If after lunch you sit down at your desk to do your chores but almost fall asleep, your parasympathetic nervous system is active. The parasympathetic nervous system is an important part of your nervous system. Among other things, it ensures that the body can relax and digest. It works without your willing influence.
Parasympathetic – general
You’ve probably heard that it’s better not to eat large meals directly before exercising. In most cases, a large portion will make you feel more like a nap than a marathon anyway. But why is it like that?
The parasympathetic nervous system is sometimes responsible for this. The parasympathetic nervous system is the part of the vegetative (= involuntary) nervous system that predominates in rest and regeneration phases. This is also referred to as the “rest and digest” mode. His opponent is the sympathetic, which predominates in «fight-and-flight» situations.
That autonomic nervous system cannot be arbitrarily controlled by humans. It is divided into sympathetic and parasympathetic parts. The sympathetic has a performance-enhancing effect, the parasympathetic has an activation-inhibiting effect.
After a meal, the body’s priority is the digestion the food ingested and the absorption of nutrients. Accordingly, the parasympathetic nervous system becomes active in such a situation. It ensures that the digestive tract is particularly well supplied with blood. As a result, the brain and muscles are supplied with relatively less blood and you feel less efficient.
The parasympathetic stimulates digestion. In general, however, the parasympathetic nervous system has an inhibitory effect on the organs of your body. Its effect is also referred to as trophotropic, i.e. aimed at building up the body’s own reserves. his opponent – the sympathetic – On the other hand, it has an ergotropic effect, i.e. increases performance.
You can find out more about the sympathetic nervous system in the article on the sympathetic nervous system here on the page.
In addition to the digestive tract, the two parts of the autonomic nervous system also influence almost all other organs, such as the eyes, heart, lungs, bladder and many more.
Parasympathetic Anatomy
The parasympathetic system is also called the craniosacral system. This is because the area of origin of the parasympathetic nerve cells is inside the skull (lat. cranial) in the brainstem and in the sacral (from lat. os sacrum = sacrum) area of the spinal cord. So the parasympathetic originates from it, just like the sympathetic central nervous system (CNS) and then continues in the periphery of the body, i.e. outside the CNS.
Basically, the parasympathetic nerves originating in the brainstem are more responsible for supplying the organs in the head area and the internal organs in the chest and abdominal cavities. The parasympathetic nerve cells originating in the sacrum, on the other hand, move to the deep regions of the abdomen and are important, among other things, for genital function and the supply of the last sections of the intestine.
The transition from the head to the sacral parasympathetic occurs at a posterior part of the large intestine. Since different supply structures interchange there, this point also has a name. In medicine it is called Cannon Boehm point designated.
The cell bodies of the first (= preganglionic) parasympathetic neuron are located in the brainstem in so-called core areas (lat. nuclei ). The parasympathetic nuclei comprise the nuclei of four cranial nerves, namely the nucleus
- the third cranial nerve (Nervus oculomotorius),
- the seventh cranial nerve (nervus facialis),
- the ninth cranial nerve (glossopharyngeal nerve) and
- of the tenth cranial nerve (nervus vagus).
Nerve cells, which go from the central nervous system to a ganglion, are also referred to as preganglionic. In contrast, nerve cells that move from the ganglion to an organ are referred to as postganglionic.
The cell bodies of the preganglionic, parasympathetic neuron are located in the spinal cord. These are in side horn located in the gray matter of the spinal cord at the level of the sacrum. In the sacral area of the spinal cord, however, the lateral horns are not as pronounced as in the thoracic and lumbar areas, from which the sympathetic nervous system emerges.
The parasympathetic nerve fibers that depart from the S2 to S4 spinal cord segments are called the pelvic splanchnic nerves. They supply the organs of the pelvic cavity parasympathetically. They are therefore important for defecation (= emptying of the rectum) and micturition (= urination) because they supply parts of the large intestine and the urinary bladder. In addition, are important for genital functions, such as erection in men.
The ganglia of the parasympathetic nervous system
The ganglia are located near the respective organs that are supplied by the parasympathetic nervous system. In these lie the cell bodies of the second sympathetic neuron. Here a switch from the pre- to the post-ganglionic neuron takes place. This happens with the Nervi splanchnici pelvici in the ganglia of the intestinal wall and in the lower abdominal network.
Apart from the ganglia close to the organs, there are the head ganglia, in which switching of the parasympathetic nerves also takes place. There are four parasympathetic head ganglia:
- Ciliary ganglion: Located in the eye socket, it supplies the ciliary and pupillary muscles with blood. Here the neurons from the core area of the N. oculomotorius are switched.
