Final answer:
Sleep is composed of different stages with coordinated brain activity. It can be divided into REM sleep and non-REM sleep, each associated with specific brain wave patterns.
Step-by-step explanation:
Sleep is not a uniform state of being. Instead, sleep is composed of several different stages that can be differentiated from one another by the patterns of brain wave activity that occur during each stage. During sleep, the brain exhibits coordinated brain activity that is distinct from periods of wakefulness. Sleep can be divided into two general phases: REM sleep, characterized by brain waves similar to wakefulness, and non-REM sleep, which is further divided into three stages with distinctive brain wave patterns.