EEG, Sleep and Circadian Rhythms Flashcards
What does sleep occur due to?
Active inhibitory processes that originate in the pons
What happens, in terms of sleep, if there is destruction of the brainstem at the level of mid-pons?
Creates a brain that never sleeps
How do drugs that block serotonin affect sleep?
Inhibit sleep
What is serotonin?
Precursor of melatonin
What does activity in the SCN cause?
Promotion of melatonin production
What does the hypothalamus release?
Orexin - excitatory neurotransmitter required for wakefulness
What causes narcolepsy?
Defective orexin signalling
What happens during wakefulness?
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
What happens when active cells become fatigued and excitatory signals fade?
Inhibitory peptide signals from sleep centres take over and rapidly inhibit the weakening excitatory signals which leads to rapid progression into sleep state
What is an EEG?
Recording of wave patterns that reflect electrical activity of the brain
How can waves of an EEG be analysed?
Amplitude
Frequency
What happens to frequency of waves on an EEG with neuronal excitation?
Increases
What happens to amplitude of waves on an EEG when we become more alert?
Decreases
what are the four main type of wave patterns seen on an EEG?
Alpha
Beta
Theta
Delta
How is an EEG characterised in the relaxed awake state?
High frequency, high amplitude waves - Alpha waves
How is an EEG characterised in the alert, awake state?
Higher frequency, low amplitude asynchronous waves - Beta waves
How are theta waves characterised?
Low frequency waves, vary enormously in amplitude
When are theta waves common?
Children and times of emotional stress and frustration in adults
Can also occur during sleep in adults and children
How are delta waves characterised and when do they occur?
Very low frequency but high amplitude
Occur in deep sleep
What is stage 1 of the sleep cycle?
Slow wave non REM, S-sleep
Slow eye movements, light sleep and easily aroused
High amplitude, low frequency theta waves
What is stage 2 of the sleep cycle?
Eye movements stop, frequency slows further but EEG shows burst of rapid waves - sleep spindles
What is stage 3 of the sleep cycle?
High amplitude, very slow delta waves interspersed with short episodes of faster waves
Spindle activity declines
What is stage 4 of the sleep cycle?
Exclusively delta waves
Slow waves big amplitude
What is REM sleep?
Rapid eye movements
Characterised by fast waves
25% of sleep, when dreams occur
What is the order of the sleep cycle?
Stage 1 - stage 2 - stage 3 - stage 4 - stage 3 - stage 2 - REM - stage 2 - stage 3 - stage 4
What are the physiological characteristics of deep, slow sleep?
Decreased vascular tone, respiratory and metabolic rate
Dreams may occur but rarely remembered
What are the physiological characteristics of REM sleep?
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
What effect do anticholinesterases have on REM sleep?
Increase time spent in REM sleep
What is the EEG pattern of REM sleep?
Mimics beta waves associated with highly alert state
What do sleep deprived subjects demonstrate?
Impairment of cognitive function
Impairment of physical performance
Sluggishness
Irritability
What does sleep support?
Neuronal plasticity Learning and memory Cognition Clearance of waste products from CNS Conservation of energy Immune function
How does sleep change over a lifetime?
Toal sleep time decreases
Percentage of REM sleep declines
What is insomnia?
Chronic inability to obtain necessary amount or quality of sleep to maintain adequate daytime behaviour
Where is the ‘master clock’ located?
Suprachiasmatic nucleus of the hypothalamus - just above the optic chiasma
Neurons have an inherent 24 hour cycle which is entwined by external cues
