The autonomic nervous system (VNS) controls many vital bodily functions. These include, for example, breathing, digestion and metabolism. Whether blood pressure rises, veins dilate or saliva flows cannot be influenced by the will. Higher-level centers in the brain and hormones control the autonomic nervous system. Together with the hormone system, it ensures that the organs function properly. Nerve impulses are used to quickly adapt organ function to changing requirements. Hormones must first be transported to the target organ by the bloodstream.
When a person gets up in the morning, for example, the autonomic nervous system immediately sends a signal to increase blood pressure and prevent dizziness. If a person is warm, the system ensures better blood circulation to 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, the heart or the intestines.
According to the course of the nerve cords and their function, physicians distinguish three parts of the autonomic nervous system:
- Sympathetic nervous system,
- Intestinal nervous system (enteric nervous system);
The sympathetic and parasympathetic nerve pathways lead from the central nervous system (CNS = brain and spinal cord) to the organs. They end, for example, at muscle cells of the intestinal wall, the heart, the sweat glands or muscles that regulate pupil width. Sympathetic and parasympathetic nervous systems basically act as counterparts in the body. In some functions, the two systems complement each other.
Sympathetic nervous system – fight and flight
The sympathetic nervous system prepares the organism for physical and mental performance. It ensures that the heart beats faster and stronger, the respiratory tract expands to allow better breathing, and intestinal activity is inhibited. In short, the sympathetic nervous system makes the body ready to fight or flee.
Nerves conduct electrical impulses. With the help of chemical messengers, they pass on signals to other nerve cells or the target cells in the organs. Sympathetic nerve cells communicate with each other using acetylcholine and with their target cells using norepinephrine.
Parasympathetic nervous system – resting and digesting
The parasympathetic nervous system takes care of bodily functions at rest as well as regeneration and the build-up of the body’s own reserves. It activates digestion, boosts various metabolic processes and ensures relaxation.
The central cells of the parasympathetic nervous system are located in the brain stem and in the lower part of the spinal cord (sacral medulla). In nerve nodes near the target organs or in the organs themselves, they relay their message to the second nerve cells. The parasympathetic nerve cords transmit all signals with the neurotransmitter acetylcholine.
Counterparts in the body
| Organ | Effect of the sympathetic nervous system | Effect of the parasympathetic nervous system |
| – Eye | Dilation of the pupils | Constriction of the pupils and stronger curvature of the lens |
| – Salivary glands | Decrease in salivary secretion (little and viscous saliva) | Increase of salivary secretion (much and thin saliva) |
| Acceleration of the heart rate | Deceleration of the heart rate | |
| – Lungs | Dilatation of bronchial tubes and decrease of bronchial mucus | Constriction of bronchial tubes and increase of bronchial mucus |
| – Gastrointestinal tract | Decreased intestinal movement and decreased secretion of gastric and intestinal juices | Increased intestinal motility and increased secretion of gastric and intestinal juices @ |
| – Pancreas | Decreased secretion of digestive juices | Increased secretion of digestive juices |
| – Male sexual organs | Ejaculation | Erection |
| – Skin | Constriction of blood vessels, secretion of sweat, erection of hair | No effect |
Enteric nervous system
The visceral nervous system ((enteric nervous system) consists of a plexus of nerves located between the muscles in the intestinal wall. In principle, these nerve fibers work independently of other nerves, but are strongly influenced by the parasympathetic and sympathetic nervous systems. The enteric nervous system takes care of digestion: for example, it increases the movement of the intestinal muscles, ensures that more fluid is secreted into the intestinal tube, and increases blood flow in the intestinal wall.
