EEG, Sleep and Circadian Rhythms

Question 1

What does sleep occur due to?

Answer 1

Active inhibitory processes that originate in the pons

Question 2

What happens, in terms of sleep, if there is destruction of the brainstem at the level of mid-pons?

Answer 2

Creates a brain that never sleeps

Question 3

How do drugs that block serotonin affect sleep?

Answer 3

Inhibit sleep

Question 4

What is serotonin?

Answer 4

Precursor of melatonin

Question 5

What does activity in the SCN cause?

Answer 5

Promotion of melatonin production

Question 6

What does the hypothalamus release?

Answer 6

Orexin - excitatory neurotransmitter required for wakefulness

Question 7

What causes narcolepsy?

Answer 7

Defective orexin signalling

Question 8

What happens during wakefulness?

Answer 8

Excitatory neurons in ascending reticular activating system released from inhibition from sleep centres in reticular formation
Stimulate excitatory pathways in both CNS and PNS
Positive feedback from CNS and PNS sustains wakefulness in individual for many hours

Question 9

What happens when active cells become fatigued and excitatory signals fade?

Answer 9

Inhibitory peptide signals from sleep centres take over and rapidly inhibit the weakening excitatory signals which leads to rapid progression into sleep state

Question 10

What is an EEG?

Answer 10

Recording of wave patterns that reflect electrical activity of the brain

Question 11

How can waves of an EEG be analysed?

Answer 11

Amplitude

Frequency

Question 12

What happens to frequency of waves on an EEG with neuronal excitation?

Answer 12

Increases

Question 13

What happens to amplitude of waves on an EEG when we become more alert?

Answer 13

Decreases

Question 14

what are the four main type of wave patterns seen on an EEG?

Answer 14

Alpha
Beta
Theta
Delta

Question 15

How is an EEG characterised in the relaxed awake state?

Answer 15

High frequency, high amplitude waves - Alpha waves

Question 16

How is an EEG characterised in the alert, awake state?

Answer 16

Higher frequency, low amplitude asynchronous waves - Beta waves

Question 17

How are theta waves characterised?

Answer 17

Low frequency waves, vary enormously in amplitude

Question 18

When are theta waves common?

Answer 18

Children and times of emotional stress and frustration in adults
Can also occur during sleep in adults and children

Question 19

How are delta waves characterised and when do they occur?

Answer 19

Very low frequency but high amplitude

Occur in deep sleep

Question 20

What is stage 1 of the sleep cycle?

Answer 20

Slow wave non REM, S-sleep
Slow eye movements, light sleep and easily aroused
High amplitude, low frequency theta waves

Question 21

What is stage 2 of the sleep cycle?

Answer 21

Eye movements stop, frequency slows further but EEG shows burst of rapid waves - sleep spindles

Question 22

What is stage 3 of the sleep cycle?

Answer 22

High amplitude, very slow delta waves interspersed with short episodes of faster waves
Spindle activity declines

Question 23

What is stage 4 of the sleep cycle?

Answer 23

Exclusively delta waves

Slow waves big amplitude

Question 24

What is REM sleep?

Answer 24

Rapid eye movements
Characterised by fast waves
25% of sleep, when dreams occur

Question 25

What is the order of the sleep cycle?

Answer 25

Stage 1 - stage 2 - stage 3 - stage 4 - stage 3 - stage 2 - REM - stage 2 - stage 3 - stage 4

Question 26

What are the physiological characteristics of deep, slow sleep?

Answer 26

Decreased vascular tone, respiratory and metabolic rate | Dreams may occur but rarely remembered

Question 27

What are the physiological characteristics of REM sleep?

Answer 27

Lasts 5-30min every 90 mins Eye muscles show bursts of rapid activity - profound inhibition of all other skeletal muscles - prevents acting out of dreams Dependent on cholinergic pathways within reticular formation and their projections HR/RR become irregular and brain metabolism increases

Question 28

What effect do anticholinesterases have on REM sleep?

Answer 28

Increase time spent in REM sleep

Question 29

What is the EEG pattern of REM sleep?

Answer 29

Mimics beta waves associated with highly alert state

Question 30

What do sleep deprived subjects demonstrate?

Answer 30

Impairment of cognitive function Impairment of physical performance Sluggishness Irritability

Question 31

What does sleep support?

Answer 31

``` Neuronal plasticity Learning and memory Cognition Clearance of waste products from CNS Conservation of energy Immune function ```

Question 32

How does sleep change over a lifetime?

Answer 32

Toal sleep time decreases | Percentage of REM sleep declines

Question 33

What is insomnia?

Answer 33

Chronic inability to obtain necessary amount or quality of sleep to maintain adequate daytime behaviour

Question 34

Where is the 'master clock' located?

Answer 34

Suprachiasmatic nucleus of the hypothalamus - just above the optic chiasma Neurons have an inherent 24 hour cycle which is entwined by external cues