LESSON 4
AUTONOMIC AND CARDIOVASCULAR DRUGS
Section I. THE AUTONOMIC NERVOUS SYSTEM
4-1.
INTRODUCTION
The autonomic nervous system is the part of the nervous system that controls
the automatic or involuntary functions of the body. Its nerves lead to the heart, blood
vessels, glands, stomach, intestines, and other organs that have muscular actions
independent of conscious will. The autonomic nervous system is divided into two parts,
the sympathetic nervous system and the parasympathetic nervous system. These have
nerves leading to the same organs, but the effects of the nerves belonging to each
system are different. The basic differences in functions of the two systems are
depicted in Table 4-1. Note that the sympathetic nervous system induces a state
characteristic of fear or anger and prepares the body for coping with danger by "fight or
flight," and the parasympathetic system induces a state characteristic of calmness and
security. These states are produced by chemical substances released by the nerve
endings of the two systems. The nerve endings of the sympathetic nervous system
release norepinephrine, chemically similar to epinephrine (Adrenalin). The nerve
endings of the parasympathetic system release acetylcholine (ACh). When these
substances are released, the characteristic effects of their respective nervous systems
are produced. Norepinephrine produces adrenergic effects, characteristic of fear and
stress. ACh produces cholinergic effects, also called muscarinic effects, characteristic
of calm, unstrenuous life. In the body, ACh is rapidly hydrolyzed (broken down in a
reaction with water) by the action of an enzyme called acetylcholinesterase.
4-2.
A sympathomimetic (adrenergic) is a drug that mimics the action of
norepinephrine, the substance produced by the nerve endings of the sympathetic
nervous system. A sympatholytic (antiadrenergic) is a drug that blocks the response of
the effector organs to adrenergic stimulation. A parasympathomimetic (cholinergic) is a
drug that mimics the action of acetylcholine (ACh), the substance produced by the
nerve endings of the parasympathetic nervous system. A parasympatholytic
(anticholinergic) is a drug that blocks the parasympathomimetic (muscarinic) effects of
ACh.
MD0913
4-2