Where Are Prevertebral Ganglia Located?
Prevertebral ganglia belong to the sympathetic ganglia. Unlike parasympathetic ganglia, which are located in close proximity to or within the target organ, sympathetic ganglia are situated at a distance from the organs they innervate.
The prevertebral ganglion is located peripherally to the sympathetic trunk. Prevertebral ganglia are situated within the abdominal cavity; they include the celiac plexus and mesenteric ganglia. Additionally, the celiac plexus, superior and inferior mesenteric ganglia, and cervical ganglia are classified as prevertebral structures.
Which Nerve Fibers Pass Through the Ganglion?
- Preganglionic sympathetic fibers: Originate in the spinal cord, emerge via the ventral root, branch off as white rami communicantes, and enter the sympathetic trunk. Within the sympathetic trunk, some preganglionic fibers pass through without synapsing, terminating instead on secondary neurons within the prevertebral ganglia.
- Postganglionic sympathetic fibers: After synapsing in the ganglia, they form perivascular plexuses that extend toward the organs.
- Afferent fibers: Diagrams demonstrate a sensory fiber from the intestinal wall passing through the prevertebral ganglion, sympathetic trunk, white ramus communicans, and dorsal root into the spinal cord. Extensive connections between gastric nerves and nerves of adjacent organs—such as the liver, duodenum, and pancreas—explain referred pain and the impairment of one organ's function during diseases of another.
Mechanism of Synaptic Transmission
In prevertebral ganglia, excitation is transmitted from a preganglionic fiber to a postganglionic neuron. This mechanism of transmission from the preganglionic fiber to the postganglionic neuron is identical for both the sympathetic and parasympathetic systems.
- Neurotransmitter: Acetylcholine (ACh).
- Receptor type: Nicotinic acetylcholine receptors (N-cholinergic receptors).
Celiac Plexus
The celiac plexus (plexus celiac or plexus coeliacus) is the largest autonomic plexus in the abdominal cavity; in older literature, it is referred to as the "solar plexus".
- Topography: Located in the retroperitoneal space at the level of the 12th thoracic vertebra. It lies on the anterior surface of the aorta, flanking the celiac trunk; its position is also noted on the sides of the base of the truncus celiac, lateral to the aorta and near the adrenal glands. Anteriorly, it lies within the retroperitoneal fat of the posterior abdominal wall and is covered by the parietal peritoneum of the posterior wall of the omental bursa. The lower boundary is the level where the renal arteries branch off from the aorta.
- Composition of ganglia: Includes two celiac ganglia (ganglia celiaca), two aortorenal ganglia (ganglia aortorenalia), and the unpaired superior mesenteric ganglion (ganglion mesentericum superius).
- Fibers and branches: Entered by the greater and lesser splanchnic nerves (nn. splanchnici major et minor), which carry preganglionic sympathetic fibers; branches of the nn. splanchnici thoracici major et minor, vagus nerve (n. vagus), and phrenicoabdominal branches (rr. phrenicoabdominales) via the celiac plexus are also involved.
- Connections: Connected superiorly with the thoracic aortic plexus (plexus aorticus thoracicus) and inferiorly with the superior mesenteric plexus (plexus mesentericus superior).
Innervated Structures
Postganglionic fibers that synapse in the prevertebral ganglion innervate internal organs.
- Celiac plexus: Innervates organs of the upper abdominal cavity: stomach, liver, pancreas, and kidneys. Sources of innervation for the duodenum include the celiac plexus, superior mesenteric plexus, and other periarterial plexuses.
- Superior mesenteric plexus: Innervates the intestines.
- Inferior mesenteric plexus: Innervates pelvic organs: the urinary bladder and reproductive organs.
- Cervical ganglia: The superior cervical ganglion innervates structures of the head, including the eye.