Neurons are the structural & functional unit of Nervous system (Brain). Reflex actions are sudden responses. The sensory nerves that detect the heat are connected to the nerves that move the muscles of the hand. Such a connection of detecting the signal from the nerves and responding to it quickly is known as reflex arc. Reflex arcs are formed in the spinal cord and the information reaches the brain and brain responses to it.

â passing of information takes place –

(i) By Electric impulse (inside the neuron) and

(ii) In the form of chemicals (At synapse)

This tells that neurons are the medium by which stimuli is sent to the brain and then to the action centre where the response has to occur.

Like this:

Stimulus → Receptor organ → Sensory nerve → Spinal cord →Effector organs→ Response