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The autonomic system (vegetative system) controls many very different processes - it affects, among others, affects the heart rate, the condition of the pupil and the rate of breathing, but is also responsible for the peristalsis in the digestive tract. There are two parts of the autonomic system - the sympathetic system and the parasympathetic system - whose opposing action is to adjust the state of the human body to its current needs.

The autonomic system( vegetative systemy) together with the somatic system make up the human nervous system. The autonomic nervous system is responsible for phenomena such as the function of intestinal loops, pupil dilation and heart rate - that is, aspects that we do not consciously control. The somatic system is its opposite - it is responsible for performing conscious activities - if we decide, for example, to reach for a cup, the somatic nervous system is responsible for controlling this activity.

Autonomous system: structure

There are two parts to the autonomic nervous system:

  • sympathetic nervous system (sympathetic)
  • parasympathetic (parasympathetic)

Both of these structures act in opposition to each other - when the sympathetic nervous system stimulates the body's reaction, the parasympathetic system usually inhibits it. The differences concern not only the functions of individual parts of the autonomic system, but also the neurotransmitters operating within them, as well as the location of the centers of the sympathetic and parasympathetic systems.

Before we start discussing the exact structure of the autonomic nervous system, it is worth mentioning a phenomenon characteristic of this part of the nervous system. We are talking about the existence of the coils of the autonomic system. The vegetative system has a characteristic structure with pre-ganglion fibers and post-ganglion fibers. In the somatic nervous system, the transmitted stimuli go directly to the effectors (e.g. to muscle cells), while in the autonomic system the nervous stimulus - before it finally reaches the structure it is supposed to affect - first reaches the ganglion of the autonomic system with a pre-ganglion fiber, and only later, through the postganglionic nerve fiber, it eventually reaches its destination.

Sympathetic nervous system:location of centers and neurotransmitters

The primary centers of the sympathetic nervous system are located in the spinal cord and extend between the C8 and L2-L3 levels of the spinal cord (that is, the bodies of the sympathetic neurons are located between the terminal cervical and lumbar spinal cord). It is from these structures that the pre-ganglion sympathetic fibers are directed to various parts of the body, and they reach the above-mentioned sympathetic ganglia. There are, among others, the cervical ganglion (upper, middle and lower), the stellate ganglion, the thoracic ganglion, and the lumbar and sacral ganglia. The poles of the sympathetic ganglia, extending on both sides of the spine, connected with each other by intergranular nerve branches, together form an element of the sympathetic nervous system known as the sympathetic trunk.

Among the structures of the sympathetic nervous system, there are also numerous nerve plexuses (e.g. cardiac plexus, visceral plexus or lower and upper abdominal plexus), as well as the entire network of the so-called visceral nerves.

Interestingly, the structures of the sympathetic nervous system, and more specifically its various ganglia, also include the adrenal medulla. The autonomic system also has a characteristic system of neurotransmitters. In the case of sympathetic fibers, acetylcholine is secreted in the pre-ganglion ends. The postganglionic fibers of this part of the autonomic system, in turn, secrete mainly norepinephrine - the differences, however, in this case concern the sympathetic endings innervating sweat glands (secreting acetylcholine) and the adrenal glands (which release norepinephrine into the circulation, but in a much larger amount the adrenal core releases adrenaline).

Parasympathetic system: location of centers and neurotransmitters

Meanwhile, the structure of the parasympathetic system is slightly different. Its centers are located not only in the spinal cord, but also in the brain stem. In the second location of the parasympathetic system, its structures exist in the parasympathetic nuclei of the four cranial nerves: the nucleus of the oculomotor nerve, the nucleus of the facial nerve, the nucleus of the glossopharyngeal nerve and the nucleus of the vagus nerve. As for the spinal cord, its parasympathetic centers are located in segments S2-S4 (sacral part of the spinal cord). Like the sympathetic system, the parasympathetic system also has its own ganglia (including the ciliary ganglion, the pterygoid palatine ganglion, the ear ganglion, and the submandibular ganglion), as well as plexuses and nerves reaching individual organs.

