Table of Contents
Sympathetic ganglia are the clusters of neuronal cell bodies present at different locations. These are the locations where preganglionic and postganglionic neurons make connections and relay information. Sympathetic ganglia usually comprise 20,000 to 30,000 afferent and efferent neuron cell bodies. Afferent cell fibers in the sympathetic ganglia bring about sensory information from the body to the CNS while efferent ganglionic fibers transfer information from CNS to the effectors which produce a response.
The sympathetic ganglia, as the name implies, are concerned with sympathetic body response and bring about a “fight or flight” response upon sensing danger. A normal “fight or flight” response is directed to enable the body to either face or escape the danger. If the response is malfunctioning, the person doesn’t respond appropriately to the dangerous stimuli. Overactivity of this system is also linked to many neurological disorders if the activity crosses a certain criterion.
Anatomy of sympathetic ganglia
Sympathetic ganglia are neuronal cell body collections that are either present around the spine or present near the wall of body organs. They are generally classified into two types:
- Paravertebral ganglia
- Prevertebral ganglia
Paravertebral Sympathetic Ganglia
Paravertebral Sympathetic Ganglia are present in the form of a long interconnected ganglionic chain around the entire length of the spine. The number of ganglia in each region of the spine is variable and is just located lateral to the vertebrae. In the neck region, there are 3 ganglia, in the thorax, their number is 11 to 12, in the lumber region there are 4 to 5 ganglia and in the sacral region, they are also 4 to 5 in number.
In the neck region, they are located anteriorly to the transverse processes of the cervical vertebrae; in the thorax, they are anterior to the heads of ribs or lie on the sides of vertebral bodies; in the abdomen, these ganglia make their position on the anterolateral aspect of the bodies of lumber vertebrae; in sacral region, they are anterior to sacrum. Below the sacral level, two trunks of the right and left sides join together to form ganglion impar.
Paravertebral sympathetic ganglia are divided into four groups depending upon their location adjacent to the spine. These are
- Cervical ganglia
- Thoracic ganglia
- Lumber ganglia
- Sacral ganglia
These ganglia make a regional part of the sympathetic trunk in these areas and are interconnected to each other. It’s better to study them groupwise.
Cervical ganglia
There are three cervical ganglia; superior, middle, and inferior, which make up the cervical part of the thoracic sympathetic trunk. There are no white rami communicantes in this part of the sympathetic trunk and it’s formed by fibers emerging from T1 to T4 segments of the spinal cord ascending into the cervical area. Theoretically, we may get confused that there should be eight sympathetic ganglia in the cervical region due to eight cervical segments of the spinal cord. However, it’s not true as there are only three ganglia in this region due to the fusion of ganglia.
Superior cervical ganglia
The superior cervical ganglia are the largest of all and are formed by the fusion of the upper four cervical ganglia. It is spindle-shaped and lies just below the skull. It is located opposite C2 and C3 and is behind the carotid sheath and in front of the prevertebral fascia. It communicates with cranial nerves IX, X, and XII and with external & recurrent laryngeal nerves.
The bodies of the nerve fiber entering into the superior cervical ganglia are located in the lateral horn of the spinal cord and the postganglionic fibers which originate from the superior cervical ganglia, synapse with preganglionic fibers here and move away to innervate the target organs of the head and neck region. The superior cervical ganglion gives off several branches such as grey rami communicantes to the upper four cervical nerves, and the internal carotid nerve arising from the upper part of the ganglion which forms the plexus around the internal carotid artery.
Some of the branches of the ganglion also join the deep petrosal nerve and take part in the formation of the pterygopalatine ganglion located in the pterygopalatine fossa. The external carotid branches arising from the superior cervical ganglion take part in the formation of the plexus around the external carotid artery. The left superior cervical cardiac branch arising from the ganglion goes to the superficial cardiac plexus while the right branch goes to the deep cardiac plexus.
Middle cervical ganglion
The middle cervical ganglion is a comparatively smaller ganglion and it may be divided into two or three parts. It is situated adjacent to the C6 vertebra above the inferior thyroid artery and behind the carotid sheath it is formed by the fusion of the 5th and 6th cervical ganglions. It is connected to the inferior cervical ganglion either directly or through a looped structure that winds around the subclavian artery to form a structure called ansa subclavia.
It gives several branches which include grey rami communicantes that join ventral rami of the 5th and 6th cervical nerves. It also gives off thyroid branches that accompany the inferior thyroid artery to the thyroid gland and also supply to parathyroid glands. It also gives sympathetic twigs to the trachea and esophagus. It gives the middle cervical cardiac branch which is the largest sympathetic cardiac branch; it goes to the deep cardiac plexus.
