The Sympathetic Nervous System
The sympathetic nervous system (SNS), along with the parasympathetic nervous system (PNS) form the autonomic nervous system, regulating blood pressure, heart rate, resipration, water balance, and many other homeostatic functions. Autonomic neurons control smooth and cardiac muscle, many glands, and some adipose tissue.
The sympathetic nervous system leaves the spinal cord at the thoracic and lumbar roots. Preganglionic fibres join the sympathetic chain via white communicating rami, so names because preganglionic fibres are white. Postganglioic fibres are unmyelinated, however, thus leaving through the gray communicating rami.
Symathetic neurons leave the spinal cord and synapse in one of the (x) ganglia running alongside the spinal column. Like all efferent preganglionic neurons, these secrete ACh and act on nicotinic receptors. From the ganglia, post-ganglionic fibres run to the innervated tissue.