A reflex arc is the pathway taken by the nerve impulses that produce a reflex action. Reflex actions are automatic and rapid responses that protect the body from harm.

Key Stages in the Reflex Arc:

1. Stimulus Detection: A stimulus (e.g., heat, light) is detected by receptors.
2. Sensory Neuron Activation: The receptors send an electrical impulse along a sensory neuron to the spinal cord (part of the central nervous system).
3. Relay Neuron in the CNS: In the spinal cord, the impulse passes to a relay neuron (also known as an interneuron).
4. Motor Neuron Activation: The relay neuron passes the impulse to a motor neuron.
5. Effector Response: The motor neuron carries the impulse to an effector (a muscle or gland), causing it to respond (e.g., a muscle contracts to move a hand away from a hot surface).