This response from the central controlling area is carried to the various organs and muscles along efferent pathways. The input to the central controlling area is from the various sensors via the afferent pathways. The central controlling area for breathing, called the respiratory centre , is in the lower part of the brain stem, in the medulla oblongata. These two groups of neurones automatically maintain a rhythmic cycling pattern of inspiration and expiration. This automatic rhythm can be modified by the afferent information.
Chemoreceptors are cells that respond to chemical stimuli.
An acidic CSF causes hyperventilation this is the reason for dyspnoea with conditions such as diabetic ketoacidosis. An alkaline CSF inhibits the respiratory centre. This increase in CSF acidity causes hyperventilation which lowers the carbon dioxide concentration in the blood. This may delay the return of spontaneous breathing at the end of surgery. The carotid and aortic bodies are small pieces of tissue that contain chemoreceptors which respond to the oxygen and carbon dioxide concentrations in arterial blood.