Medullary chemoreceptor trigger zone
(anatomy and physiology)
It is located in the Medulla (i.e. Part of the brain) that is responsible for monitoring the bloodstream and the cerebrospinal fluid (CSF) for signs of foreign toxins that might be harmful to the body. It plays an indirect role in stimulation of vomiting that when triggered it sends signals to the vomiting Center (which is also located in the Medulla) of the brain. If the signals persist the vomiting Center will in turn send sickness-inducing signals through the vagus nerve to the stomach.
Examples of cases wherein CTZ is triggered are the presence of bacteria or viruses irritating the stomach lining, inhalation/ingestion of chemicals/drugs/toxin detexcted in the blood of cerebrospinal fluid, over-eating (i.e. when too much food in the stomach leads to irritation of the stomach wall). However, few exceptions are emotional/psychological causes (e.g. Fear, disgust, anxiety) wherein the CTZ is by-passed altogether and the higher brain centers (ones that control emotions and memories) stimulate the vomiting Center.