**Sleep onset** - The period when we are falling asleep
**Alpha waves** are produced when we are drowsy but awake
Between stages 1 and 2, **theta waves** are produced (high frequency, low amplitude) and they get progressively slower and higher in amplitude
In stage 2, the EEG starts to show **sleep spindles** which are short bursts of rapid brain waves
In stages 3 and 4, **delta waves** are produced and get progressively slower
* Delta sleep is important in replenishing the body’s chemical supplies, releasing growth hormones, and fortifying immune systems.