EEG, Sleep and Circadian Rhythms Flashcards
Where does the process of sleep originate from
The reticular formation of the brain stem
What is the function of the reticular formation
An area that controls the state of consciousness
If brain stem was destroyed at the level of the midpons what would occur
Brain never sleeps
How does the reticular formation promote sleep
Inhibitory impulses to thalamus and higher cortical areas to dampen down activity in cortex and put in state of unawareness
What are many neurones within the reticular formation,
Serotonergic
What is serotonergic
a nerve ending that releases and is stimulated by serotonin
What neurotransmitter is critical for sleep induction
Serotonin
What is serotonin a precursor of
Melatonin
What induces natural sleep
Serotonin
Melatonin
Sleep inducing peptides (isolated from CSF of a different sleep deprived animal)
How is the hypothalamus involved in the induction of sleep
Due to suprachiasmatic nuclei lying just above the optic chiasma creating a 24hr circadian rhythm
What causes the the electrical stimulation of the SCN that promotes sleep
Darkness - when light stops hitting the back of the retina
nerve fibres in the optic nerve pass to SCN
What does the electrical stimulation of the SCN stimulate
The release of melatonin from the pineal gland - which corresponds to the sleepiness in humans
What neurotransmitter does the hypothalamus release thats required for wakefulness
The excretory neurotransmitter - orexin (aka hypocretin)
Active during wake state and stop firing during sleep
What does defective orexin signalling cause
Narcolepsy - suddenly fall asleep
How is the wakefulness cycle sustained for many hours
Excitatory neurons in the Ascending Reticular Activating System (ARAS), are released from Sleep Centres in Reticular Formation stimulating excretory pathways in both CNS and PNS creating a positive feedback loop
What occurs for sleep cycle to occur from wakefulness cycle
Active cells become fatigues causing excretory signals to fade, so inhibitory peptide signals from sleep centres in the reticular formation dominate weakened excretory signal and lead to progression into sleep state
How is sleep cycle overthrown from wakeful cycle
Inhibitory cells fatigue and excretory cells are reinvigorated
What is the two methods to asses level of consciousness in an awake person
Look at their behaviour/alertness/skills /ability
EEG - record patterns of brain activity
What occurs in an EEG
Electrodes placed on scalp to record activity of underlying neurones
What are brain waves from EEG analysed by
Amplitude - size of the wave
Frequency - number of waves per second
Frequency is the most important factor of brain activity so what is the affect of Increased neuronal excitation on it
Frequency increased with neuronal excitation
What are the four main types of brain waves patterns recored on an EEG
Alpha
Beta
Theta
Delta
What causes the various characteristic of wave pattern
Different states of consciousness
What is the characteristics of alpha waves
High frequency and high amplitude
What is the characteristic of beta waves
The highest frequency and low amplitude
What waves are involved in a relaxed awake state
Alpha waves
What waves are a involved in alert wake state
Beta waves
Why do you have a higher amplitude of waves in a relaxed state
Not music info coming into the brain so waves are sync with each other, therefore add together give a larger wave
Why do you have a high frequency and low amplitude in a alert state
Alert state means you have lots of info coming into the brain giving a greater frequency and this means waves become asynchronous and cancel each other out creating a lower amplitude
What is theta waves characterised by
Low frequency and varies enormously in amplitude
When is theta waves common
Children,
Times of emotional stress and frustration in adults
What are delta waves characterised by
Low frequency but high amplitude
What waves are seen in sleep of both adults and children
Theta waves
What waves are seen in deep sleep
Delta waves
How many stages occur in a sleep cycle
5
What occurs in stage 1 of sleep cycle
Slow wave, non-REM, S-sleep.
Slow eye movements.
Light sleep. Easily roused.
High amplitude, low frequency theta waves.
What occurs in stage 2 of sleep cycle
Eye movements stop.
Frequency slows further but EEG shows bursts of rapid waves called “sleep spindles”
(clusters of rhythmic waves, ~12-14Hz)
What occurs in stage 3 sleep cycle
High amplitude, very slow (2Hz) delta waves interspersed with short episodes of faster waves, spindle activity declines.
