A study has been made of conditions that support monosynaptic reflex transmission from afferent fibers of one part of a synergic muscle mass to motoneurons of another part. Heteronymous response so called can be brought on by prior tetanization of the afferent pathway and by asphyxiation to a critical stage. The response is facilitated by cooling and may appear in the cold preparation without need for prior tetanization.
By appropriate asymmetrical subdivision of a monosynaptic reflex system an afferent inflow can be obtained that is sufficiently powerful to secure heteronymous transmission without the need for prior tetanization or cooling. Each junction between a monosynaptic afferent fiber and a motoneuron possesses some degree of potentiality for transmitting. Transmitter potentiality of an afferent fiber at its several junctions with motoneurons varies widely. Reasons are advanced for supposing the variation to be graded rather than stepwise, and quantitative rather than qualitative.