Noun | 1. | parasympathetic nervous system - originates in the brain stem and lower part of the spinal cord; opposes physiological effects of the sympathetic nervous system: stimulates digestive secretions; slows the heart; constricts the pupils; dilates blood vessels nervous system, systema nervosum - the sensory and control apparatus consisting of a network of nerve cells ANS, autonomic nervous system - the part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands |