The sympathetic nervous system originates specifically from the thoracolumbar region (T1-L2) of the spinal cord, where its preganglionic neurons are located in the lateral horn. This anatomical layout is crucial for understanding the distribution of sympathetic fibers and planning surgical interventions such as sympathectomy. Injuries or lesions outside this region typically do not affect sympathetic outflow directly. Knowledge of this region helps in avoiding damage to sympathetic pathways during spine or thoracic surgeries.

Reference: Gray's Anatomy, Standring S., 42nd Edition.