Which reflex is triggered by stretch of the lungs and inhibits respiration?

• A. Frank-Starling reflex
• B. Pneumotaxic reflex
• C. Hering-Breuer reflex
• D. Apneustic reflex

Answer: (C)

When the lungs are stretched, receptors in the airway walls sense that distension and send signals through the vagus nerve to the brainstem. This input dampens the activity of the inspiratory neurons, effectively halting or shortening inspiration and allowing expiration to begin. This protective response, known as the Hering-Breuer inflation reflex, helps prevent overinflation of the lungs during deep or forced breaths. In adults it’s most evident with large tidal breaths; during normal quiet breathing it’s less prominent. The other reflexes regulate breathing timing and depth in different ways: the pneumotaxic influences the transition between inspiration and expiration, the apneustic promotes sustained inspiration, and the Frank-Starling mechanism relates to heart muscle stretch and stroke volume rather than airway stretch.