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.
How Nerve Cells Talk
Nerve cells talk to each other and to other cells (such as muscle or gland cells) by sending chemical messages. These messages are called neurotransmitters.
An electrical signal travels down one nerve cell, causing it to release the neurotransmitter into a small gap between cells called the synapse. The neurotransmitter travels across the gap, binds to a protein on the receiving cell membrane called a receptor, and causes a change (electrical, chemical or mechanical) in the receiving cell. The neurotransmitter and receptor are specific to each other, like a lock and key. Neurotransmitters can either excite the receiving cell to cause a response or inhibit the receiving cell from stimulation.
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 would have the effect of making things sluggish, which matches the behavior you see in a drunk person. Glutamine is an excitatory neurotransmitter that alcohol weakens. By making this excitatory neurotransmitter less effective, you also get 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)
Summary of alcohol's effects on the brain. Move your cursor over the colored bar in the lower left-hand corner to see which areas of the brain are affected by increasing BAC.