Temperature is sensed at the skin surface, in deep tissues, the spinal cord, the brain, and the hypothalamus. Integration of thermal input occurs at various levels, but the hypothalamus is the most important controller in mammals. The most important eff erent autonomic responses are sweating, arteriovenous shunt vasoconstriction, and shivering. Behavioural responses (any volitional responses) are by far the strongest defences, but not usually available to surgical patients. Each response is characterised by its threshold (triggering core temperature), gain (increase in response intensity with further deviation in core temperature), and maximum response intensity.