Abstract

The characteristics of post-synaptic potentials in a single human motoneurone can be derived from the profiles of post-stimulus time histograms (PSTH) of that neurone when it is firing rhythmically. We have used this method to explore the synaptic connections to individual tibialis anterior motoneurones in man. Agonist group 1 volleys produced short latency excitation of 85% of tibialis anterior motoneurones probably representing the 1a EPSP. Excitation, at a latency of 70 ms, is attributed to a long loop reflex. Antagonist group 1 volleys produced short latency inhibition of 65% of tibialis anterior motoneurones probably representing the 1a IPSP. Excitation, at a latency of 97 ms, may represent spino-bulbo-spinal reflex. None of these effects are due to the excitation of cutaneous afferent nerve fibres.