Differences in monosynaptic EPSPs elicited by masseter and temporalis spindle afferents in anaesthetised rats.

We have used the intracellular variant of the spike triggered averaging method to examine the monosynaptic connexions of masseter and temporalis spindle afferents on jaw-elevator motoneurones. Temporalis spindle afferents elicited larger averaged EPSPs in motoneurones than masseter spindle afferents, in part because transmission at synapses of temporalis afferents was associated with lower incidences of failures. We conclude that EPSP amplitude in this motor system in governed, at least in part, by the presynaptic neurone rather than the identity of the postsynaptic neurone.