Sleep Flashcards
What is sleep?
State of unconsciousness from which individual can be aroused by normal stimuli, light, touch, sound ect. Cyclical
What is a coma?
State of unconsciousness from which individual cannot be aroused and does not responds to stimuli.
Why does sleep occur?
Due to active inhibitory processes that originate in the pons
What does destruction of the brainstem at the level of the mid-pons create?
A brain that never sleeps
Which part of the hypothalamus is also involved in sleep?
Suprachiasmatic nuclei
What does SCN demonstrate?
24hr circadian rhythm
What can electrical stimulation of the SCN do?
Promote sleep
What can damage to the SCN do?
Disrupt the sleep-wake cycle
What does activity in the SCN stimulate the release of?
Melatonin from the pineal gland
Where is melatonin released from?
The pineal gland
What does melatonin correspond with in humans?
Feelings of sleepiness but not immediately
What else does the hypothalamus release to to help wakefulness?
Orexin
What do orexin neurons do?
Orexin neurons are active during the waking state and stop firing during sleep.
What does defective orexin signalling cause?
Narcolepsy; individual will suddenly fall asleep, sometimes even when talking.
Where does evidence suggest that sleeping activity originates?
Reticular formation of the brainstem
What is the reticular formation closely associated with?
Controlling the state of consciousness
How do you asses the level of consciousness in an awake person?
Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills. Spell words backwards or count backwards,
How do you record patterns of brain activity?
Record patterns of brain activity using ElectroEncepheloGram (EEG). EEG uses electrodes placed on the scalp to record activity of underlying neurons.
What is more informative frequency or amplitude?
Frequency
What is frequency?
Number of waves per second
What is amplitude of waves?
The size of waves
What are the 4 main type of wave patterns seen?
Alpha
Beta
Theta
Delta
In the relaxed awake state what is the EEG characterised by?
High frequency, high amplitude waves
Alpha waves
In the alert awake state what is the EEG characterised by?
Even higher frequency, low amplitude asynchronous waves termed waves.
Why does the alert phase create low amplitude waves?
Increase in activity is asynchronous as brain is doing so many things at once, and opposing polarities of the signals cancel each other out and do not get recorded on EEG.
What are theta waves characterised by?
Low frequency waves that can vary enormously in amplitude
Who are theta waves common in?
Children
Which waves occur during sleep in both adults and children?
Theta waves
What are delta waves characterised by?
Very low frequency but high amplitude
When do delta waves occur?
In Deep sleep
What is stage 1 sleep?
Slow wave, non-REM, S-sleep. Slow eye movements. Light sleep. Easily roused. High amplitude, low frequency theta waves.
What is stage 2 sleep?
Eye movements stop. Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles” (clusters of rhythmic waves, ~12-14Hz)
What is stage 3 sleep?
High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines.
What is stage 4 sleep?
exclusively delta waves.
Very difficult to rouse from stage 3 and 4 sleep. Known as Deep Sleep. Sleep walking/talking occurs during these stages.
What is REM sleep?
REM sleep is characterised by fast waves, eerily similar to those of the awake state (what gives it a similar pattern to our awake state)
What occurs in REM sleep?
Rapid Eye Movements
What % of sleep in REM?
25%
As the night progresses what happens to our sleep?
We spend less and less time in a deep sleep and more and more time in REM sleep
What patterns of waves is REM sleep similar to?
The awake state
During which phase of sleep do dreams occur?
REM
If dreams occur in deep sleep are they remembered?
Rarely
When does deep sleep occur?
In the first few hours of sleep
Which is the most restful type of sleep?
Deep slow wave sleep
How long does REM sleep last?
5-30 mins every 90 mins or so during normal nights sleep
When is REM sleep less frequent?
Early in the night
When is REM sleep more frequent?
Later in the night as rest and recovery are established
What happens to HR and RR in REM sleep?
It becomes irregular
What happens to brain metabolism in REM sleep?
It increases
Is it easy or difficult to arouse someone from REM sleep?
Difficult
What do sleep deprived subjects demonstrate without exception?
- Impairment of cognitive function
- Impairment of physical performance
- Sluggishness
- Irritability
Is sleep crucial to maintain life?
Yes
What does sleep support?
- Neuronal plasticity
- Learning and memory
- Cognition
- Clearance of waste products from CNS
- Conservation of whole body energy (although cerebral O2 consumption may actually increase, esp. during REM sleep)
- Immune function (reason sleep increases when ill?)
How does sleep change through childhood and adolescence?
Total sleep time decreases as we age
What happens to REM sleep as we age?
It decreases 80% in 10 week premature infant, 50% at full term declining to a stable 2 5% in adulthood. May be absent by 80+ years old
What is insomnia?
“chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour”,
What % of adults does insomnia affect?
33%
What is chronic primary insomnia?
Where there is usually no identifiable psychological or physical cause
What is temporary, secondary insomnia?
Insomnia in response to pain, bereavement or other crisis, usually short lives
How do Benzodiazepines affect REM sleep?
Less effect
What is the issue with benzodiazepines?
There are highly addictive and cause many problems on withdrawal
What are nightmares?
have a strong visual component and are seen during REM sleep, typically occur quite far in the night sleep
What stops nightmares?
Wakening
Does the indiviual have a clear recollection of nightmares?
Yes
During which sleep do night terrors occur?
Deep sleep and delta sleep
Who are night terrors common in?
Young children
Does the individual recollect a night terror?
No
What is somnambulism?
Sleep walking
When do night terrors commonly occur?
Early night
When does sleep walking exclusively occur?
In non-REM sleep
Who is sleep walking common in?
Children and young adults
What do individuals do when sleep walking?
Walk with their eyes open, can see and will avoid objects, can carry out reasonably complex task such as prepare food
Can sleep walkers recall the incident?
No
What is narcolepsy?
When a patient enters directly into REM sleep with little warning
What is narcolepsy thought to be caused by?
Dysfunctional orexin release
What type of rhythm is sleep part of?
Circadian rhythm
What is circadian rhythm?
Biological systems that work in 24 hours
Where is the master clock located?
Suprachiasmatic nucleus (SCN) of the hypothalamus, lying just above the optic chiasma
What external signals can help the master clock?
E.g light and dark outside
If the SCN is destroyed what is lost?
Circadian rhythm of sleep
What is believed to happen when we enter the sleep state?
active cells become fatigued and excitatory signals fade. At this point inhibitory, peptide signals from the Sleep Centres in the Reticular Formation likely take over and rapidly dominate the weakening excitatory signals leading to rapid progression into the sleep state.
What is believed to happen during waking?
The inhibitory cells fatigue and the excitatory cells are reinvigorated (been resting overnight).
