Well, the reflex arc causes our body to react almost immediately when our body, that is our sensory structures sense danger. In short it causes a reflex action...like when you touch a hot pan and not even a second after you remove your hand because it is too hot....All that is because a signal has travelled from the neurons in your hand via a network of them (in the shortest way) until reaching your brain which gives a signal back causing the muscles in your hand to retract back and thus move your hand away. Hope that this answer will help you.