The hypothalamus is a region of the brain that plays an important role in temperature regulation. It is responsible for detecting the temperature of the external environment and the body, and for initiating appropriate thermoregulatory responses when either of those temperatures is outside of the normal range. It does this by sending signals to the sympathetic and parasympathetic nervous systems to reduce or increase heat production and loss, respectively. For example, when the ambient temperature is too cold, the hypothalamus will send signals to shiver and constrict blood vessels to conserve heat. When it is too hot, it will stimulate sweating and dilate blood vessels to facilitate heat loss.