TRANSMITTER POTENTIALITY OF HOMONYMOUS AND HETERONYMOUS MONOSYNAPTIC REFLEX CONNECTIONS OF INDIVIDUAL MOTONEURONS

An assemblage of 110 individual tricipital motoneurons has been examined with the aim of determining those factors that predispose certain motoneurons to heteronymous response in post-tetanic potentiation. Motoneurons that respond most readily to homonymous volleys are not those that respond most readily to post-tetanically potentiated heteronymous volleys. Hence differences in presynaptic organization rather than differences in mean postsynaptic threshold determine differences in readiness for response. Every motoneuron exhibits a distinct asymmetry in transmitter potentiality of homonymous and heteronymous monosynaptic reflex connections. The range of transmitter potentialities is wide and that of heteronymous connections to some motoneurons is greater than that of homonymous connections to some other motoneurons.