8 - SLEEP WAKE CYCLE

Question 1

several biological systems co-vary with the sleep wake cycle

(3)

Answer 1

• sugar
• insulin
• cortisol

Question 2

what happens if you have sugar before bed?

Answer 2

• blood sugar levels rise
• insulin levels rise
• blood sugar levels drop
• cortisol increases (to make new sugar - but can’t keep producing cortisol due to negative feedback loop)
• sleep cycle is disrupted
• someone who struggles to sleep could be because of eating before bed (not due to mental health)
• metabolism decreases with age - so sugar has a larger effect on the sleep cycle
• sugary snack = higher insulin so higher cortisol = disrupts sleep
• suggest not eating sugary snack after middday

Question 3

why does cortisol increase when we’re about to wake up?

Answer 3

• stress response to kick body into action

- cortisol lowest when we’re about to go to sleep = calm for sleeping

Question 4

how is cortisol released?

Answer 4

hypothalamus CRH > pituitary ACTH > adrenal gland cortisol

Question 5

why is cortisol released?

Answer 5

• in response to STRESS or LOW BLOOD SUGAR

Question 6

what is the function of cortisol?

2

Answer 6

1 - gluconeogenesis = “sugar-new-making”
- sugar from scratch, things other than from glycogen or fatty acids

2 - immune suppression

further effects

• increases blood pressure (eg stress)
• inhibits CRH (corticotropin releasing hormone)(negative feedback loop)

Question 7

what are cycles controlled by?

2

Answer 7

1 - internally generated (endogenous) ‘biological clocks’ (one or more)

2 - external cues (‘zeitgeber’) reset biological clocks (eg change between day and night)

Question 8

what happens if there is no zeitgeber?

Answer 8

• sleep-wake cycle moves
  = FREE RUN of internally generated rhythm
• can be 23/24/25 hours etc
• usually still sleep the same amount and still have a regular pattern, the cycle just shifts

Question 9

how does a zeitgeber affect sleep

Answer 9

• cycle matches the environment
• reset biologically clocks every day
• can be any form of external cues such as food delivery etc

Question 10

how active is the brain in REM sleep?

Answer 10

• sleeping brain is typically less active
• but MORE ACTIVE IN REM SLEEP
• electrical and metabolic brain activity almost like waking state
• most vivid dreaming (detailed and story like)

Question 11

what is hertz (Hz)

Answer 11

• waves past a certain point per second

Question 12

what are the sleep stages characterised by?

Answer 12

• specific bodily states
• specific electrical brain activity
• specific muscle activity

Question 13

what are metabolic and electrical activity like during the sleep stages?

Answer 13

wakefulness = high

non REM sleep = reduced

REM sleep = high

= multistage process

Question 14

electrical brain activity in the sleep stages

Answer 14

awake = beta (>13Hz) (alert peak)
awake = alpha (8-13Hz)

stage 1 drowsy = theta and alpha (3-7Hz)

stage 2 light sleep = sleep spindles (high frequency clump - 12-14Hz) and K-complexes (really high amplitude)

stage 3 = waves get longer and slower

stage 4 deep sleep (SWS) = delta (0.5-2Hz) large

REM = beta (>13Hz) and sawtooth waves (slightly higher)

Question 15

skeletal muscle activity during the sleep stages

Answer 15

awake (active) = beta
awake (relaxed) = alpha

over the stages (1-4)

• EEG synchronises
• heart rate slows down
• EMG (electromyogram) = little muscle activity
• EOG (electroculargram) = little eye movement

REM 
- EEG desynchronises (like beta)
- no muscle activity
- rapid eye movements
- heart rate speeds up 
PARADOXICAL SLEEP = dreaming

Question 16

what is paradoxical sleep

Answer 16

• body held in paralysis
• brain activity resembles waking state
• sleep stage with the move vivid dreams

Question 17

what is there no muscle activity in REM?

