The cerebellum coordinates the movement of muscles. The brain impulses that begin 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 loses his or her balance frequently. At this stage, this person might be described as "falling down drunk."