A model for refractoriness accumulation and secondary range firing in spinal motoneurones

A model is presented in which the potassium conductance (G_K) changes responsible for the afterhyperpolarization (AHP) in motoneurones are postulated to follow a kinetics coherent with Hodgkin-Huxley membrane model. Such G_Kkinetics, which operates as a bistable system switched from one state to the other by the action potential, can be expressed by simple analytical expressions if the spike is approximated to a rectangular pulse. Accumulation of G_Kby repetitive activation of the model accurately describes the different features of AHP summation in motoneurones; moreover, this accumulation process enables a model for repetitive firing of motoneurones to display secondary range firing at steady state.