Sleep and Consciousness Flashcards
Behavioural criteria for sleep
- Stereotypic or species-specific posture
- Minimal movement
- Reduced responsiveness to external stimuli
- Reversible with stimulation – unlike coma, anaesthesia or death
Stages of sleep and their characteristics
In the first two stages, we start to see a change in the EEG(brain activity-slowing down). The eye movements are suppressed and there is less muscle activity (slowing down on EOG- eye movement and EMG-muscle activity).
NREM = non-Rapid Eye Movement sleep.
Stages 3 and 4 still count as NREM, because although there is EOG activity, there are not rapid eye movements. At the end of the sequence (stage 5), we get REM sleep.
REM sleep
Mainly dream in this stage
- EOG increases massively in stage 5
- During stage 5, EMG activity is suppressed more – when you dream, you don’t want to act dreams out
- there is an increase in HR and respiratory rate
Cycles of sleep
If you get lots of sleep you can have between 4-6 sleep cycles
Each cycle lasting about 90 minutes
Maintenance of arousal
Reticular activating system controls consciousness
-when active- you are awake
Starts in the brainstem, projects up and influences the activity of the cerebral cortex. It can do this directly or through indirect input via the intralaminar nuclei in the thalamus. The higher the level of activity in this system, the higher the level of arousal.
Interactions of RAS and parts of the hypothalamus to control arousal and sleep
The lateral hypothalamus promotes wakefulness
- Within the lateral hypothalamus is the orexin system (hypocretin system) – Promotes wakefulness
- The ventrolateral preoptic nucleus in the anterior hypothalamus – promotes sleep
Circadian synchronisation of sleep/wake cycle
The suprachiasmatic nucleus synchronises sleep with falling light level
The SCN provides a link between the level of light that’s around, and the arousal systems
- There are direct projections going from the retina to the hypothalamus
- Light tells the brain that it is day time – not time to sleep
Effects of sleep deprivation
Psychiatric and neurological
* Sleepiness, irritability, stress, mood fluctuations, depression, impulsivity, hallucinations
Neurological
- Impaired attention, memory, executive function, risk of errors and accidents
- Neurodegeneration – sleep problems can be a warning sign for neurodegenerative disease
Somatic- can lead to death
- Glucose intolerance
- Reduced leptin/increased appetite- obesity
- Impaired immunity
- Increased risk of cardiovascular disease and cancer
Function of sleep
- Restoration and recovery – but active individuals do not sleep more
- Energy conservation – 10% drop in BMR – but lying still is just as effective
- Specific brain functions – memory consolidation
How sleep loss effects sleep
- Reduced latency to sleep onset
- Increase of slow wave sleep (NREM)
- Increase of REM sleep (after selective REM sleep deprivation)
Insomnia causes
- Physiological e.g. sleep apnea (obstructive and central), chronic pain
- Brain dysfunction e.g. depression, fatal familial insomnia, night working
Insomnia treatment
Most hypnotics (sleeping tablets) enhance GABAergic circuits- inhibitory mechanisms
Narcolepsy
- Falling asleep repeatedly during the day and disturbed sleep during the night
- Dysfunction of control of REM sleep
- Orexin/hypocretin deficiency – if you lose these neurones, you lose the effects of the RAS
Condition narcolepsy is linked with
Cataplexy-sudden, brief loss of voluntary muscle tone, often triggered by strong emotions e.g. laughter
Lewy-body disease
Type of dementia where patients can act out their dreams, often in a very violent way
Improving sleep quality
- Establishing fixed times for going to bed/waking up
- Creating a relaxing bedtime routine
- Only going to bed when you feel tired
- Maintaining a comfortable sleeping environment e.g. lighting
- Not napping during the day – disrupts your normal cycle
- Avoiding caffeine, nicotine and alcohol late at night
- Avoiding eating a heavy meal late at night
- Don’t use back-lit devices shortly before going to bed
