That part of the AUTONOMIC NERVOUS SYSTEM which is connected with the BRAIN and SPINAL CORD through certain nerve centres in the mid-brain, medulla, and lower end of the cord. The nerves from these centres are carried in the third, seventh, ninth and tenth cranial nerves and the second, third and fourth sacral nerves. The action of the parasympathetic system is usually antagonistic to that of the sympathetic system. Thus it inhibits the action of the HEART and augments the action of the INTESTINE; whereas the sympathetic augments the action of the heart and inhibits that of the intestine. (See diagram of sympathetic and parasympathetic nervous systems under NERVOUS SYSTEM.)