Somatic nervous system
The somatic nervous system (s. N .; from ancient Greek σῶμα soma , German , body ' ), animale or animal nervous system (from latin anima , the Beseelte' , air puff ', Wind') or cerebrospinal nervous system or arbitrary nervous system designated one of the two main divisions of the vertebrate nervous system (including humans). The other main division is the autonomic nervous system (v. N.). In contrast to the latter, the human somatic nervous system enables a conscious perception of the environment and one's own body via the sensory organs and voluntary actions via the muscles ( voluntary motor skills ).
Criteria for differentiation
The distinction between the somatic and vegetative nervous system is based on anatomical, physiological and pharmacological criteria.
Anatomy and histology
Similar to the vegetative nervous system, the somatic nervous system is also divided into afferents and efferents .
Afferents
The afferent neurons of the somatic nervous system form the ascending projection paths . They lead to the projection centers and indirectly also to the association centers . Afferents are generally the nerve tracts of the sensory organs running to the cerebral projection centers such as the olfactory tract (Tractus olfactorius) NI, the visual tract (Tractus opticus) N.II, the auditory tract N.VIII, the equilibrium tract N.VIII and the taste tracts of various cranial nerves ( Tractus solitarii) ) N.VII and N.IX. These pathways consist of differently staggered chains of neurons . B. from a chain of a total of 4 neurons, the dorsal auditory path from a chain of 3 neurons.
Efferents
Efferent motor nerve fibers of the somatic nervous system always supply striated muscles (mostly skeletal muscles). The motor pathways of the somatic nervous system include the motor parts of the cranial nerves that supply striated muscles, and the pyramidal pathway (PS) that supplies the rest of the skeletal muscles. The extrapyramidal motor system (EPS) also supplies striated muscles. However, the corresponding motor processes are largely automated because the EPS takes over the arbitrary movements that the PS has already "retracted". The following cranial nerves have somatomotor components: Nn. III, IV, VI, XI and XII. The motor cranial nerve fibers of the Nn. V, VII, IX, and X are called the branchial arch nerves . Their activity is partly branchiomotor (ie supplying the muscles that have developed from the gill arch) and partly visceromotor (efferents of the autonomic nervous system). The nerve fibers of the muscles supplied by the pyramidal tract consist of two motor neurons connected in series, the fibers of the muscles supplied by the cranial nerves consist of one motor neuron.
histology
While efferent motor nerve fibers of the somatic nervous system always supply striated muscles (mostly skeletal muscles), efferent motor nerve fibers of the vegetative nervous system usually innervate smooth muscles (e.g. vessels or intestines). Exception: The nerves of the vegetative nervous system also supply some of the skeletal muscle fibers.
pharmacology
Pharmacologically, reference should be made to different transmitter substances ( neurotransmitters ) for the vegetative and somatic nervous system. So-called adrenergic and nicotine-like neurotransmitters are only effective in the autonomic nervous system. In the somatic nervous system, only acetylcholine should be mentioned as a physiological transmitter substance. However, overlapping with the vegetative, it also has an effect on the parasympathetic nerves of the vegetative nervous system. There are also specific pharmacological inhibitors such as alpha blockers and beta blockers for the sympathetic nervous system, atropine for the parasympathetic nervous system and e.g. B. Curare for the somatic nervous system.
Interaction with the vegetative nervous system
The partially consciously controllable activity of the striated muscles is dependent on the support of the vegetative (vegetative nervous system) to increase performance. So-called ergotropic reactions are essential for increasing the performance of cerebrospinal functions . These are guaranteed by the sympathetic nervous system. Afferent vegetative nerves of internal organs sometimes have a conscious signal effect (e.g. discomfort in the gastrointestinal area). On the other hand, the olfactory and taste buds have links to the digestive system, which is the largest vegetative organ system. These are a few examples of the interaction between the cerebrospinal and vegetative nervous systems.
Nomenclature and structure
Both the vegetative and the somatic nervous system have peripheral and central parts - this division reflects a topographical approach. This gives rise to the following combinations: central-somatic, central-vegetative, peripheral-somatic, peripheral-vegetative.
The same applies to the third approach to a structure: the direction of the signal. A distinction is made here between sensory and motor or between afferent and efferent .
See also
Individual evidence
- ^ A b Hermann Voss , Robert Herrlinger : Taschenbuch der Anatomie. Volume III: nervous system, sensory system, skin system, increment system. Fischer, Jena 1964; (a) Re. “Number of linked neurons”: p. 69ff .; (b) Reg. "EPS": p. 21f.
- ↑ Eduard MW Weber: Schemes of human conduction pathways. Lehmanns, Munich 1960; Tab. IV, Nervi craniales
- ↑ Max Watzka: Short textbook of the histology and microscopic anatomy of humans . 3. Edition. Schattauer, Stuttgart 1964, p. 49ff.
- ↑ Alfred Benninghoff a . a .: Textbook of human anatomy. Shown with preference given to functional relationships. Volume 3: nervous system, skin and sensory organs. Urban and Schwarzenberg, Munich 1964, p. 356.
- ↑ G. Kuschinsky, H. Lüllmann: Pharmakologie. 3. Edition. Thieme, Stuttgart 1967, pp. 1ff. and 100ff.
- ^ Hermann Rein , Max Schneider : Human Physiology. 15th edition. Springer, Berlin 1964; on "Ergotropic reaction": pp. 405, 543; Regarding district “Cerebrospinal nervous system”: p. 471ff.