Neurophysiology of the cough reflex.

Cough is due to activation of sensory receptors in the larynx and lower respiratory tract, sending impulses to the brainstem. The central organization of cough is poorly understood. The afferent pathways for cough are from receptors in and under the epithelium of the airways. These receptors are rapidly adapting, with thin myelinated fibres in the vagus nerves, which can be directly stimulated by tussive agents. Activation of C-fibre receptors in the airway releases sensory neuropeptides. These cause neurogenic inflammation and may activate rapidly adapting receptors to cause cough. The central connections of the C-fibre receptors inhibit cough. Thus, the sensitivity of the cough reflex and its pattern of response is due to a complex interaction between C-fibre receptors and rapidly adapting receptors, with peripheral and central nervous interactions. How these mechanisms apply to clinical cough in patients is at present poorly understood, but is beginning to be clarified.