portion of the autonomic nervous system that receives its fibers of connection with the central nervous system through the thoracolumbar outflow of visceral efferent fibers; sympathetic preganglionic fibers originate in neurons of the intermediolateral column of the spinal cord and project to the paravertebral and prevertebral ganglia, which in turn project to target organs; the sympathetic nervous system mediates the body's response to stressful situations, i.e, the fight or flight reactions, and often acts reciprocally to the parasympathetic system.