respiratory center, a group of nerve cells in the pons and medulla of the brain that controls the rhythm of breathing in response to changes in levels of oxygen, carbon dioxide, and hydrogen ions in the blood and cerebrospinal fluid. Such changes activate central and peripheral chemoreceptors, which send impulses to the respiratory center, triggering an increase or a decrease in the breathing rate. In patients with retention of carbon dioxide, the respiratory center becomes insensitive to carbon dioxide, and the main stimulus to ventilation is hypoxemia. If such patients inhale air with a high oxygen content, breathing may be depressed, leading to a further rise in blood carbon dioxide levels. The respiratory center is inhibited by barbiturates, anesthetics, tranquilizing agents, and morphine. See also hyperventilation, hypoventilation, hypoxia.
