Final answer:
Thermoreceptors, specifically the free nerve endings, detect temperature.
Step-by-step explanation:
The structure that detects temperature is the thermoreceptor. Thermoreceptors perceive sensations related to the temperature of objects and can be categorized as hot or cold receptors. In the skin, the most common thermoreceptors are the free nerve endings. These nerve endings are sensitive to painful stimuli, as well as hot and cold temperatures.