0:00
so sleep is made up of stages and cycles
0:03
and each stage occurs one after the
0:05
other in a similar loop to the figure
0:07
that you see above my head here and once
0:10
each of those stages is complete they
0:12
then repeat in what's called a cycle now
0:16
each one of these sleep cycles takes
0:18
about 90 minutes to complete and there
0:21
are about four to six cycles per sleep
0:24
interval as we go to bed and wake up
0:26
there's about four to six of
0:28
these and Sleep can be thought of as
0:31
breaking down into two different types
0:33
which we will talk about here moving
0:35
forward in this lecture these types are
0:38
considered to be NRM or what's called
0:41
nonrapid eye movement sleep or rapid eye
0:45
movement sleep and I'll explain a bit
0:47
here about what that actually means so
0:50
we'll start by talking about the various
0:51
stages of sleep and the first stage that
0:54
we'll talk about is what's called stage
0:55
one sleep so stage one sleep is light
0:58
sleep it lasts anywhere from about 1 to
1:01
5 minutes and it's during this stage
1:03
that we start to experience drops in
1:06
heart rate relaxation of the musculature
1:09
and also a reduction in our breathing
1:12
rate it's also during this stage of
1:15
sleep that we experience a hypnic jerk
1:18
now a hypnic jerk is a feeling that
1:21
we're falling and we jerk awake and it's
1:25
considered to be a miscommunication
1:27
between the brain and the body where the
1:29
brain perceives that the body is falling
1:30
simply because the body's relaxing and
1:33
this may wake up your partner or those
1:35
around you but typically people are able
1:38
to fall back into stage one sleep right
1:40
after they wake up now following stage
1:43
one sleep we reach what's called NRM
1:46
stage two sleep and this stage of sleep
1:49
lasts anywhere from about 20 to 25
1:51
minutes and it's during this stage of
1:53
sleep that we start to see a decrease in
1:56
our body temperature and this decrease
1:59
in body temperature is essential for our
2:01
progression into the later stages of
2:03
sleep and this is why some individuals
2:06
actually reduce the temperature in the
2:08
room prior to going to sleep they set
2:10
their thermostats to something like 68
2:12
or 69 degrees and this really
2:14
facilitates a cooling of the body so
2:17
that you can progress and rest more
2:19
effectively it's also during this stage
2:21
of sleep that we experience what's
2:23
called a sleep spindle and this is a
2:26
burst of brain activity that is
2:28
considered to be a function where we are
2:33
blocking out noises in our external
2:35
environment and it's almost said to be
2:38
the brain's do not disturb mode that's
2:40
getting turned on so that we can
2:42
progress into deeper stages of sleep so
2:45
moving next into some of the deeper
2:47
stages of sleep and starting first with
2:49
NRM stage three sleep or what's actually
2:51
called deep sleep now this stage of
2:54
sleep lasts anywhere from about 20 to 40
2:56
minutes and it is during this stage of
2:59
sleep where we begin to see improvements
3:01
in our body's ability to heal itself we
3:04
see improvements in muscle recovery and
3:06
improvements in other organ systems and
3:09
part of the reason for this is that
3:10
growth hormone which is a hormone that
3:12
helps our body recover overall is
3:14
beginning to elevate during this time
3:16
period additionally our brain waves are
3:19
beginning to slow down during this
3:21
period of time which facilitates a drop
3:23
in energy expenditure in our body and
3:26
it's also quite difficult to wake up
3:28
during this period now for instance if
3:30
your alarm clock goes off when you're in
3:31
one of these stages of sleep stage three
3:33
or stage four which we'll talk about
3:35
next you feel quite groggy waking up and
3:38
it's it's quite difficult to wake up in
3:40
this stage versus let's say NRM stage
3:43
one or NRM stage two which we had talked
3:45
about
3:46
previously so following this NRAM stage
3:50
three phase of sleep we move next into
3:54
sleep now sleep is also about 20 to 40
3:58
minutes and it's during this period of
4:00
time where that growth hormone that
4:02
facilitates recovery is at its greatest
4:05
we also see that dreams are occurring
4:07
during this stage and our muscles are
4:10
essentially paralyzed we're really not
4:12
moving our body at all during this stage
4:15
and it's considered that this stage of
4:18
sleep is essential for memory
4:20
consolidation and our ability to focus
4:22
cognitively as we move through our day
4:25
it's an important stage as well for
4:27
consolidation of emotional effects
4:29
emotional experiences that we've had
4:31
through the day and it's generally
4:32
considered to be the most robustly
4:34
helpful stage of sleep for processing
4:37
our mental state and really these are
4:41
the the four essential stages of sleep
4:44
and it can be quite difficult to
4:45
distinguish between all four of them but
4:48
primarily these last two stage three and
4:50
stage four which are often grouped
4:52
together and can be difficult to uh to
4:55
tell apart