Students should be able to explain that homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes. • Homeostasis maintains optimal conditions for enzyme action and all cell functions. • These automatic control systems may involve nervous responses or chemical responses. • All control systems include: cells called receptors, which detect stimuli (changes in the environment); coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors; effectors, muscles or glands, which bring about responses which restore optimum levels.