RT Book, Section A1 Gill, Jatinder S. A2 Bajwa, Zahid H. A2 Wootton, R. Joshua A2 Warfield, Carol A. SR Print(0) ID 1131937762 T1 Sympathetic Blocks T2 Principles and Practice of Pain Medicine, 3e YR 2016 FD 2016 PB McGraw-Hill Education PP New York, NY SN 9780071766838 LK neurology.mhmedical.com/content.aspx?aid=1131937762 RD 2024/10/10 AB The autonomic nervous system (ANS) is a powerful system that has important homeostatic functions. Disorders of this system can lead to many disease states and may contribute to some pain disorders such as complex regional pain syndrome (CRPS). Having a good working knowledge of the anatomy and physiology of the ANS is of paramount importance when considering sympathetic blocks. The higher neural centers in the brainstem, the hypothalamus, and the prefrontal cortex have nerve cells that tightly control the function and the output of the ANS. The ANS is composed of the sympathetic and parasympathetic nervous systems. The parasympathetic outflow has cranial (several cranial nerves), vagal (mainly via the vagus nerve, which innervates many intrathoracic and intraabdominal structures), and sacral outflow that controls the urinary and reproductive organs. The sympathetic nervous system is formed by neurons in the intermediolateral cell column of the thoracolumbar spinal cord. These are in turn modulated by descending autonomic projections from the hypothalamus, the suprachiasmatic nucleus, and the supraparaventricular nucleus.1 Axons from these neuron cells exit the spinal cord by the anterior spinal roots and white rami communicantes to the sympathetic chain ganglia located along the left and right anterolateral margins of the spinal column. Upon reaching these paravertebral ganglia, the preganglionic sympathetic axons may synapse, pass cephalad or caudad for variable distances within the sympathetic chain before synapsing, or continue uninterrupted to a more distant ganglion or plexus, such as the celiac or hypogastric plexus.