Final answer:
Breathing is initiated by the medullary respiratory centers and modified by inputs from stretch receptors and chemoreceptors in the lungs/chest wall, with the correct answer being A) Medullary respiratory centers, stretch receptors, chemoreceptors.
Step-by-step explanation:
Breathing is initiated by medullary respiratory centers and is modified by higher structures in the CNS and input from stretch receptors and chemoreceptors in the lungs/chest wall. The correct option is A) Medullary respiratory centers, stretch receptors, chemoreceptors.
The medulla oblongata and the pons are structures in the brain that primarily control respiration. These centers receive input from chemoreceptors located in the brain and in the peripheral areas like the carotid arteries and aortic arch. These chemoreceptors detect changes in levels of carbon dioxide and hydrogen ions, which affect the blood's pH. Additionally, stretch receptors in the lungs provide feedback about the lung's expansion, informing the respiratory centers about the depth and rate of breathing necessary to accommodate the body's oxygen needs.
The medullary respiratory centers initiate contraction of the diaphragm and intercostal muscles for normal breathing, while the pons is involved in refining the breathing rhythm and in forced respiration during activities like exercise. As respiratory rate and depth are influenced by chemical changes in the blood, these structures of the brain respond to maintain homeostasis.