Characteristics of Autonomic Organ Innervation

• Usually, parasympathetic and sympathetic systems are physiological antagonists; that is, if one system facilitates or augments a process the other system inhibits the process.

• Since most visceral organs are innervated by both systems, the activity of the organ is influenced by both, even though one system may be dominant.

• The general pattern of antagonism between sympathetic and parasympathetic systems is not always applicable. The interaction between sympathetic and parasympathetic systems may be independent or interdependent.

• Examples of Antagonistic Interactions between Sympathetic and Parasympathetic Systems

  • Actions of sympathetic and parasympathetic influences on the heart.

  • Actions of sympathetic and parasympathetic influences on the iris.

• Interdependent or Complementary Sympathetic and Parasympathetic Effects

  • Actions of sympathetic and parasympathetic systems on male sexual organs are complementary.

• Independent Effects

  • Vascular resistance is mainly controlled by sympathetic tone.

Category: Pharmacology Notes