The generation of post-inspiratory activity in laryngeal motoneurons: a review

Breathing is a vegetative function that is altered during more complex behaviours such as exercise, vocalisation and respiratory protective reflexes. Recent years have seen recognition of the importance of respiratory pattern generation in addition to rhythm generation. Respiratory-modulated cranial motoneurons (laryngeal, pharyngeal, hypoglossal, facial) offer a unique insight into the control of respiration since: (1) they receive rhythmic respiratory inputs but; (2) their respiratory-modulated firing pattern differs to that of phrenic neurons to suit their function, (for example, hypoglossal motoneurons begin firing and thus the tongue depresses before the onset of phrenic nerve discharge and diaphragmatic during inspiration) and; (3) their activity is often altered in parallel with changes in respiration during stereotypical non-respiratory behaviours such as coughing, swallowing and sneeze. Here we review some mechanisms that modulate the respiratory-related activity of laryngeal motoneurons with an emphasis on the generation of post-inspiratory activity.