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All animal species that vomit have a brainstem ‘vomiting centre’, which is a group of several nuclei that act in concert to coordinate the somatomotor events involved in expelling gastric contents. Non‐vomiting species such as horses, rodents and rabbits also have the brainstem nuclei and motor systems necessary for emesis but lack the complex synaptic interaction between the nuclei and viscera required for a coordinated reflex.

There does not appear to be a discrete vomiting centre within the reticular formation of the medulla oblongata. Rather, there is an ‘emetic complex’ that refers to groups of loosely organised neurons distributed throughout the medulla, which are sequentially activated and play a role in emesis. This complex will be referred to in this chapter as the vomiting centre, however, as conceptually this assists the understanding of the physiology and pathophysiology involved.

The vomiting centre receives input from vagal and sympathetic neurons, the CRTZ, the vestibular apparatus and the cerebral cortex. It may also be stimulated directly by blood‐borne toxins that can cross the blood–brain barrier (BBB).