ABSTRACT
The respiratory system of birds consists of the non-expandable lungs and a series of air sacs providing a unidirectional system of air flow. Airway receptors are classified on the basis of their sensitivities to a variety of stimuli and their axonal conduction velocity. Neuroepithelial cells rich in secretory granules have been described in the airways of all vertebrates studied, including birds, and can be seen as individual cells or as aggregations forming neuroepithelial bodies. In mammals injections of cholera toxin B-chain into the airway lumen result in the labelling of neurons near and within nucleus ambiguus and the authors suggested that some of these vagal motoneurons may provide direct innervation of epithelial or vascular effector organs in the airway mucosa. The similarities in the airway receptors and the central nervous system structures with which they are connected speak of the conservative nature of the respiratory system.
