Sleep Flashcards
Outline the behavioral criteria of sleep
Behavioral Criteria of Sleep
- Stereotypic or species-‐specific posture
- Minimal movement
- Responsiveness to external stimuli with stimulation -‐ unlike coma, anaesthesia or death
(brain is actually really active during sleep)
Measurements:
EEG: electroencephalogram - brain activity
EOG: electrooculogram - eye muscle movement activity
EMG: electromyography - muscle movement
The FIVE Stages of Sleep
There is quite fast brain rhythm in the EEG (beta rhythm)
This can be up to around 30 Hz
There is a reasonable amount of muscle tone because you are maintaining your posture and are ready for action
Stages of sleep: define the stages of sleep
Stage 1 and 2
- The first two stages are light sleep
- The person is becoming more and more drowsy and the EEG activity is slowing
- Gradually you go from beta activity to theta activity (4-‐8 Hz)
- There are NO eye movements
- The general muscle activity has been reduced considerably
Stage 3 and 4 (still counts as normal REM)
- There is a translation from theta activity to delta activity
- This is the slowest rhythm (around 1 Hz)
- There is minimal eye movement at this point
- There is continued relaxation of the muscles
- This is very deep sleep
Stage 5 -‐ REM Sleep (Rapid Eye Movement)
- Brain activity shifts abruptly back to fast rhythm
- This is quite similar to the activity you see in awake subjects
- You get rapid eye movement even though the subject is asleep
- The muscle activity is at its lowest so the person is basically paralysed
- Dreams occur here
NOTE: the first four stages are called NON-‐REM sleep (NREM)
These five stages together form a full sleep cycle
Discuss sleep cycles
Sleep Cycles: They happen periodically through the night
You start off being awake with beta activity
Up to stage 4, the rhythm gets slower and slower
Then there is a short transition period and then you get REM sleep
A single sleep cycle lasts about 1-‐1.5 hours
During a complete night’s sleep you go through these cycles one after the other
You tend to get more slow wave sleep at the beginning of the night and more
REM sleep at the end of the night
Other changes during sleep: sequential changes and patterns throughout sleep
Not just the same nerve activity but a series of sequential actions
Heart rate is slow during slow wave sleep and is faster during REM sleep
The same pattern occurs with respiration rate -‐ it is faster during REM
Control of sleep: explain how the sleep / wake cycle is controlled by the lateral hypothalamus and ventrolateral preoptic nucleus, and explain how the this is synchornised to day length
Maintenance of Arousal
- Consciousness is mainly controlled by the RETICULAR ACTIVATING SYSTEM
- This is a system that starts in the brainstem, then 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
- Generally speaking, the higher the level of activity in this system, the higher the level of arousal
There are TWO nuclei in the hypothalamus that influence the RAS and so control the sleep-‐wake cycle
1. Lateral Hypothalamus = EXCITATORY input to the RAS
- Tends to be active during the day
- This enables a higher level of activity in the cortex when awake
- Increased orezin/hypocretin
2. Ventrolateral Preoptic Nucleus = NEGATIVE effect on the RAS
- This promotes sleep
- There is an antagonistic relationship between these two nuclei -‐ when one is active, it inhibits the activity of the other
- At the beginning of the day, LH is more active and towards the end of the day VLP is more active and the LH activity is reduced
- There must be another system that is synchronising this system to what is happening outside
Suprachiasmatic Nucleus -‐ synchronises sleep with falling light level
It receives an input from the retina -‐ this is not from the usual photogenic cells (rods and cones) but actually from a special type of ganglion cell that is responsive to light
As the light levels fall, the suprachiasmatic nucleus becomes more active and this then activates a large number of nuclei within the hypothalamus
It will inhibit the LH nucleus and it will stimulate the VLP nucleus so towards the end of the day you become more sleepy
It also has more direct effects on the reticular activating system resulting in a reduction in traffic in the RAS at the end of the day
IMPORTANT: the suprachiasmatic nucleus has a projection to the PINEAL GLAND
- The pineal gland is a small gland in the midline at the back of the 3rd ventricle
- The suprachiasmatic nucleus activates the pineal gland towards the end of the day and this secretes a higher level of MELATONIN and continues to secrete this through the night
- The melatonin adjusts various physiological processes in the body that fit with sleep
- At the end of the night the melatonin levels fall
Summary
- There are TWO nuclei within the hypothalamus, which, through their reciprocal relationship, can shift the RAS either towards sleep or wakefulness
- This system is synchronised with day length by the suprachiasmatic nucleus
Outline the effects of sleep deprivation
Is sleep necessary?
