The area postrema is a pair of small swellings in the medulla oblongata, at the lowest tip of the fourth ventricle’s floor, just before the obex. It is a circumventricular organ with no blood–brain barrier, so its neurons can sense substances circulating in the blood. [1][2]
The 3D brain needs JavaScript. The text below still says where the area postrema is and what it does.
Opens cut by a side (sagittal) slice through the medulla oblongata, which holds the area postrema. Drag to turn, pinch or scroll to zoom, tap any part to name it; .
Not a separate shape in this atlas; lit: the part that holds it. Lit: the whole medulla oblongata. The area postrema lies on the back surface of the medulla oblongata, at the bottom of the fourth ventricle; BodyParts3D has no shape for it, so the whole medulla is lit and nothing is drawn at a guessed point. Look at the back face of the lit medulla, where the floor of the fourth ventricle narrows to its lowest point. [1][2]
Lit here: the medulla oblongata, the part that holds the area postrema — see it on its own page.
It is a paired bump at the lower back limit of the fourth ventricle, in the caudal medulla oblongata near where the brainstem joins the spinal cord. [1][2]
In humans, as in most mammals studied, it is a swelling on each side wall of the fourth ventricle; in rodents and rabbits it is a single midline structure. [2]
It lies right against the nucleus of the solitary tract, the medulla’s relay for signals from the gut and internal organs, and connects to it. [1][3]
What it does
It is one of the three sensory circumventricular organs, with the subfornical organ and the vascular organ of the lamina terminalis: places where the capillaries are highly permeable instead of forming the blood–brain barrier found in the rest of the brain. [2]
Its capillaries are fenestrated (holed); a tanycyte barrier partly makes up for that, and the capillaries of its ventral (deeper) subregion are relatively tight, closer to the rest of the brain’s. [1]
Because it can read the blood, it takes part in regulating food intake, the body’s fluid balance and the heart and blood vessels. [1]
Angiotensin II, a blood-pressure hormone, acts here: it raises arterial blood pressure in a dose-dependent way, and the area postrema is a site where angiotensin stimulates glucose metabolism. [1][2]
Honest limit: relatively little is known about how the area postrema works in humans; much of the detail comes from animal studies. [2]
Connections
It is excited by nerve signals from the gut, carried by sympathetic and vagal fibres. [1]
It sends fibres to the parts of the brain that run the automatic control of the heart, blood vessels and breathing. [2]
Other names
It is also called the chemoreceptor trigger zone (CTZ), a name for its role as a sensor of chemicals carried in the blood. [1][2]
Size
The model has no shape for the area postrema itself, so it is not measured here. The medulla oblongata that holds it measures about 33 mm front to back, 41 mm top to bottom and 27 mm side to side on this model (the box it fits in, not its volume). [4]
Facts describe anatomy and normal function only. The 3D model is the adult male BodyParts3D brain (credits and licence); real brains vary in size and shape, so its measurements describe one model, not anyone’s brain.