Editing Chemoreceptor trigger zone (section)

==Evolutionary significance==
The CTZ is in the medulla oblongata, which is [[phylogenetically]] the oldest part of the central nervous system.{{citation needed|date=December 2013}} Early lifeforms developed a [[brainstem]], or inner brain, and nothing more.{{citation needed|date=June 2019}} This part of the brain is responsible for basic survival instincts and reactions, for example to make an organism turn its head and look where an auditory stimulus was heard. The brainstem is where the medulla is located, and therefore also the area postrema and the CTZ. Then later lifeforms developed another segment of the brain, which includes the [[limbic system]]. This area of the brain is responsible for producing emotion and emotional responses to external stimuli, and also is significantly involved in memory and reward systems. Evolutionarily, the [[cerebral cortex]] is the most recent development. This area of the brain is responsible for critical thinking and reasoning, and is actively involved in decision making. It has been discovered that a major cause of increased intelligence in species including humans is the increase in cortical neurons in the brain.<ref>{{cite journal|last1=Root|first1=AR|last2=Nucci|first2=NV|last3=Sanford|first3=JD|last4=Rubin|first4=BS|last5=Trudeau|first5=VL|last6=Sower|first6=SA|title=In situ characterization of gonadotropin- releasing hormone-I, -III, and glutamic acid decarboxylase expression in the brain of the sea lamprey, Petromyzon marinus|journal=Brain, Behavior and Evolution|date=2005|volume=65|issue=1|pages=60–70|doi=10.1159/000081354|pmid=15475659|s2cid=4815723}}</ref> The emetic response was selected for protective purposes, and serves as a safeguard against poisoning of the body. This response gets toxins and drugs out of the body by summoning control over motor neurons which stimulate muscles in the chest and [[thoracic diaphragm]] to expel contents from the stomach.