REM atonia

Answer 17

• could be defensive to prevent us from acting out our dreams
• nuclei in the pons and medulla actively paralyse the body by lowering muscle tone of skeletal muscles

Question 18

information:

same sleep pattern in mice and humans

Answer 18

-

Question 19

psychoanalytical interpretation of negative dreams

Answer 19

• subconscious mind = battle ground
• we want something forbidden but we know it’s forbidden so we hide it from ourselves and punish ourselves for wanting it
• hence causes negative feelings

Question 20

psychobiological interpretation of negative dreams

Answer 20

• subconscious mind perceives the body as immobilised and helpless
• which we are in REM sleep (paralysed)
• potentially dangerous as were vulnerable to predators

Question 21

systematic progression in the sleep stages

Answer 21

• during sleep, REM and non REM stages alternate
• time spent in each phase changes systematically
• more time spent in deep sleep (stages 3 and 4) in the first half of the night
• more time spent in REM and light sleep in the second half of the night
• week 8, pg 5 for diagram*
• REM = red
• stage 4 (SWS) = dark brown
• light sleep = orange

Question 22

life span changes of sleep patterns

Answer 22

infancy

• more than half of sleep is REM
• REM and overall sleep decreases with age
• early infancy = sleep around 16 hours a day

childhood

• sleep around 12 hours a day
• mainly SWS

adolescence/adulthood

• teenager = same REM as adult
• SWS decreases
• REM constant from 5

Question 23

sleep wake cycle in infant

Answer 23

• don’t sleep constantly

- in and out of sleep all day

Question 24

sleep wake cycle in childhood

Answer 24

• a couple of naps during the day

- sleep during the night

Question 25

sleep wake cycle in adults

Answer 25

- sleep around 8 hours at night

Question 26

sleep stages in childhood

Answer 26

- children have higher SWS | - each episode lasts longer

Question 27

elderly sleep stages

Answer 27

- wake up repeatedly | - struggle to get into REM sleep

Question 28

animal studies into sleep deprivation

Answer 28

``` - initially decrease in body temp metabolism appetite (saving energy?) ``` - subsequently failure to immune system loss of resistance to infection death could be due to the stress of being kept awake and not due to lack of sleep?

Question 29

human sleep deprivation

Answer 29

- results in impaired physical and cognitive function - impaired speech - impaired memory - hallucinations = asleep on your feet - large inter-individual variety - most people need approx 8 hours - but some can function on less than 4 hours

Question 30

REM rebound

Answer 30

after sleep deprivation - body will try to ‘catch up’ on missed sleep - can be selective - miss out on REM sleep - next nights sleep will catch up and include more REM sleep

Question 31

evolutionary perspective to sleep the paradox of sleep

Answer 31

- sleep is dangerous = vulnerable - but all animals with breaking show some form of sleep (even insects have periods of rest) - in higher animals, sleep is controlled by a complicated system of interacting neuro-endocrine functions - therefore there must be some advantage to sleep - don’t know fully what it is yet (but DNA repair could be one - don’t know if we need sleep to do repairs or if they just repair when asleep)

Question 32

information: some animals have developed a method to stay away when sleeping - dolphins - one hemisphere sleeps whilst the other has beta activity - vital in marine mammals - need to go to surface for air

Answer 32

-

Question 33

REM and memory consolidation

Answer 33

- higher levels of Ach in REM | - and known to be involved in memory

Question 34

hormones with a circadian rhythm

Answer 34

- cortisol - growth hormones - testosterone - peak around midday and lowest around midnight in males - also in women, but shallower peaks etc

Question 35

which rhythm does progesterone have

Answer 35

- infradian | - menstrual cycle

Question 36

what is a sleep spindle?

Answer 36

- high frequency wave cluster in stage 2 sleep - periodic bursts of activity around 12-14Hz and last around 1-2 seconds - due to interaction of thalamic and cortical neurons PINK PATCH ON DIAGRAM - closer together frequency