- Pterygopalatine ganglion: It is located near the palate and supplies the mucous membrane of the palate and nose, as well as the lacrimal gland. Here the neurons from the core area of the N. facialis are switched.
- Ganglion oticum: It lies in the area of the base of the skull and supplies the parotid and buccal salivary glands, among other things. Here the neurons from the core area of the N. glossopharyngeus are switched.
- Submandibular ganglion: Located in the lower jaw region, it supplies the sublingual and submandibular salivary glands; here also switching of nerves from the core area of the N. facialis)
The ganglia are also referred to as nerve knots because they can even be seen with the naked eye as knotty, thickened areas of a nerve.
In addition to the parasympathetic nerve fibers, nerve fibers with other fiber qualities also pass through the ganglia, eg motor or sympathetic nerve fibers, which, however, are not switched there.
The vagus nerve
The largest nerve in the parasympathetic nervous system is the vagus nerve, the tenth cranial nerve. It plays an important role in the parasympathetic innervation of most internal organs. It leaves the skull and runs together with the carotid artery to the chest cavity, where it supplies the heart and bronchi, for example. In its further course, it still moves to many large organs such as the liver, kidneys and spleen.
The vagus nerve is the main parasympathetic nerve in the thoracic and abdominal cavities. However, in addition to parasympathetic functions, it also fulfills other functions, for example the sensory innervation of the pharynx and, to some extent, the motor innervation of the palate.
While the ganglia of the parasympathetic nervous system lie close to the effector organs, the sympathetic ganglia lie in a lateral nerve network close to the spinal column. This will be as limit strand designated. That is why the preganglionic neuron – the neuron originating in the CNS – is short in the sympathetic nervous system. In contrast, the postganglionic sympathetic neuron, which runs after the ganglion to the effector organ, is long.
In the parasympathetic nervous system, on the other hand, the opposite is true. The ganglion lies Organ-near. Most of the time, it is connected just before the successful organ. Accordingly, the preganglionic neuron is long and the postganglionic neuron is relatively short.
Parasympathetic – neurotransmitters
In order for neurons to be able to communicate with other cells, they need signals or signals messenger substances. In the nervous system these are referred to as neurotransmitters.
This is the essential parasympathetic neurotransmitter acetylcholine (short ACh). It is used in both the ganglia and the effector organ, as you can see in Figure 2.
Through the use of different neurotransmitters by the two systems, the organ knows how to react to the transmitted stimuli and the activity either increases or decreases.
Acetylcholine is an important neurotransmitter that not only plays an important role in the autonomic nervous system.
For example, ACh is also at the neuromuscular junction where a nerve cell meets a muscle cell. After being released in the synaptic cleft, acetylcholine is broken down by the enzyme acetylcholinesterase. Many medicines work by inhibiting this enzyme.
There are two different types of acetylcholine receptors in the parasympathetic nervous system: nicotine high and muscarinic receptors. In addition to acetylcholine, nicotine can also bind to nicotinic acetylcholine receptors. These receptors are found in the autonomic ganglia. The muscarinic acetylcholine receptors are not only activated by acetylcholine, but also by the fungal toxin muscarine. They can be further divided into subtypes located on different organs.
For example, the M2 receptor is found in the heart and the M3 receptor in the bronchi.
Parasympathetic – Functions
The parasympathetic nervous system is one of the three parts of the autonomic nervous system. The autonomic nervous system, also known as autonomous The nervous system controls the involuntary processes in the body. These processes cannot be directly controlled consciously.
As already mentioned, the autonomic nervous system consists of three parts:
The enteric nervous system lies in the wall of the gastrointestinal tract and acts there as an independent nervous system. Nevertheless, sympathetic and parasympathetic have an influence on it. That stands for the vegetative nervous system somatic nervous system opposite. It is also referred to as the animal or voluntary nervous system because it controls conscious bodily functions, such as conscious movements.
In addition to the functional division into the vegetative and the somatic nervous system, there is also a topographical division according to the position in the body. This is where you differentiate central nervous systemconsisting of spinal cord and brain, and that peripheral nervous system.
The parasympathetic nervous system is responsible for the development of reserves and the recreation. You will get to know how it influences the various organs in the next few sections.
Effect of the parasympathetic nervous system on the eyes
The parasympathetic leads to the eye miosis, i.e. to constrict the pupil. This is due to parasympathetic nerves that go to the constrictors of the pupil. In addition, parasympathetic nerves supply the ciliary muscle. This muscle is essential for near accommodation, i.e. focusing the lens at close range.
In the near accommodation The refractive power of the lens is adjusted using the ciliary muscle so that objects appear sharp at close range. For this purpose, the muscle and the zonula fibers contract, on which the lens…