Alcohol sedates nerve cells throughout the body. Here’s alcohol in action. Note: Blood Alcohol Content (BAC) is a measure of the percentage of alcohol in an individual’s blood. Jane is an “average” 140-pound woman who doesn’t drink often.
Jane arrives at a friend’s cocktail party. After drinking a glass of wine she’s relaxed and ready to mingle. Alcohol stimulates the release of endorphins and dopamine, which may enhance mood.
Heading to chat with someone she recognizes, Jane bumps into a chair. Her speech is slightly slurred. Alcohol slows nerve signals from the brain to the muscles, contributing to both Jane’s clumsiness and her affected speech. Other functions are likely to be impaired too and could be a problem if Jane were to attempt driving under challenging circumstances (bad weather, heavy traffic) even if she hasn’t reach the legal driving limit of 0.08.
Quiet Jane is now the life of the party. Alcohol is affecting many parts of the brain, including the prefrontal cortex, which controls reasoning and judgment. If Jane keeps drinking, she may do or say things she’ll regret in the morning.
Jane knocks a drink over. She staggers as she looks for a towel to clean up the mess. Her movements are impaired due to alcohol’s effects on the cerebellum, the part of the brain that affects motor coordination. Even though the hostess is not upset, Jane becomes overly apologetic and emotional because her brain is having trouble fully assessing social situations.
Jane feels unsteady and queasy—alcohol irritates the stomach. She plops down into a chair. When someone asks if she’s OK, she is slow to respond and her speech is very slurred because alcohol has greatly reduced her brain’s signaling and functioning.
Jane begins having memory lapses called “blackouts,” a form of amnesia that occurs when alcohol affects the hippocampus, the brain’s center for short-term memory. She feels the room spinning around her as alcohol affects the fluids in the inner ear responsible for spatial orientation.
Jane is extremely intoxicated—over twice the legal driving limit in most states. If she continues to drink, alcohol will significantly affect the brain stem, which regulates the heart and lungs. This could cause her heart rate and breathing to slow to potentially lethal rates.
Blood Alcohol Content numbers and effects are estimated based on population data and assume that Jane metabolizes alcohol at a rate that brings her BAC down by 0.015 percent every hour. To describe the physiological effects that occur at higher BACs, we had Jane drinking very quickly—two drinks every 40 minutes. Spacing alcoholic drinks over a longer period would result in lower BACs. Blood alcohol levels are also affected by size (larger people can tolerate more), gender (compared to men, women generally have more fat, which contains less water than muscle, so they don’t dilute alcohol in the blood as much and get drunk faster), tolerance, whether food was eaten before drinking and how much, and variations in levels of alcohol dehydrogenase, the enzyme that breaks down alcohol.
Source: Mark Egli, Ph.D., of the National Institute on Alcohol Abuse and Alcoholism