16. Sleep Flashcards
1
Q
What is the behavioural criteria of sleep?
A
- Stereotypic or species-specific posture
- Minimal movement
- Reduced responsiveness to external stimuli
- Reversible with stimulation - unlike coma, anaesthesia or death
- The brain is usually very active when you are asleep
2
Q
What could be used to monitor sleep?
A
- Electroencephalogramm (EEG)
- Electrooculogramm (EOG)
- Electromyogramm (EMG)
3
Q
Describe the 5 stages of sleep.
A
-
Awake
- 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 - EMG
-
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
- 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 (EOG)
- The muscle activity is at its lowest so the person is basically paralysed
- NOTE: the first four stages are called NON-REM sleep (NREM)
- These five stages together form a full sleep cycle
4
Q
Describe a single sleep cycle.
A
- 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
5
Q
What happens to heart and resp rate during sleep?
A
- 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
6
Q
Describe the function of the reticular activating system.
A
- Consciousness is mainly controlled by the RETICULAR ACTIVATING SYSTEM (RAS)
- 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
7
Q
Describe the control of RAS (reticular activating system)
A
- There are TWO nuclei in the hypothalamus that influence the RAS and so control the sleep-wake cycle
-
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
-
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
8
Q
Describe the Circadian Synchronisation of the Sleep/wake cycle.
A
- 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:
- Inhibits the LH nucleus
-
Stimulate the VLP nucleus
- So towards the day you become more sleepy
- Also has a direct effect on the RAS 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 SCN 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.
9
Q
What are the effects of sleep deprivation?
A
- Sleepiness, irritability
- Performance decrements/increased risk of errors and accidents
- Concentration/learning difficulties
- 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
10
Q
How is sleep regulated after sleep loss?
A
- 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)
11
Q
Define the functions of sleep.
A
- 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
12
Q
What happens during dreaming? When do we dream?
A
- 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
13
Q
Describe insomnia. (prevalence, causes, treatment)
A
- 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
- Treatment:
- 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
14
Q
Define Narcolepsy.
A
Falling asleep repeatedly during the day and disturbed sleep during the night
15
Q
Define cataplexy.
A
-
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
occurs in narcolpesy
