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Autonomic nervous system: anatomy, physiology, and relevance in anaesthesia and critical care medicine

R Bankenahally MBBS DA FRCA FCAI, H Krovvidi MBBS MD FRCA
DOI: http://dx.doi.org/10.1093/bjaed/mkw011 381-387 First published online: 22 April 2016
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Key points

  • The autonomic nervous system (ANS) regulates involuntary functions. Anaesthesia, surgery, and critical illness lead to a varied degree of physiological stress that alters the ANS.

  • The organization of ANS is on the basis of the reflex arc and it has an afferent limb, efferent limb, and a central integrating system.

  • Neurotransmitters and receptors are an integral part of the ANS.

  • Autonomic neuropathy refers to damage to the autonomic nerves and diabetes mellitus is the most common cause.

  • Autonomic neuropathy involves a number of organs and has serious clinical consequences in the perioperative period and during their management in the critical care unit.

The autonomic nervous system (ANS) is the part of the nervous system that regulates involuntary functions.1 Examples are the heartbeat, the digestive functions of the intestines, control of respiration, and secretion by glands.

Basic anatomy and physiology

The organization of the ANS is on the basis of the reflex arc and it has an afferent limb, efferent limb, and a central integrating system.1

Afferent limb

The afferent limb transmits information from the periphery to the central nervous system (CNS). The receptors are present in the abdominal and thoracic viscera.1 The transmissions from these receptors are conducted along neural pathways into the spinal cord via the dorsal root ganglion or to the brain stem via cranial nerves. Baroreceptors and chemoreceptors are examples of the afferent pathway. These are present in the aortic arch and carotid sinus. The sensory impulses from these receptors are transmitted via glossopharyngeal and vagus nerves to the brain stem.

Efferent limb

The efferent limb is made up of preganglionic and post-ganglionic fibres and an autonomic ganglion. The efferent limb is further subdivided based on its anatomic and physiological differences into sympathetic and parasympathetic components. A useful generalization is that the sympathetic system responds for ‘flight-or-fight’ and prepares the body for …

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