Properties of single fibre excitatory post‐synaptic potentials in triceps surae motoneurones.

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Abstract
EPSP [excitatory post synaptic potentials] and terminal potentials (TP) produced by the action of single medial gastrocnemius Ia afferent fibers were examined with intracellular microelectrodes in cat triceps surae motoneurons. Simple terminal potentials (TP) appeared as positive-negative diphasic waves with a single positive peak. Shape indices of (EPSP) recorded in conjunction with simple TP indicate that these EPSPs were generated at an electrotonically confined compartment on the motoneuron somadendritic membrane. Compound TP were similar to single ones, except that they had 2 or more positive peaks. Shape indices of EPSP recorded in conjunction with compound TP indicate that these EPSP were generated at 2 or more electrotonically separate compartments. EPSP latency and post-synaptic electrotonic delay were determined for a group of single fiber EPSPs with simple TP. The shortest record latency was 0.26 ms. By subtracting estimated electrotonic delay, the shortest synaptic delay obtained for a medial gastrocnemius Ia single fiber EPSP was 0.17 ms. The finding of a significant synaptic delay supports the hypothesis that the Ia-motoneuron synapse is a chemically mediated synapse.