sleep phases, questions about a normal nights sleep Options

[Vertigo]

ok, I'm not sure if this should go in neuroscience or in cognitive science & psychology but I think neuroscience is more fitting... Basically I've heard a little bit about REM and different phases of sleep, particularly the brainwave patterns (alpha, beta, theta and delta waves) and have three questions:

first, what (under normal circumstances) is a typical sequence of sleep phases we go through? What order, how long does each phase last and what is the total time spent with in each type? I know it's not always the same (ie. someone who has been deprived of REM by something physiological may be likely to rebound, getting excessive REM once they are able to) but I'm looking for an approximate answer that will be somewhere near the mark for most cases.

second, when we switch from theta to delta (for example) is it like switching gears - suddenly our brain wave patterns just change to another state - or is there a gradual transition from one to the other in the sense of a slowly escalating or descending frequency or amplitude?

third, are the phases consistent? Do we spend lengths of time with our brains using just theta or just delta waves (for example) or is it just mostly one type at any given time with a potential for fairly frequent deviations from the pattern?

...and with these questions in mind, knowing that I've already done some aimless wiki-surfing and am in the process of on-going googling, if you've got any recommendations for specific sources of information (preferably online) you think I would find informative on the subject of sleeping brain activity, please do let me know

[J_B]

anyone? I'm interested as well.

[Vertigo]

Not a lot of time but I thought I'd share some information I just came across, from an unreliable source so quite possibly inaccurate.

Supposedly, we tend to first dream around 70-90 minutes into our sleep and then we go through a repeating 90 minute cycle with around 20 minutes of REM (dream) sleep which usually correlates to theta brain waves. The REM phases grow longer with each succeeding one, usually a bit under 20 minutes in the first few phases and a bit over 20 minutes after several hours of sleep. We also (if not for alarm clocks and other disturbances) tend to sleep for an approximate total of a multiple of 90 minutes.

Any answers to my original questions, confirmations of the above information, or corrects would be appreciated.

Thanks