Final answer:
Heat or cold outside the range of thermoreceptors activates pain receptors and is perceived as painful.
Step-by-step explanation:
Heat or cold outside the range of thermoreceptors activates pain receptors and is perceived as painful. Thermoreceptors are responsible for sensing temperature changes in the body, and when the temperature is too extreme, it can activate pain receptors. These pain receptors, also known as nociceptors, detect potentially damaging stimuli and send pain signals to the brain.