Alcohol acts primarily on the nerve cells within the brain. Alcohol interferes with communication between nerve cells and all other cells, suppressing the activities of excitatory nerve pathways and increasing the activities of inhibitory nerve pathways.
For example, University of Chicago Medical Center: Alcohol and Anesthetic Actions talks about the ability of alcohol (and inhaled anesthetics) to enhance the effects of the neurotransmitter GABA, which is an inhibitory neurotransmitter. Enhancing an inhibitor generally induces sluggishness, which matches the behavior you see in a drunk person. Alcohol not only enhances an inhibitor, it also weakens an excitatory neurotransmitter called glutamine. Dampening the effect of an excitatory neurotransmitter also produces sluggishness. Alcohol does this by interacting with the receptors on the receiving cells in these pathways.
Alcohol affects various centers in the brain, both higher and lower order. The centers are not equally affected by the same BAC — the higher-order centers are more sensitive than the lower-order centers. As the BAC increases, more and more centers of the brain are affected.
The order in which alcohol affects the various brain centers is as follows:
- Cerebral cortex
- Limbic system
- Hypothalamus and pituitary gland
- Medulla (brain stem)