The inferior mesenteric ganglion is located in the abdomen and collects fibers from the greater splanchnic nerve and the lesser splanchnic nerve, which continue as the inferior mesenteric plexus and are responsible for sympathetic regulation of some intestinal segments. Missing cells in the inferior mesenteric ganglion may contribute to the development of Hirschsprung disease.
What is the inferior mesenteric ganglion?
The mesenteric inferior ganglion is a cluster of nerve cell bodies (somata) in the peripheral nervous system, from which nerve fibers branch off that pass through the trunk as the splanchnic nerve major and splanchnic nerve minor. The inferior mesenteric ganglion lies in the abdominal cavity and thus belongs to the prevertebral ganglia (“nerve nodes before the vertebrae”). At the level of the third lumbar vertebra, it is located at the point where the inferior visceral artery (inferior mesenteric artery) branches off from the abdominal aorta (abdominal aorta). The other three prevertebral ganglia are also located along the spine; they are the coeliaca ganglia, the aorticorenalia ganglia, and the inferior mesenteric ganglion.
Anatomy and structure
Some fibers from the border cord initially move on to other neurons without switching; at the mesenteric inferior ganglion and the other prevertebral ganglia, they accordingly transmit their signals to a downstream neuron via a synapse for the first time since the border cord ganglia. The inferior mesenteric ganglion belongs to the sympathetic nervous system, which predominantly exerts a performance-enhancing effect (ergotropy) on the organism. The fibers that converge in the mesenteric inferior ganglion originate predominantly from the greater visceral nerve (splanchnic nerve major) and the lesser visceral nerve (splanchnic nerve minor). From the ganglion, they run as the inferior mesenteric plexus along the inferior mesenteric artery. The inferior mesenteric plexus is a plexus of nerves comprising mainly viscerosensitive and motor fibers, the latter controlling not only intestinal movements but also the secretion of secretions from glands.
Function and tasks
The function of the ganglion is to switch incoming neurons (preganglionic neurons) to others (postganglionic neurons). The switching is done with the help of synapses, which are located at the junction between two nerves. A synapse consists of the end buttons of the preganglionic nerve cells, which contain vesicles filled with biochemical messengers (neurotransmitters). When the electrical stimulus reaches the end of the nerve fiber, the terminal buttons release their neurotransmitters; the more action potentials the preganglionic neuron receives, the more neurotransmitters it releases. The most important neurotransmitter in the sympathetic nervous system is acetylcholine. The molecules thus enter the synaptic cleft and can reach the membrane of the postganglionic neuron on the other side. Receptors are located in the membrane to which the neurotransmitters bind temporarily, thereby inducing the response of the next neuron: Ion channels open in the postsynaptic membrane and depolarize the cell. The electrical voltage of the neuron changes and generates a new action potential in the postganglionic cell, which can again propagate along the nerve fiber. In the inferior mesenteric ganglion, not only two neurons meet, but many; they can therefore influence each other by inhibiting or reinforcing each other. This process is of great importance for the filtering of information. Very weak signals or spontaneous activity of neurons is thus less likely to result in a response from the end organ, because it may be lost along the way. Conversely, ganglia can in this way focus sensory information destined for the brain, for example. Nerve fibers from the inferior mesenteric ganglion participate in the regulation of three intestinal segments. The descending colon, like the sigmoid colon, which directly adjoins it, is part of the colon. Finally, the digestive organ opens into the rectum, also known as the rectum, which leads to the anus or bowel outlet.
Diseases
The inferior mesenteric ganglion plays an important role in the development of Hirschsprung’s disease, among other diseases.The disease is also known as (intestinal) aganglionosis, congenital aganglionic megacolon or megacolon congenitum. Pediatrician Harald Hirschsprung first described the congenital obstruction in 1888. In Hirschsprung’s disease, the ganglion cells between the ring and longitudinal muscles of the colon and rectum are not (sufficiently) present. At the same time, the parasympathetic pathways located in the lamina propria mucosae as well as the lamina muscularis mucosae of the intestinal segment are overdeveloped. As a result, more acetylcholine is available: The permanent irritation causes the intestinal muscles to spasm, causing the intestine to dilate greatly. The malformation impairs the functioning of the digestive organ in affected newborns and usually manifests as a swollen abdomen. Hirschsprung’s disease can result in intestinal obstruction (ileus) if the first stool is not expelled artificially, which in turn can lead to necrotizing enterocolitis. This is an inflammation of the bowel characterized by a distended abdomen, lack of bowel movement, discernible bowel loops, vomiting, and mucus and blood in the stool. In addition, necrotizing enterocolitis can cause respiratory failure (apnea), bradycardia, fluctuations in body temperature, weakness in drinking, and grayish skin. Severe cases of Hirschsprung’s disease can often be detected by doctors shortly after birth, but symptoms may also manifest for the first time after weaning and the associated change in diet. Treatment options include surgery, in which a doctor creates an artificial anus and removes the affected section of bowel. Hirschsprung disease is particularly common in children with trisomy 21, Waardenburg syndrome, Laurence-Moon-Biedl syndrome, Smith-Lemli-Opitz syndrome, and other congenital malformations.