Dextromethorphan suppresses the cough reflex by acting on which part of the body?

Dextromethorphan is an antitussive medication commonly used to relieve coughing. Its primary action is to suppress the cough reflex by targeting the cough center in the brain, specifically in the medulla oblongata. This area is responsible for controlling the cough reflex and by acting on it, dextromethorphan reduces the urge to cough, providing symptomatic relief for conditions that involve persistent coughing.

The other options do not accurately reflect the mechanism of action of dextromethorphan. While the lungs and bronchial tubes play a role in the respiratory system, dextromethorphan does not directly act on these structures to suppress coughing. Similarly, smooth muscles are involved in various physiological processes including breathing and airway resistance, but they are not the target of dextromethorphan for cough suppression. Thus, the correct focus of the drug's action is indeed the cough center of the brain.