1) Enter spinal nerves
Some sympathetic preganglionic neurons synapse with postganglionic neurons in the sympathetic trunk – either in the ganglion at that level or in a ganglion farther up or down the trunk. Some of these postganglionic neurons leave the trunk by entering the Gray Ramus and then merge with the ventral ramus of the spinal nerve. Collectively, the gray rami are known as the Gray Rami Communicantes and are structures that contain sympathetic postganglionic axons connecting sympathetic trunk ganglia to spinal nerves. The gray in the name indicates that they contain unmyelinated axons. There is a gray ramus leading to each of the 42 pairs of spinal nerves.
2) Form cephalic periarterial nerves
Some sympathetic preganglionic neurons enter the trunk and ascend to the superior cervical ganglion where they synapse with postganglionic neurons. The axons of some postganglionic neurons leave the trunk to form Cephalic Periarterial Nerves that extend to the head and following the course of various arteries.
3) Form sympathetic nerves
Some of the incoming sympathetic preganglionic neurons synapse with postganglionic neurons in one or more ganglia of the sympathetic trunk. The axons of the postganglionic neurons then leave the trunk forming Sympathetic Nerves that extend to the visceral effectors in the thoracic cavity (heart and lungs).
4) Form Splanchnic nerves
Some sympathetic preganglionic neurons pass right through the trunk without terminating there and beyond the trunk they form nerves known as Splanchnic Nerves which extend to Prevertebral Ganglia. Most splanchinc nerves are destined to innervate organs of the abdominal-pelvic cavity and the adrenal medulla to release hormones into the bloodstream (epinephrine 80%, norepinephrine 20%, trace amount of dopamine).
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