Autonomic Nervous System

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Independent control center

The autonomic nervous system (VNS) controls many vital body functions. These include, for example, breathing, digestion and metabolism. Whether the blood pressure rises, the veins dilate or the saliva flows cannot be influenced with one's will. Superordinate centers in the brain and hormones control the autonomic nervous system. Together with the endocrine system, it ensures that the organs function well. The organ function is quickly adapted to changing requirements via nerve impulses. Hormones first have to be transported to the target organ in the bloodstream.

When you get up in the morning, for example, the autonomic nervous system immediately sends a signal to increase your blood pressure and avoid dizziness. When a person is warm, the system ensures better blood circulation in the skin and activates the sweat glands. The nerve tracts also transmit important nerve impulses (reflexes) from the organs to the brain, for example from the bladder, heart or intestine.

According to the course of the nerve cords and their function, doctors distinguish three parts of the autonomic nervous system:

• Sympathetic,
• Parasympathetic nervous system,
• Visceral nervous system (enteric nervous system);

The nerve tracts of the sympathetic and parasympathetic nervous system lead from the central nervous system (CNS = brain and spinal cord) to the organs. They end, for example, in muscle cells in the intestinal wall, in the heart, in the sweat glands or in muscles that regulate the pupil size. The sympathetic and parasympathetic nerves basically act as opponents in the body. Both systems complement each other for some functions.

Sympathetic - fighting and fleeing

The sympathetic system prepares the organism for physical and mental performance. It ensures that the heart beats faster and stronger, the airways expand so that you can breathe better and the bowel movements are inhibited. In short: the sympathetic makes the body ready to fight or to flee.

The first sympathetic nerve cells are located in the spinal cord. Their processes run to cell nodes (ganglia) on both sides of the spine. Almost all signals are switched to a second nerve cell there, which brings the message to the target organ. Some nerve tracts skip this switching station. They only pass on their message in nerve nodes deep in the body or bring it directly to the target organ (e.g. intestine).

Nerves conduct electrical impulses. With the help of chemical messenger substances, they transmit signals to other nerve cells or the target cells in the organs. The sympathetic nerve cells communicate with each other with acetylcholine and with their target cells with noradrenaline.

Parasympathetic Nervous System - resting and digesting

The parasympathetic nervous system takes care of the body's functions at rest as well as the regeneration and development of the body's own reserves. It activates digestion, stimulates various metabolic processes and ensures relaxation.

The central cells of the parasympathetic nervous system are located in the brain stem and in the lower area of ​​the spinal cord (sacral cord). In nerve nodes near the target organs or in the organs themselves, they forward their message to the second nerve cells. The nerve cords of the parasympathetic nervous system transmit all signals with the messenger substance acetylcholine.

Opponent in the body

organ	Effect of the sympathetic system	Effect of the parasympathetic nervous system
• Eye	Dilatation of the pupils	Narrowing of the pupils and increased curvature of the lens
• Salivary glands	Reduced saliva secretion (little and tough saliva)	Increase in saliva secretion (a lot and thin saliva)
• Heart	Acceleration of the heart rate	Slowing your heart rate
• lungs	Expansion of the bronchi and reduction of bronchial mucus	Narrowing of the bronchi and increase in bronchial mucus
• gastrointestinal tract	Decreased bowel movement and decreased secretion of gastric and intestinal juices	Increased bowel movement and increased secretion of gastric and intestinal juice
• pancreatic gland	Decreased secretion of digestive juices	Increased secretion of digestive juices
• Male sexual organs	ejaculation	erection
• Skin	Narrowing of the blood vessels, sweat secretion, hair standing up	No effect

Visceral nervous system

The visceral nervous system ((enteric nervous system) consists of a network of nerves that is located between the muscles in the intestinal wall. These nerve fibers work in principle independently of other nerves, but are strongly influenced by the parasympathetic and sympathetic nervous system. The enteric nervous system takes care of digestion: it For example, increases the movement of the intestinal muscles, ensures that more fluid is excreted into the intestinal tube, and increases blood flow in the intestinal wall.

Head zones

It used to be assumed that the autonomic nervous system only passed signals from the spinal cord to the periphery of the body. Today we know that along with the sympathetic and parasympathetic nerve cords, signals from the organs also reach the central nervous system. About five percent of all pain stimuli in the body take this route. Scientists suspect that these fibers end at the same point in the spinal cord as nerve fibers that transmit pain stimuli from the skin. This can lead to the perception of pain caused by gallstones on the shoulder skin, for example. Depending on the organ, the pain is always projected onto the same areas. These skin zones are called head zones - after their first description, the British neurologist Sir Henry Head.

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