Lecture 6: Sleep and biological rhythms

Question 1

How is sleep measured?

Answer 1

EEG-Electrical activity
EMG- Muscle activity
EOG-Eye movements
PSG-the whole system of assessment plus O2 levels, heart and breathing

Question 2

Beta activity

Answer 2

Arousal

Irregular electrical activity of 13-30 Hz

Question 3

Alpha activity

Answer 3

Relaxation

Smooth electrical activity of 8-12Hz

Question 4

Theta activity

Answer 4

transition between wakefulness and sleep

EEG activity of 3.5-7.5 Hz

Question 5

Delta activity

Answer 5

Regular, synchronous electrical activity less than 4Hz

Question 6

Sleep stage 1

Answer 6

sleep is characterised by drowsiness, muscle activity slows, eye movement slows down, its not uncommon to experience hypnic myoclonia “Startle-like muscle jerks often preceded by the sensation of having to fall.”

Question 7

Sleep stage 2

Answer 7

eye movement stops and brain activity slows down – k complexes and sleep spindles observed in eeg / definitely asleep but easy to wake up.

Question 8

Sleep stage 3/4

Answer 8

sleep characterised by delta activity (v slow) and deep sleep. S3 30%, S4 50%. Very difficult to wake. Lose all muscle tone. Groggy if woken up. Number of sleep disorders occur during S4

Question 9

REM sleep

Answer 9

brain activity becomes desynchronised and resembles alert state / breathing becomes irregular and shallow / eyes jerk rapidly in different directions (hence REM) / limb muscles become paralys ed (paradoxical sleep) / heart rate and blood pressure rises / erections and vaginal excretions occur / dreaming happens.

Question 10

Sleep cycle

Answer 10

Sleep cycles through these stages approximately every 90 minutes. Most slow wave sleep (stages 3 and 4) occurs in the first half of the night. As the night draws on most of our sleep is stage 2 and we see that periods of REM become longer and stage 4 sleep becomes shorter.

Question 11

Typical nights sleep

Answer 11

•	50% Stage 2
•	20% REM
•	30% other stages
•	Sleep needs across species:
	Two-toed sloth – 20 hours
	Infants – 16 hours (50% REM)
	Teenagers – 9 hours
	Adults – 7-8 hours
	Elderly - <7
	Horses – 2 hours

Prem babies 80% in REM

Question 12

How many people suffer from sleep disorder?

Answer 12

33%

Question 13

Insomnia

Answer 13

Occurrence - 25% of pop occasionally and 9% regularly

•Inability to fall asleep, sleep through the night, and / or fall back to sleep after early waking

Question 14

Sleep apnea

Answer 14

Occurrence: 1-6% adults and 2% children

pauses in breathing or periods of shallow breathing during sleep. Pauses can last for a few seconds to a few minutes and occur many times a night

During sleep apnea, carbon dioxide in the blood stimulates chemoreceptors and person wakes up gasping for air. The oxygen levels return to normal, the person falls asleep and the cycle happens over again.

Question 15

Narcolepsy

Answer 15

affects less than 1% of the population

-frequent and intense urges to sleep at inappropriate times

Sleep paralysis: inability to move just before sleep or just after waking while lying down

Question 16

Cataplexy

Answer 16

=varying amount of muscle weakness
sometimes completely paralysed but can still see/hear

-triggered by strong emotional reactions or by sudden physical effort

Question 17

Hypnogogic hallucinations

Answer 17

=dreaming whilst aware and awake

Question 18

Evolutionary hypothesis

Answer 18

sleep allows us to conserve energy and evade risk
• Animals who have fewer predators tend to sleep longer
• Predatory danger negatively correlates with NREM
and REM sleep
• Only adaptive if safety assured
Importance of REM sleep for brain development
• Early brain development? – premature infants spend 80% in REM sleep vs 50% in non-prem, decreases to 30% in 6 month olds and 22% in 8 year olds
• Sleep facilitates maze learning in rats
• Link with REM time and giftedness in children

Question 19

Rebound phenomenon

Answer 19

-particular stages of sleep seem to have more importance for survival

rebound effects
-deprivation followed by increase in proportion of stage 4 and REM sleep, at the expense of other stages

