The autonomic nervous system (physiology)

The autonomic nervous system (VNS) (also known as the autonomic nervous system, ANS) is part of the peripheral nervous system together with the somatic efferent (motor) system (carrying impulses from the CNS to the will-controlled striated muscles) and sensory (afferent) fibers (conducting sensation and pain). VNS ensures the transfer of impulses between the central nervous system (CNS) and effector tissues independent of volitional control (smooth muscle, myocardium, exocrine glands...).

The vegetative nervous system is divided into motor (efferent) and sensory (afferent) parts. Although afferent fibers play an important role in the regulation of homeostasis (e.g. cholinergic fibers from baroreceptors in the glomus caroticum ), they are pharmacologically affected by a minimum of drugs. Attention is therefore focused on the study of the efferent part. It anatomically consists of 2 systems - sympathetic and parasympathetic. A somewhat separate unit is the enteric nervous system (ENS), which, because of its relative independence from other parts of the VNS, is often singled out as an independent third part of the VNS with a specific function in the control of function gastrointestinal tract.

Anatomie VNS
The efferent (motor) pathways of the VNS consist of 2 neurons, which are interpolated in the vegetative ganglia – preganglionic and postganglionic neurons are distinguished according to their position. There are significant differences in the arrangement of these pathways between the sympathetic and parasympathetic.

Sympatikus
The bodies of the sympathetic preganglionic neurons are located in the lateral corners of the gray matter of the spinal cord in the area of ​​the thoracic and lumbar segments (Th1-L3). The axons of these neurons leave the spinal cord in the corresponding segments, therefore the sympathetic system is referred to as the thoraco-lumbar system. The sympathetic autonomic ganglia are well organized and form two paravertebral chains along the spine. Excitations to the abdominal and pelvic organs are interpolated in ganglia located prevertebrally. It follows from the above that the axons of preganglionic neurons are much shorter than the axons of postganglionic neurons.

Parasympatikus
The preganglionic fibers of the parasympathetic leave the CNS via some cranial nerves(n. III, VII, IX and X) and the anterior horns of the spinal cord in the area of ​​the sacral segments (S2–S4) – the parasympathetic is therefore referred to as  the cranio-sacral system. Vegetative parasympathetic ganglia are located mainly in the wall of effector organs, preganglionic fibers are therefore much longer than axons of postganglionic neurons. With exceptions (ggl. cilliare, submandibulare and pelvic ganglia), parasympathetic ganglia are not precisely organized and the connections between pre- and postganglionic neurons are rather diffusely scattered in the wall of the effector organs.

Mediátory VNS
Noradrenalin je mediátorem na většině postgangliových vláken sympatiku.

Acetylcholin se jako mediátor uplatňuje na všech pregangliových vláknech VNS, všech postgangliových vláknech parasympatiku a některých postgangliových vláknech sympatiku (např. potní žlázy). Acetylcholin se uplatňuje také jako mediátor ve dřeni nadledvin, kde její buňky vývojově odpovídají sympatickému gangliu a tudíž jsou inervovány pregangliovými vlákny sympatiku. Samotné buňky po stimulaci uvolňují adrenalin.

Dle medátorů dělíme vlákna VNS na adrenergní a cholinergní.

Funkce VNS
Tabulka 1 nabízí přehled základních funkcí které jsou ovlivňovány vegetativním nervovým systémem. Většina tkání kontrolovaných VNS přijímá inervaci od parasympatiku i sympatiku, které zde obvykle působí protichůdně. Nicméně vliv jednoho systému v dané tkání většinou převažuje – např. cévy jsou primárně pod vlivem sympatiku, GIT a SA uzel pod vlivem parasympatiku.

Související články

 * Vegetativní nervová soustava (farmakologie) • Sympatomimetika • Sympatolytika • Parasympatomimetika • Parasympatolytika
 * Vegetativní nervová soustava (anatomie)

Zdroj



 * LINCOVÁ, Dagmar a Hassan FARGHALI. Základní a aplikovaná farmakologie. 1. vyd. Praha: Galén, 2002, xxiv, 601 s. ISBN 80-7262-168-8.


 * SLÍVA, Jiří a Martin VOTAVA. Farmakologie. 1. vyd. Praha: Triton, 2011, 394 s. Lékařské repetitorium. ISBN 978-80-7387-500-8.