Sympathetic ganglion

Sympathetic ganglion
Autonomic nervous system innervation, showing the sympathetic (thoracolumbar) and parasympathetic (craniosacral) systems, in red and blue, respectively
Diagram of the course and branches of a typical intercostal nerve. (Sympathetic ganglion visible at center top.)
Details
Identifiers
Latin	ganglion sympathicum
Dorlands /Elsevier	g_02/12385047
TA	A14.2.00.011
FMA	5890
*Anatomical terminology* [edit on Wikidata]

Sympathetic ganglia are the ganglia of the sympathetic nervous system. They deliver information to the body about stress and impending danger, and are responsible for the familiar fight-or-flight response. They contain approximately 20,000–30,000 nerve cell bodies and are located close to and on either side of the spinal cord in long chains. Sympathetic ganglia are the tissue from which neuroblastoma tumours arise.

Structure

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 coccygeal ganglion. 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: 3 in the cervical region, 11 in the thoracic region (note the presence of the stellate cervicothoracic ganglia), 4 in the lumbar region and 4-5 in the sacral region. Throughout human evolution, the first thoracic and inferior cervical ganglia merged - and this resulting ganglion is called the stellate ganglion (so called because of its radiating pattern similar in appearance to a star).

The general rule of interaction of the nerve fibres 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 fibres: (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.

Upon exiting the sympathetic chain, the fibres enter a less-myelinated gray ramus communicans. There is still a myelin sheath present - just in far lower amounts compared to the white ramus communicans. This ramus then enters the spinal nerve and is sent to its synapsing target, or becomes a visceral branch to enter a plexus (e.g. the superficial or deep cardiac plexuses), or synapses directly onto a target.

Collateral ganglia

Neurons of the collateral ganglia, also called the prevertebral ganglia, receive input from the splanchnic nerves and innervate organs of the abdominal and pelvic region. These include the celiac ganglia, superior mesenteric ganglia, and inferior mesenteric ganglia.

Additional images

Schematic Illustration of Sympathetic Innervation
The thoracic aorta, viewed from the left side.
Scheme showing structure of a typical spinal nerve.
Transverse section of human embryo eight and a half to nine weeks old.

External links

thoraxlesson5 at The Anatomy Lesson by Wesley Norman (Georgetown University) (paravertebralregion)

Anatomy of the autonomic nervous system

Head

Sympathetic	Ciliary ganglion: roots Sensory Sympathetic Short ciliary

Parasympathetic	Ciliary ganglion: roots Sensory Parasympathetic Short ciliary Pterygopalatine ganglion: deep petrosal nerve of pterygoid canal branches of distribution: greater palatine inferior posterior nasal branches lesser palatine nasopalatine medial superior posterior nasal branches pharyngeal Submandibular ganglion Otic ganglion

Neck

Sympathetic	paravertebral ganglia: Cervical ganglia Superior Middle Inferior Stellate ganglion prevertebral plexus: Cavernous plexus Internal carotid

Chest

Sympathetic	paravertebral ganglia: Thoracic ganglia prevertebral plexus: Cardiac plexus Esophageal plexus Pulmonary plexus Thoracic aortic plexus splanchnic nerves: cardiopulmonary thoracic cardiac nerves: Superior Middle Inferior

Abdomen

Sympathetic	paravertebral ganglia: Lumbar ganglia prevertebral ganglia: Celiac ganglia Aorticorenal Superior mesenteric ganglion Inferior mesenteric ganglion prevertebral plexus: Celiac plexus Hepatic Splenic Pancreatic aorticorenal Abdominal aortic plexus Renal/Suprarenal Superior mesenteric Gastric Inferior mesenteric Spermatic Ovarian Superior hypogastric hypogastric nerve Superior rectal Inferior hypogastric Vesical Prostatic / Cavernous nerves of penis Uterovaginal Middle rectal splanchnic nerves: Lumbar splanchnic nerves

Enteric	Submucous plexus Myenteric plexus

Pelvis

Sympathetic	paravertebral ganglia: Sacral ganglia Ganglion impar splanchnic nerves: Sacral splanchnic nerves

Parasympathetic	splanchnic nerves: Pelvic splanchnic nerves

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