The afferent nerves regulating
cough have been reasonably well defined. The selective effects of
general anesthesia on C-fiber-dependent
cough and the opposing effects of C-fiber subtypes in
cough have led to some uncertainty about their regulation of this defensive reflex. But a role for C-fibers in
cough seems almost certain, given the unique pharmacological properties of these unmyelinated vagal afferent nerves and the ability of many C-fiber-selective stimulants to evoke
cough. The role of myelinated laryngeal, tracheal, and bronchial afferent nerve subtypes that can be activated by punctate mechanical stimuli, inhaled particulates, accumulated secretions, and
acid has also been demonstrated. These "
cough receptors" are distinct from the slowly and rapidly adapting intrapulmonary stretch receptors responding to lung inflation. Indeed, intrapulmonary rapidly and slowly adapting receptors and pulmonary C-fibers may play no role or a nonessential role in
cough, or might even actively inhibit
cough upon activation. A critical review of the studies of the afferent nerve subtypes most often implicated in
cough is provided.