Sleep Flashcards
What are the stages of sleep?
Awake:
- Fast brain activity in the EEG (beta rhythm) – 30Hz
- Reasonable amount of muscle tone
Stage 1 & 2 – light sleep:
- EEG activity slows as the person becomes drowsy
- Beta -> theta activity (4-8Hz)
- NO eye movements and general muscle activity is reduced
Stage 3 & 4 – deep sleep:
- Theta -> delta activity – slowest rhythm at around 1Hz
- Minimal eye movements and continued relaxation of muscles
Stage 5 – REM Sleep:
- Brain activity shifts back to a fast rhythm
- REMs are seen
- Muscle activity is lowest – paralysed
What happens during sleep cycles?
You have multiple sleep cycles per night - each cycle lasts ~1-1.5 hours
You tend to get more slow-wave sleep at the beginning of the night and more REM sleep towards the end of the night
- Heart rate is slow during slow-wave sleep and faster during REM sleep - same pattern with respiration rate.
What mainly controls consciousness?
reticular activating system - starts in brainstem and projects into and influences cerebral cortex
effects of the RAS can be direct or through intralaminar nuclei in the thalamus
What nuclei control the RAS?
Lateral hypothalamus – excitatory input to RAS.
- Active during the day
Ventrolateral Preoptic Nucleus – negative effect on the RAS
- This promotes sleep
There is an antagonist relationship between the nuclei – activity of one inhibits the other
What causes the circadian synchronisation of the sleep/wake cycle?
Suprachiasmatic nucleus – synchronises sleep with falling light level
- Receives input from the retina via a special type of ganglionic cell (not RGC)
- Light levels fall which activates the SN more to activate more nuclei within the hypothalamus
- This inhibits the LH nucleus and stimulates VLP nucleus whilst also having direct effects on the RAS resulting in reduction of traffic
The suprachiasmatic nucleus also has a projection to the PINEAL GLAND
The SN activates the pineal gland to secrete melatonin which continues throughout the night - melatonin adjusts physiological processes in the body to fit it with sleep
What are the effects of sleep deprivation?
- Sleepiness and irritability
- Performance decrements/increased risk of error
- Concentration and learning difficulties
- Glucose intolerance
Reduced leptin – increased appetite - Hallucinations – after long sleep deprivation
- Death – fatal familial insomnia
How is sleep regulated after sleep loss?
Reduced latency to sleep onset – if you lose a night’s sleep, you go to bed earlier the next day
Increase of NREM (slow wave sleep) – so you sleep for longer if sleep deprived
Increase of REM sleep – after specifically, selective REM sleep deprivation
What is the function of sleep?
Restoration and recovery – but active individuals do not sleep more
Energy conservation – 10% drop in BMR but to lying still is just as effective
Predator avoidance
Specific brain functions
When do dream occur?
Dreams can occur in REM and/or NREM sleep however they are most frequently REM sleep
Dreams can more easily be recalled in REM sleep
Contents of dreams are more emotional than ‘real life’
Brain activity in the limbic system is higher than in the frontal lobe during dreams
- Limbic system = emotions.
- Frontal lobe = logical thought and informed decision making
What are the functions of dreams?
Dreams act as a safety valve for antisocial emotions
Sorting of memory and disposing of unwanted memories
Memory consolidation
- NREM sleep – declarative memory – facts and events
- REM sleep – procedural memory – learning skills
What are the causes of and treatment for insomnia?
- Insomnia has a high prevalence and most cases are transient (comes and goes)
Causes:
- Physiological – e.g. sleep apnoea, chronic pain
- Brain dysfunction – e.g. depression, fatal familial insomnia, night work
Treatment:
- Remove cause
- Hypnotics – enhance inhibitory circuits in the brain – GABAergic circuits
What is sleep hygiene?
- establishing fixed times for going to bed and waking up (don’t lounge in bed after waking up)
- creating a relaxing bed time routine- only going to bed when you feel tired
- maintaining a comfortable sleeping environment
- not napping during the day
- avoid caffeine, nicotine and alcohol late at night
- avoid eating a heavy meal late at night
- don’t use back-lit devices shortly before going to bed
What is hypersomnia?
sleepy during the day
usually secondary to something else e.g waking up continuously during the night due to sleep apnoea
headache and dry mouth in the morning
What is narcolepsy?
Falling asleep repeatedly during the day and disturbed sleep at night
Cataplexy – sudden onset muscle weakness that may be precipitated by excitement or emotion.
- Sometimes in just one part of the body but can occur in most muscles -> falling over
- REM sleep = low muscle tone!
Cause:
- Orexin deficiency – orexin is a neuropeptide which is the transmitter used by the lateral hypothalamus
Cause could be genetic or autoimmune
Normally treatment is a strict regimen of sleeping routines
