Effect

The effect of the sympathetic nervous system has already been mentioned above and will be summarized here once again in tabular form: Eye Pupil dilation Heart Faster beating (increased frequency and increased contraction force) Lung Dilatation of the airways Salivary glands Decreased salivation Skin (includes sweat glands) Increased sweating; erection of hairs; narrowing of blood vessels (cold hands during excitement) Gastrointestinal tract Decreased digestive activity Blood vessels (except those of the skin and gastrointestinal tract) Dilatation so that more blood can flow per timeThe sympathetic nervous system increases the heart rate, so the pulse rate increases. But it also has other effects on the heart, all of which increase the overall performance of the heart. For example, the properties of the heart muscle cells are changed, which means that they can contract more strongly, allowing the blood to be pumped with more force.

The electrical properties of the nerve cells that lead to the muscle cells are also affected. As a result, a lower level of stimulation is already sufficient to trigger a full contraction of the heart muscle cells and the transmission of excitation along the nerve cells is also accelerated. However, for a muscle cell to be fully functional, it must relax completely for a few milliseconds between each individual contraction.

The time until complete relaxation, also called refractory time, is shortened by the sympathetic nervous system. In summary, the sympathetic nervous system has a stimulating effect, i.e. it has a positive influence on the heart rate (chronotropy), the strength of the heart (inotropy), the transmission of excitation (dromotropy), the stimulus threshold (bathmotropy) and relaxation (lusitropy). By increasing these functions, the heart can pump more and faster blood, which supplies the body with oxygen.

The sympathetic nervous system thus ensures that the increased demand, especially of the brain and muscles, is always met. The sympathetic nervous system also plays a decisive role at the pupil. When it gets dark, the sympathetic nerve fibers that move towards the eye are stimulated.

This stimulates a muscle that lies like a ring around the pupil, called the Musculus dilatator pupillae. It contracts and thus dilates the pupil.The wider the pupil, the more light can enter the eye and the better we can see in already low light conditions. But the sympathetic nervous system also has an influence on the lens in the eye.

Here it is interesting to know the anatomy of the eye a little bit. The lens, is suspended on fibers. These fibers are in turn attached to a muscle, the ciliary muscle.

This muscle is excited by the parasympathetic nervous system, the antagonist of the sympathetic nervous system. As a result, the lens rounds itself off and we can see nearby objects well. The sympathetic nervous system, on the other hand, relaxes the muscle, causing the lens to flatten and we can see more clearly at a distance.

In order to explain the function of the sympathetic nervous system at the kidney in an understandable way, we first need to look at the function of the kidneys. Among other things, they are responsible for maintaining the water and salt balance in the body. The water balance has a direct influence on blood pressure, which brings us to the function of the sympathetic nervous system.

As mentioned above, blood pressure is raised by the sympathetic nervous system. On the one hand, the sympathetic nervous system has a direct constricting effect on the vessels, on the other hand, it stimulates certain cells of the kidneys. These cells produce the hormone renin.

Renin is the first step in a long chain of events, at the end of which the synthesis of the hormone angiotensin takes place. If the term angiotensin is translated from the Greek, it means “vasoconstrictive”. It is actually the most effective substance that the body can produce itself to constrict vessels.

The narrower a vessel, the higher the pressure that must be built up to allow blood to flow through it. This means that the effect of the sympathetic nervous system at the kidney is to increase blood pressure. In the short term, this is a very useful mechanism. Unfortunately, however, nowadays we are often under far too much stress for far too long, which is why this acute state of blood pressure increase turns into a long-term one. This leads to chronic high blood pressure, which then often has to be treated with medication.