EEG, sleep & circadian rhythms Flashcards
Define sleep
State of unconsciousness from which you can be aroused by stimuli (light, touch, sound)
Sleep occurs due to active inhibitory processes that originate where in the brain
Pons
Something below the level of the … must be actively sending … to the cortex
Evidence suggests this activity originates in the … of the brainstem
Mid-pons
Inhibitory impulses
Reticular formation
Many neurons within the reticular formation are…
Serotonergic - produce serotonin
Drugs that block serotonin formation inhibit or induce
Inhibit, so serotonin is critical to sleep induction
Serotonin is a precursor of what chemical
Melatonin
Melatonin levels in the blood increase at morning or night
Night
By the morning, melatonin levels have rised or dropped
Dropped completely
What is the circadian rhythm
24-hour internal clock that is running in the background of your brain and cycles between sleepiness and alertness at regular intervals
It’s also known as your sleep/wake cycle
What part of the brain controls the circadian rhythm
Suprachiasmatic nucleus (SCN) in the hypothalamus
Suprachiasmatic nucleus (SCN) in the hypothalamus that controls the circadian rhythm sits above what structure in the brain
Optic chasm
The circadian rhythm is entrained by external cues such as
Light/dark cycles but is not the entrainment as blind people have circadian rhythms too
Activity in the SCN stimulates release of what chemical
Melatonin
What gland produces melatonin
Pineal gland
The hypothalamus releases what excitatory neurotransmitter that’s required for wakefulness (2 different names)
Orexin (aka hypocretin)
Defective orexin signalling can cause what condition + describe a bit about it
Narcolepsy - suddenly fall asleep, enter directly into REM sleep with little warning
If the SCN is destroyed, then the circadian rhythm of sleep is lost, explain the likely reason for this
Loss of melatonin signalling and disruption of orexin signalling in the hypothalamus, (wakefulness normally being stimulated in the morning, when orexin level rises; sleep occurring at night when orexin levels fall).
Are orexin levels high in the morning or night
Morning
Name the 2 centres in the reticular formation
arousal centre + sleep centre
Where is the reticular formation (regulates sleep and consciousness) located
Brainstem
How do we have a self-sustaining cycle of wakefulness for many hours
Excitatory neurons in the Ascending Reticular Activating System (ARAS) stimulate excitatory pathways in the CNS & PNS
–> These further excitatory pathways then create a positive feedback cycle from the CNS and PNS back to the ARAS, boosting the ARAS
Towards the end of the day, excitatory neurons and signals become fatigued and fade. At this point, what takes over
Inhibitory peptide signals from the Sleep Centres in the Reticular Formation
What investigation can assess level of consciousness in an awake person
EEG (Electroencephalogram)
What does EEG record
wave patterns that reflect the electrical activity of the brain
What 2 things are interpreted from the wave patterns reflecting electrical activity on an EEG reading + describe what each of these are
Amplitude (wavelength): the size of the wave (ranges from 0-200 µV)
Frequency: number of waves per second (ranges from 1-50+)
In increasing consciousness,
- frequency increases or decreases
- amplitude increases or decreases
frequency increases
amplitude decreases
In decreasing consciousness,
- frequency increases or decreases
- amplitude increases or decreases
frequency decreases
amplitude increases
Describe the frequency and amplitude of an EEG of someone
- under anaesthesia
- in a seizure
Under anaesthesia:
High amplitude
Low frequency
In a seizure:
High frequency
Low amplitude
4 main types of wave pattern of an EEG
1) Alpha
2) Beta
3) Theta
4) Delta
In awake, relaxed state, what type of wave is seen on an EEG
Alpha waves
When there’s less stimuli to the brain, neurons firing synchronously…
Summate and so increase their amplitude
Describe the amplitude and frequency of an EEG of someone in the
- awake, relaxed state
- awake, alert state
Awake & relaxed:
High frequency
High amplitude
Awake & alert:
Even higher frequency
Low amplitude
In awake, alert state, what type of wave is seen on an EEG
Beta waves
Why is the amplitude low but the frequency high on an EEG of someone in the awake, ALERT state
So much electrical activity going on in the alert state that neurons fire asynchronously (out of sequence with each other) because so many stimuli –> desynchronised waves cancel each other out and don’t get recorded on EEG
Are theta waves high or low frequency waves
Low
When do you see theta waves on an EEG (3)
Common in children,
and during times of emotional stress and frustration in adults
Also occur during sleep
Describe the frequency and amplitude of delta waves
Very low frequency
High amplitude
When do you see delta waves on an EEG
Deep sleep
How many stages of sleep
5
Describe stage 1 sleep (S-sleep)
- eye movements
- light/deep
- amplitude & frequency & wave type
Slow eye movements.
