Forms the ventral/lower/lower, smaller, part of the midbrain (diencephalon). The hypothalamus also includes the pituitary stalk and the posterior lobe.

In the hypothalamus lies a large number of nuclei and areas of fundamental importance for the survival of the individual and the genus. It is about centers for hunger, thirst, satiety, desire, uneasiness, hormone control, circadian rhythm, mating behavior, energy metabolism, body temperature, etc. These include the following core areas, of which the bold ones are among the more talked about:

Area hypothalamica lateralis Nucleus anterior hypothalami Nucleus arcuatus hypothalami Nucleus dorsomedialis hypothalami Nucleus mammillaris lateralis Nucleus mammillaris medialis Nucleus paraventricularis hypothalami Nucleus perifornicalis Nucleus posterior hypothalami Nucleus premammillaris dorsalis Nucleus premammillaris ventralis Nucleus preopticus lateralis Nucleus preopticus medialis Nucleus preopticus medianus Nucleus preopticus periventricularis Nucleus suprachiasmaticus Nucleus supramammillaris Nucleus supraopticus Nucleus tuberomamillaris Nucleusventromedialis hypothalami
It is the hypothalamus that is responsible for maintaining the correct balance in the internal body environment; i.e. that homeostasis is maintained. This is a prerequisite for the normal functioning of life processes.

According to some beliefs, the hypothalamus is the most important part of the cerebrum in terms of maintaining the basic life processes. Such structures as the cerebral cortex and the telencephalic nuclei can then be considered as support of the hypothalamus.