Final answer:
The Hering-Breuer reflex prevents overexpansion of the lungs during spontaneous breathing by inhibiting inhalation when the lungs inflate significantly. This reflex, triggered by the vagus nerve, is part of the body's means to unconsciously control the rhythm of breathing and protect the lungs.
Step-by-step explanation:
During spontaneous breathing, the reflex that prevents overexpansion of the lungs is known as the Hering-Breuer reflex. This is a protective mechanism that triggers as the lungs inflate to a significant degree, sending inhibitory signals via the vagus nerve to the respiratory centers in the brain to terminate the inhalation phase and induce exhalation. This reflex helps to regulate the volume of air taken in and protects the lungs from damage due to overinflation.
Unconscious breathing, which occurs without conscious effort, is controlled by the respiratory centers in the brain. Reflexes such as coughing, and the ability of the lungs to regulate oxygen and carbon dioxide levels, are also governed by the autonomic nervous system. In particular, sensory nerve fibers arising from the vagus nerve are responsible for triggering the Hering-Breuer reflex.
Nasal breathing is generally superior to mouth breathing because it warms and humidifies the incoming air and can filter out dust and other particles. Furthermore, nasal breathing can help to regulate the amount of air entering the lungs better than mouth breathing.
Regarding the movement of the diaphragm during the breathing process: A. The diaphragm moves downward during inhalation (I), creating negative pressure in the thoracic cavity. B. The diaphragm relaxes during exhalation (E), allowing the lungs to recoil and push the air out.