Neural Control of Airway Smooth Muscle

Airway smooth muscle (ASM) is the primary effector cell responsible for controlling airway caliber and thus the resistance to airflow of the entire tracheobronchial tree. ASM tone is regulated by the autonomic nervous system involving parasympathetic, sympathetic, and nonadrenergic, noncholinergic mechanisms. Bronchoconstriction is an important component of airway defense reflexes elicited by activation of airway sensory nerves that are sensitive to inhaled irritants and endogenous inflammatory mediators. Hypersensitivity of these sensory nerves and/or dysregulation of the autonomic nervous system play an essential role in the pathogenesis of bronchospasm, a common symptom of airway inflammatory and infectious diseases.