This site is intended for healthcare professionals

Go to /sign-in page

You can view 5 more pages before signing in

Autonomic nervous system

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

The autonomic nervous system controls many involuntary bodily functions such as arterial blood pressure regulation, heart rate and pupillary dilatation. A large proportion of its work is on physiological systems which require ongoing assessment and correction - homeostatic maintenance of an internally stable environment.

The autonomic nervous system is divided into two limbs with generally opposing functional effects:

  • the sympathetic nervous system
  • the parasympathetic nervous system

Both have efferent - motor - and afferent - sensory - limbs. They share parts of their anatomical pathways both within the central and peripheral nervous systems. However, parasympathetic fibres emerge from the brain stem and sacral region of the spinal cord - the craniosacral outflow - whereas the sympathetic nervous system emerges from the thoracic and lumbar segments of the spinal cord - thoracolumbar outflow.

One key difference between the autonomic and somatic nervous systems is that the efferent pathways of the former consist of two neurones in series between a central nervous system neurone and a target cell. In the somatic nervous system, there is only one. In the ANS, the synapse of the first and second neurones in the circuit is within a ganglion. Therefore, the proximal neurone that commences in the CNS is termed pre-ganglionic whereas the distal one that terminates on the effector cell is termed post-ganglionic. The anatomical position of the ganglion varies between the sympathetic and parasympathetic nervous systems. The pre-ganglionic neurotransmitter is acetylcholine for both limbs; however, the postganglionic neurotransmitter varies:

  • parasympathetic: acetylcholine
  • sympathetic: noradrenaline; acetylcholine only for sweat glands

Related pages

Create an account to add page annotations

Add information to this page that would be handy to have on hand during a consultation, such as a web address or phone number. This information will always be displayed when you visit this page

The content herein is provided for informational purposes and does not replace the need to apply professional clinical judgement when diagnosing or treating any medical condition. A licensed medical practitioner should be consulted for diagnosis and treatment of any and all medical conditions.


Copyright 2024 Oxbridge Solutions Limited, a subsidiary of OmniaMed Communications Limited. All rights reserved. Any distribution or duplication of the information contained herein is strictly prohibited. Oxbridge Solutions receives funding from advertising but maintains editorial independence.