Hypothalamus

A major function of the nervous system is to maintain the constancy of the internal environment. In 1878, Claude Bernard pointed out the remarkable distinction between our highly variable external environment (i.e., the environment that we live in and that is subject to major changes with regard to temperature, humidity, and food availability) and our rather invariable internal environment (i.e., the fluids surrounding our bodily tissues, whose composition is very constant). Conversely, Walter Cannon later put forward that our internal environment is not in fact constant, but rather shows a limited variability. He called the mechanism that maintains this limited variability “homeostasis.” Although in principle the whole brain is involved in homeostasis, the central brain region for homeostasis is the hypothalamus, a small area of the diencephalon that comprises less than 1% of the total volume of the human brain. The name hypothalamus was coined and introduced by Wilhelm Hess in 1893.