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A thermal neutral zone essentially an endotherm's temperature tolerance range. Within the TNZ the basal rate of heat production is in equilibrium with the rate of heat loss to the external environment. The endotherm does not have to use large amounts of energy to control its temperature within the thermal neutral zone, the organism adjusts to the temperatures within the zone through different responses requiring little energy. It can show postural changes where it changes its’ body shape or moves and exposes different areas to the sun/shade, and through radiation, convection and conduction, heat exchange occurs. Vasomotor responses allow control of the flow of blood between the periphery and the core to control heat loss from the surface of the body. Lastly, the organism can show insulation adjustments; a common example being “goosebumps” in humans where hair follicles are raised by pilomotor muscles, also shown in animals’ pelage and plumage.^[1] This allows heat to be trapped between hairs. Below the thermal neutral zone there is the zone of LCT (lower critical temperature) and above there is the zone of UCT (upper critical temperature). The organism reaches the LCT when the Ta (ambient temp.) decreases. When an organism reaches this stage the metabolic rate increases significantly and thermogenesis increases the Tb (body temp.) If the Ta continues to decrease far below the LCT hypothermia occurs. When the Ta reaches too far out of the UCT the rate heat gain and heat production become higher than the rate of heat dissipation (heat loss through evaporative cooling), resulting in hyperthermia.

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