1. While You were Sleeping…

2. The nervous system is a system in the body which sends signals around the body.
It lets people and animals respond to what is around them.
The brain is like a computer that controls the body's functions, and the nervous system is like a network that relays messages to parts of the body. 

3. What are neurons?
Neurons are the main type of cell in the nervous system
also known as nerve cells
Carry electrical impulses
Basic unit of the brain

4. What are Brainwaves?
At the root of all our thoughts, emotions and behaviours is the communication between neurons within our brains.
Brainwaves are produced by synchronised electrical pulses from masses of neurons communicating with each other.
Brainwaves are detected using sensors placed on the scalp

5. What are Brainwaves?
Think of them as a continuous spectrum of consciousness; from slow, loud and functional - to fast, subtle, and complex.
It is a handy analogy to think of brainwaves as musical notes - the low frequency waves are like a deeply penetrating drum beat, while the higher frequency brainwaves are more like a subtle high pitched flute.
- images showing examples of the different brain waves

6. Circadian Rhythm Our 24 hour biological clock.
designed to regulate feelings of sleepiness and wakefulness over a 24-hour period.
This complex timekeeper is controlled by an area of the brain that responds to light, which is why humans are most alert while the sun is shining and are ready to sleep when it’s dark outside.
This is called the SCN

7. Circadian Rhythm
Most people feel the strongest desire to sleep between 1:00pm and 3:00pm (a.k.a. the post-lunch, afternoon crash) and then again between 2:00am and 4:00am, but this can vary from person to person.
That’s why some people are “morning people,” while others function best in the evening.
If you follow your body’s natural cues regarding when to go to sleep and wake up, your circadian rhythm should stay balanced, but a change in your schedule (like if you stay up late pulling long hours with friends one day or sleep in one Saturday), can disrupt your body clock.

8. The Master Timekeeper
a group of about 20,000 nerve cells (neurons) that form a structure called the suprachiasmatic nucleus, or SCN.
The SCN is
located in a part of the brain called the hypothalamus and receives direct input from the eyes

9. How do we know to go to sleep?
When it gets dark, the retina detects failing light, and triggers the SCN
The SCN triggers the pineal gland which creates and releases the hormone MELATONIN
This is a key hormone for sleeping
The level of melatonin gradually increases, reaching its peak in the middle of the night in natural circumstances9.

10. The Master Timekeeper
Melatonin is not a sedative, but is a cue for innate night-time behaviour.
In the morning, your retina is triggered by light, which causes the SCN to alert the pineal gland to stop making melatonin\
It is melatonin that causes your body to slow down, to reduce heat, etc.

11. Sleep Stages
If you sleep for 8 hours a day, you will on average get 2 hours of deep sleep, 2 hours of REM sleep and 4 hours of light sleep.
There are 4 identified stages of sleep (used to be 5).
The sleep stages replace each other in phases of approximately 1.5 hours, and most people repeat it 4-6 times during the night.

12. Sleep Stages

13. Feel like you’re falling? Movements slowing? Eyes rolling slightly?
Stage 1
Feel like you’re falling?
Movements slowing?
Eyes rolling slightly?
YOU ARE IN STAGE 1 (or N1) SLEEP

14. STAGE 1 “falling asleep” – transition between awake and asleep
lasts between 1 and 5 minutes – no more than 7 minutes
Less than 10% of a normal night of sleep.
Brain waves: begin to slow from waking brain waves

15. YOU ARE IN STAGE 2 (or N2) SLEEP
Heartbeat and breathing slow
Muscles relax more
Body temp drops
Eyes stop moving
YOU ARE IN STAGE 2 (or N2) SLEEP

16. STAGE 2 A light sleep Spend more time in this stage than any other
45-60“% of a normal night of sleep.
Brain waves: slow down but spike at times – might be involved in memory/learning formation

17. YOU ARE IN STAGE 3 (or N3) SLEEP
Stage 3 (and 4)
Heartbeat and breathing slow the most in this stage
Muscles very relaxed
May be difficult to wake you
YOU ARE IN STAGE 3 (or N3) SLEEP

18. Stage 3 (and4)
This is the deep sleep that you need to feel refreshed in the morning
Occurs in longer periods during the first half of the night. 
Brain waves: slow down even more

19. YOU ARE IN REM SLEEP REM Sleep
REM: Rapid Eye Movement – eyes move quickly during this stage
Body becomes relaxed and immobilized – you are paralyzed!
This is because of 2 different neurotransmitters that are produced in the brain
Dreams occur
YOU ARE IN REM SLEEP

20. REM Sleep This is a very active stage of sleep.
Composes % of a normal nights sleep.
Breathing, heart rate and brain wave activity quicken.
Vivid Dreams can occur.
From REM, you go back to Stage 2