What is the antagonism between the sympathetic and the parasympathetic neural actions?

In general the actions of the sympathetic and the parasympathetic are antagonistic, i.e., whereas one stimulates something the other inhibits and vice versa. The organs, with few exceptions, get efferences from these two systems and the antagonism among them serves to modulate their effects. For instance, the parasympathetic stimulates salivation while the sympathetic inhibits it; the parasympathetic constricts pupils whereas the sympathetic dilates it; the parasympathetic contracts the bronchi while the sympathetic relaxes them; the parasympathetic excites the genital organs whereas the parasympathetic inhibits the excitation.