The cerebral cortex is the highest portion of the brain. The cortex processes information from your senses, does your "thought" processing and consciousness (in combination with a structure called the basal ganglia), initiates most voluntary muscle movements and influences lower-order brain centers. In the cortex, alcohol does the following:
- Depresses the behavioral inhibitory centers: The person becomes more talkative, more self-confident and less socially inhibited.
- Slows down the processing of information from the senses: The person has trouble seeing, hearing, smelling, touching and tasting; also, the threshold for pain is raised.
- Inhibits thought processes: The person does not use good judgment or think clearly.
These effects get more pronounced as the BAC increases.
The limbic system consists of areas of the brain called the hippocampus and septal area. The limbic system controls emotions and memory. As alcohol affects this system, the person is subject to exaggerated states of emotion (anger, aggressiveness, withdrawal) and memory loss.
The cerebellum coordinates the movement of muscles. The brain impulses that initiate muscle movement originate in the motor centers of the cerebral cortex and travel through the medulla and spinal cord to the muscles. As the nerve signals pass through the medulla, they are influenced by nerve impulses from the cerebellum. The cerebellum controls fine movements. For example, you can normally touch your finger to your nose in one smooth motion with your eyes closed; if your cerebellum were not functioning, the motion would be extremely shaky or jerky. As alcohol affects the cerebellum, muscle movements become uncoordinated.
In addition to coordinating voluntary muscle movements, the cerebellum also coordinates the fine muscle movements involved in maintaining your balance. So, as alcohol affects the cerebellum, a person may lose their balance frequently. At this stage, this person might be described as "falling down drunk."
The hypothalamus is an area of the brain that controls and influences many automatic functions of the brain through actions on the medulla, and coordinates many chemical or endocrine functions (secretions of sex, thyroid and growth hormones) through chemical and nerve impulse actions on the pituitary gland. Alcohol has two noticeable effects on the hypothalamus and pituitary gland, which influence sexual behavior and urinary excretion.
Alcohol depresses the nerve centers in the hypothalamus that control sexual arousal and performance. As BAC increases, sexual behavior increases, but sexual performance declines.
Excessive drinking also inhibits the pituitary secretion of anti-diuretic hormone (ADH), which acts on the kidney to reabsorb water. Alcohol acts on the hypothalamus/pituitary to reduce the circulating levels of ADH. When ADH levels drop, the kidneys do not reabsorb as much water; consequently, the kidneys produce more urine.
The medulla, or brain stem, controls or influences all of the bodily functions that are involuntary, like breathing, heart rate, temperature and consciousness. As alcohol starts to influence upper centers in the medulla, such as the reticular formation, a person will start to feel sleepy and may eventually become unconscious as BAC increases. If the BAC gets high enough to influence the breathing, heart rate and temperature centers, a person will breathe slowly or stop breathing altogether, and both blood pressure and body temperature will fall. These conditions can be fatal.