Chapter 41 - Autonomic Control of the Lower Airways

Abstract

This chapter focuses on autonomic control of the lower airways and airway innervation. There is a close interrelationship between inflammation and neural responses in the airways, since inflammatory mediators may influence the release of neurotransmitters via activation of sensory nerves leading to reflex effects and via stimulation of prejunctional receptors that influence the release of neurotransmitters. Cough is an important defense reflex that may be triggered from either laryngeal or lower airway afferents. Sympathetic innervation of human airways is sparse and there is no functional evidence for direct innervation of airway smooth muscle, although sympathetic nerves regulate bronchial blood flow and to a lesser extent mucus secretion. The bronchodilator nerves in human airways are nonadrenergic noncholinergic (NANC) and the major neurotransmitter is nitric oxide (NO). Neuronal NO synthase is expressed mainly in cholinergic neurons. Multiple neuropeptides have been localized to nerves in the respiratory tract and function as cotransmitters of classical autonomic nerves to fine-tune airway function.