Synonyms in a broader sense
vegetative nervous system, sympaticus
Definition
The sympathetic nervous system is the antagonist of the parasympathetic nervous system and is – like the latter – a part of the vegetative (also: autonomous) nervous system. The autonomic nervous system is important for the control of our organs and glands, it is called autonomous because we cannot control it arbitrarily, it runs “alongside” without being constantly aware of it (just think of breathing, for example, Digestion and sweating)In order to define the sympathetic nervous system with its tasks very scarcely, one could say that it triggers all that what constitutes an escape reaction (at that time, hundreds of years ago because of the tiger in the thicket, today, it is perhaps instead of “escape” often rather stress or panic because of a directly upcoming examination or similar). Through increased activity of the sympathetic nervous system, our bodily functions therefore change as follows: Now it has become clear WHAT triggers the sympathetic nervous system, but HOW it does it and WHERE in the body it is located at all remains to be clarified.
- Faster heartbeat (higher heart rate and stronger contraction)
- Vasodilatation (so that more blood can flow, because the heart needs more oxygen to work harder)
- Faster breathing
- Increased sweating
- Elevated blood pressure
- Pupil dilation
- Reduced activity of the digestive tract
- Reduced urge to urinate (continence)
The sympathetic nervous system should not be imagined as a single “point” in the body. Rather, it is distributed over a fairly large part of the body. It has a place of origin (i.e.
the cells, which are a kind of command center) and a kind of rail system (i.e. the fibers that emanate from the cells and ensure that what the command center “cell” commands is passed on to the recipient). The recipients of the commands are the organs on which the sympathetic nervous system acts (heart, lungs, gastrointestinal tract, vessels, eye, glands, skin). The sympathetic nervous system is a thoracolumbar system, i.e. its points of origin are located in the thoracic region (thorax (Latin) = ribcage) and in the lumbar region (lumbus (Latin) = loin).
This is in the lateral horn of the spinal cord. The cells of origin there are nerve cells (neurons), which send their information-transmitting nerve cell extensions (axons) via intermediate stations to the organs to be controlled. The intermediate stations are so-called ganglia (ganglion (Latin) = nodes).
Multipolar nerve cells are located here. Multipolar means that they contain an information-transmitting extension, the axon, and more than 2 information-receiving extensions, the dendrites. There are two types of ganglia in the sympathetic system: paravertebral ganglia (para = next to, i.e.
ganglia next to the spinal column), which are also known as border ganglia in German prevertebral ganglia (pre = before, i.e. ganglia that lie in front of the spinal column). A switch of information that a nerve cell passes on always occurs in only one of the two types of ganglia mentioned above, not in both. The sequence of information conduction is therefore: original cell in the spinal cord (1) – multipolar nerve cell in a ganglion (2) – organWhat is the information?
Because the cell cannot talk, but has to make clear what it “wants” with electrical stimuli or a substance. This substance is the so-called neurotransmitter. Neurotransmitters are chemical messengers which – as the name suggests – can transmit information to different places, so they are a kind of “messenger”.
A distinction is made between excitatory (excitatory) and inhibitory (inhibiting) neurotransmitters. The neurotransmitters are used for chemical information transmission, while the electrical potentials that run through the cell and its extensions (axons and dendrites) are used for electrical information transmission. The chemical transmission of information is always important when the information is to pass from one cell to another, because there is always a gap between cells – even if it is relatively small – which the information cannot simply skip.
Once the electrical line has reached the “end” of the cell, i.e. its axon end, it ensures that a type of neurotransmitter is released from the axon end. The axon end from which it is released is called the presynapse (pre = before, i.e. the synapse before the synaptic cleft).The neurotransmitter is secreted into the so-called synaptic gap, which is located between cell 1 (information line) and cell 2 (information reception), between which it is necessary to switch. After its release, the neurotransmitter “migrates” (diffuses) through the synaptic gap to the extension of the second cell, the post-synapse (post = after, i.e. the synapse after the synaptic gap).
This contains receptors that are designed for exactly this neurotransmitter. Thus, it can bind to it. Through its binding, an electrical potential is now generated again at the second cell.
When switching information from one cell to the next, the sequence of information types is therefore: electrically up to the axon end of the first cell – chemically in the synaptic cleft – electrically from the binding of the neurotransmitter to the second cell Cell 2 can now react in two ways by binding the neurotransmitter: Either it is excited and generates a so-called action potential or it is inhibited and the probability that it generates an action potential and thus excites further cells decreases. Which of the two ways a cell takes is determined by the type of neurotransmitter and the type of receptor. So now we can specify what happens at the various “switchover points” of the sympathetic nervous system: The first cell (original cell) in the spinal cord is excited by higher centers (e.g. the hypothalamus and the brain stem).
The excitation continues through its entire axon up to the first switch point (which is now already in the ganglion). There, the neurotransmitters acetylcholine is released from the presynapse as a result of the continued excitation. Acetylcholine diffuses through the synaptic cleft towards the synapse of the second cell (post-synapse) where it binds to a suitable receptor.
The cell is excited by this binding (because acetylcholine is one of the excitatory neurotransmitters). Just like in the first cell, this excitation is again transmitted through the cell and its extensions to the recipient: the organ. There – as a result of the excitation – another neurotransmitter is released from the synapse of cell 2 – this time it is noradrenaline. This neurotransmitter then acts directly on the organ. The sympathetic nervous system thus works with two different neurotransmitters: The 1st (original cell – cell 2) is always acetylcholine The 2nd (cell 2 – organ) is always noradrenaline
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