The greater splanchnic nerve is a sympathetic nerve of the autonomic nervous system that supplies the blood vessels, the building organs, and the adrenal medulla. The adrenal medulla is stimulated to release adrenaline and noradrenaline via the sympathetic fibers of the nerve. The result is a stress response that plays a role in acute shock, for example.
What is the splanchnic nerve major?
The human nervous system consists of a somatic and an autonomic part. The former part of the nervous system can be consciously controlled by humans. The autonomic nervous system, on the other hand, escapes voluntary control and thus behaves “autonomously.” Above all, the vegetative body functions are subject to automatic control by the autonomic nervous system. These autonomic functions include, for example, the cardiovascular system, parts of the respiratory system and activities of the internal organs. The autonomic vegetative nervous system includes the so-called nervi splanchnici, which are involved in the control of the internal organs. One of them is the nervus splanchnicus major, is the one that originates from the thoracic part at the truncus sympathicus. With some exceptions, the nervi splanchnici, and thus the nervus splanchnicus mahor, belong to the sympathetic nervous system. In German literature, the nerve is also called the great visceral nerve.
Anatomy and structure
Like most splanchnic nerves, the greater splanchnic nerve arises from ganglia on the thoracic border cord (truncus sympathicus). The nerve takes up both efferent and afferent nerve fibers from the fifth through ninth thoracic ganglions of the border cord. In its course, the greater splanchnic nerve passes through the middle lumbar fissure of the diaphragmatic structure, thus passing over the ganglia coeliaca to the coeliac plexus of the truncus coeliacus. The course of the nerve bears interruptions corresponding to a thoracic splanchnic ganglion. The greater splanchnic nerve is principally the major sympathetic nerve of the peripheral nervous system. It is connected to the viscera of the abdomen via preganglionic sympathetic nerve fibers. Together with the splanchnic nerve minor, the nerve passes above the spine through the so-called psoasarcade of the pars lumbalis in the diaphragm.
Function and Tasks
As part of the autonomic nervous system, the splanchnic nerve major performs vital functions in the human body. In addition to the ganglia coeliaca and ganglia aorticorenalia, the nerve innervates a large portion of the abdominal viscera with preganglionic sympathetic fibers. After the nerve fibers are connected to a second postsynaptic neuron, individual sympathetic fibers of the nerve travel to the adrenal medulla. Greatly simplified, the sympathetic nervous system with its sympathetic nerve conduction pathways enables a rapid response to stimuli from the environment and from within the body. In addition, the sympathetic nervous system has a stimulating effect and mobilizes the body’s forces. In this context, biologists also speak of stress reactions, which prepare the organism for efforts such as flight or fight in extreme situations. The greater splanchnic nerve connects the sympathetic nervous system with the abdominal viscera, the vessels and the adrenal medulla. Sympathetic nerve fibers have a regulating effect on the vessels. In stressful situations, for example, the sympathetic nervous system mediates constriction of blood vessels of the viscera via the splanchnic nerve major. This decreased blood flow to organs of the upper abdomen occurs through vasoconstriction. The heart and lungs, as primarily vital organs, thus have more blood available. Survival can be ensured. The digestive organs reduce their activity due to the reduced blood flow. This inhibitory effect on the function of the entire gastrointestinal tract allows concentration on primarily vital body processes. In the second reaction chain of a stress response, the sympathetic nervous system mediates stimulation of the adrenal medulla via the splanchnic nerve major. After activation, the adrenal medulla releases adrenaline and noradrenaline within a few seconds. The stress hormone epinephrine, in particular, regulates a variety of bodily processes during stress responses.
Diseases
The greater splanchnic nerve plays an essential role in the state of any acute shock response. Shock reactions are the body’s attempt to stabilize its own blood pressure.During the shock reaction, the sympathetic nervous system stimulates the release of adrenaline and noradrenaline via the splanchnic nerve major, which causes the heart rate to increase and the arterioles and venules to constrict. Blood pressure rises after these processes to maintain blood flow to the heart and brain for as long as possible. Since the blood flow in the rest of the body is throttled, an undersupply of peripheral tissues occurs. Because of the associated undersupply of oxygen, acidic end products from anaerobic carbohydrate metabolism accumulate in the tissues, thereby overacidifying the body. In addition to this metabolic acidosis, fluid leakage from the hair vessels into the tissues occurs, causing the blood volume to decrease. Arterial smaller vessels slacken due to acidosis. Draining blood vessels do not slacken, so that red blood cells accumulate in the hair vessels and microthrombi form. The result can be a consumption coagulopathy. Shock reactions of this type occur, for example, after blood loss that greatly reduces blood volume and thus reduces the pumping capacity of the heart. In addition, shock states can occur in the context of heart failure, which primarily reduces the pumping capacity of the heart. Another cause of acute shock states may be sepsis or anaphylaxis. In these phenomena, damage to the capillaries results in fluid loss from the vessels, which lowers the pumping capacity of the heart, causing acidosis and further vascular damage. Any acute shock condition is a life-threatening situation that requires immediate intervention. Patients are usually treated in the intensive care unit, where their circulation is monitored and stabilized.
