Chapter 4:  Autonomic (ANS) Pharmacology: Introduction

Autonomic Nervous System: Anatomical Considerations

Figure by Poul-Erik Paulev, M.D., D.Sci, used with permission

Autonomic and Somatic Innervation

• 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

Autonomic Reflex Arc

• 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?

• Mediated Information:

  •  visceral sensation (pain;referred pain)

  •  vasomotor reflexes

  •  respiratory reflexes

  •  viscerosomatic reflexes: Definition: Viscerosomatic: Pertaining to the viscera and body

Autonomic Reflex Arc: First Link

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

  • Somatostatin

  • Vasoactive intestinal peptide (VIP)

  • Cholecystokinin (CCK)

  • 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

CNS and the Autonomic Nervous System

• Spinal Cord Reflexes

  •  sweating

  •  blood pressure changes

  •  temperature-induced changes in vasomotor tone

  • emptying of the bowels, bladder, seminal vesicles

•  Hypothalamic and Nucleus tractus solitarii

  • Integration of ANS Functions

    • body temperature regulation

    • emotions

    • water balance

    • sexual response

    • fat/carbohydrate metabolism

    • sleep

    • blood pressure

    • respiration

• Higher Centers

  • 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

• Peripheral ANS: Divisions

  • Sympathetic: (Thoracolumbar outflow)

  • Parasympathetic; (Craniosacral Outflow)

• Autonomic Nervous System Neurotransmitters: Summary

  • Neurotransmitter: Acetylcholine

    • All preganglionic autonomic fibers

    • Parasympatheticfibers

    • A few post-ganglionic sympathetic fibers

  • Neurotransmitter: Norepinephrine

    • Postganglionic Sympathetic Fibers

  • Neurotransmitter: Primary Afferents

    • Substance P and/or glutamate

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) TheMcGraw-Hill Companies, Inc.,1996, pp.105-107.