Which subclass of CNS depressants inhibits nerve impulses by acting on the brainstem and gamma-aminobutyric acid (GABA) receptors, resulting in inhibition of nerve impulses in the cerebral cortex?

• A. Benzodiazepines
• B. Opioids
• C. Antidepressants
• D. Barbiturates

Answer: (D)

Barbiturates produce CNS depression by enhancing GABAergic inhibition at the GABA_A receptor. They bind to the receptor–chloride channel complex and prolong the opening of the chloride channel when GABA is present, which hyperpolarizes neurons and lowers their excitability. This broad dampening of neuronal firing reduces nerve impulses, especially in the cerebral cortex. Their effects also involve depressing brainstem centers that regulate arousal and respiration, which explains the strong overall CNS depressant action. This combination—GABA_A receptor–mediated inhibition plus brainstem depression—fits the description of inhibiting cortical nerve impulses through GABAergic mechanisms. Compared with benzodiazepines, barbiturates tend to produce deeper CNS depression and can act even when GABA levels are low, reflecting their broader and more potent depressant effect.