Somatic nervous system

The somatic nervous system (see N.; from Greek σῶμα soma " body " ), animale or animal nervous system (from Latin anima " The souled, breath of air, wind " ) or cerebrospinal nervous system or even arbitrary nervous system refers to a functional subdivision and delineation of the nervous system of humans and all other vertebrates. It is compared with the autonomic nervous system ( N. v. ). In contrast to the autonomic nervous system, the somatic nervous system for the deliberate establishment of contacts with the environment through the sense organs and subjected to the will of motor function ( voluntary movement ) is excellent.

• 2.1 Anatomy and Histology 2.1.1 afferents
• 2.1.2 Efferenzen
• 2.1.3 Histology

Awareness criterion

The somatic nervous system is the share of the nervous system, for the conscious perception of environmental stimuli ( Exterozeption ) and stimuli from inside the body ( proprioception ), for the conscious or voluntary control of motor functions as well as for the conscious message processing ( integration ) is responsible.

One problem is the consciousness criterion is in vertebrates, where a somatic nervous system is also awarded ( see Introduction). Also in case of doubt regarding the applying of this condition also a classification of body reactions is not dismissed that run automatically ( autonomic nervous system) and those that are willfully usually controlled by environmental stimuli ( somatic nervous system).

Validity of consciousness criterion

The differentiation of the somatic from the autonomic nervous system on the basis of consciousness criterion draws a hard distinction that so in reality can not be maintained: Many visceral afferent signals have quite a conscious expectant component, such as for example, odor and taste, or " visceral pain ". That smell and taste are still visceral / autonomic stimulus trains, can be recognized by the strong Affekthaftigkeit these perceptions and the visceral reactions they are able to trigger (vomiting, nausea ). On the other side also exists in higher vertebrates something like a semi- arbitrary motor activity in the pharyngeal arch muscles: The facial expressions of the face, for example, for a fraction of arbitrary subject, affects come here also involuntarily or even against the will expressed. The swallowing process as another example, both randomly and involuntarily be initiated ( Extrapyramidal -motor nervous system).

A strict distinction between conscious and unconscious neural functions is also difficult because the terms are consciously and unconsciously Although logically separate, but not in practice, because in addition to this conceptual pair of opposites, especially in the psychology of perception consist flowing preconscious transitions. In the definition of the so-called psychophysical levels therefore a zone of " no man's land " should be considered.

In the purely conceptual distinction between vegetative and animalem nervous system and historical distinctions expressed, relating to the well-known since Galen and Paracelsus concepts of " animal spirits " come, were continued by the theories of animism and vitalism and to the mind-body related problem. However, this problem can not be seen independently of the consciousness criterion. To designate → " somatic " see also explained under this keyword importance in neurology.

Other criteria

The distinction between somatic and vegetative nervous system is possible not only because of consciousness criterion, but also due to anatomical, physiological and pharmacological criteria.

Anatomy and Histology

Similar to the autonomic nervous system and the somatic nervous system in afferent and efferent fibers is divided.

Afferents

The afferent neurons of the somatic nervous system are the ascending projection pathways. They lead to the projection and indirectly also to the association centers. Ascending projection paths are eg the optic radiation and parts of the auditory pathway. Afferents are generally extending to the cerebral centers of projection pathways of the sensory organs such as the olfactory tract ( olfactory tract ) NI, the visual pathway ( optic tract ) N.II, the auditory pathway N.VII, the equilibrium orbit N.VII and taste pathways of various cranial nerves ( tractus solitarius ) NV, N.VII, N.IX, NX These tracks consist of different neurons staggered chains that visual pathway, for example, of a chain of 4 neurons, the dorsal auditory pathway of a chain of three neurons.

Efferents

Efferent motor nerve fibers of the somatic nervous system supply always striated muscle ( skeletal muscle ). Among the motor pathways of the somatic nervous system the motor portions of the cranial nerves may be mentioned that supply striated muscles and the pyramidal tract ( PS), which supplies the rest of the skeletal muscles. Also the extrapyramidal system (EPS ) supplies striated muscles, the corresponding motor processes are largely automated, because the EPS assumes the already " retracted " from PS voluntary movements. Somatomotor shares have the following cranial nerves: Nn. III, IV, VI, XI and XII. The motor cranial nerve fibers of the nerves. V, VII, IX and X are called branchial arch nerves, its activity as viszeromotorisch. The nerve fibers of the muscles supplied by the pyramidal tract consists of two series-connected motor neurons, the fibers of the muscles supplied by the cranial nerves from a motor neuron.

Histology

While efferent motor nerve fibers of the somatic nervous system always provide striated muscle ( skeletal muscle ), innervate efferent motor nerve fibers of the autonomic nervous system usually smooth muscles (eg vessels or intestines). Exception: The nerves of the autonomic nervous system to be partly also skeletal muscle fibers.

Physiology

The consciousness imputed activity of striated muscle is dependent on the increase in power to support the vegetative ( autonomic nervous system ). To improve performance, cerebrospinal functions are called ergotropic reactions significantly. These are guaranteed by the sympathetic. Afferent autonomic nervous internal organs have some awareness enabled signal effect. Odor and taste buds have on the other hand as I said close relations with the digestive system, which is considered as the largest vegetative organ. This is also a relationship of cerebrospinal to the autonomic nervous system given. The cerebrum as a place of conscious awareness not only has primary olfactory and gustatory centers, but is also equipped with autonomic sympathetic and parasympathetic nerves.

Pharmacology

Pharmacologically, it should have different transfer agents for vegetative and somatic nervous system. So-called adrenergic and nicotine-like neurotransmitters are effective only in the vegetative nervous system. In the somatic nervous system acetylcholine is only to mention a physiological transmitter substance. However, it has overlapping with the vegetative system also effect for the parasympathetic nerves of the autonomic 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, eg, curare for the somatic nervous system.

Nomenclature and classification

Both vegetative and somatic nervous system peripheral and central portions - this classification reflects a topographical approach. This results in the combinations: central - somatic, vegetative Central, peripheral somatic, peripheral vegetatively.

The same applies to the third approach, an outline: the direction of the signal. Here we distinguish between sensory and motor efferent and afferent or between.