Light sleep so easily aroused.
High amplitude, low frequency theta waves
Describe stage 2 sleep
- eye movements
- frequency of waves (2)
Eye movements stop
Frequency slows overall
- but there’s bursts of rapid waves called sleep spindles (clusters of high frequency waves)
Describe stage 3 sleep
- amplitude & frequency of waves
- wave type
- light/deep sleep
High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves
Spindle activity (bursts of high frequency waves) declines
DEEP SLEEP
Describe stage 4 sleep
- wave type
- amplitude & frequency of waves
- light/deep sleep
delta waves - high amplitude, low frequency
Deep sleep
Describe stage 5 sleep
- eye movements
- frequency & amplitude
REM sleep - rapid eye movements
Fast, high frequency waves, low amplitude like those of the awake state
What percentage of sleep is REM sleep
25%
Slow wave sleep = what stages of sleep
Stages 1-4
How long do the 5 stages take before the cycle repeats itself again
90 mins
Time spent in REM sleep increases or decreases as the sleep cycle repeats
Time spent in deep sleep increases or decreases as the sleep cycle repeats
Increases
Decreases
Most restful sleep is in what stage of sleep
4
What stage is S-wave sleep (Deep slow wave sleep)
4
Physiological characteristics of stage 4 sleep (3)
Decreased vascular tone (and therefore BP), respiratory and basal metabolic rate
How long does REM sleep last
5-30 mins
Why do only the eye muscles move during REM sleep but no other skeletal muscles
due to inhibitory projections from pons to spinal cord
REM sleep is dependent on what neurotransmittory pathway
Cholinergic pathways
- anticholinesterases increase time spent in REM sleep because they boost ACh release
What happens to HR, RR and brain metabolism in REM sleep (D-sleep)
Increases
What wave type does the EEG pattern during REM sleep mimic
Beta waves associated with alert, awake state
Is it easy or hard to arouse someone from REM sleep
Hard
Sleep deprived people demonstrate what characteristics (4)
- Impairment of cognitive function (detected in early hours of sleep deprivation)
- Impairment of physical performance (detected in early hours of sleep deprivation)
- Sluggishness
- Irritability
Sleep supports what physiological functions (5)
- Neuronal plasticity (needed for learning + memory)
- Learning and memory
- Cognition
- Clearance of waste products from CNS (rejuvenates neurons)
- Conservation of whole body energy
Percentage of sleep that is REM sleep in full term babies
50%
Define insomnia
chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
2 types of insomnia
a) chronic, primary insomnia where there is usually no identifiable psychological or physical cause
b) temporary, secondary insomnia in response to pain, bereavement or other crisis.
What drug used to be used to treat insomnia but not anymore + why (consequences)
Barbiturates
Chronic use increases time taken to fall asleep, decreases time spent in REM and stage 3 and 4 sleep, and increases no. of times awake during night
Dose required to treat insomnia too close to toxic dose
Preferred insomnia treatment instead of barbiturates and benzodiazepines
Lifestyle habits that induce sleep
What stage of the sleep cycle do night terrors occur
Deep, delta sleep (stage 4)
Nightmares v night terrors
Nightmares are during REM sleep
Night terrors during stage 4 deep sleep, don’t really remember night terrors
What is somnambulism + when does it occur
Sleep walking
Mainly in stage 4 sleep, never in REM
No recollection of it when waking up
