The hypothalamus is a part of the brain composed of small clusters of neurons which hold a variety of functions. Its most important function is to connect the nervous system to the endocrine system through the pituitary gland (hypophysis). The hypothalamus is located between the thalamus and the brain stem. The human hypothalamus, is closely the size of an almond. The hypothalamus controls body temperature, hunger, thirst, fatigue, and the 24-hour-cycles of our inner biological clock. It also carries some metabolic processes and other activities of the Autonomic Nervous System.