Final answer:
Tranquilizers and sedative hypnotics affect the central nervous system by acting as depressants and relieving symptoms of anxiety and tension.
Step-by-step explanation:
Tranquilizers and other sedative hypnotics affect the central nervous system by acting as depressants. They relieve symptoms of anxiety and tension by causing calming effects and drowsiness. These drugs work by facilitating the activity of the neurotransmitter gamma-Aminobutyric acid (GABA) in the brain, which has a quieting effect. Examples of tranquilizers include diazepam (valium) and chlordiazepoxide (Librium).