- Sympathetic nervous system
- A part of the nervous system that serves to accelerate the heart rate, constrict blood vessels, and raise blood pressure. The sympathetic nervous system and the parasympathetic nervous system constitute the autonomic nervous system, the branch of the nervous system that performs involuntary functions.
* * *sympathetic nervous system n the part of the autonomic nervous system that is concerned esp. with preparing the body to react to situations of stress or emergency, that contains chiefly adrenergic fibers and tends to depress secretion, decrease the tone and contractility of smooth muscle, increase heart rate, and that consists essentially of preganglionic fibers arising in the thoracic and upper lumbar parts of the spinal cord and passing through delicate white rami communicantes to ganglia located in a pair of sympathetic chains situated one on each side of the spinal column or to more peripheral ganglia or ganglionated plexuses and postganglionic fibers passing typically through gray rami communicantes to spinal nerves with which they are distributed to various end organs called also sympathetic system compare PARASYMPATHETIC NERVOUS SYSTEM
* * *(SNS) the 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. These fibers (preganglionic fibers) arise from cells in the thoracic and upper lumbar levels of the spinal cord, leave by way of ventral roots, and, by way of rami communicantes, enter sympathetic trunks, where some synapse with ganglion cells. Distal to these ganglia, there are postganglionic fibers that either return to spinal nerves by way of rami communicantes to supply blood vessels, smooth muscles, and glands of the trunk and limbs, or go as visceral branches to blood vessels, smooth muscles, glands of the head and neck, and viscera of the thorax, abdomen, and pelvis. Some preganglionic fibers pass through the sympathetic trunks and synapse in the prevertebral ganglia; postganglionic fibers from those ganglia supply adjacent viscera. In TA terminology, called pars sympathica divisionis autonomici systematis nervosi. Called also thoracolumbar division and thoracolumbar part of autonomic nervous system. See Plate 42.
Medical dictionary. 2011.