- Most/all animals sleep
- Sleep deprivation is detrimental
- Sleep is regulated accurately
Effects of Sleep Deprivation
- Psychiatric and neurological
* Sleepiness, irritability, stress, mood fluctuations, depression, impulsivity, hallucinations - Neurological
- Impaired attention, memory, executive function
- Performance decrements/increased risk of errors and accidents
- Concentration/learning difficulties
- Neurodegeneration:
- Somatic
- Glucose intolerance -‐ risk of diabetes
- Reduced leptin/increased appetite -‐ risk of obesity
- Hallucinations (after long sleep deprivation)
- Death -‐ rats (14-‐40 days)
- Humans -‐ fatal familial insomnia
Sleep is regulated accurately (BRAIN compensation methods)
After sleep loss:
Reduced latency to sleep onset (if you’ve lost a night’s sleep you will go to bed earlier the next day)
Increase of slow wave sleep (NREM) -‐ if you’ve been sleep deprived then are given the opportunity to sleep, you will probably sleep for longer
Increase of REM sleep (after selective REM sleep deprivation
Sleep: summarise the functions of sleep and clinical examples of sleep disturbance
Functions of Sleep
- Restoration and recovery -‐ but active individuals do not sleep more
- Energy Conservation -‐ 10% drop in BMR but just lying still and not sleeping does this as well
- Predator Avoidance -‐ but just hiding in a corner awake will also do this
Sleep is complex so it must have specific brain functions
Specific brain function – memory consolidation
Dreams
We can dream in REM AND NREM sleep but it is mostly during REM sleep
Dreams are also more easily recalled during REM sleep
Contents of dreams tend to be more emotional than in real life
Brain activity in the limbic system is higher than in the frontal lobe during dreams
Limbic system is involved with emotions
Frontal lobe is more important for logical thought and informed decision making
Safety valve for antisocial emotions (you often have to modify or suppress your emotions in real life situations)
Disposal of unwanted memories -‐ a lot of small things that happen during the day are not necessary to remember
Memory consolidation -‐ there seems to be specialisation between REM and NREM:
NREM sleep = declarative memory -‐ facts and events
REM sleep = procedural memory -‐ learning skills
Insomnia
High prevalence
Most cases are transient
Causes of chronic cases:
Physiological e.g. sleep apnoea, chronic pain
Brain dysfunction e.g. depression, fatal familial insomnia, night working
Sleep hygiene
Try and remove the cause if possible
If not you will need pharmaceutical treatment: hypnotics
Hypnotics mainly work by enhancing the inhibitory circuits in the brain -‐ GABAergic circuits Sleep CBT (behaviour therapy)
Hypersomnia
Excessive daytime sleepiness
Common:
Obstructive sleep apnoea
Restless legs syndrome and periodic limb movements
Narcolepsy
Falling asleep repeatedly during the day and disturbed sleep during the night
Cataplexy -‐ sudden onset of muscle weakness that may be precipitated by excitement or emotion
- Sometimes this is just in one part of the body
- Sometimes most of the muscles can suddenly relax and the person can fall over
- REMEMBER: one of the characteristics of REM sleep is low muscle tone
- Tends to be due to a dysfunction of control of REM sleep
- People go straight into REM sleep without going through the other four stages first
- Not well understood
- In most cases there seems to be an OREXIN deficiency
- Orexin is a neuropeptide, which, in this context, is the transmitter that is used by the lateral hypothalamus
- This could be genetic or autoimmune
- The best way of managing it seems to be trying to manage the patient’s sleeping pattern very rigidly
- You give them a framework so they can nap at certain times of the day
- You may have to resort to pharmaceuticals -‐ some sort of stimulant to keep them awake
Shift Work
Night work can make physiological processes become desynchronised
This can lead to sleep disorders, fatigue and increased risk of some conditions such as obesity, diabetes and cancer
Sleep disorders can be results of neurodegenerative disease -> Abnormal neurotransmitter disease – Sleep/circadian rhythm disruption – Co-morbid pathologies – stress activation
Louis body dementia – lack of atonia during sleep
