The cough reflex protects the airway. AFFERENT limb: irritants, mucus, or inflammation activate vagal sensory afferents — C-fibers (via TRPV1/TRPA1) and rapidly-adapting receptors — which relay through the nucleus tractus solitarius to a medullary cough-generating network. EFFERENT limb: the cough center drives a coordinated deep inspiration, glottic closure, and forced expiration. Central antitussives suppress the brainstem cough network: dextromethorphan (sigma-1 / NMDA modulator, non-opioid) and codeine (μ-opioid agonist; also a morphine prodrug). Peripheral protussives/mucolytics act on the airway side instead. Cross-link: mu_opioid.
Organ Systems
respiratory
nervous
Pathway Steps
airway-irritant → sensory-afferent-activation — via irritant/mechanical → TRPV1 / TRPA1 on vagal C-fibers + rapidly-adapting receptors. Irritants, mucus, or airway inflammation activate vagal sensory afferents — the trigger limb of the cough reflex.
sensory-afferent → medullary-cough-center — via vagus → nucleus tractus solitarius → brainstem cough-generating network. Afferents relay through the NTS to a medullary network that organizes the motor cough.
cough-center → cough-motor-output — via efferent → inspiration + glottic closure + forced expiration. The cough center coordinates the cough. Central antitussives dampen this network: dextromethorphan (sigma-1/NMDA, non-opioid) and codeine (μ-opioid). Cross-link: mu_opioid.
Known Modulators
dextromethorphan (inhibitor) — central cough center (sigma-1 / NMDA) → ↓cough, non-opioid antitussive
codeine (inhibitor) — central cough center via μ-opioid agonism → ↓cough