Chapter 4: Autonomic (ANS) Pharmacology: Introduction
Figure by Poul-Erik Paulev, M.D., D.Sci, used with permission
Skeletal muscle is innervated by somatic nerves, controlling voluntary actions
All other innervated structures are supplied by the autonomic or involuntary system.
Somatic system: No ganglia present
Autonomic nervous system (ANS) has ganglia.
These ganglia are sites at which preganglionic fibers form synaptic connections with postganglionic neurons
These ganglia are located outside the cerebrospinal axis
Other differences between Somatic and Autonomic Innervation
Motor nerves to skeletal muscle: myelinated
Postganglionic autonomic nerves are nonmyelinated
Denervation of skeletal muscle results in paralysis and atrophy
Denervated smooth muscle or glands retain some activity
First link: Visceral autonomic afferents to the CNS
Non-myelinated, carried to the cerebrospinal axis by autonomic nerves (e.g.vagus and splanchnic)
Some autonomic afferents from skeletal muscle blood vessels and integumental structures may be carried in somatic nerves
Cell bodies of visceral afferents: (a) spinal nerves--in dorsal root ganglia; (b) cranial nerves-- in sensory ganglia
What information gets transmitted?
Visceral sensation (pain;referred pain)
Viscerosomatic reflexes: Definition: Viscerosomatic: Pertaining to the viscera and body
|Figure by Poul-Erik Paulev, M.D., D.Sci, used with permission|
Substance P is an important sensory neurotransmitter, probably especially important in nociception, and is found in:
Sensory afferent fibers
Dorsal root ganglia
Dorsal spinal cord horn
Other agents found in sensory neurons
Vasoactive intestinal peptide (VIP)
Calcitonin gene-related peptide (CGRP) (found with Substance P in cardiovascular sensory nerve fibers)
Dorsal Spinal Cord (substantia gelatinosa) Interneurons
Enkephalins: Antinociceptive due to inhibition of substance P release and reduced transmission to higher centers
Blood pressure changes
Temperature-induced changes in vasomotor tone
Emptying of the bowels, bladder, seminal vesicles
Integration of ANS Functions
Body temperature regulation
Posterior and Lateral Hypothalamic Nuclei are associated with integration of autonomic sympathetic input
Midline nuclei in the region of the Tuber cinereum and anterior nuclei Nuclei are associated with integration of autonomic parasympathetic input
Sympathetic: (Thoracolumbar outflow)
Parasympathetic; (Craniosacral Outflow)
Neurotransmitter: Acetylcholine at these sites:
All preganglionic autonomic fibers
A few post-ganglionic sympathetic fibers
Neurotransmitter: Norepinephrine at:
Postganglionic Sympathetic Fibers
Neurotransmitter: Primary Afferents
Substance P and/or glutamate
Sympathetic system has a broader distribution, innervating effectors throughout the body
Sympathetic fibers show greater ramification.
Sympathetic preganglionic fibers may traverse through many ganglia before terminiating at its post-ganglionic cell.
Synaptic terminal arborization results in a single preganglionic fiber terminating on many post-ganglionic cells.
This anatomical characteristic is the basis for the diffuse nature of sympathic response in the human and other species.
Parasympathetic system is relatively limited
The parasympathetic system has its terminal ganglia near the end-organ.
Sometimes there is but a one-to-one ratio relationship between pre-and post-ganglionic fibers.
The ratio between preganglionic vagal fibers and ganglion cells may be much higher, e.g. 1:8000 for Auerbach's plexus.
Lefkowitz, R.J, Hoffman, B.B and Taylor, P. Neurotrasmission: The Autonomic and Somatic Motor Nervous Systems, In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) The McGraw-Hill Companies, Inc.,1996, pp.107