Introduction to Autonomic Pharmacology

The autonomic nervous system is anatomically divided into two major divisions – The sympathetic and parasympathetic divisions.

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 are myelinated

  • Postganglionic autonomic nerves are nonmyelinated

  • Denervation of skeletal muscle results in paralysis and atrophy

  • Denervated smooth muscle or glands retain some activity

• 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 terminating at its post-ganglionic cell.

    • 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.

Category: Pharmacology Notes