Which blood change is the major stimulus that drives the medulla and pons to increase ventilation?

1. It feels natural to assume that a lack of oxygen is what makes us breathe. 2. The major factor is not oxygen concentration but the concentration of carbon dioxide in the blood. 3. Rising carbon dioxide raises hydrogen ion levels and lowers pH, which the central chemoreceptors detect. 4. The respiratory centres then increase rate and depth so more carbon dioxide is expelled. 5. So the third option is correct and the first is the intuitive trap. 6. Nitrogen is inert in this setting and its concentration plays no part in driving ventilation. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.3 The Process of Breathing_