneurones.
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Hounsgaard, J., Hultborn, H., Jespersen, B. et al. Intrinsic membrane properties causing a bistable behaviour of α-motoneurones. Exp Brain Res 55, 391–394 (1984). https://doi.org/10.1007/BF00237290
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DOI: https://doi.org/10.1007/BF00237290