What is reflex action? How is reflex arc formed?

(N/A) Reflex action is the entire process of response to a peripheral nervous stimulation that occurs involuntarily,without conscious effort or thought,and requires the involvement of a part of the central nervous system $(CNS)$.
We experience sudden withdrawal of a body part when it comes in contact with objects that are extremely hot,cold,pointed,or animals that are scary or poisonous.
The reflex pathway,known as the reflex arc,comprises at least one afferent neuron (receptor) and one efferent (effector) neuron appropriately arranged in a series.
The afferent neuron receives a signal from a sensory organ and transmits the impulse via a dorsal nerve root into the $CNS$ at the level of the spinal cord.
The efferent neuron then carries signals from the $CNS$ to the effector (muscle or gland). The stimulus and response thus form a reflex arc,as shown in the knee-jerk reflex.