Central Nervous System Drugs
The central nervous system (CNS)Ñthe brain and spinal cordÑis the target of a diverse group of drugs that can treat problems ranging from pain to psychiatric disorders. General anesthetic drugs act on brain nerve cells to inhibit electrical transmission that is necessary for consciousness and for the perception of pain. Strong analgesic drugs, some of which are called narcotics (from the Greek "narkosis," or numbing), such as morphine, bind to special receptors in the region of the brain that perceives pain, to alter nerve impulse transmission. As a result, the pain-producing stimuli are still unaltered and recognized as being present but they are no longer perceived as being unpleasant. Some drugs in this class, such as codeine, also prevent coughing, which is controlled by the brain.
Psychotherapeutic drugs include drugs for depression, anxiety, and psychosis. Antidepressants such as Elavil and Prozac can increase the levels of the neurotransmitters norepinephrine and serotonin, respectively, which are necessary for electrical impulses to pass from one cell to the next. Antipsychotic drugs such as Haldol and Clozaril, used to treat schizophrenia, decrease the effectiveness of dopamine. Valium and Triazolam, used to treat anxiety, inhibit electrical transmission in some regions of the brain by opening channels in the nerve membrane. Valium-like drugs can also promote sleep in patients with insomnia and can cause muscle relaxation by inhibiting nerve cells in the spinal cord that control the muscles of the body. The antiepileptic drugs phenobarbital and phenytoin act on nerve cells to inhibit the irregular and uncontrolled electrical pulses initiated in some abnormal regions of the brain, which may cause convulsions.
Some drugs that act on the CNS are taken because they can alter mood (heroin) or perception (hallucinogens such as LSD) or provide a feeling of euphoria (cocaine) by altering the transmission of electrical pulses in the regions of the brain controlling these sensations. Addiction to strong analgesic and mood-altering drugs can occur.