Original: The ANS is divided into two limbs, the parasympathetic nervous system which is primarily involved in, and the sympathetic nervous system which causes the body to become more active as in the "fight or flight" response.
Simplified: The ANS is divided into two sub-sections, the parasympathetic nervous system which is mostly involved in, and the sympathetic nervous system which causes the body to become more active as in the "fight or flight" response.