EEG, Sleep and Circadian Rhythms Flashcards
What part of the brain is responsible for the inhibatory process causing sleep?
The pons
Activity originates in the reticular formation of the brainstem - known to be losely associated with controlling the state of consciousness
Where does the reticular formatino send its projections?
To the thalamus and higher cortical areas
Describe the nerves in the reticular formation?
Serotonergic - denoting a nerve ending that releases and is stimulated by serotonin.
What evidence suggests that seratonin is responsible for sleep induction?
Drugs that block serotonin formation inhibit sleep suggesting serotonin must be critical to sleep induction. Possibly because serotonin is a precursor of melatonin
Which part of the hypothalamus shows circadian rhythm?
Suprchiasmatic nuclei
The hypothalamus is thought to be involved with the induction of sleep
What effect does the suprachiasmatic nuclei have on the pineal gland?
Stimulates the pineal gland to release melatonin - corresponds with feelings of sleepiness in humans.
What is the hormone responsible for wakefulness produced by the hypothalamus?
Orexin
What is the condition associated with defective orexin signalling?
Narcolepsy
How does the ascending reticular activating system and the sleep centres in the reticular formation interact during wakefulness?
Excitatory neurones of the ascending reticular activating system are no longer held in inhibition by the sleep centres
This stimulates excitatory pathways both the CNS and PNS
Which then reduces the inhibition of the sleep centres and the cycle continues
What happens when the orexin producing cells fatigue?
Inhibitory, peptide signals from the Sleep Centres in the Reticular Formation likely take over and rapidly dominate the weakening excitatory signals leading to rapid progression into the sleep state. The opposite is believed to happen during waking – the inhibitory cells fatigue and the excitatory cells are reinvigorated.
How do you assess consciousness in an awake person?
- Look at their behaviour, general alertness, speech patterns, speech content, reading, writing and calculating skills. Spell words backwards or count backwards,
- Record patterns of brain activity using ElectroEncepheloGram (EEG). EEG uses electrodes placed on the scalp to record activity of underlying neurons.
What does frequency vary with on an EEG?
Neuronal excitation
List 5 states of increasing frequency on an EEG?
Anaesthesia
Sleep
Awake - relaxed
Awake - alert
Tonic - clonic epilepsy
What are the 4 main types of wave pattern on an EEG?
Aphpa
Beta
Theta
Delta
What are a waves and when are they seen?
HIgh frequency - high amplitude
Seen in the awake - relaxed state
What are beta waves and what causes them to come about?
Beta waves are high frequency and low amplitude asynchronous waves
Come about as a result of awake - alert state of consciousness
Why are beta waves low apmlitude?
Brain is producing many signals, opposing polarities of singals cancel each other out - they do not get recorded on an EEG
What are theta waves and when do they appear?
Theta waves are low frequency, but vary enormously in amplitude
Happen during times of emotional stress and frustration in adults. They also occur during sleep in both adults and children
What are delta waves and when do they occur?
Very low frequency but high amplitude.
They occur in deep sleep
What is stage 1 sleep cycle?
Slow eye movements, light sleep, easily roused
Theta waves
What is stage 2 sleep cycle?
Eye movements stop
Frequency slows down
EEG shows bursts of waves called sleep spindles
What is stage 3 sleep cycle?
Delta waves interspersed with short episodes of faster waves
Spindle activity declines
What is stage 4 of sleep cycle?
Delta waves
What is stage 5 of sleep cycle?
REM sleep
Dreams occur in REM sleep
What stages of sleeping are deep sleep?
Very difficult to rouse from stage 3 and 4 sleep. Known as Deep Sleep. Sleep walking/talking occurs during these stages.
Large amplitude is associated with deep sleep
Which stages of the sleep cycle are slow wave?
What are the physiological characteristics of deep slow wave sleep?
- Deep sleep that occurs in the first hours of sleep
- Most restful type of sleep.
- Associated with decreased vascular tone (and therefore BP), respiratory and basal metabolic rate (hence drop in BT).
- Dreams may occur but are rarely remembered.
Why is REM sleep described as paradoxical sleep?
