All parts of the brain › Functions › Vomiting reflex

What part of the brain controls vomiting?

In the medulla oblongata, at the bottom of the brainstem. [1][2][3]

The medulla oblongata and the spinal cord (central canal) lit in red on a 3D model of the brain, seen from the front left and above

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Lit: whole parts; region borders not drawn.

Slice

All 2 parts are lit together. Drag to turn, pinch or scroll to zoom, tap a part on the brain or a name in the list to focus it; .

The “vomiting centre” is not one nucleus but loosely organised groups of neurons in the medulla. They act on signals from the area postrema, a chemoreceptor trigger zone on the floor of the fourth ventricle that samples the blood, and from the vagus nerve, which reports on the gut; both reach the solitary nucleus. The reflex is protective: it empties the stomach of something harmful. [1][2][3]

The area postrema is a region on the medulla oblongata, not a separate shape. The 3D model has no shape for it, so the whole medulla oblongata is lit; the region’s exact border is not drawn.

The solitary nucleus is a region on the medulla oblongata, not a separate shape. The 3D model has no shape for it, so the whole medulla oblongata is lit; the region’s exact border is not drawn.

The dorsal vagal nucleus is a region on the medulla oblongata, not a separate shape. The 3D model has no shape for it, so the whole medulla oblongata is lit; the region’s exact border is not drawn.

Vomiting reflex: 2 parts lit

Medulla oblongata and spinal cord (central canal). Tap one to see where it is and what it does.

The parts and their roles

Holds the whole sensing and deciding part of the reflex: the area postrema at the lower tip of the fourth ventricle, which detects emetic substances in the blood; the solitary nucleus beside it, where the vagus nerve’s signals from the gut end; and the dorsal vagal nucleus, the three together making up the dorsal vagal complex. A coordinator with no sensing role of its own, in the lateral reticular formation of the medulla, runs the act. [2][1][3] Where is the medulla oblongata?
Carries out the push: the brainstem drives motor neurons in the spinal cord, the phrenic motor neurons (cervical segments C3 to C5) that work the diaphragm and those that work the abdominal and intercostal muscles. In retching the diaphragm and abdominal muscles contract together; in vomiting the costal diaphragm, abdominal and intercostal muscles press the stomach’s contents up. [4][5] Where is the spinal cord?

Named areas on the lit gyri

The area postrema, on the : A pair of small swellings at the lower tip of the fourth ventricle’s floor, just before the obex. Its leaky capillaries let it sample the blood, and it is the chemoreceptor trigger zone that relays the presence of emetic agents to the solitary nucleus. [2][1]
The solitary nucleus, on the : Where the reflex’s two main inputs meet: the area postrema connects to it, and it is a main ending of the vagus nerve’s sensory fibres from the gut. [2][1][6]
The dorsal vagal nucleus, on the : The third part of the dorsal vagal complex, with the solitary nucleus and the area postrema; its neurons give the vagus nerve its parasympathetic supply to the gut. [2][7]

How they work together

Four kinds of signal can start it: the area postrema reading the blood; the vagus nerve and the gut’s own nerves reporting on the stomach and intestines; the vestibular system, reporting motion through cranial nerve VIII; and higher brain centres. [3]
The act runs in a fixed order. Extra saliva comes first, protecting tooth enamel from stomach acid, then a deep breath so nothing is inhaled. In retching the abdominal muscles and diaphragm contract in a few coordinated rounds against a closed glottis; then the lower and upper oesophageal sphincters relax and the pressure drives the stomach’s contents out. The stomach itself does not squeeze. [3]
It is a safeguard: the reflex was selected because it expels harmful substances from the body, and the area postrema can trigger it from the blood because it is a circumventricular organ, without the blood–brain barrier that shields the rest of the brain. [1][2]
The two-part picture dates from Borison and Wang in 1953: a chemosensing trigger zone in the area postrema, and a separate coordinator with no chemosensing role in the lateral reticular formation of the medulla. [2]
Not every mammal has the reflex. In a 2013 comparison of ten species, none of the seven rodents tested, among them the rat and the mouse, retched or vomited, while the musk shrew, ferret and cat did; the authors judged a missing brainstem component the most likely reason. [4]
Honest limit: the medulla and spinal cord are lit whole; the area postrema, solitary nucleus and dorsal vagal nucleus are small groups of cells inside the medulla, not shapes in this model. Much of the circuit was worked out in animals such as cats, ferrets and musk shrews, because rats and mice cannot vomit, and this page describes the normal reflex only. [4][2]

The gag reflex, another protective reflex of the throat, passes through the same solitary nucleus: the glossopharyngeal nerve’s signal from the throat ends there and is passed to the nucleus ambiguus. [6][8] What part of the brain controls coughing and sneezing?

Sources

Facts describe anatomy and normal function only. A part lit here takes part in the vomiting reflex; it does not do it alone, and it does other jobs too. The 3D model is the adult male BodyParts3D brain (credits and licence); on it the brainstem includes the midbrain, pons and medulla, so lighting the brainstem lights all three.