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Autonomic Nervous System

German: Autonomes Nervensystem

1 Definition

The autonomic nervous system (ANS) is that part of the nervous system which is largely exempt from arbitrary or conscious controll; it behaves “autonomously”. According to classical anatomical categorisation it is associated with the somatic nervous system to form the human peripheral nervous system (PNS).

2 Background

An exact distinction between the autonomic and the somatic nervous systems cannot be made because some parts of the somatic nervous system are also subject to subconscious controll mechanisms (e. g. Motor reflexes). Furthermore, there are many vegetative control centres located in the brain (e.g. the respiratory centre), so that the vegetative nervous system is by no means simply a part of the PNS.

The autonomic nervous system controls vital functions such as respiration, digestion and metabolism. Individual organs and systems, like the reproductive system or the internal eye muscles are influenced by the vegetative nervous system.

3 Classification

The autonomic nervous system is divided into three main areas:

  • Sympathetic
  • Parasympathetic
  • Enteric.

The enteric nervous system is considered by some authors to be an individual, independant nervous system.

The sympathetic and parasympathetic pathways possess antagonistic effects on their target organs. In short, the sympathetic NS is responsible for quick reactions to external influences on the body (fight or flight), whereas the parasympathetic NS suppresses these reactions and stimulates more static bodily functions (rest and digest). However, the example of antagonisation is a much simplified concept. The simultaneous interaction of many body responses for a variety of functions (e. g. Sexual activity) is vital.

The autonomic NS can register sensory impulses and send out motor commands just like the somatic nervous system. For this reason viscerosensible fibres and motor neurons are distinguished from each other.

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