Sympathetic chain ganglia The bilaterally symmetric sympathetic chain ganglia, also called the paravertebral ganglia, are located just ventral and lateral to the
spinal cord. The chain extends from the upper neck down to the
coccyx, forming the unpaired
ganglion impar. Ganglia within this chain are either cervical, thoracic, lumbar, or sacral. Preganglionic nerves from the
spinal cord synapse at one of the chain ganglia, and the postganglionic fiber extends to an effector, a
visceral organ in the
thoracic cavity,
abdominal cavity, or
pelvic cavity. There are usually 22–23 pairs of these ganglia: three
cervical ganglia, 12
thoracic ganglia (the
stellate ganglion (cervicothoracic) is formed from the fusion of the first thoracic ganglion with the inferior cervical ganglion), four
lumbar ganglia, and four or five
sacral ganglia. In the area of the
coccyx there is a small
ganglion impar. The stellate ganglion is so named due to its radiating pattern similar in appearance to a star. The general rule of interaction of the nerve fibers in the sympathetic nervous system begins at the spinal cord. Here they arise from the thoracolumbar (T1–L2) regions' lateral horn of grey and emerge via the ventral root. They enter their respective spinal nerve (e.g. T5), and thus enter the
white ramus communicans. This myelinated division can then enter the sympathetic chain. Here four options are available to the fibers: (1) they can run up the chain and synapse, (2) they can synapse at the level of entry, (3) they can pass straight through and synapse elsewhere – such as in the case of T5–12 (the splanchnic nerves), or (4) they can enter the chain and descend to synapse. It is this ability to move superiorly and inferiorly along the chain that results in the mass response to the sympathetic nervous system. A preganglionic fibre may synapse to 15–20 postganglionic fibres. The postganglionic neurons extend across most of the body. Upon exiting the sympathetic chain, the fibres enter a less-myelinated
gray ramus communicans. There is still a myelin sheath present – but in far lower amounts compared to the white ramus communicans. This ramus then enters the spinal nerve and is either sent to its synapsing target, or becomes a visceral branch to enter a plexus such as the superficial or deep
cardiac plexuses.
Prevertebral ganglia Neurons of the
prevertebral ganglia, also called collateral ganglia, receive input from the
splanchnic nerves and innervate organs of the
abdomen and
pelvis. These include the
celiac ganglia,
superior mesenteric ganglia, and
inferior mesenteric ganglia. ==Additional images==