What is Sleep?

Did you ever ask yourself why do we sleep, how sleep evolved, what are the anatomical and biochemical basis of sleep? Find out in part 1 of this exploration of Sleep.

Almost all species studied engage in sleep; however how and why sleep evolved is under current investigation and has not been completely unraveled.
Different species have evolved different patterns of sleep. For example, dolphins and migratory birds engage in uni-hemispheric sleep.
The sleep cycle consists of rapid eye movement (REM) sleep and non-REM (NREM) sleep; these phases of sleep can be studied using electroencephalogram (EEG) and behavioral patterns.
There are several neurotransmitters such as acetylcholine, noradrenaline, gamma aminobutyric acid (GABA), and galanin that are involved in sleep and wakefulness.
Regions of the brain such as the cerebral cortex, pons, hypothalamus work together to create a state of sleep.
Scientists have suggested several reasons why sleep is critical: for rest and repair, for memory consolidation, clearance of brain waste products, and for effects on the immune system.