Phrenic motoneuron membrane potential trajectories in decerebrate rats exhibit three stages; depolarisation during inspiration, a decreased depolarisation during early expiration and hyperpolarization during late expiration. These trajectories are a result of excitation by ventral-group medullary inspiratory neurons and upper-cervical inspiratory neurons during inspiration and the early part of expiration, and inhibition from Bötzinger-complex expiratory neurons during the late part of expiration.