Inferior cervical ganglion
The inferior cervical ganglion is formed by the fusion of the 7th and 8th cervical ganglions. It may also be fused with the first ganglion to form a cervicothoracic ganglion also called a stellate ganglion due to its star shape. It is situated adjacent to the C7 vertebra and the neck of the first rib. Inferior cervical ganglion gives grey rami communicantes to the ventral rami of nerves C7 and C8. It also gives the vertebral branches forming a plexus around the vertebral artery, subclavian branches forming the plexus around the subclavian artery, and the inferior cervical cardiac branch which goes to the deep cardiac plexus.
Thoracic sympathetic ganglia
Thoracic Sympathetic ganglia form the thoracic part of the sympathetic trunk which is continuous superiorly with the cervical part of the sympathetic chain while inferiorly it is continuous with the lumber part of the sympathetic chain. Theoretically, the thoracic part of the sympathetic trunk should have 12 sympathetic ganglia. However, the first thoracic ganglion is fused with the inferior cervical ganglion to form the cervicothoracic ganglion or stellate ganglion. The remaining ganglia are located at the level of corresponding intervertebral discs and intercostal nerves. The ganglia of the thoracic sympathetic trunk have both white and grey rami communicantes. The white rami communicantes carry the sympathetic fibers arising in the spinal cord into the sympathetic trunk while the grey rami communicantes carry out the postganglionic fibers back from the ganglion to the spinal nerves.
The thoracic part of the sympathetic chain descends downwards in front of the posterior intercostal vessels and intercostal nerves. It passes deep to the medial arcuate ligament and becomes continuous with the lumbar part of the sympathetic trunk. Each ganglion in the thoracic part of the sympathetic chain is connected to the corresponding spinal nerves by two rami, grey and white rami, they provide the sympathetic supply to the structures in the skin and blood vessels of the skeletal muscles of the whole body.
The branches arising from the medial side of the upper 5 ganglia get distributed to the internal body organs and greater blood vessels. Pulmonary branches form the pulmonary plexus; cardiac branches take part in the formation of deep cardiac plexus; aortic branches pass to the thoracic aortic plexus and esophageal branches join the esophageal plexus.
Splanchnic nerves
The medial branches arise from the lower 7 thoracic ganglia from the three splanchnic nerves, greater splanchnic nerve, lesser splanchnic nerve, and least splanchnic nerve. These splanchnic nerves arising from the thoracic sympathetic chain descend into the abdomen and supply the structures there.
The greater splanchnic nerve is formed by the combination of roots from the 5th to 9th ganglia. It descends the vertebral bodies obliquely and pierces the crus of the diaphragm and enters into the abdominal cavity. It mainly ends in the coeliac ganglion and also partially supplies the aortic renal ganglion. The greater splanchnic nerve alters the activity of the enteric nervous system supplying the foregut. It causes the contraction of splanchnic vasculature and helps to increase blood pressure. It also gives a sympathetic supply to the adrenal gland and causes catecholamine release. It may give sensory twigs to the pancreas.
The lesser splanchnic nerve is formed by the combination of roots of the 10th and 11th ganglion. Its course is similar to the greater splanchnic nerve. It also descends and pierces the crus of the diaphragm and enters into the abdominal cavity. It also ends in the coeliac ganglion. Its fibers also synapse with the superior mesenteric ganglion and aortic renal ganglion. It modulates the activity of the enteric nervous system supplying the midgut.
The least splanchnic nerve is the smaller nerve. It arises from the root of the 12th ganglion and pierces the crus of the diaphragm and enters into the abdominal cavity. Its fibers are involved in the formation of the renal plexus.
Lumbar sympathetic ganglia
Lumbar sympathetic ganglia are the paravertebral ganglia which are located around the lumbar part of the vertebral column and they form the lumbar sympathetic trunk continuous superiorly with the thoracic sympathetic chain passing deep to arcuate ligament and inferiorly with the sacral sympathetic chain behind the common iliac vessels. Lumber ganglia are 4 or 5 in number and they form the lumber splanchnic nerves here which take part in the nearby nerve plexuses.
The first and second lumbar ganglia receive the white communicantes from the anterior primary rami of the first two lumber nerves. All the lumbar nerves receive the grey rami communicantes from the corresponding lumbar ganglia. These grey rami-carrying nerve fibers are distributed to the lower abdominal wall and to the structures in the lower limb. Lumbar sympathetic chains give rise to four lumbar splanchnic nerves. The upper 2 nerves join the coeliac plexus while the lower two nerves join the superior hypogastric plexus.
Sacral sympathetic ganglia
Sacral sympathetic ganglia are 4 or 5 in number and form the sacral part of the sympathetic chain descending in front of the body of the sacrum. Sacral sympathetic ganglia give off grey rami communicantes to all sacral and coccygeal ventral rami. The upper ganglia give branches to the inferior hypogastric plexus while the lower ganglia give branches supplying the median sacral artery. Lower ganglia also give branches to the rectum.
