The autonomic nervous system (ANS) controls visceral functions like cardiac muscle and smooth muscle of blood vessels. It has two divisions - the sympathetic and parasympathetic nervous systems. The sympathetic division prepares the body for "fight or flight" while the parasympathetic division conserves energy and promotes "rest and digest". Both work to maintain homeostasis through a balance of stimulation. The ANS uses a two-neuron chain and ganglia located outside the CNS. It is not under voluntary control.