The lesser splanchnic nerve is a visceral nerve and affects the function of the digestive system as well as certain blood vessels in the abdomen. Its fibers include both efferent and afferent pathways.
What is the splanchnic nerve minor?
The splanchnic nerve minor is the small visceral nerve; it mainly affects digestion as well as blood vessels located in the abdominal cavity. The nerve belongs to the sympathetic nervous system, which is a functional part of the autonomic nervous system. The autonomic nervous system is characterized by automated processes that humans cannot directly influence at will. Sympathetic activation is mainly associated with stimulating and performance-enhancing processes, while parasympathetic activation predominantly promotes regenerative processes. For this reason, the two subunits of the autonomic nervous system are considered to be opposites. Activity in parasympathetic nerves in many cases leads to a simultaneous inhibition of the respective sympathetic counterpart – conversely, an inhibition of sympathetic processes also takes place when parasympathetic activity predominates. In addition, a third subunit of the autonomic nervous system exists: the enteric nervous system includes fibers located near the stomach and intestines.
Anatomy and structure
The lesser splanchnic nerve is part of the border cord (sympathetic trunk), which runs parallel to the spinal cord through the trunk and consists of 22-23 ganglia and their nerve fibers. From the thoracic region of the border cord, the splanchnic nerve minor crosses the diaphragm and eventually reaches the coeliac plexus. The coeliac plexus is a plexus of nerves surrounding the coeliac trunk. The blood vessel divides into three arteries at this point, which include the splenic artery (splenic artery), the left gastric artery (gastrica sinstra artery), and the common hepatic artery. In some people, a branch branches off from the lesser splanchnic nerve at the coeliac plexus and leads to the renal plexus. This nerve plexus surrounds the renal artery (renal artery). Alternatively, another nerve, the splanchnic nerve imus, may provide this connection between the coeliac plexus and the renal plexus. The fibers of the splanchnic nerve imus originate from the 12th thoracic ganglion, whereas processes of neurons from the 9th to 11th thoracic ganglions form the fibers of the splanchnic nerve minor. Numerous nerve cell bodies lie close together in the ganglia. They have the significance of switching points in the peripheral nervous system, since the nerve fibers of the preganglionic nerves end in them and they pass on their information to postganglionic neurons. However, nerve fibers can also cross the ganglion without switching. Ganglia that contain fibers of the splanchnic nerve, among others, are the coeliac ganglion, the aorticorenal ganglion, and the superior mesenteric ganglion.
Function and Tasks
With the help of electrical signals, the lesser splanchnic nerve affects digestion in humans. In addition, the nerve affects some blood vessels. Humans cannot consciously control the function of the splanchnic nerve minor because it belongs to the pathways of the autonomic or vegetative nervous system. The fibers of the splanchnic nerve minor carry information from the central nervous system to the periphery with the help of efferent fibers. Conversely, afferent nerve fibers carry signals from the peripheral nervous system to the spinal cord and brain. The same is true for the large visceral nerve, the splanchnic nerve major, which has similar functions to the splanchnic nerve minor. Like other pathways, the splanchnic nerve minor transmits its information through the nerve fibers in the form of action potentials. At some points, these electrical signals must be switched to other nerve cells; the human body uses mostly chemical synapses for this purpose. The presynaptic nerve fibers have thickenings known as terminal buttons that contain membrane-enveloped vesicles. These contain messenger substances (neurotransmitters). When an action potential stimulates the terminal button, calcium ions flow into its interior and cause some vesicles to fuse with the outer membrane. In this way, the neurotransmitters enter the synaptic cleft and can occupy receptors on the postsynaptic membrane on the other side.Ion channels that open in response change the voltage of the downstream neuron; if this change exceeds a critical threshold, a new action potential is generated at the axon hillock of the neuron and the neuron can carry the signal further. The more action potentials in succession that reach the terminal button, the more neurotransmitter the presynapse releases and the greater the depolarization of the postsynaptic neuron.
Diseases
Ganglion blockers can affect the cell body accumulations that are found at numerous sites in the peripheral nervous system. In the past, medicine used ganglion blockers to treat anxiety and agitation, among other conditions; they were also widely used as sleep aids. Today, their use is less common because ganglion blockers have a nonspecific effect on the nervous system and are therefore more prone to side effects compared with more modern agents. Instead, physicians use benzodiazepines and other drugs, for example, to achieve similar effects. This is also the case with amobarbital. The ganglion blocker was once used as a sleep aid and sedative and is considered a “truth serum.” A ganglion blocker that is still in common use is hydroxyzine, which physicians may order for anxiety, tension, agitation, sleep disorders, and certain severe allergic reactions. Phenobarbital, on the other hand, is approved for the treatment of epilepsy and is used in anesthesia preparation. The abdominal ganglia, which also contain fibers of the lesser splanchnic nerve, are significant for the proper functioning of the digestive system. Accordingly, impairments to these clusters of nerve cell bodies can lead to a very wide variety of complaints affecting the digestive system.
