A basic view of the neural mechanisms controlling breathing is provided in Figure 1. The notion of a respiratory central pattern generator, essentially a timer that paces the rhythm, now enjoys wide acceptance but limited experimental proof.2 According to this concept, the output of this generator somehow gates the activity of neuronal networks that shape the inspiratory burst producing ramp-like activity for bulbospinal neurons and a square wave pattern for “upper airway motoneurons.” As shown in Figure 1, an important feature of the proposed central pattern generator is that it functions only when it receives an excitatory input, ie, chemoreceptor input must reach an adequate level before any rhythm is generated. Figure 1 also depicts a nonche-moreceptive influence provided by wakefulness that impinges on the respiratory neural network. As described below, this wakefulness influence can offset the requirement for a chemoreceptive input. In addition, this wakefulness influence can provide a compensatory motor output in patients having primary abnormalities of the pharyngeal airway or of the respiratory pump, as described below. buy asthma inhalers
Figure 1. Schematic diagram depicting the functional relationships of the neural components controlling breathing. A central pattern generator produces a rhythmic output when activated by adequate chemoreceptor input. The output of this pattern generator is processed by interneurons and ultimately reaches upper airway and spinal respiratory motoneurons to cause rhythmic bursts of action potentials that cause contractions of the respiratory muscles. Wakefulness conveys an excitatory influence that compensates for mechanical or neuromuscular abnormalities.