Cholinergic modulation of upper airway control: maturational changes and mechanisms at cellular and synaptic levels.

Respiration is governed by a central rhythm and pattern generator, which has the pre-Bötzinger complex as the inspiratory oscillator initiating the coordinated activity of several respiratory muscles, including the diaphragm, intercostals, and upper airway muscles. The diaphragm is the main inspiratory pump muscle driving inflow, whereas dilator upper airway muscles, such as tongue muscles, reduce airway resistance during inspiration. Breathing exhibits a marked state-dependent pattern attributed to changes in neuromodulatory tone in respiratory-related brain regions, including decreases in noradrenaline and serotonin and increases in acetylcholine levels during rapid eye movement (REM) sleep.