[Effects of partial unfused contractions of the gastrocnemius medialis muscle on homonymous and synergist motor neurons in cats].

Autogenetic inhibition of homonymous and synergist motoneurones can be elicited by very weak partial twitches of gastrocnemius medialis muscle, but during sustained contractions the amplitude of inhibitory post-synaptic potentials decreases quickly. A similar decrease also occurs during stronger contractions. The mechanism responsible for this decrease is still active in low spinal preparations. Pre-synaptic inhibition of Ib afferent fibres might contribute to this reduction of efficiency in the transmission of Ib afferent inputs to motoneurones.