EEG waves are desynchronized, high frequency, low amplitude, very like the awake state
Describe the frewuency and duration of REM sleep
Lasts 5-30mins every 90mins or so during a normal nights sleep, becoming more frequent as night progresses and rest and recovery are established
When do dreams mostly occur?
REM sleep
What causes the skeletal muscles to be inhibited during REM sleep?
Inhibitory projections from pons to spinal cord - stops acting out dreams
What type of pathways is REM sleep dependant on?
Dependant on cholinergic pathways within the reticular formation and their projections to the thalamus, hypothalamus and cortex
What is the effect of anticholinesterases on REM sleep?
1.Anticholinesterases increase time spent in REM sleep.
What is the activity of heart rate, respiratory rate and brain metabolism during REM?
HR/RR become irregular and brain metabolism increases
What waves does REM sleep imitate?
REM sleep looks very similar to Beta waves - alert awake
Describe the arousal of someone in REM sleep
Very difficult to arouse an individual from REM sleep, although we often spontaneously awaken in the morning from this stage of sleep, vividly recalling our dreams.
What is the result of REM sleep deprivation?
There is always a catch up when able to sleep again indicating that REM sleep must have an important physiological function
What are the features of sleep deprived subjects?
- Impairment of cognitive function
- Impairment of physical performance
- Sluggishness
- Irritability
What is the likely cause of death in a sleep deprived individual?
Death because the body is unable to regulate body temperature and the immune system fails
What are the benefits of sleep?
Sleep supports:
- Neuronal plasticity (The brain’s ability to reorganize itself by forming new neural connections throughout life)
- Learning and memory
- Cognition
- Clearance of waste products from CNS
- Conservation of whole body energy (although cerebral O2 consumption may actually increase, esp. during REM sleep)
- Immune function (reason sleep increases when ill?)
What are the changes in sleep as you get older?
Total sleep time decreases
Percentage of REM sleep also declines: 80% in 10 week premature infant, 50% at full term declining to a stable 25% in adulthood. May be absent by 80+ years old
When is total sleep time greatest?
During development when brain maturation and synaptic formation is occurring rapidly
Define insomnia
Chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
What is the difference between chronic and temporary insomnia?
Chronic - primary cause - usually unidentifiable
Temporary - secondary insomnia in response to pain, bereavement or other crisis. Usually short lived.
What are the issues associated with barbituates and benzodiazepenes?
Barbituates - depress REM sleep and delta sleep - Chronic use increases time taken to fall asleep, decreases time spent in REM and stage 3 and 4 sleep, and increases no. of times awake during night.
Benzodiazepenes - have less effect on REM sleep but are addictive and cause many problems on withdrawal.
When do nightmares typically occur?
During REM sleep, typically occurring quite far on through the night
What type of sleep do night terrors occur in?
Occur in Delta sleep, typically early in the night
What is a typical night terror?
Children thrash and scream and may sit or stand up with their eyes open but are not properly awake and often fail to recognise their parents. The child does not remember the episode on waking the following morning.
What is Somnambulism?
Sleep walking
When does sleep walking occur?
Occurs exclusively in non-REM sleep, mainly in Stage 4 sleep and is more common in children and young adults, probably due to the decline in Stage 4 sleep with age
What is narcolepsy?
Patients enter directly into REM sleep with little warning.
What is narcolepsy linked to the dysfunction of?
Linked to dysfunctional orexin release from the hypothalamus (see earlier).
What is meant by the circadian rhythm?
Biological systems show oscillations with an » 24 hour period.
Where is the ‘master clock’ located?
In the suprachiasmatic nucleus (SCN) of the hypothalamus, lying just above the optic chiasma
What entrains the inherent 24 hour cycle of the neurones present in the suprachiasmatic nucleus?
Entrained by external cues such as light/dark cycles, probably because some of the nerve fibres in the optic nerve pass to the SCN. However this cannot be the only entrainment as blind people also have circadian rhythms.
Why is circadian rhythm lost when the SCN is destroyed?
Loss of melatonin signalling and disruption of orexin signalling in the hypothalamus
(wakefulness normally being stimulated in the morning, when orexin level rises and sleep occurring at night, when orexin levels fall).
