A cyclical state of consciousness from which an individual can be roused by normal stimuli such as light, sound, touch.
What neural pathways are involved in the sleep/wake process?
- Seratogenic sleep centres in the Pons
- Other sleep inducing peptides found in CSF
- Melatonin release triggered by the Suprachiasmaticnuclei of the hypothalamus
- Excitatory orexin neurons in hypothalamus
How do seratogenic sleep centres in the pons affect sleep?
- Recticular Formation in the Pons
- Contains seratonin releasing neurons
We know this is involved in sleep as destroying it or blocking seratonin prevents sleep
How is the hypothalamus involved in inducing sleep?
- Suprachiasmaticnuclei in Hypothalamus
- SCN activity leads to melatonin release from pineal gland –> Corresponds with sleepiness
We know that electrically stimulating the SCN induces sleep and damages it disrupts sleep-wake cycle
How is the hypothalamus involved in wakefullness?
Excitatory neurons in the hypothalamus release Orexin (hypocretin) during waking, this maintains wakefullness.
They stop during sleep
Describe how the sleep wake cycle occurs:
Excitatory neurons (in Ascending Reticular Activating System) overtake inhibitory cells
- -> Stimulates excitatory pathways in CNS/PNS
- -> +ve feedback maintains wakefullness for many hours
- -> Excitatory cells fatigue & signals fade
- -> Inhibitory signals from the reticular formation sleep centres overtake the excitatory signals
- -> Sleep
- -> Overnight the inhibitory cells fatigue, excitatory ones rest and take over again in the morning
What would we do to assess the level of consciousness in a patient?
Alertness = Speech content/patterns = Reading = Writing = Calculating skills = Spell/count backwards
What does an electroencephalogram measure?
Electrical activity of the brain
In Amplitude and Frequency (rises with neuronal excitation)
Sometimes brain activity is very high but the amplitude is low, why is this?
The brain waves are asynchronous.
This means the brain is doing lots of things at once and the opposing polarities of its signals cancel eachother out on the EEG
What are the types of EEG wave patterns?
When do each type of EEG wave occur?
Alpha - Awake but relaxed
Beta - Awake and Alert
Theta - Emotional stress/frustration/sleep stage 1&2
Delta - Deep Sleep (stages 3 & 4)
Describe the characteristics of the different EEG wave types?
- High F & A
- High F
- Low A (Asynchronous)
- Low F
- Variable A
- Low F
- High A
What are the stages of the sleep cycle?
Stage 1 - Slow Wave non-rem sleep (S-sleep) - Theta Stage 2 - Theta (but even slower F) Stage 3 - Delta Waves Stage 4 - Delta Waves Stage 5 - REM Sleep (Beta Waves)
1-4 are known as slow wave sleep
REM sleep has rapid waves
During what stages of sleep do eye movements occur?
Stage 1 - Slow eye movements
REM - Rapid eye movements
Stage 2 of sleep is very low Frequency Theta waves, what else happens?
Bursts of rapid waves called sleep spindles
What stages of sleep are known as deep sleep?
Stages 3 & 4
Why would we call REM sleep Paradoxical sleep?
Because the High frequency, Low amplitude waves mimic awake/alert beta waves
What stage of sleep are dreams remembered from?
How does the sleep cycle change over the night?
As the night progresses we spend more time in REM sleep and less in Deep Sleep
What physiological changes occur during deep sleep?
Its the most restful period
Decreased Vascular Tone –> Drop in BP
Drop in Respiratory & metabolic rate
How long is a sleep cycle?
Why do our eyes move during REM sleep?
Because the rest of the bodies skeletal muscles are inhibited by projection from the pons to prevent you acting out your dream
What happens if there’s dysfunction in the inhibitory projections from the Pons to the spinal cord?
REM Sleep Behavioural Disorder
People act out their dreams, which can be very dangerous
What effect do anticholinesterases have on the sleep cycle?
They increase the time spent in REM sleep.
Because REM sleep is dependent on cholinergic pathways in the reticular formation of the pons and their projection to the thalamus, hypothalamus and cortex
What physiological changes occur during REM sleep?
Heart & Resp Rate are irregular
Brain metabolism rises
Compare the physiological characteristics of deep sleep vs REM sleep?
- Drop in resp rate, metabolic rate & vascular tone (Blood Pressure)
- Irregular Heart & resp rate
- Rise in brain metabolism
What happens if your deprived of REM sleep one night?
The next chance you get to sleep your body undergoes a catch up stage.
Indicating its very important
What processes are supported by sleep?
- Neuronal Plasticity
- Waste clearance from CNS
- Conserving energy
- Immune Function
So what are the effects of sleep deprivation?
- Impaired cognitive function
- Impaired physical function & Sluggishness
Also disrupts neuronal plasticity, immune function, energy levels and waste clearance
How does sleep change throughout life?
Total Sleep time & REM sleep % are highest in childhood, probably due to brain development occuring.
Both drop off again after ~65 yrs
REM sleep can be completely absent in those >80
How common are sleep disorders?
~25% of people are affected by sleep disorders at some point in their life?