Final answer:
A sensory neuron is the first type of neuron activated when touching a warm plate due to the stimulation of thermoreceptors in the skin, which trigger an action potential.
Step-by-step explanation:
When you touch a warm plate of food being handed around the dinner table, the first type of neuron to be activated is a sensory neuron.
Sensory neurons are responsible for carrying information from sensory receptors to the central nervous system. In the case of touching a warm plate, the temperature-sensitive receptors called thermoreceptors found in the skin are stimulated. These thermoreceptors then cause a change in the voltage of the cell membrane, which, if the stimulus is strong enough, creates an action potential. This action potential propagates along the axon of the sensory neuron to the central nervous system, where it can lead to a response, such as reflexively pulling your hand away to avoid getting burned.