Final answer:
The Hering Breuer Reflex is a protective mechanism that prevents over-inflation of the lungs and is mediated by the vagus nerve, which triggers expiration when the lung stretch receptors are activated.
Step-by-step explanation:
The Hering Breuer Reflex is mediated by the vagus nerve when stretch receptors detect inflation of lungs. This allows expiration to occur. The correct answer is A) Vagus nerve, expiration. Dilation and constriction of the airway are controlled by both the parasympathetic and sympathetic nervous systems. The vagus nerve, which is part of the parasympathetic system, releases sensory nerve fibers that influence reflex responses in the lungs. When the lungs inflate and the stretch receptors are activated, the vagus nerve helps to initiate expiration by relaxing the muscles involved in inspiration. This nervous control is essential for regular breathing and is connected with the respiratory centers in the brain, particularly the dorsal respiratory group (DRG) in the medulla oblongata, which regulates the rhythm of breathing.