-sleep efficiency rather than length of sleep increases

Question 20

Repair and restoration theory

Answer 20

• Function of sleep is to enable body/brain to repair after exertions of the day
• Priority given to recovery of stage 4 sleep suggests this type may be particularly important for recuperation

Question 21

Support for repair and restoration theory

Answer 21

 Growth hormone mainly secreted during S4 important for tissue growth and cell repair, i.e. “beauty sleep”
 Lowered cerebral metabolic rate – delta waves falls to 75% of waking levels – people in S4 can only be woken by intense stimuli and it takes them a long time to become alert – suggesting the brain is resting

Question 22

Problems with repair and restoration theory

Answer 22

 Forced sedentariness does not decrease time in sleep
 No effect of physical exercise on sleep duration
 Fitter active people do not sleep longer than unfit sedentary people

Question 23

Refinement to RR theory: recovery from cerebral activity specifically

Answer 23

 Sleep and sleepiness increases following a behaviourally and mentally but not physically “active” day
 Similar sleep duration in an active compared to non-active day
 Increased time spent in S4 slow wave sleep

Question 24

Refinement to RR theory: role in learning and memory?

Answer 24

 Improvement in declarative memory following nap or overnight sleep
 Brain appears to rehearse newly learned information during SWS
 Consolidation effects of word learning from ST to LT memory with sleep and napping: gets rid of information that isnt needed

Question 25

What neurotransmitters control arousal system?

Answer 25

	   Acetylcholine (Ach)
	   Norepinephrine (NE)
	   Serotonin (5-HT)
	   Histamine
	   Orexin (Ox)

Question 26

VLPA

Answer 26

=key switch in the hypothalamus that inhibits arousal system

 Destruction of VLPA causes insomnia
 Stimulation of VLPA causes sleep
• Other hypothalamic neurons stabilize the switch, and their
absence results in inappropriate switching of behavioural states, such as occurs in narcolepsy

Question 27

Flip-flop switch

Answer 27

What is interesting about the VLPA and brain stem arousal systems is that they have reciprocal pathways that inhibit each other

-because these systems inhibit each other, explains how bursts of arousal might then inadvertently trigger the VLPA circuit as the arousal system tries to regulate itself – explains symptoms of narcolepsy and sudden flip-flop between excitement to deep sleep

Question 28

ARAS

Answer 28

inhibits neurons in the VLPA and releases Its that mediate arousal

Question 29

VLPA

Answer 29

GABAergic neurons inhibit ARAS followed by drowsiness and sleep

unstable-always rapidly one or other, no in-between

Question 30

Orexin

Answer 30

Neurons in the lateral hypothalamus secrete orexin to prevent suddenly collapsing to the floor

-activated when there’s motivation to stay awake or when something brings you out of sleep eg noise

support the maintenance of arousal and work to stabilize the flip-flop switch – by keeping VLPA inhibited.

Question 31

Acetylcholine and REM sleep

Answer 31

• exposure to an insecticide associated with acetylcholine release caused vivid hallucinations
• stimulation of Ach by agonist during sleep prolonged the cycle duration of REM sleep while antagonists shortened it

Question 32

Circadian rhythms

Answer 32

Zeitgeber = a stimulus (usually light) that resets the biological clock responsible for circadian rhythms

• Studies conducted in animals and humans where the influence of zeitgebers has been removed to see if the circadian rhythm persists:
• they find is that there are individual differences within species (so everyone’s cycle length might differ) and that the sleep-wake cycle in humans tends towards 25 hours rather than 24.
• What keeps everyone’s cycles together is the presence of zeitgebers which entrain the biological rhythms.

Question 33

Suprachiasmatic nucleus (SCN)

Answer 33

• Regulates circadian rhythm
• Lesions = circadian rhythms (wheel running, drinking, hormone secretion, body temp and sleep) become
less consistent (occur throughout 24 hr period rather than just one half of the day)
• If removed from brain, SCN neurons
continue to produce circadian rhythm of
action potentials
• Transplants of SCN’s producing “faulty”
rhythms caused recipients to develop similarly
faulty circadian cycles (in hamsters)

Question 34

SCN and sleep cycle

Answer 34

• SCN appears to regulate wake-sleep via its effects on other brain areas (e.g. pineal gland)
• In response to signals from the SCN, the pineal gland releases a hormone called melatonin
• Melatonin, released almost exclusively at night, increases sleepiness