What occurs during stage 4 of sleep cycle
exclusively delta waves
What occurs during stage 5 of sleep cycle
REM sleep - during which there are rapid eye movements (paradoxical sleep)
What occurs during REM sleep
Dreams
- if spontaneously awaken in the morning during this stage of sleep will vividly recall dreams
What percentage of sleep is REM
25% of sleep is REM
When does deep sleep occur - become difficult to rouse
From stage 3 -4
What is stage 1-4 classified as
Slow wave sleep
How is REM sleep characterised
Fast waves, similar to those of awake state
When the amplitude is the highest in sleep what does this indicate
deep sleep
What is the 4 physiological characteristic 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 the term paradoxical sleep used
Due to REM sleep occurring which is very similar to awake state as mimics the beta waves
How frequent and long does REM sleep last
Lasts 5-30mins every 90mins or so during a normal nights sleep, becomes more frequent as night progresses
How does inhibition of all other skeletal muscles (minus eye muscle) occur in REM sleep
Due to inhibitory projections from pons to spinal cord
What pathway is REM sleep dependent on
Cholingeric pathway within the reticular formation
Where does the REM pathways projections go
Thalamus
Hypothlamus
Cortex
What is the affect of anticholinesterases
Increase time spent in REM sleep
What is REMs affect on Heart /respiration rate and brain metabolism
HR/RR become irregular
Brain metabolism increases
What occurs if you are deprived of REM sleep and what does this show
there is always a catch up when able to sleep again indicating that REM sleep must have an important physiological function
What is 4 features are demonstrated in sleep deprived subjects
Impairment of cognitive function
Impairment of physical performance
Sluggishness
Irritability
What can occur with severe sleep deprivation
Psychosis
Death
What important functions does sleep support
Neuronal plasticity
Learning and memory
Cognition
Clearance of waste products from CNS
Conservation of whole body energy
Immune function (when ill, increase sleep)
What are sleep changes seen over a lifetime
Total sleep time decrease rapidly through childhood and adolescence
Percentage of REM sleep declines
What is the percentage of REM sleep over lifetime
80% in 10 week premature infant,
50% at full term declining to a stable 25% in adulthood
Can be absent by 80+years
Why is total time asleep greatest during development
Brain maturation and synaptic formation is occurring rapidly
Name 5 sleep disorders
Insomnia
Night mares
Night terrors
Somnambulism (sleep-walking)
Narcolepsy
Define insomnia
a “chronic inability to obtain the necessary amount or quality of sleep to maintain adequate daytime behaviour
What is the two types of insomnia
chronic, primary insomnia
temporary, secondary insomnia
In chronic insomnia there is no identifiable cause, but what is the potential cause of temporary insomnia
Pain
Bereavement
Or other crisis
What occurs during a nightmare
Nightmares have a strong visual component and are seen during REM sleep, typically occurring quite far on through the night. Waking will stop the nightmare and the individual will have a clear recollection of the “dream”
When do night terrors occur
Deep, delta sleep
common in children 3-8 years
Occurring early in the night
What occurs in night terrors
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.
When does Somnambulism (Sleep-walking) occur
Stage 4 deep sleep
non REM sleep
Why is sleep walking more common in children and young adults
due to the decline in Stage 4 sleep with age
What occurs in Somnambulism (Sleep-walking)
Somnambulists walk with their eyes open, can see and will avoid objects, can carry out reasonably complex task such as prepare food and will often obey instructions but have no recall of the episode when woken
What occurs in narcolepsy
Patients enter directly into REM sleep with little warning.
Symptoms could be interpreted as intrusion of REM sleep characteristics onto the waking state
How is circadian rhythm lost if SCN is destroyed
due to the loss of melatonin signalling and disruption of orexin signalling in the hypothalamus
How can blind people form a circadian rhythm from the SCN as don’t have eternal cues such as light and dark cycles
wakefulness normally being stimulated in the morning, when orexin level rises and sleep occurring at night, when orexin levels fall