Transmission of nerve impulses in the parasympathetic system is similar to the sympathetic nervous system, i.e.through the pre- and post-ganglion fibers. The difference, however, is with the use of which neurotransmitter sends nerve stimuli - in the parasympathetic system, both types of its fibers secrete acetylcholine.

Autonomic system: functions of the sympathetic nervous system

The sympathetic nervous system is generally considered to be the part of the autonomic system that is responsible for mobilizing the body. The function of the sympathetic system is based on increasing the human ability to act - under the influence of sympathetic arousal, the body generally becomes ready to fight. An example of a situation in which the sympathetic nervous system is significantly stimulated is, for example, the experience of stress.

The phenomena caused by the sympathetic nervous system include:

  • pupil dilation
  • increased heart rate
  • increased sweating
  • increasing contractility of the heart muscle cells
  • breathing faster
  • bronchodilation
  • increase in blood pressure
  • slowing down of gastrointestinal peristalsis with simultaneous contraction of its sphincters,
  • relaxation of the muscles of the bladder and ureters and contraction of the bladder sphincter,
  • changes in blood distribution in the body (the sympathetic system causes, by constricting the vessels supplying the gastrointestinal tract, to inhibition of blood supply to the intestines; blood reaches dilated vessels in other parts of the body, e.g. those within the muscles) ,
  • stimulation of the processes by which the body gains energy (the sympathetic system enhances lipolysis, i.e. the breakdown of adipose tissue, or stimulates glycogenolysis, i.e. the breakdown of glycogen; in addition, the sympathetic system may lead to an increase in blood glucose by inhibiting insulin secretion by pancreas)

Autonomic system: functions of the parasympathetic system

The role of the parasympathetic system is definitely the opposite to that of the sympathetic system - the parasympathetic system is the one whose activity is most intense in conditions of relaxation and rest. The phenomena to which the parasympathetic system contributes include:

  • pupil constriction
  • stimulation of secretion in the salivary glands
  • slower heart rate and decreased contractility of its cells
  • bronchial lumen constriction
  • drop in blood pressure
  • dilatation of blood vessels in the digestive tract, favoring the absorption of digested food
  • stimulation of peristalsis in the digestive tract as wellrelaxation of his sphincters
  • contraction of the muscles of the bladder and ureters and relaxation of the bladder sphincter
  • stimulation of insulin secretion by the pancreas
  • erection and other phenomena related to sexual arousal

Autonomic system: diseases of the vegetative system

Taking into account the above descriptions, you can clearly see how large the range of functions of the autonomous system is. It is for this reason that various processes disrupting the functioning of the autonomic system can actually lead to the occurrence of various symptoms in patients. Ailments such as impotence, orthostatic hypotension or sweating disorders (consisting both in exceptionally significant sweating and complete inhibition of sweating) can convince about the dysfunction of the autonomic system. Other problems that may be related to the dysfunction of the autonomic system are dry mouth, urination disorders (including urinary retention in the bladder and urinary incontinence), and digestive disorders (e.g. constipation) .

Damage to the structures of the autonomic system can actually be caused by many different diseases. The most common causes of dysautonomia (also known as autonomic neuropathy) include:

  • diabetes
  • multiple sclerosis
  • Parkinson's disease
  • celiac disease
  • multi-system decay
  • Sjogren's band
  • diseases of the peripheral nerves

The dysfunction of the autonomic system may appear in people not only due to the development of various diseases, but also it may be a kind of natural phenomenon. It is noticeable that with age the functioning of this part of the nervous system gradually deteriorates, and this is one of the reasons why older people are at an increased risk of, for example, syncope or constipation.

About the authorBow. Tomasz NęckiA graduate of medicine at the Medical University of Poznań. An admirer of the Polish sea (most willingly strolling along its shores with headphones in his ears), cats and books. In working with patients, he focuses on always listening to them and spending as much time as they need.

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Category:

Neurology