Figure 1

Neurotransmitters of currently unknown identities (labelled '?') are responsible for the influence of sleep/awake neuronal mechanisms on pharyngeal muscle activity via their effects on motor neurone activity and reflex responses. Identifying these neurotransmitters, which may be different between non-REM and REM sleep, and their corresponding receptors will help in understanding the pathogenesis of obstructive apnoeas by explaining the modulation of respiratory and reflex inputs that underlies reduced pharyngeal muscle activity in sleep, thereby precipitating airway obstructions in susceptible individuals.