Positive feedback to a muscle receptor stabilized by concurrent self-inhibition.

The two non-spiking afferent neurones (T and S fibres) of the crab's thoracic-coxal muscle receptor organ mediate antagonistic reflex controls upon the specific receptor motoneurone (Rm1). Depolarization of the 'in-series' T fibre, by receptor muscle stretch or intracellular current injection, reflexly excites Rm1, whereas length- or current-induced S fibre depolarization inhibits Rm1. The latter, autogenetic negative feedback stabilizes the concurrent positive feedback over the physiological range of receptor muscle lengths.