Final answer:
The autonomic reflex centers for heart rate and breathing are located in the medulla oblongata, which contains the cardiovascular and respiratory centers.
Step-by-step explanation:
The autonomic reflex centers for heart rate and breathing are located in the medulla oblongata. This area of the brain contains the cardiovascular center, which is responsible for regulating cardiac function such as heart rate and blood pressure, and respiratory centers which control the rate of breathing. The cardiovascular center includes cardioaccelerator and cardioinhibitory areas that influence heart rate through sympathetic and parasympathetic stimulation, respectively. The medulla's respiratory centers adjust breathing rate based on the body's needs, primarily determined by blood pH levels.