A.Stimulus
B.Sensory Neurons
C.Spinal Column
D.Interneuron
E.Motor Neuron
F.Muscle
G.Bone

In a reflex arc, an action potential never travels to the brain for processing and so results in a much quicker reaction.  When a stimulus (pain) is encountered, the signal from that stimulus will travel up the sensory neuron to the spinal column.  There, it will likely pass through a short interneuron before continuing down a motor neuron to the origin of the signal. Then, a contraction of the muscles is triggered.
Own work
Verona Dethran