PHRENIC MOTO-NEURONS IN THE CAT - SUB-POPULATIONS AND NATURE OF RESPIRATORY DRIVE POTENTIALS

During hyperolarizing current injection the inspiratory phase membrane potential trajectory of all PM became a ramp depolarization similar to that seen during control conditions in type A cells. These results support the conclusion that all cells within the PM pool are receiving a similar central excitatory synaptic input during inspiration. The rapid initial depolarization of type B and their concomitant early spike onset is a consequence in part of a rebound excitation from their expiratory phase inhibition as well as a higher input resistance, probably due to a smaller cell size. Expiratory related neural activity was recorded within the phrenic motor nucleus. It is suggested that these expiratory related neural elements, based on the temporal pattern of their activity, may be responsible for the active inhibition of PM.