Nursing Pharmacology Autonomic (ANS) Pharmacology: Introduction

• 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 at these sites:

      • All preganglionic autonomic fibers

      • Parasympatheticfibers

      • A few post-ganglionic sympathetic fibers

    • Neurotransmitter: Norepinephrine at:

      • Postganglionic Sympathetic Fibers

    • Neurotransmitter: Primary Afferents

      • Substance P and/or glutamate

    • Comparisons between Sympathetic and Parasympathetic Nerves

      • 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