User:JLB1117/anatomy and connectivity section

The area postrema is found at the inferoposterior limit of the fourth ventricle. Specialized ependymal cells are found within the area postrema. These ependymal cells are specialized because they differ slightly from the majority of ependymal cells (ependymocytes) forming a unicellular epithelium lining of the ventricles and central canal.

The area postrema is a small protrusion separated from the vagal triangle by the funiculus separans, a thin semitransparent ridge. The vagal triangle overlies the dorsal vagal nucleus and it situated on the caudal end of the rhomboid fossa or 'floor' of the fourth ventricle. The area postrema is situated just before the obex, the inferior apex of the caudal ventricular floor. Both the funiculus separans and area postrema have a similar thick ependyma-containing tanycyte covering. Ependyma and tanycytes can participate in transport of neurochemicals into and out of the cerebrospinal fluid from its cells or adjacent neurons, glia or vessels. Epednyma and tanycytes may also participate in chemoreception. The area postrema additionally contains neurons.

The eminence of the area postrema is considered a circumventricular organ because its endothelial cells do not contain tight junctions, which allows for free exchange of molecules between blood and brain tissue. This unique breakdown in the blood-brain barrier is partially rectified by the presence of a tanycyte barrier. 1222

Gray's Anatomy, 38th Edition pg. 940, 1094, 1208-1209