ABSTRACT
The autonomic nervous system, termed the visceral or vegetative nervous system, is concerned with the regulation of visceral functions and contributes nerves to internal organs and their coverings. Parasympathetic nuclei are located at both extremities of the central nervous system: the midbrain and medulla and the sacral area of the spinal cord. Sacral nuclei contribute fibers to pelvic viscera and to the distal part of the digestive tract. Epidural and spinal anesthesias have considerable effects on fibers originating in this part of the parasympathetic nervous system. Efferent parasympathetic pathways always involve two different neurons, termed preganglionic and postganglionic. The vagus nerve represents the most important nerve of the peripheral parasympathetic system; it consists of both preganglionic efferent and visceral afferent fibers. Parasympathetic autonomic ganglia may be divided into two groups: prevertebral ganglia and terminal ganglia. The neurotransmitter substance of postganglionic parasympathetic fibers is acetylcholine.
