ABSTRACT

Many anaesthetic agents and neuroaxial blocks interfere with the autonomic nervous system (ANS). The ANS is a collection of nerves and ganglia that are involved in the involuntary control of homeostasis and the stress response. The ANS consists of two divisions, the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS). The ANS receives afferent information from chemoreceptors, baroreceptors, mechanoreceptors and from regions within the central nervous system. The efferent pathways of the PNS and SNS consist of a pre-ganglionic fibre, an autonomic ganglion and a post-ganglionic fibre. Most target tissues receive dual innervation from the ANS. However, structures that only receive SNS innervation are the sweat glands, arrector pili muscles, adipose cells, kidneys and most blood vessels. The lacrimal glands only receive PNS innervation. Receptors on the effector organs innervated by the PNS are muscarinic acetylcholine receptors while those innervated by the SNS are adrenergic receptors.