Control of human inspiratory motoneurones during voluntary and involuntary contractions

In this review, we consider the discharge of human respiratory motoneurones during involuntary and voluntary contractions and what this reveals about the neural control of respiratory muscles. Motoneurone discharge is the final output of neural drive and can be recorded in humans during a range of experimental protocols. However, human studies have limitations and recordings can only be made indirectly from motoneurones. Animal data allows us to hypothesise how neural drive to these motoneurones is organised in humans. We propose that premotoneuronal networks, perhaps in the spinal cord (i.e. ‘spinal distribution networks’), sculpt descending drive from multiple sources. This would determine the differential pattern of activation across inspiratory muscles, preserve the neural and mechanical coupling when voluntary breaths are taken and allow for different patterns of activation in non-respiratory contractions.