The term medial preoptic area refers to a subdivision of the preoptic area. The medial preoptic nucleus is bounded laterally by the lateral preoptic nucleus, medially by the preoptic periventricular nucleus, dorsally by the anterior commissure and the thalamus, ventrally by the optic chiasm, rostrally by the nucleus of the diagonal band and caudally by the anterior hypothalamic area. It releases gonadotropin-releasing hormone (GnRH), controls copulation in males, and is larger in males than in females. It's internal structure varies considerably by species. In the human it is relatively undifferentiated.