Ganglion impar
Ganglion impar is a retroperitoneal structure located anteriorly to the sacrococcygeal junction. The ganglion is formed by the combination of sympathetic trunks of the right and left sides. There are no white rami communicantes from spinal nerves to the ganglion impar. Visceral afferents from the perineum, distal rectum, anus, vulva, distal 3rd of the vagina, and distal urethra pass through the ganglion impar. Ganglion impar block is used to relieve pain in the lower pelvis and groin in conditions such as vaginal or vulvar cancer, scrotal cancer, rectal or anal cancer, pain in the coccyx, rectal pain, bladder cancer, etc.
Prevertebral ganglia
Prevertebral ganglia are part of the sympathetic nervous system and they are located between the sympathetic chain and the target organ. These ganglia include coeliac ganglia (which include aortic renal ganglia), superior mesenteric ganglia, and inferior mesenteric ganglia. Similar to the paravertebral ganglia, the prevertebral ganglia are also the locations where the presynaptic fibers make synapses with the postsynaptic fibers.
Coeliac ganglion
The coeliac ganglion is the largest ganglion located in the human body. They are located on the sides of the coeliac trunk. The coeliac ganglion is irregular in outline and usually divided into the upper part where the greater splanchnic nerve ends and the small lower part, called the aortic renal ganglion which receives the lesser splanchnic nerve. The solar plexus also called the coeliac plexus is closely related to the coeliac ganglion. The coeliac plexus is located on the inferior vena cava and pancreas. Different fibers make up the plexes which are the preganglionic sympathetic fibers from greater and lesser splanchnic nerves, postganglionic fibers from coeliac ganglion, preganglionic vagal fibers, and sensory fibers from the diaphragm. The coeliac plexus forms a number of secondary plexus which include phrenic plexus, hepatic plexus, left gastric plexus, splenic plexus, suprarenal plexus, testicular plexus, ovarian plexus, abdominal aortic plexus, and superior & inferior mesenteric plexus.
Superior mesenteric ganglion
The superior mesenteric ganglion is the ganglion located in the upper part of the superior mesenteric plexus and it lies close to the origin of the superior mesenteric artery. The superior mesenteric ganglion is also a point where are presynaptic and postsynaptic sympathetic fibers make synapses. The superior mesenteric ganglion basically arises from the lesser splanchnic nerve and supplies the jejunum, ileum, ascending colon, and transverse colon.
Inferior mesenteric ganglion
The inferior mesenteric ganglion is located near the branches of the inferior mesenteric artery and gives off the hypogastric nerve involved in the formation of the pelvic plexus.
Summary
Sympathetic ganglia are the structures in the body where preganglionic sympathetic fibers arising from the spinal cord synapse with the postganglionic sympathetic fibers, supplying the target structures. These ganglia are broadly classified into two types, paravertebral and prevertebral ganglia, depending upon their location in the body.
Paravertebral ganglia are located in the form of a long sympathetic chain adjacent to the vertebral column extending from the base of the skull to the coccyx. The paravertebral sympathetic chain is divided into four parts depending upon its association with different spinal segments which include the cervical part, thoracic part, lumbar part, and sacral part.
In the cervical part of the sympathetic chain, ganglions fuse together to form three cervical ganglions, superior, middle, and inferior cervical ganglions. The inferior cervical ganglion is fused to the 1st thoracic ganglion to form the cervicothoracic ganglion or stellate ganglion. Cervical ganglions give sympathetic supply to the several structures in the head & neck region and are also involved in the formation of superficial and deep cardiac plexuses.
Thoracic sympathetic ganglia are twelve in number, out of which 1st one is fused with the inferior cervical ganglion. They give the sympathetic supply to the vasculature of the greater part of the body and are involved in the formation of the aortic plexus, esophageal plexus, pulmonary plexus, and cardiac plexus. They also give greater, lesser, and least splanchnic nerves which supply several structures in the abdominal cavity by communicating with coeliac and aortic renal ganglion.
Lumber ganglia are 4 or 5 in number and are involved in the formation of coeliac and superior hypogastric plexus. Sacral ganglia are also 4 or 5 in number and give branches to the inferior hypogastric plexus. Below this level, the sympathetic chain of two sides fuses to form ganglion impar.
Prevertebral ganglia include coeliac ganglia and superior & inferior mesenteric ganglia. They form several neuronal plexus-supplying structures in the abdominal cavity and perineum.
References
Kattar N, Flowers T. Anatomy, Head and Neck, Sympathetic Chain. [Updated 2022 Sep 26]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK563206/