The cough center generates an efferent signal that travels down the vagus, phrenic, and spinal motor nerves to expiratory musculature to produce the cough. Impulses from stimulated cough receptors traverse an afferent pathway via the vagus nerve to a ‘cough center’ in the medulla, which itself may be under some control by higher cortical centers. These are probably mechanical receptors only, which can be stimulated by triggers such as touch or displacement. In addition, more airway receptors are in the external auditory canals, eardrums, paranasal sinuses, pharynx, diaphragm, pleura, pericardium, and stomach. Chemical receptors sensitive to acid, heat, and capsaicin-like compounds trigger the cough reflex via activation of the type 1 vanilloid (capsaicin) receptor. Laryngeal and tracheobronchial receptors respond to both mechanical and chemical stimuli. This is initiated by the irritation of cough receptors which are found in the trachea, main carina, branching points of large airways, and more distal smaller airways also, they are present in the pharynx. These contrasting consequences of coughing can be attributed to the parallel afferent pathways regulating this important defensive reflex of the airways.Įach cough occurs through the stimulation of a complex reflex arc. Under normal conditions cough serves an important protective role in the airways and lungs, but in some conditions it may become excessive and nonproductive, and is troublesome and potentially harmful to the airway mucosa. Coughing is an important defensive reflex that enhances clearance of secretions and particulates from the airways and protects from aspiration of foreign materials occurring as a consequence of aspiration or inhalation of particulate matter, pathogens, accumulated secretions, postnasal drip, inflammation, and mediators associated with inflammation. Cough is one of the most common symptoms for which outpatient care is asked, accounting for up to 40% of the practice activity.
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