What is a reflex action?

When a stimulus activates a receptor and a very quick response is required by the body, eg when a hand touches hot something burning hot and the hand needs to be moved away quickly, an a response is produced without being coordinated by the brain. 1) receptor detects stimulus/ change in the environment 2) sensory neuron sends signal to relay neuron 3) motor neuron sends signal to effector 4) effector produces a response